Tesla shares 48V architecture with other automakers | Hacker News Reader

Tesla shares 48V architecture with other automakers

electrek.co

316 pointstoomuchtodo484 comments

Many comments here seem to be confusing the accessories circuit voltage with the electrical vehicle motor and drive system. The vehicle motors have a combined power output of 450KW which requires a high voltage 800V system or the wiring would be so heavy it would not be feasible.

This spec appears to be the accessories circuit with Tesla pushing for a new 48V standard. That’s super smart because it immediately means you need roughly a quarter of the metal in wiring that you needed previously. It’s cheaper, lighter and more environmentally friendly. And it enables the use of higher power devices. If you’ve ever had to wire your 1000W sub woofer amp directly to your battery you know what I’m talking about.

It’s worth noting that newer GA aircraft like Cessna 172 use a 24 volt system. So non 12V systems for accessory power isn’t a totally new idea. And older 172s have 12 volt systems. So the transition was made in that space anyway.

A lot of commercial trucks use 24V systems also.

Stuff like buses have used 24 volt for ages. Basically anywhere with larger accessory loads.

48 volt has been 'on the radar' in automotive spaces for a couple decades.

Dumb question but why does deciding to run at a higher voltage decrease the amount of wiring necessary? And why not increase it even further then?

Watts = Amps * Volts (or, more scientifically, P = I * V)

If something draws 48 Watts of power, you can either supply it with 4 Amps @ 12 Volt, or 1 Amp @ 48 Volt.

It's the amps that determine how thick the wiring needs to be, so by lowering the amperage, you lower the amount of wiring needed.

I believe the only reason cars are 12 V is because that's a practical voltage to build lead-acid batteries at (which is actually closer to 14 V in practice). Early car electric systems were only 6 V back when the only accessories were the front lights and the horn, but as more stuff was added on cars moved to 12 V.

Things like stator motors were also probably quite difficult to do at 6v.

I know the older Honda CT110 postie bikes came in 6v in the old days. That was a kick start.

Car electrical systems typically run at 13.8-14.4V while the alternator is charging and drops slightly after the battery is topped off. When the engine is off the battery regulates a 12v output

Resistance is proportional to the square of current. This would mean 1/16th the loss instead of 1/4th.

Nope. Consumed power is voltage*amperage, and it’s constant, so 4x more voltage means 1/4 the amps. Wire heating is I squared R, so with both I reduced and R increased the losses are just 1/4, not 1/16 of the 12V system. Because you wouldn’t keep the same wire gauges you’ve had in the 12V system, you’d reduce them to actually have some benefits from conversion.

Isn't the resistance of a wire usually modeled as a constant value?

Power dissipated in the wire as heat is proportional to the square of the current. It's equal to the voltage drop times current (P = I * V). Voltage drop is current times resistance (V = I * R). So P = I^2 * R.

This makes such little sense to me. I'm probably just stupid, but if the same amount of power is flowing through the wire, don't you need the same size of wire? A higher voltage system will push more energy through the same component, so you need thicker wires. If you up the resistance of the component to consume the same amount of energy as before, you arrive at the same size of wire you were using before, don't you?

What exactly is magical about higher voltages that makes them suddenly able to carry more power across the exact same wire? I know you just said it's "lower amperage" but I don't understand how amperage can be the only thing dictating the required size of a wire.

A higher voltage system enables the same energy at a lower amperage, so constrained to wanting to do a particular thing (loud stereo, bright headlights, ...), higher voltages result in lower amperages. I'll opt to not try to explain that intuitively, hoping that somebody else chimes in.

For the other half, "why do amps determine wire size?" Amps are coulombs per second -- how much electrical stuff moves through a cross section in a second. The amount of heat produced is directly proportional to amperage (every bit of movement has a chance to whack into something and produce heat, and more movement per second or more seconds generates more heat). Wire size is ultimately constrained by being able to release that heat while still acting like a wire (not melting, not sublimating, still conducting, not setting anything else on fire, ...). The amount of heat released is proportional to surface area (proportional to the square root of diameter, but that difference doesn't matter a ton right now), and the amount of heat produced is proportional to amperage and approximately nothing else. The point where those two terms are equal is the limit for the system (engineers add in huge safety factors to account for conduit and insulation and other imperfections), above which your wire melts and below which it behaves reasonably. Higher amperages require higher surface area to release the extra heat (so much higher thicknesses), so a given amount of power (stuff you want your electrical system to do) requires lower amps or thicker wires to work appropriately, because you can achieve the same power by increasing the voltage on the same amperage, thereby solving your power problems without extra heat.

Edit: Heat released is also proportional to the temperature differential between the wire and the outside world, as well as a constant associated with how well it's thermally insulated. The wire temperature rises till either some sort of breakdown occurs or that rate of heat release balances the rate of heat production. The spirit of that original comment is correct, but this feels like a nuance that might matter to somebody new to the topic.

The power loss by the resistance scales in the square of the current and linearly to the resistance. So doubling voltage reduces resistance power loss to one quarter so you could lower wire size and increase its resistance to double and still resistance power loss would be halved

What matters is energy but what's being carried by the wire is charge. A given amount of charge can have more or less energy, which is what voltage is. So if you give each unit of charge more energy then you can carry more power by only moving the same amount of charge. You get a similar thing in mechanical systems: a shaft is sized based on the maximum amount of torque it can withstand, but the amount of power going through it also depends on the RPM. More RPM = more power, for the same amount of torque, so if you are for some reason limited in the size of the shaft, you can use a gearing mechanism to rotate it faster and then gear down the other side and get more power through a smaller shaft. It's just that in mechanical systems gears are a lot less convenient than changing voltages is in electrical systems.

(RPM and voltage are in fact related in EVs as well: generally speaking a higher voltage motor will be able to produce more power for the same amount of space and materials, but mostly by spinning faster, not producting more torque. You then need to gear it down to be practical in a car. But the trend is that things that make higher voltages and higher RPMs possible (the technology in transistors, insulation, bearings) are already cheap or getting cheaper, while things that make higher currents and torques possible (generally more raw material like copper and steel) are staying the same or getting more expensive. So EVs in general are pushing to higher voltages for lots of things)

Just as further confirmation, remember that long distance power delivery uses high voltage, often measured in kilovolts. Because of reduced losses that way.

Imagine you've got an object you want to move by shooting water at it from a hose.

If the pressure coming from the hose is high, then you don't actually need a lot of water, and so you can use a narrow hose. On the other hand, if the pressure is low, you'll need to use a lot more water at once, so a wider hose.

It's the same thing for electrical components. If you'll excuse the mixed analogy, if you need to push an object with 480 watts of water to get it to move the speed you want it to, you can either do it with 48 volts of pressure with a hose 10 amps wide, or do it with 12 volts of pressure 40 amps wide.

Higher the voltage the lower the amp draw, so smaller wires can be used.

For your first question, power = voltage x current. To transmit the same power, if you double the voltage you only need half the current. This is important because the resistance losses in conductors are related to the current not voltage, so you can use thinner wires without overheating.

60 volts DC is a safety threshold. You start to move current through tissue at higher voltages.

Yes but state of your body/skin (R) and current (I) is what matters with regard to 60 volts being really dangerous (also the current path as the article below states).

60 volts is nothing UNLESS you are completely wet or sweaty.

"It is estimated at 150 ohms for completely wet skin (in water), 1000 ohms for sweaty skin, and 100,000 ohms to 500,000 ohms for dry skin."

Assuming a worst-case scenario with dry skin providing a resistance of 100,000 ohms, fatality becomes a possibility if the current exceeds 50 mAmp.

Therefore, the lethal voltage would be above 0.05 (50 mAmp)×100,000=5000 Volts. [1]

So if you are wet or sweaty, it could be 7.5V to 50V that gets dangerous.

So it makes sense why 60 volts is a safety threshold, especially for those that live in Florida or Arizona.

[1] https://www.scienceabc.com/humans/how-many-volts-amps-kill-y...

> 60 volts is nothing UNLESS you are completely wet or sweaty.

Ha, it’s always easy to tell when people have experience with these things.

Doorbell wiring is 48V. Go hold those in each hand and tell me how impossible it is to feel if your hands are dry.

Doorbell voltage in the US is typically 12V or 24V AC in the US. I can’t feel that with dry hands.

You might be confused with POTS (landline phone service) which is 48V DC with all phones not in use.

Just don't be holding on when it rings! That's painful, with 90 VRMS at 20 Hz.

What you stated is incorrect. Anyway, V=IR is a truth. If you touch 48v DV dry. You are going to be fine.

> 60 volts is nothing UNLESS you are completely wet or sweaty.

From experience I'm not touching 60v, sweaty or dry as sand - that voltage hurts! And 48v is seriously uncomfortable. People have died from less DC voltage in industrial settings.

Following EN61010, the max safe DC voltage in laboratory equipment is 35v for wet locations. For a car, we ought to assume that being wet is a possibility.

48V is good because a lot of safety standards have the cut off for 'extra-low voltage' at 60V DC, gives you a bit of margin (when battery charging it pushes up to be in the 50s for example). Some battery systems I've seen at 56 volts nominal too. so sometimes people do have a bit higher-voltage ELV systems.

48V still lets you touch both conductors with dry hands and it's still very unlikely for you to be able to get any current to flow through you, you can't even feel it (although with safe working practices you'd only touch either positive or negative at one time, not both). Obviously it's very much not the case to be able to touch the 800V conductors safely in the traction systems in EVs, that side is extremely dangerous and requires extreme caution and safety procedures!

> requires extreme caution and safety procedures

As long as the battery pack is still sealed and the interlock systems are undamaged and working correctly, it's no big deal. You follow the manufacturer's instructions to make it safe, then work on it like there's no voltage present.

If the battery pack is broken or a prototype or whatever, yeah, then you need to think things through carefully before doing them. And have a plan for what you're going to do when things go wrong.

Source: I work in electric aviation and work on battery packs.

GP was talking about the low voltage system (the 12-volt system in most cars) and choosing a voltage for it, not anything about the traction battery.

No, they were comparing the difference in precautions between 12/48v accessory battery and the 400/800V traction battery.

You are correct; thanks; I missed the precise context of the snipped text.

If you can't feel 48 V with your hands I'd recommend moisturizer, because you have very dry skin.

You've already gotten a bunch of answers but to be honest I find all of them a little incomplete if you don't have any electrical background, so here is my attempt to be quite thorough from (almost) first principles.

---

The equation for power delivered by an ideal system is P = IV, or power (P) = current (I) * voltage (V). Power is measured in watts, and that is generally the overall number that matters, in terms of what you can run off of your system at the same time.

So to increase the wattage (power) of your system you can either increase the voltage or the current.

- Increasing the voltage of a system increases the amount of resistance it can "break through". In "danger to human" terms, our skin is generally not a great conductor, so voltages lower than 50V usually won't enter the body (read: vital organs) at all. Voltages above 50V will start to enter the body depending on conditions, which is when electricity becomes much more dangerous.

- However even if the voltage is high enough to enter the body, if the current (I) isn't very high it still won't be dangerous. Current is measured in Amperes (A), and the usual number at which a current inside the body becomes dangerous is above 30mA. 30mA can cause respiratory failure if it passes through the lungs, current as low as 100mA can cause cardiac arrest if it passes through the heart. In a car's electrical system, the currents we're operating with are definitely going to be over the 30mA threshold we just established, so we want to keep the voltage under 50V instead.

Anyway back to cars and ignoring danger to humans for a second. Resistance is the main thing you want to overcome when it comes to the efficiency of such a system. The equation for power loss is P = I^2 * R, or "power dissipated (as heat) is proportional to the square of the current times the resistance". So if you increase the current of your system (in order to deliver more watts) you will also increase the amount of power you lose as heat. You can decrease the loss by decreasing the Resistance.

The equation for resistance through a material is: R = ρ * (L/A), or Resistance = resistivity (an innate property of the material) * Length / Area. In other words, the longer your wire is the more current you will lose to resistance. But if you increase the cross-sectional area of your wire (A) by making the wires thicker, you decrease the resistance.

So in short: if you have a high current (amperage) system, you use thicker wires in order to ameliorate resistive heat loss. But you can alternatively just decrease the amperage to reduce your resistive heat loss, which means thinner (and therefore much lighter) wires. But then you need to increase the voltage of your system in order to offset the power you're losing by decreasing the current. If you increase the voltage by 4x, from 12V to to 48V, this keeps it under the human danger zone (of 50-60V) and means your wires can be up to 16x thinner, taking up less space and less weight. Having it be a nice multiple of the previous system (4x) should make upgrading the relevant circuits a little more straightforward as well.

The reason to not keep going higher is purely practicality because stepping down bigger voltage gaps for lower voltage applications begins to become less efficient/more waste heat.

If you design 100v computers, monitor, headlights, seat adjustment motors, window/windshield motors, pumps, etc. you could cut these 48v wires in half again but if you end up stepping everything down anyway it loses its utility.

The safety rules about voltage and the human body are often poorly overstated, as is the addage that 'its the amps that kill you, not the volts.' in reality it takes a whole lot of both [0].

As further research, here[1] is styropyro touching 2 contacts which have more current than the largest bolts of lightning (enough to almost instantly vaporize a crowbar) with his bare hands, but because it is 12V it is not able to pass through him.

[0] https://youtu.be/BGD-oSwJv3E

[1] https://youtu.be/ywaTX-nLm6Y

Just don't try that with wet hands.

Even with wet hands it's hard to get much out of 12v.

As an analogy, if you have a hose squirting out water at a certain rate, and you increase the pressure, then all other things being equal you'll get a higher rate of water. But then that means you could now reduce the size of the hose, keeping the new higher pressure, and achieve the original rate of water delivery with a smaller, cheaper, lighter hose.

It's very similar with electricy: water pressure is voltage and the rate of water delivery is power.

Bad analogy: for the electrons, Volts are (inverse) latency, and wire thickness is maximum bandwidth (or max amp). That is, make electrons go faster, instead of pushing more electrons at the same time.

Of course none of this really makes sense, for example you can't increase wire thickness to increase amps etc.

48V has been considered for automotive for decades. The problem was not know how.

It simply has never been worth it before to retool things in practice.

It's also electrically a lot more noisy. The limit of what is considered low volt is like 60v or something.

Why is it inherently noisier?

Faster slew rate for all switch supplies in the system. Nothing directly runs 48v.

I’m still skeptical. Why can’t it be filtered out

It can, it just requires up to a dollar more per device.

Nothing "directly" runs on 12V either. All electronics will have stepdown converters in both the 12V and 48V use case. Motors, solenoids and incandescent bulbs can be made to work with either voltage (the same way we do for 24V systems in heavy goods vehicles here in Europe).

> Nothing "directly" runs on 12V either.

Motors, bulbs, relays.

Not true.

Your motors and actuators operate directly on 48V (in fact, most actuators would prefer a higher voltage like 96V). That's really significant.

Microelectronics is effectively a "don't care" since everything is behind a regulator or a PHY.

Yeah, 48V tolerant switching regulators are going to be a bit more expensive until the volume gets rolling, but that problem solves itself while ethernet and CAN PHY chips are already 48V tolerant.

Lights and motors can easily take 48V. It's only the digital devices that require switching supplies, and that's still much better that 200-300V rectified mains power.

It was never worth it to retool for decades?

Or was there a pathological lock-in between suppliers and manufacturers that prevented even the most obvious innovations from happening if they required any amount of coordination?

Since car manufacturing, and design, wasn't held back at all by something like auxiliary current, the reason more likely was people not wanting to waste energy to improve on something that is working just fine for everyone.

Well according to Tesla it wasn't working just fine for everyone - they have been able to massively simplify their internal wiring.

Classic example of legacy automakers happy to maintain the status-quo because it is easiest, while the new kid on the block is pointing out that things don't have to be the way they are just because they are that way.

Its the same with aluminum casting. The car makers used the technology once in a while in some specific parts, Tesla was like 'why not make half the car out of one casting'.

Tesla worked closely with a supplier, did lots of its own research and development and continue to work with a supplier to make the technology better over time.

This was considered stupid at first. This is now very widely copied. First automakers from China copied it. And now others are copying it as well. Even Toyota (who everybody believes are some kind of gods of manufacturing) are copying this now.

If you have been doing something one way for long enough, going into a radically different direction is hard. Your whole workforce knows about welding steel sheets together, and nobody knows anything about casting. Your whole workforce knows about V12 and the ecosystem for that.

Its hard to fundamentally change how you do things when you are producing millions of vehicles a year.

A quick search turned up this:

>> S&P Global Mobility forecasts 15% to 20% of traditional body-in-white (BIW) stampings in 2030 may be at risk from these gigacastings. Underbody components typically comprise about 50% of a vehicle's BIW shell, and this soft underbelly is the target of gigacasting's focus.

Source: https://www.spglobal.com/mobility/en/research-analysis/gigac...

Obviously not a technical journal, nor did I double check anything.

What the numbers say 15-20% might be replaced by gigastampings (sidenote: I ak surprised Elon didn't rename Twitter to Giga-X). Which, ok, is a thing. But nowhere near the revolution people seem to believe. First, it has to happen. Second, others have to consider it better, read overall cheaper, and continue doing it. Then we can properly judge. Until then, it might as well be in the category of Teslas fully automated factories that ended with Elon doing pyjama parties with his workers on the shopfloor and ad-hoc tents.

And Toyota, as per the linked article, is not copying it, they are "eyeing" it. And believe itbor not, manufacturers are eyeing new production tech all the time.

And Toyotas reputation in car manufacturing is well earned.

You are underestimating how long things take in the car industry. 2030 is really, really soon.

The majority of cars sold then will be existing models with minor updates.

And car companies only upgrade their major platforms every 5-7 years. Many companies are currently planning their second (or first real) EV platform.

But by 2030 even the waste number of EV will be on first generation EV platforms still.

Companies have 100s of million invested in their current body lines. So unless you build a totally new factory you are not gone adopt this technology.

When Toyota came out with their production system it took decades for all the practices to become established.

I'm more an aerospace guy, but I am fully aware of the time scale around production technology changes. Thing is so, 2030 is an estimate, not a commitment. And I didn't find anything about actual investments or announcememts from OEMs around that.

Also, 20% of castings still means a lot of welding before a car body is made.

One thing regarding Toyotas production system so: it is all about management and processes and not about the actual machinery. And it share a lot of principles ranging as far back as Venice's Arsenal in the 16/17th century and, especially, WW2 mass manifavturing of, e.g., planes.

Anothet major difference: TPS is a proven methodology for longer than Tesla, let alone any production tech coming out of Tesla, exists as a company.

Legacy automakers have no need for a 48v system. Most vehicles have an ICEs and they will for the next decade(s) as EV and PHEV adoption rises. 12 years is the average age for cars in the EU/US.

Why would they upgrade a system when they don’t need to? Tesla can be a front runner and companies like Bosch will start creating 48v parts as EVs become more popular for legacy auto to use.

Also 48 V semiconductors are more expensive and not so easily available.

I mean there have always been a market for 48V components. The problem is that the market is much smaller so as a customer, you’re paying a lot more and it’s hard to justify raising the price of your car because you decided to go 48V.

Try counting the number of businesses involved in making a vehicle.

24V is common in trucks, and yet never made it to regular cars because there was never sufficient reason.

Using a higher voltage is not an innovation (it's an obvious change, and we've gone from 6V to 12V to, in some cases, 24V already) - rather it's just a slight efficiency improvement in largely non-critical systems, with not a lot of incentive to take on the cost of transition.

In a a personal ICE vehicle, the only real significant power was to the starter motor and from the generator, and the distance there was short so the copper didn't really matter and thus no one cared for 24V - unlike industry where you might have significant aux systems. With EVs, you have heat pumps and brake boosters on the auxillary power, so you now have a stronger driver for conversion.

Even within 12V, you'd get a larger weight reduction from not carrying an aux battery, and just feeding through a converter from the HV system.

The 12v battery performs the very significant safety feature of allowing the HV battery to be disconnected when the car isn’t ready to move. You’d need to have a converter in the HV battery to avoid that down side, and then you have a new downside of a fault could cause your 12v line to be HV instead.

Fair point, but I imagine disconnecting is mainly to avoid live HV wiring throughout the vehicle, and thus reducing risk of catastrophic shorts or arcing.

If the aux supply is near or in the battery, leaving that connected would while the rest of HV is interrupted would probably not cause any notable increase in risk.

At the same time, vehicle fires have been caused by a shorted auxillary battery (I have personally experienced an entire industrial building burn down because the 12V battery in a parked ICE car shorted and went up in flames), so I imagine only having one battery to worry about is a risk reduction.

> The limit of what is considered low volt is like 60v or something.

As far as i know, 60 V is the limit for alternating current. For DC it is 24 V.

Depends on the region. 56V AC and 72V DC here. -48V has been the standard voltage in telecoms for +100years, so 48V systems and parts are not that exotic.

Mercedes-Benz has been using 48V systems since 2016.

https://paultan.org/2016/10/31/mercedes-benz-reveals-first-d...

This dynamic, where Tesla "announces" something that the rest of the industry has been doing for a while anyway, and a bunch of star-struck enthusiasts and stock manipulators tout it as an example of Tesla' "super smart innovation", is getting tiresome.

That's a complete misunderstanding of what Tesla did. Having a component in the car that is 48V and having the whole car being on a 48V PoE architecture are totally different things. The sad part is that these company actually have the beginning of a 48V system but never actually pushed threw and did it all.

This is like when SpaceX landed a first stage and everybody was like 'DC-X did it SpaceX did nothing new'.

There is a reason lots of people, including experts are exited of what Tesla did here.

Of course Tesla has taken it further which is interesting and could be useful - but it's not quite true that the whole car is on 48V, they've already said that ~20% of the common / supplier-provided components are still 12V. For pure EVs, sticking with higher voltage makes a lot of sense and Tesla was perfectly suited to lead the charge here since they have built so much of their supply chain from scratch and can spec everything to be 48V where other EV manufacturers mostly just reused components from their ICE cars.

Previous 48V systems were only partial for good reason as well - traditional manufacturers have been using "mild hybrid" 48V systems since ~2001. Many of the electrical components on ICE vehicles are parasitic engine loads since they need power than can be provided with 12V, so e.g. the water pump and AC compressor have separate belts that always are 'robbing' the engine power regardless if they're needed or not. Adding that 48V system allows for the engine to be freed from the draw that those components require and adding some light regenerative braking is sufficient to keep the batteries supplying that system charged.

That these 48v systems aren't universal should provide some color on how successful / important the manufacturers had found them to be.

Jup happens all the time. Tesla also made the CyberTruck a drive by wire system, now fans are claiming it has the unique ability to have variable steering angles based on speed which is "far ahead of any other manufacturer"

Except that BMW 5-series and 7-series from 2010 onward have had this option... They've done it in a smarter way using a plantery gear system to keep a physical steering wheel connection as a backup instead of going the cheap and less safe drive by wire way that Tesla put on the CyberTruck.

That is a link to a press release. As best as I can tell from other sources, they started shipping some high end, low volume models the next year that added a separate 48V curcuit in addition to the 12V. Color me impressed...

There is still a large benefit to this. Because Tesla is seen as a leader in the EV space it prods others to follow them. In some cases like this it gives people in the supply chain or internally at other automakers justification to make changes they've been prevented from making in the past.

All sorts of people have all sorts of random ideas that never go anywhere until an industry "golden child" says it's the way forward. Without that effect the change can take much longer to happen.

U mean Apple?

How is DC more noisy?

48V is also used on some boats (eg. certain trolling motors)

"super smart" - more like completely obvious to everyone for decades

That’s what Elon said, no innovation, just made the step

> Tesla pushing for a new 48V standard. That’s super smart

48V is a dangerous voltage. Better not touch any wire.

> 1000W sub woofer amp Your car subwoofer is surely not so stiff that it needs so much power. But after using it, your ears will definitely be.

48V is also currently used on the supporting electric traction motor of "Mild Hybrid" cars.

I get this a lot

I work at an electronics store in Australia

This week I had a customer dumbfounded why his 3,500W inverter almost caught fire

He was using 8-gauge wire (~56A max)

He needed 00-gauge (almost 300A max)

If he’d have run the system at 48V instead of 12V he’d have saved $200+ per metre on cabling his inverter

My advice on voltage selection for a vehicle is once you’re needing more than a few metres of 0-gauge, you should possibly increase the voltage of the system

High current cabling means expensive ANL, mega or other high performance fuses or other expensive circuit protection methods

I strongly believe that 48V systems are inherently safer than 12V systems when it comes to the public doing DIY work

Good look doing DIY work on the 48V network of a modern car, ICE or EV or 12, 24 or 48 V doesn't matter.

And the past 12 V systems are dead easy to work on. On older cars that is, as soon as you have electronics and bus systems DIY basically requires deep car electronics knowledge and skills.

Do you have examples of what kind of DIY work is hard?

I haven’t done a ton of work on newer cars, but at least adding wiring for a hitch on my Kona EV was just as easy as any wiring I’ve done on my old truck.

Is a job like adding amps and better speakers trickier?

I have a defender and added a bunch of stuff to it: cruise control, motor pre-heater, rear camera, working lights in the rear. I'll also add a diesel heater and more electrics at some point. On 12V it's easy, can't imagine doing work like that with 48V. Not sure how this works, and if you maybe just can use 12V anyway. But wanted to make the point of camper vans and overlanders and offroaders.

An old or a new one?

Ah right, should've specified that. Of course an old one ;) A Td5. I call the other one "New Defender"

And a TD5 is already modern-ish enough, but very nice regardless! Personally, I would be at a loss working in anything built after the early 80s, so for a Defender that would be the dual-carb V8s, and 200/300 TDis.

My 1982 Range Rover has all of three fuses, so electrically I'm fine! Except the mess previous owners did to the original wiring... No idea why it is so difficult to just make your own wiring for after market accesories instead of butchering the OEM one up beyond recognition. It works, so I don't touch it. I have no idea why it works so...

Yeah I don't touch anything in the box beneath the passenger front seat ;) The previous owner thankfully already fixed the "oil creeps up the wires" issue, so I can leave it. Nothing I'm too keen on, but simple enough I figure.

> I have no idea why it works so...

I know that feeling haha. Adding wiring is so much easier than ripping up existing stuff ...

When a mechanic from Land Rover saw the wiring, he said something along the lines of "just fault location would be 2k, none of the colors I see should be there". A mess... But hey, the 80s and 90s were a wild time, and it is rust free!

Depends on where you connect stuff. Directly to some wiring loom that is already there? Bad idea, not all connected equipment will take the aditional loads well. Going directly to the car battery with dedicated wiring? Doable, but since start-stop is a thing, battery management and other stuff migjt not like that very well neither. Second batery? A bitch since start-stopp.

Hence, one needs some good knowledge around that, what to connect where.

In the old days, well, just go directly to the main battery with your aftermarket wiring and Bob's your uncle.

And none of that, battery management, which equipment can be connected where, has anything to do with the voltage but rather with all the other stuff modern cars have (bus management, battery management, ECus,...) all of which might or might not accept voltage and amp fluctuations very well.

Dead easy is relative I guess, I once tried to track down an issue with the wiring loom of my 400cc motorbike and ended up giving up…

> as soon as you have electronics and bus systems DIY basically requires deep car electronics knowledge and skills.

So how is this done on cars? Dores each manufacturer have their own proprietary bus system (what i imagine), or is there a standard that everyone can use?

Nah there’s been mandated standards since the 90s eg OBD I/II/III

Protocols like CAN, LIN, SENT and XCP are all standardised point to point and bus protocols for automotive stuff

I personally think the standardisation is actually a bit limiting[1]

Just like SpaceX found massive cost savings in using networking tech over hard wired interconnects, I think there’s a good chance China or other manufacturers might catch on

[1]I think interconnect failure rates are so low out of factory it’s not unethical to begin making things more lean, obviously with sufficient human safety testing

But I’m not an expert, just a former engineer working in an electronics shop…

I guess you work at Jaycar too? Always a fun conversation trying to explain voltage drop to someone who wants to cheap out on cable with our inverters and DC/DC chargers.

I'm sure a 48V bus would solve all those F1 errors too.

That's funny, I assumed the same.

Not an employee, but a very happy reoccurring customer.

Yeah my dude

Didn’t think there’d be more than one of us on here

Such a wild west company to work for. I enjoy meeting the many very bright people who work for us before they inevitably move onto other things

Back in the '80s I was helping a buddy upgrade the stereo system in his RX-7. The teenager down the street comes by and educates us that "you should be using really thin wire, like telephone wire, because otherwise the amp sucks all your power." My buddy was an electrical engineer at Hewlett-Packard.

How do you integrate the 48V system with the existing 12V system when doing aftermarket/DIY work? Do you add a 48V inverter? A buck-boost DC-DC converter? between the battery (or main fuse block) and the 48V system?

You don't. 48V battery and separate circuits if it's an RV, otherwise forget it.

Do not attempt a hybrid system with different voltages DIY

In an industrial setting it can be done but you need an extremely well designed and made termination point for one system and an interconnect for another, I’ve seen customers using floating grounds (and negative voltages) to enforce it

If upgrading to 24V or 48V I recommend having a solid grasp on circuit protection first, and if you have concerns, pay the 30 minutes or so labour for an automotive electrician to inspect it

Thanks for posting this - I only noticed your reply now. Exactly this. Installing inverters for my own projects is what really highlighted the amp/volts/gaugerelationship. I quickly moved to 24V and will push for 48V for my next. As an aside I use Victron gear which I'm very happy with. Biggest install is for a film van and has dual 5KW inverters that can deliver 8KW continuous - and it's a 24V system.

Victron is an amazing manufacturer

I love that they don’t keep releasing new products so they can properly support their existing (extremely well made) lineup

Look into data centre infrastructure if you want to find interesting brands and solutions

A lot of automotive/DIY marketed gear seems to be reinventing the wheel and charging a much higher premium for it

Given the choice almost any EE would probably pick the higher voltage system for cost saving reasons, but I imagine they were mostly constrained by legacy compatibility requirements here.

It’a “smart”, but there are probably reasons it hasn’t already changed everywhere else.

> but there are probably reasons it hasn’t already changed everywhere else

Yes, the legacy OEMs are constrained by their suppliers, who dictate what they can (not) do.

In automotive, it is usually the other way round. Regardless, what exactly was wrong with the existing 12 and 24 V systems for auxiliaries that absolutely needed to be changed?

High current (amperage) requiring thicker wires, or more wires, thicker/heavier connections, more expensive switches, more cooling etc.

The move to 48V means much less power is lost (power loss = (IxI)xR ), cables can be much smaller, cables and terminals can be much lighter and much less copper can be used used.

Basically it's just a more efficient way of doing things.

Elon has said it's not a revolution, or ground breaking in any way, it is simply a step improvement. Anyone could have done it. Tesla did it.

As others pointed out lready, others did it, too.

Re-read the comments, others have not done it.

Audi has a mild-hybrid 48V (as do many others) that also runs some other things like active roll control and the power steering pump.

They still have a 12v system running infotainment, seat heaters, defrosters, powered seats, lights, etc. etc.

As I never knowingly listen to music on 48V, is it reall so much better than 12V?

It's not about making the music sound better anymore than getting rid of an internal combustion engine is about getting you there faster. Have you ever seen the size of the wires in a car that go the amplifiers? They're as thick as your thumb.

The move to 48V means much less power is lost (power loss = (IxI)xR ), cables can be much smaller, cables and terminals can be much lighter and much less copper can be used used.

Basically it's just a more efficient way of doing things.

> what exactly was wrong with the existing 12 and 24 V systems for auxiliaries that absolutely needed to be changed?

The same thing that was wrong with vehicles that get 10mpg.

The same thing that was wrong with laptops that get so hot they burn your lap and the fan sounds like a jet engine.

The same thing that was wrong with incandescent bulbs getting hot instead of using that energy for light.

This is about making things more efficient.

Of course it didn't 'absolutely' need to be changed. But the same can be said for 1000000 other innovations cars made since the Model T.

In the long term it will safe money while while being more efficient. As cars get more and more electronics it becomes more and more relevant.

Its something everybody has understood for decades, but nobody had a long term enough look to make it happen. Car companies were struggling t show profit. And in the 2000s companies like GM literally went bust.

And yes its true, OEM can tell suppliers what to do. But if you want something that suppliers don't have at hand, your gone pay for development. And if you are say GM, to move to 48v you need to literally coordinate the work of 100ish suppliers to bring the product together.

And remember, these OEM since the 90s have outsourced the majority of all electronics devices and the waste majority of the software. Do they have the internal expertise to manage such a transition?

Look at over-the-air updates, its still not standard. And even those cars that can over-the-air update, that mostly only for some of the core main components. Lots of the supplier delivered parts can still not be upgraded like that.

And the car industry had plenty of troubles in the 2000s so its not surprising they didn't do stuff like that.

Do Tesla have 800 V batteries yet? I thought they were still using 400 V for all the cars.

Cybertruck is the first Tesla vehicle with 800v architecture. The S3XY lineup uses 400v.

Musk did an interview with Sandy Munro about it. Worth watching.

And FWIW... 24V is very common for DC circuits in industrial control systems. 48V is used too but less common; however, 48V is very common in telecom.

up till now most ev‘s used 400v there are some with 800v and more premium models do get 800v

>48V architecture also potentially improves overall electrical efficiency for reasons that I am not sufficiently qualified to explain beyond a kindergarten level

This is double bad in a green energy and EV website: On one hand, they admit they don't now why that happens, but on the other hand, they also didn't research just a bit more on that, and that's bad journalism.

Most of the comment threads in this HN post are a lot more informative than the article

Also, "But don't you dare threaten to replace me with an LLM. Journalism is a sacred cornerstone of democracy and intellectual life!"

I don't know if I would call a self proclaimed content marketer a Journalist.

He said "Journalism". A non-journalist can produce material that can be considered journalism. A student can teach. A homemaker can even write working code.

The labels we give to others to divide us

> The labels we give to others to divide us

They gave the label to themselves

I always wondered why there's not some kind of nonprofit volunteer journalism organization you can get involved with.

It doesn't appear to be something anyone tries to get normal citizens into, despite the fact that we constantly try to convince people to learn other stuff with much less individual scale value, sometimes even somewhat crazy stuff like home chemistry experiments with lead salts.

I always thought that's what I'd want to do with my life if I wasn't coding, and maybe I'd be happier if I had gone to college and studied journalism...

Have you tried writing for Wikinews?

https://en.wikinews.org/wiki/Main_Page

Unlike Wikipedia, Wikinews allows and encourages original reporting. You don't need a journalism degree to contribute an article.

Because it would probably be overrun by the very opinionated.

This happens frequently with new political parties: Someone starts an organisation, it get some amount of traction. Suddenly a lot of new people join and turn the whole thing into a tool to spread their views.

AFD in Germany started like this, it almost happens to The Pirate Party, one can argue that Green Parties tend to suffer from this phenomenon.

> The labels we give to others to divide us

Labels are an optimisation, an imperfect shortcut. They are a way we represent ourselves to others. If you don't tell me you're an engineer, I have to ask a ton of questions to assess your area of competence and skill. If you tell me you're an engineer I can save minutes or hours by putting you in a rough box. If that box is unnecessarily constraining it'll become clear as we spend more time together.

When race, gender, sexuality are involved we agree that labeling to save time isn't something accepted. For all of the reasons why shouldn't label those groups applies other labeling.

Most agree that we shouldn't actively do it, but we definitely do it consciously and subconsciously. It's a very human trait, even if we don't like it. The brain just doesn't have the capacity to evaluate everyone from scratch every time, so it takes shortcuts, and 'accepts' people based on the way they present themselves. The kinds of clothes they wear, shoes they're wearing, and accreditation from mutually trusted institutions. I agree the shortcuts that cause harm should be curbed to the best of our abilities but we can at best notice it and correct after the fact - but it'll still happen.

(Shrug) He called himself one, although admittedly in a former role before moving to Electrek.

The point stands. People who DGAF about their jobs are going to lose them, and that's not a bad thing.

In before the ex-content marketers are breaking into your house to steal things to fence on Amazon…

Nonsense. It’s a bit of self deprecating humor and gives readers enough information to follow along.

"Before joining Electrek, David was a mobile technology journalist for over a decade at Android Police, where he started as a writer and went on to serve as Editor-in-Chief. He later accepted a side quest in the world of startup marketing, heading up content and product marketing initiatives at two SaaS companies."

I mean… it’s definitely more of a blog than a strict journalism outlet in the vein of say Bloomberg and whoever is on the EV beat.

The writer isn’t publishing false information, and it’s good that the comments are able to add more value! It’s a casual style that has humility and a touch of personality. That’s ok!

I wish the article had more info too. But I appreciate the author acknowledging the limit of their work and not trying to bullshit or skip over it.

I read Electrek daily and find it very useful. They cover a broad range of topic with more insight and voice than the usual crappy blogs that just rewrite press releases or someone else's articles. I particularly like the articles (like this one) that have "Electrek's Take". The Weird Alibaba EV articles are good fun too: https://electrek.co/guides/alibaba/

>potentially improves overall electrical efficiency

Looks like he understood it the entire time :)

I wasn't sure, so I asked:

> Higher voltage systems experience lower power losses over the same distance compared to lower voltage systems. This is due to the fact that power loss in a conductor is proportional to the square of the current. By using higher voltage, you can transmit the same amount of power with less current, reducing resistive losses in the wires.

12 Volts is 12 Watts per Amp.

48 Volts is 48 Watts per Amp.

Woosh. There's potentially a joke in there if you read it again while understanding the applicable equation for electrical power.

(V^2)/R

Woosh indeed, haha. I'm no EE but it sounded plausible. Maybe I'll get the joke if I do some actual reading. :)

> they admit they don't now why that happens

No, they said “not sufficiently qualified to explain”. Which is not the same as not knowing, given that the same phenomenon can be explained on a lot of different levels depending on when you get tired of asking “why?” - see this video of Richard Feynman “explaining” magnets: https://m.youtube.com/watch?v=MO0r930Sn_8

To me that difference doesn't really matter. At the very least they should have educated themselves, and then provided links to resources to allow people to understand if they didn't feel comfortable explaining it directly.

This is not too surprising for Electrek, which is run by Tesla/Elon fanboys and mostly got popular by accident during the rise of the EV.

I like Ars Technica's car coverage: https://arstechnica.com/cars/

Eh, I'm not sufficiently qualified to explain relativistic time dilation, but I'm quite certain it exists and we can count on it.

>Most of the comment threads in this HN post are a lot more informative than the article

To be fair, how many commenters on HN would accept a job in journalism if it was offered to them?

We're lucky that so many qualified people share their takes for free on this website.

Audi also has a 48v architecture in use for mild hybrids like my SQ5. This is an older article but explains it well https://www.greencarcongress.com/2017/06/20170602-audi.html

My 2021 is fully 48v except for an inverter for necessary 12v circuits (like cigarette outlets and the jumper pins) and a small motorcycle battery that is used for minimal 12v functionality. The mild hybrid battery is under the rear seats and spins the alternator to keep accessories running.

https://www.autoweek.com/news/a36331077/48-volt-hybrid-syste...

My guess is that handing this out is a very nice thing to do but perhaps irrelevant in a world where 400v and 800v drive systems are the state of the art. Those systems can’t rely on the car body as a common ground for all sources of current and have a lot of inherent safety concerns that force a lot of electrical engineering that my old Camaro didn’t need to have.

Most automotive parts are 12V so that just means due to economy of scale, 48V parts are more expensive. They are trying to reduce their cost basis by getting everyone to move over to a common, more efficient voltage spec. This is good industry advocacy.

There's a crossover where ROI results in lower wiring costs.

My understanding was that nearly every production vehicle on the road is 12V and that Tesla and perhaps Audi as you mentioned are doing things differently. Who is using 400-800V systems? That sounds extremely dangerous.

They're getting mixed up, the 400-800V systems are _only_ for the motors, everything else in the car still uses low voltage.

In fact, afaik every single electric car has two separate systems. There's a high voltage system (the main battery and motor(s)) and the low voltage (almost always 12v) system, usually with a traditional lead-acid 12v battery that is charged via a DC-DC converter connected to the high voltage battery.

Not true in most EVs regarding 'only the motors'. The AC/heat pump compressor is run off the HVDC, typically. Since it runs for long periods of time and consumes kilowatts, you want to run it straight off the main HV battery. Also, any vehicle that still uses resistive heating (older EVs tended to do this, Tesla included) use the HVDC for that.

I’m speaking about the power planes. What they drive is irrelevant from the standpoint that higher voltage systems create safety issues that lower voltage systems do not have. No one is going to be ok with “occasionally being shocked by 48v” or “occasionally seeing arcing in their car from a high voltage system.”

Running 48v to a radio is not an engineering marvel. Running it safely and reliably in an automotive environment full of vibration and weather is.

If you can do that with 400v, I argue you can do it with 48v, so the secret sauce they’re sharing is less relevant than if they did this ten years ago.

I feel like you're mixing up points now, running 48V is fine _because_ the voltage is low enough that it's unlikely to kill anyone if you mess it up. The 400V system in the meantime has a lot more care taken and limiting the systems it works on to ONLY high power systems lessens the number of things that can go wrong.

A ton of trucks are 24V, especially in EU. 48V in automotive industry is something new; I can't remember seeing it on any commercial trucks.

Electric bikes use 12V, 24V, 28V and even 56V. Nobody loves the weight and the cost of thick copper wires.

400V or 800V are charging voltages, because it's the operation with the highest current; to keep it manageable while transferring more energy you need really high voltages. AFAICT, motors inside a Tesla use 320V. I suppose that ICE-electric hybrids also use some reasonably high voltage to feed the electric motors.

Tesla uses 800v only to run the Cybertruck's drive motors. Every other electric load in the truck uses 48v. Both of these are much higher in the Cybertruck than all other Tesla models. All other Tesla models use 400v [IIRC] for the drive motors and 12v for everything else.

Newer builds are using 16v lithium batteries for low voltage.

Pretty sure the AC/heat pump on the Cybertruck runs off the 800V pack. Since it consumes so much power for long periods of time, it makes little sense to run it off the 48V. Existing other Tesla's use the main pack voltage for AC/heat pump.

Good point and makes sense.

Mercedes introduced their 48V hybrid in 2016. Kia in 2018. Peugeot just introduced theirs this year.

Jalopnik was talking about the "48V revolution" in 2017:

https://jalopnik.com/everything-you-need-to-know-about-the-u...

At least once delivered early then? Sharing tech 6 years before their annoncement of sharing it!

Alternative take: Everybody else was aware 48 V networks work as well for decades, there was just no real benefot in switching yet. And Tesla has nothing to do with it.

What's next, Tesla annoncing they will share the revolutionary tech of windscreens and doors?

>Who is using 400-800V systems? That sounds extremely dangerous.

Every electric vehicle. And yes, it is dangerous to work on the HV circuit.

Not all of them. The Kia Niro I’m driving as a rental this week has a 240v battery. Level 3 charging it feels wildly slow compared to my car.

But yes, you’re right the increased voltages add a lot of risk that has to be managed.

And, thankfully, high-voltage systems are extremely well-managed in EVs.

Evidence in support of this claim is that EVs are statistically 4-5 times less likely to catch on fire compared to ICE vehicles.

https://gmauthority.com/blog/2023/11/ev-fires-less-likely-th...

Not sure how relevant this is, but curious readers might be interested: In those 400-800 volt systems, the low-voltage system is used to wake up the battery's computer and close a normally-open contactor inside the battery that connects the high-voltage system.

So indeed they might not ground HV stuff to the chassis, and the hundreds-of-volts sources are disconnected if the car is turned off and unplugged.

Exactly. Apart from waking up the vehicle and closing the high voltage connectors, a whole myriad of things run off the low-voltage system, including lights, climate, infotainment and most (if not all) actuators.

> This is an older article but explains it well

https://www.greencarcongress.com/2017/06/20170602-audi.html

From the article:

> The 12-volt system is connected to the main electrical system via a DC/DC converter

> Audi also offers the new MHEV technology with the conventional 12-volt electrical system

> 48-volt vehicle electrical system. In a different layout—without MHEV—the 48-volt constant voltage system already entered volume production in 2016 as the Audi SQ7 TDI. In this vehicle, the alternator still operates on a 12-volt basis, and a DC converter couples the 48-volt electrical subsystem

> Small consumers such as control units or lights will remain in the 12-volt system well into the future, however

The article makes it very clear that what Audi are doing is not similar to what Tesla have done with the Cybertruck. The Cybertruck has no 12v system, everything runs on 48v. The power seats. The seat heaters. The rear defroster, the interior lights, literally everything. They can have much smaller and lighter wires and use way less copper.

Using a 48V system for a mild hybrid is very common, even Jeep do that.

Realistically, using 12 volt and 48 volt for accessory systems are pretty similar. 48 volts just reduces your current, and you have to design everything for ~56 volts instead of ~14. But it's not really a different exercise.

> 48 volts just reduces your current

"Just" is doing an awful lot of work in that sentence.

Yes, moving from 12v to 48v reduces the current. That means you can have much smaller gauge wires, it means you lose a lot less power ( powerloss = (II)R ), it means you use a lot less copper and it means you save a lot of weight on wiring and connectors.

That is literally the point.

Right, the reason to do it is obvious and the development work is straightforward, it's a step forward but it isn't something to get all breathless about.

Absolutely, Elon said that himself in the recent Munroe interview.

It is just bringing car wiring into the 21st century.

At least in the case of Audi it is more than just the starter used for the mild hybrid depending on market and configuration. On my generation/configuration of car it is also used to prespin the Turbo to avoid lag, it powers the active magnetic suspension, the AC compressor, and the power steering pump (annoyingly located between the feet of the driver and the seat where you can feel it when it runs).

While you’re right on the accessories voltage, In other comments I’ve made the point that I’m not trying to say anything about the merits of 48v accessories. Jim Farley and Elon’s bromance aside, the tech exists within car companies. It’s nice they shared but it’s not like NACS where a real issue is being solved. Problems of driving aren’t solved with 48v interior lights.

Supply lines are a real challenge and why my Audi still has 12v heated seats despite having a 48v system available. The head unit is 12v. I’m guessing the speaker amp is 12v even though 48v would make that less challenging. They have a 12v only model that shares parts and they apparently didn’t want to move everything to 48.

Sure, they use the 48v mild hybrid system to act like the ICE when the ice is not running to power some things that would be on the serpentine belt and need to keep spinning when the ICE is off. It's a slightly more fancy engine start/stop system.

> the tech exists within car companies

Of course. Elon said very clearly in the sandy munroe interview the move to 48v everything is nothing revolutionary, its just bringing vehicle wiring into the 21st century. Anyone could have done it, they just have not been able to pull it off before now.

> They have a 12v only model that shares parts and they apparently didn’t want to move everything to 48.

They couldn't move everything to 48v because their suppliers dictate what they can do, and that prevented them.

> except for an inverter for necessary 12v circuits

Nitpick: That's a DC-DC converter, not an inverter.

> My guess is that handing this out is a very nice thing to do but perhaps irrelevant in a world where 400v and 800v drive systems are the state of the art.

The high-voltage system for the drive motors, whether 400V or 800V, is unrelated to the low-voltage system for accessories. The transition from 12V to 48V is concerning the low-voltage system. Prior to the Cybertruck, no automobile ever had a fully 48V low-voltage system. To learn more about how this is a big deal, check out Jason Cammisa's video on the subject. I've cued it to the specific topic in the [1] link below.

[1] https://youtu.be/L6WDq0V5oBg?si=dbzsPMAkvmGiQQ8n&t=613

>and the jumper pins

It can be started through the converter? That takes something like a hundred amps. It must be pretty beefy.

No.

For safety, hybrids and electric vehicles physically disconnect the high-voltage battery from everything when it's off with massive relays. So you can end up in the somewhat stupid situation where your high-voltage battery is fully charged, but you can't do anything because the tiny 12v motorcycle battery is flat.

Starting simply requires enough 12v current to close a relay, the amps going though the "jumper pins" are tiny. And once the relay is closed, the high-voltage battery can keep the relay closed and charge the 12v battery via the dc-dc converter.

The amount of current to "jump" a hybrid or electric car is so small that they really should just install a USB-C cable, so you could just use your phone to jump start it.

That describes the situation where the 12V battery is flat but the HV battery is charged. But what happens if the HV battery is flat on a non-plug in hybrid? Can it be charged from 12V?

Wouldn’t you just start the car if the HV was flat and the LV was charged?

If they’re both flat I agree, I’m curious what you do.

There is no 12v starter motor, it always just uses one of the large motor-generator units to start the engine, and in the Prius drive chain, they require 600v (boosted from 200v from the HV battery).

So if the HV battery is flat, you can't start the engine to charge it.

Wild! Thanks!

Yeah, I started wondering the same thing as I was writing that response, as I do actually own a Lexus with the Prius drive chain.

For starters, it would be pretty hard to get into that state in the first place. My understanding is they actually report a 10% or 20% charged battery as "completely empty". And the it's completely disconnected, so it shouldn't discharge much.

Looking though the service manual, there doesn't even seem to be an error code for "HV battery low", nor any mention of the DC-DC converter being able to charge the HV battery from 12v, it only goes from HV to 12v.

So I really suspect if you do happen to end up with a flat HV battery that's too flat to start the engine, it's just going to flash the "Replace HV battery" error code. Theoretically, someone with the right tools could disassemble the battery and charge the individual modules.

And the only speculation I can find on google is that "flat HV batteries are very rare" and probably only happen when the HV battery has other issues and needs replacement.

Edit: After more googling, apparently Toyota dealers have a special charger called the THS that can charge the HV battery in non-plugin hybrids.

No. Nobody is putting in a 12v to 400v dc to dc converter. There would be no point. I haven’t done the math but I’d be surprised if you got more than a couple miles out of it. If your high voltage battery is completely dead, you’re calling a tow truck.

In the case of my Audi, the starter motor is 48v so the 12v system charges the 48v system enough to start.

In EVs the 12v system is used to power a contactor that connects the EV battery to the drive system. That’s the clicking sound you hear on power on and power off and another contactor can be heard clicking during charging.

Its not that same, that Audi still had a 12V system because all the commodity parts (control units, interior lights) are built to run on 12V. What Tesla are doing is getting rid of 12V entirely so that every little window raising motor or interior light or actuator to move the seats is running on a 48V system.

48Vdc is supposedly the highest voltage that is still considered safe. (https://electronics.stackexchange.com/questions/267789/how-s...)

It certainly sounds like a smart move on the copper savings alone.

Extra low voltage is 50v ac or 100v dv. https://en.wikipedia.org/wiki/Extra-low_voltage

For some reason people assume it's 48v DC or 50v dc. But it's double that. That said, I feel significantly more scared dealing with 100v DC than I do 48 or 24v.

That's for IEC. Under OSHA it's 50 volts, AC or DC.

ELV is not a fundamental definition of "safe". The limits of what's safe depends on the application and your risk tolerance, and ELV is just a name for a couple of definitions out of many.

Also, those numbers are for ripple-free DC, which you're not going to find in a car. They're cut roughly in half for ripple peaks.

I find 48V a lot less scary when cars are involved than 12V. Neither is particularly likely to electrocute me, but 48V comes with fuses that will trip at 1/4 the current, giving 1/16 the resistive heating if something shorts, which is a lot less likely to melt or ignite things. Also, the wires are much smaller :)

> 1/4 the current, 1/16 the resistive heating

Really underappreciated safety aspect. The currents required for your average doodad at 48V leave you with a MUCH lower chance of unscheduled welding.

Remember folks, everything is a fuse if you put enough current through it, as a rule of thumb it's good to keep "enough" pretty low.

"The job of the transistors is to protect the delicate fuses."

--old EE lore

I used to work on vacuum tube power amps. 400v+ B+ with big caps is stressful to deal with. And doing it a lot can lead to complacency.

We used to call getting shocked "getting a taste" - like getting a taste of ice cream, except it's more like a microsecond blackout.

I have been shocked by 110V DC and let me tell you, it hurts. A lot. Would not recommend.

Remember a fully charged lithium battery with nominal 48v can be close to 60v just like 12v in your car is actually closer to 14v.

However there is a lot of leeway on the "48V is the highest safe voltage" statement too. 48V has a special place in regulations because of its use in telco, but 60V DC is still very safe.

Doubling again to 96 is not safe, however. I’m not sure why they settled on powers of two. Something perhaps to do with noise filtration, and fewer new tricks to learn?

It's convenient to build things in multiples and powers of 2 and 3. A nice two-tier or four-tier battery rack full of 2-volt cells just works out nicely.

Smaller transformers with whole numbers, right? But why 4 and not 3 or 6?

We seem to stick with 7-smooth numbers, and really extra prefer highly composite numbers (https://en.m.wikipedia.org/wiki/Highly_composite_number) for things we chose before the age of calculators.

3 and 6 were the standard voltages for consumer stuff back in the days of people needing to buy multiple packs of AA cells every year

Are we not all still buying multiple packs of AA batteries every year? Or maybe it's just those with kids.

Oh I hope nobody's doing that, rechargeables have been so good for so long. I'm just now retiring some that I bought in the 2007-2011 timeframe which have started to fail, but my 2015 purchases are still going strong with hundreds and hundreds of charge cycles on 'em. I haven't used alkalines since the 80s.

I have not had great luck with rechargeables. They have a lower voltage than regular AA, so I find that most sensitive electronics just start out thinking the battery is already low and then stop running before the battery is fully discharged. My Z-wave keypad lock is one of those. AA batteries last about 2 months, rechargeables start giving a low battery warning after a week and hardly last 2-4.

Have you tried lithium rechargeables with the built in converters?

I return garbage products like that. Not supporting rechargeables in 1980 was sort of forgivable, but they've had 40 years to get their act together.

I think it might mostly just be those with kids!

And non techies. They always have a few disposable battery flashlights hanging around it seems like.

Aside from modern barrel jack supplies, none of it is actually powers of two, it's like, 13.8v lead acid or a little higher for lithium.

I think we just stay close to the numbers we do, because we just really like multiples of 12 and numbers with lots of divisors. 24 hours in a day, 360 degrees, etc.

Most numbers people really like a lot seem to be on the 7-smooth numbers(https://oeis.org/A002473) list and related/overlapping sets like highly composite numbers.

Which I think is super cool, because it means you can choose one and there's a good chance someone else chose it too for something similar, unless they were using renard numbers or something instead.

A lot of 48V infrastructure comes from the marine world - where 4 x 12V lead-acid batteries in series is common for this reason. So a lot of components already exist and can be made to work in the automotive sector with simple modifications. (In the marine world, it's much simpler to combine and split batteries in powers of 2 for cell balancing - you can take 4 x 12V batteries and charge them in parallel, discharge them in series)

Sure but they can feed the system through a regulator if they'd like. Do we have any reason to believe they are tapping directly on to a pack for this part of the system?

Normally the battery is the regulator it serves to buffer inrush loads and absorb spikes.

> Normally the battery is the regulator

For a 12v system, of course. But on a modern 48v system who knows what they decided. Having a switching regulator with built in current limits might be helpful.

Its actually difficult to for a "regulator" to do what battery does, the battery can output significant surge as needed and its resistance drops as voltage rises absorbing large spikes without issue.

In the Cybertruck there would need to be a DC-DC buck that could handle the 48v inrushes properly from the 800v traction battery and spikes would have no where to go as the DC-DC would not be bi-directional or even if it was could not react fast enough.

For battery-powered systems the nominal voltage is used. Telephone "48 volts" is 55.2 volts in practice, only falling near 48 if there's a power failure and the office generators don't autostart in a timely fashion.

That's never caused any regulatory problems for Ma Bell, despite OSHA saying 50v is the cutoff. And personally having spent roughly a decade of my career crawling all over such systems, 55.2 doesn't bother me one bit.

Span-powered T1 at 130VDC, on the other hand.... that'll poke ya. That gets little plastic covers over all the terminals, but they have been known to fall off. So there is a meaningful threshold, and 55.2 is solidly below it.

Which suggests to me that there's a good bit of leeway built into the standards, perhaps specifically so they don't have to wheedle about whether a battery system should be measured at its nominal voltage, its float voltage, its absorption voltage, its peak/equalization voltage, its....

> That's never caused any regulatory problems for Ma Bell, despite OSHA saying 50v is the cutoff

I seem to recall getting a buzz when touching phone wires - while the line was ringing. I think I measured around 100 VAC. Apparently that's "ok", safety-wise.

Ringing is 90VAC, 20Hz, current limited. And it's only on for 2 seconds and then off for 4, so it's not like you're gonna grab on and be unable to let go.

So, yeah, as a momentary thing it's not a hazard unless it tickles you off a ladder or whatever. Punchdowns and terminal blocks are normally mounted where they can be worked on from ground level so that's unlikely to be an issue.

> That's never caused any regulatory problems for Ma Bell, despite OSHA saying 50v is the cutoff.

I'd be surprised if the wired phone system is not allowed to do a lot of things that would not be allowed under current codes and standards. By 1920 about 35% of US households had a phone. Upgrading all of that to keep up with evolving safety standards would probably have been way too expensive, and so I would expect that there was a lot of grandfathering.

> That's never caused any regulatory problems for Ma Bell

Telco lines generally are not considered safe voltage. One thing is that ringing voltage is fairly squarely above the threshold and another thing is the whole outside plant thing (ground potential differences, lightning strikes...).

60V DC is the upper limit for circuits that untrained personnel can work on and be exposed to as listed in IEC 62368-1. This is the standard that most consumer goods and IT stuff use to validate and verify electrical safety. 60V isn't going to be hazardous to a person in basically any situation.

It's a bit of an arbitrary determination; 60V is the international common denominator on what various legal or civic (e.g. insurance) regulations consider safe; https://en.wikipedia.org/wiki/Extra-low_voltage#Separated_or...

48V is somewhat of a dinosaur from the days when you designed things with a 20% margin since that's what was cheaply attainable. Regular PoE is 54V these days (10% margin), and some more specific applications creep even closer to 60V. (I've seen 57V and 58.5V, which is of course 5% and 2.5%)

What's a commonly produced thing that's 48v? I don't know much about this subject. Is it most industrial type stuff or is there consumer tier products using it?

ebikes, phantom power in audio equipment...

Basically the whole telco industry runs off 48V, and has for a very long time. You'd have a rectifier box that would take the AC and output 48V, and then everything would run from that.

A lot of the satellite and wireless equipment I've worked on has inherited that and runs off 48 too.

240W USB-C uses 48V, so that should eventually become common for stuff like gaming laptops.

Pro audio - most condenser microphones (except electret) run off 48v provided via the mixer/audio interface through XLR cables

With wet hands, even 48v hurts.

On my tongue, 9V hurts. There is pain, but no harm.

The "expert" in the article got it wrong. The relationship between the voltage and the losses in the wires is not proportional. They are squared. Going from 12V to 48V is not a saving of 4x rather 16x.

For some applications you could also consider Power over Ethernet in the car, get both shielded comms and power. Or can and power over twisted pair.

The great thing about PoE standards is there's so many to choose from. https://en.wikipedia.org/wiki/Power_over_Ethernet#Standards_...

Honestly, ethernet introduces a degree of non-determinism with respect to time in the link layer, plus increased bringup times, a potentially more costly core switching fabric, and the need for critical revision of latency assumptions on any potentially safety-related control concerns. Also, max current is not high. I would wager these are the reasons it won't be rushing to an EV near you... it's basically only suitable for a subset of uses, and heterogeneous infrastructure costs more in design, installation and maintenance cost than it nominally saves in production volume standards alignment and HR familiarity. (Source: Mechatronic systems design for the last ~8 years, IANAEE)

Sure. It's also not like there are many ready made devices that are already available for PoE that could be useful in automotive industry.

I guess my main thought was that going to 48V and in the world of low power LED lights and such, combining power and comms into same wires/cables is something that might be appealing.

Historically and increasingly, automotive grade electronics are a separate genre to general electronics for reasons of safety.

It's less of a safety but more of a production and environmental constraints issue. Cat5 cables are too heavy for cars. Their connectors aren't made for vibration. They have a lot of emissions which is a problem for the mission critical parts (Ethernet Phy often isn't mission critical). They are expensive, which is actually the biggest reason they aren't good for automotive.

Automotive reliability is only an issue for your ABS sensor, airbag sensor etc. but these are a minority compared to what's in modern cars these days. Real driver is cost, compactness (cost) and harsh environment (temperature and vobrations) and EM emissions. It mainly adds to qualification time, but actual semiconductor design cycle isn't that long. That being said, data center stuff is also notoriously slow to qual.

Automotive ethernet over copper physical layer is completely different than commercial/data center ethernet. It is defined in 802.3ch for multi gigabit (2.5, 5 and 10 Gbps). It uses single shielded twisted pair cables up to 15m long. Cables and connectors are automotive grade.

The power over data line (PoDL, automotive Ethernet equivalent of PoE) is defined by a separate IEEE protocol and its critical specifications like EM emissions tests, ESD tests etc are supplemented by documents created by a consortium of car, electrinics, comnector, cablr and semiconductor producors called OPEN Alliance: https://opensig.org/ . There are parts available for PoDL. The voltage levels from 6V to 60V with 6V increments are supported.

Source: I design both data center and automotive Ethernet chips.

Regarding deterministic latency, the Time-Sensitive Networking (TSN) [1] set of IEEE standards address this. The IEEE P802.1DG project [2] in particular defines a TSN profile for automotive.

[1] https://en.wikipedia.org/wiki/Time-Sensitive_Networking [2] https://1.ieee802.org/tsn/802-1dg/

> The great thing about PoE standards is there's so many to choose from.

There is nothing to choose there. They're supersets of each other with increasing power budget, each including the previous revision as lower power classes.

(and PoDL is not PoE; PoDL is for automotive ethernet, which has nothing to do with the RJ45 you see everywhere on consumer/business IT. You never choose between PoDL and PoE, the choice is made when you decided between Xbase-T vs. Xbase-T1.)

> ethernet introduces a degree of non-determinism with respect to time in the link layer

That's what TSN is for, cf. sibling comment.

> plus increased bringup times

That's generally an IP problem, not Ethernet.

> a potentially more costly core switching fabric

I guess it depends on your application; a TSN-capable 8-port automotive ethernet switch is $10: https://www.digikey.com/en/products/detail/microchip-technol... (non-TSN non-automotive is cheaper…)

> heterogeneous infrastructure costs

Automotive ethernet is supposed to replace CAN and the various heterogeneous higher-speed interfaces that were added to deal with higher bandwidth requirements with a homogeneous ethernet world :)

(Source: I work on some software remotely related to some of this shit. Which does mean I'm biased since I don't know whether it will in fact proliferate, I just make it work ;)

Ethernet is already used to transmit radio signal over fiber which requires extremely tight variation in latency (probably more strict than automotive).

Automotive Ethernet is not 8P8C...that's not how they do it at all

Some cars even use optical networking between the front and rear of the car. I think a bit of that has gone away now that you don’t need a DVD full of map data in its own module in the trunk.

You don't need it for the DVD anymore, now it's the zillions of cameras instead. The IEEE recently standardized automotive (= single pair) multi-gigabit ethernet (2.5/5/10GE) in 802.3ch…

If you go to a higher voltage, you will typically use smaller wires.

Tesla didn’t invent 48 volts either. The EV and hybrid electric world were talking about 48 volts when Musk still worked at PayPal, if not earlier.

One of the examples pulled out at that time was that you could shave a couple pounds of copper off the alternator by running it at 4x the voltage. Much thinner wires.

Tesla's greatest innovation is simply leadership. Everyone knew castings were the way to go, but noone did it. Now people like Volvo are doing them, and I expect a lot of others to do it as well.

Everyone knew that 48V would be a big benefit, but noone did it.

TBH, in a few years, we may be saying similar things about drive-by-wire without a mechanical backup. But it is too early to say definitively.

What everyone was waiting for was for Italians to make the huge casting press so that castings could be done in mass production at automaker margins.

Despite Tesla's boastings, large casting machines have existed before. Automotive use is the new part.

Essentially it was question casting of this size being automated at car maker scale. Bigger castings were integrated before on assembly lines, but at higher costs and complexity before Italians made the large mostly automated caster that Tesla called GigaPress (iirc) - it's essentially COTS factory equipment.

What's actually new and interesting here is the combination of size and speed. Sure casting existed, but for it to be the backbone of a super fast production line like that of a Model Y, they needed to do a lot of work.

Larger parts were often dipped into liquid, because air cooling resulted the part bending.

Tesla internal materials team worked on new alloys to improve this, while working in coordination with the machine manufacture to get up the cycle times.

And they are continuing to work with them. Tesla is using newer more advanced cooling systems in Texas then they did in the California factory. Because cooling is one of the limiting factors in Cycling these machines.

Except it was Tesla that went to the Italian casting press manufacturer and the made it a project together. Tesla asked for the biggest they had and asked for bigger and basically bought 5 years of machines, allowing them to do the necessary investment. And Tesla also used its own internal materials team to develop alloys to optimize the process to make it practical for high volume production lines like Model Y.

> Everyone knew castings were the way to go…

The jury's still out on whether gigacasting is courageous, or just moves costs from production (which will not be passed to consumers) to repairs (which will).

> Everyone knew that 48V would be a big benefit, but noone did it.

Audi did in 2016 with the SQ7 TDI, no?

Car A costs $5k less to manufacture than car B because it uses castings. Car A would be wiser to build because you can get better margins, or lower prices. It'll take a lot longer for buyers to catch on to the fact that the car costs a lot more to repair.

The question is really if the castings result in more cars being written off as total loss. Any collision severe enough to damage them would likely be severe enough to also total out a car without them as well.

TBH, the repairability concerns seem to be overstated so far. There are still conventional crash structures in front of and behind them. It takes a lot to damage the casting beyond repair.

You are right, though. The jury is still out in that they haven't really been used in the real world for long.

> Audi did in 2016 with the SQ7 TDI, no?

I didn't know about that one, but it was still a dual architecture. Going full 48V is a bit different, assuming Tesla really did that.

Clearly no MGB fans at Tesla. The unibody is cool unless you live somewhere with snow, and then rust doesn’t just make your car ugly, it makes it unsafe. And expensive to fix.

Which is why I was always more of a Triumph fan.

The mechanical backup for a drive-by-wire system is different to all those other things in that it's a critical safety issue. If _anything at all_ happens to the electronics while driving then it's important that you can stop the vehicle safely. That mandates manual brakes and steering, even if they're barely effective at all without power it's a lot better than nothing.

The cybertruck has two separate steering motors for redundancy. Passenger jets have been doing "x-by-wire" for decades. Properly engineered it's as reliable as mechanical linkage.

Two motors is great and all, but that only provides motor redundancy and won't help if something happens to the electrical system.

Planes are fly by wire but that's because they literally have to be, no amount of gym time will let you move the rudder on a 737 by hand.

The 737 is not fly by wire.

Ok fair enough, it is hydraulic assisted instead but for the point I'm trying to make it's essentially the same thing in so far as it requires power.

I tend to agree, TBH. People bring up fly-by-wire, but even that is simpler. AFAIK, those systems aren't variable ratio the way CT is. CT literally will have different steering ratios depending on the speed, so one steering wheel angle will have different effects on the actual steering angle depending upon the speed.

How will that work in the real world? Could there be bugs? Will people get used to it or will it lead to mistakes?

I'm looking forward to getting a chance to try it, TBH.

I hear it’s kind of a pain in the ass to do a front end alignment on the drive by wire systems.

>> Tesla's greatest innovation is simply leadership.

Totally correct. We were making 48v power steering systems 20 years ago for OEM development projects. They simply don't have the will/commitment/leadership to bring change like that to market.

Elon sets a direction and people go that way. I can imagine someone at GM listing all the obstacles as a reason they can't change, and Elon looking at them and saying "no, you're the obstacle" or something like that.

Sure, people have been talking about 48 volts for the past 30 years. Somehow most automakers didn't actually manage to do it though.

Sandy Munro just did an interview with Musk, who said they hadn't done anything revolutionary, they just built the car up to general 21st century standards.

https://youtube.com/watch?v=ky1Z2klPalw

> The EV and hybrid electric world were talking about 48 volts when Musk still worked at PayPal, if not earlier.

You are confounding the two electrical systems in an EV or hybrid (or mild hybrid).

One is used to drive the wheels - these are very commonly 48V in a mild hybrid and something like 200V or 400V or 800V in an EV. This is only used to power the wheels - nothing else.

The other electrical system is used to power literally everything else. The infotainment system, heated seats, power windows, lights, powered seats, electric power steering, electric assist brakes, etc. This has always been 12V in every car ever ^ (ICE/hybrid/EV) (including every Tesla).

The Cybertruck is the first vehicle ever to move the 12V system to a 48V system.

^ Before about 1955 it was 6v. The move to 12v then was the last time it has changed.

I’m talking about the same thing. Pumps and compressors and electronics systems.

You're talking about some of the things that would be on the accessory belt (serpentine belt) on an ICE, that need to keep spinning even when the ICE is off (power steering, A/C, etc.). That is a slightly more fancy engine start/stop.

You are not talking about high current devices like heated and cooled seats, defrosters, infotainment and audio amps, power windows, power seats, lights, etc. etc.

Hold on a second...4x the voltage means you only need 1/4th the current. The power loss in the wire is current^2 x the wire's resistance, so 1/4th the current does indeed mean 1/16th the losses.

But 1/4th the current means you can use a higher gauge wire. Looking at a table of wire gauge current capacities it looks like if your maximum current is 1/4th you can switch to wire with 1/4th the cross section. And resistance is inversely proportional to cross section, so 1/4th the cross section means 4x the resistance.

Doesn't that then bring the savings down from the 16x you would get if you just upped the voltage down to 4x?

Yes, typically the savings would be in the weight and physical size of the wiring harness (as well as possibly allowing for tighter bend radii). You'd design for a max amount of heat generated by the wiring harness, or possibly a max voltage drop if that's a constraint. You don't need to do heat dissipation calculations yourself, there are standards like SAE AS50881 that do the heavy lifting for you.

Edit: Smaller wire is also cheaper of course. That's probably a pretty significant upside when talking about a mass-produced vehicle.

There's also a minimum wire size, based on physical durability requirements. A significant number of wires in the harness already carry no appreciable current and are merely signaling wires, but they can't be infinitely thin.

Getting most of the power wires down into the range of signal wires is a huge benefit, because it means they can use common terminals and smaller connectors, but that's where it stops.

For very low current wires, I've seen non-metalic (nylon?) strands woven in with the copper for mechanical strength.

Good point and you're not wrong. One mitigating factor is that resistance isn't constant: In copper it increases with temperature, and I^2R causes temperature to go up, which causes resistance to go up, and you get something of a positive feedback loop. Temperature rise is one of the main reasons why standard wire gauges are specified the way they are.

If you use 4x higher voltage, the temperature rise is much less significant (16x less significant to be precise) so it becomes more or less a non-issue and you can treat resistance as a constant.

> Or can and power over twisted pair.

I was reading an anti-Musk subreddit over on Reddit and I think the cybertruck is doing this? They were mad that the cybertruck uses 48V and Ethernet cables, but to me, that seems perfect for CAN and power. We already use 48V (or similar) for PoE, and CAN needs a twisted pair... so why not buy that off the shelf instead of using a custom wiring harness?

I don't think the cybertruck is a particularly attractive vehicle, but I also don't think they're crazy for trying that. You can do 10Gbps over a cat-6 cable and it works great. So I'd expect that you can easily do CAN.

Musk has publicly stated that CAN is too slow for modern cars, which is why they chose ethernet for the Cybertruck.

https://youtube.com/watch?v=ky1Z2klPalw

CAN buses run into bandwidth issues at some point. Just remove all the OTA, car-as-a-service and de-facto surveillance crap, and one should be able to get away with CAN buses.

Nothing wrong with ethernet, but listening to Musks statements, especially in fields I have some not even deep knowledge, alwqys like listening to a very confident, but otherwise clueless, 1st semester student selling you semester 2 basics as the latest and hottest shit under the sun nobody else even considered possible so far...

The question is do you want to have something that is high performance or something that you 'can get away with'.

We get it, you don't like the features of modern cars. Well sure if they built the car you would like, then CAN bus is fine. But that's simply not where the future is going, if you like it doesn't matter. Its simply not relevant when car CEO discuss what is needed for modern cars.

You solution of 'just remove X,Y,Y features' is just a laughable suggestion here. Its like saying 'you don't need a new graphics card', I play 'Star Craft: Brood War' just fine. Ok I agree, I don't play AAA games either but to criticize a Nvidia CEO for saying the need higher performance would be totally absurd.

Cars will get more electronics parts, more cameras, more safety equipment, more communication and so on and so on. Moving to higher voltage and PoE is simply a logical thing to do given that reality.

If Musk is so utterly clueless, what of the things he said is actually wrong? Musk even literally said its not 'hot shit', its just bringing things up to date. But that's the simple facts of the automotive industry, lots of 'we did it because we have always done it' and despite it not being 'hot shit' its really hard to change.

So in the automotive industry, such changes are great because if you are building millions of something, it makes a very bit difference.

Seems to me you are reading into it what you want to read into it.

Didn’t read the article, but Musk mentioned in an interview yesterday they are specifically not using CAN and are using Ethernet. He didn’t explicitly say, but it seems likely they are using PoE, saving a lot of wiring as you can daisy chain a higher bandwidth connection and you don’t need separate power cables.

https://youtube.com/watch?v=ky1Z2klPalw

Yeah, Elon talked about this in his latest interview with Munro. It seems that they just use Ethernet rather than CAN bus.[0]

[0] https://youtu.be/ky1Z2klPalw?t=791

Have a reddit link?. Search didn't help

I actually run Poe in my car to power a mini pc in the trunk. I guess I’m ahead of the game :)

TIL that 42V fizzled out https://en.wikipedia.org/wiki/42-volt_electrical_system

I welcome the move to 48V, as one gets lots of cross over synergies from the 48V telco standard.

https://www.servertech.com/blog/48vdc-power-and-the-backbone...

https://www.st.com/content/dam/AME/2019/developers-conferenc...

https://www.maximintegrated.com/content/dam/files/products/p...

https://www.infineon.com/cms/en/applications/information-com...

Agreed. 48V (actually -48V) has been used across telco central offices for decades.

It's a really nice voltage with lots of support for batteries and up/dn conversion hardware.

It's also right at the edge of what is human safe. You can burn yourself and blow up cables, but it's very difficult to electrocute yourself (afib or muscle seize) without lots of wet contact.

https://incompliancemag.com/article/experiments-of-dc-human-...

Indeed, I'm aware of only one recorded death by electrocution at 48V, iirc it was a Swiss radio amateur that had done a bunch of gardening sat down sweaty in a metallic chair and reached for the one switch of his set. Probably there were other contributory causes as well, I've been zapped multiple times from much higher voltage sources (that could have easily supplied the power required) and lived.

I can't find a reference for that Swiss case though. I'll keep looking.

I assume if you didn’t live from those zaps you wouldn’t be here making this comment.

Haha, fair point, yes, indeed. The most clear form of survivorship bias, thank you for pointing it out.

How exactly do you define a negative voltage unless you are using some other voltage as a reference?

Label the power pin+ GND and the power pin- becomes -48V

Voltages are all relative. It's like saying 'How do you get a height difference of 10 feet by digging?'

Well, you dig and then label the initial level as +10 feet, and redefine the bottom of your hole to be ground.

No. In telco, the -48V is referenced against ground, like the physical ground. If you're isolated, you can do this. but they would still need to be referencing the 'ground' to something ... likely the negative side of the main battery pack.

The reason why -48V is used is because it is provided as a bias voltage to give wiring cathodic protection, to prevent corrosion of telecom infrastructure. If you used 48V, it would not work. You need a negative voltage referenced against ground.

Ground positive terminal of battery string instead of grounding negative terminal.

I see this more often on European stuff

Generally with respect to ground. There are many good reasons to connect your power system to ground and so this is commonly done. (there are pros and cons to connecting to ground, but it gets complex fast)

It is with respect to ground, the positive pole of the battery is connected to ground.

The telegraph system figured this out very quickly. Most water in nature has at least a bit of salt in it, which is present as positive sodium ions and negative chloride ions. By making the outdoor wiring negative with respect to ground, the chloride ions are repelled, and such wires corrode much more slowly than those that're positive with respect to ground.

Since most of the telegraph network, later the telephone network, is outdoors, this is a pretty big deal.

> that’re

First time I’ve ever seen this typed

What’re you talking about?

I guess he refers to the shortening of "that are" into that're

I think you're missing your parent's joke.

Now I see it, thanks :-)

It's a matter of perspective.

You tie one of the leads to earth (literally grounding it)[1], leaving the other non-grounded. Depending on if you tie the negative or the positive lead to ground, you get 48V or -48V with respect to ground. As long as the potential between the most positive lead and the least positive lead is 48V, the circuit itself doesn't care.

As mentioned here[2], the reason for grounding the positive lead is to prevent galvanic corrosion[3] destroying the buried copper.

[1]: https://www.bicsi.org/docs/default-source/conference-present...

[2]: https://www.poweringthenetwork.com/uncategorized/negative-48...

[3]: https://en.wikipedia.org/wiki/Galvanic_corrosion

Apparently in cars it’s weirder. Wire it one way and the wiring corrodes. Go the other way and the body corrodes.

Voltage is a measure of charge difference so there must always be a reference, usually the reference is 0 V.

I don't think they'll be able to use much of that with their 48v PoE ethernet standard...

As mentioned in the 42v article they went with that due to 48v nominal being too close to 60v max on alternator/fully charged which is the limit shock hazard.

Not sure what chemistry/cell count will be for the 48v battery (which I assume it has) but 48v could mean 13s - 16s packs.

Are you telling us that 42 wasn't the answer after all?

Nah you have the wrong question. You'll need a bigger computer.

It is, just be patient and the battery will be drained to 42V eventually.

I liked the interview with auto engineer Sandy Munro discussing the change https://youtu.be/ADwGGEj8sqQ?si=qp6akvy1yyWPTYNe

- moving the voltage up means you can drop current

- increase the data rate by using ethernet and PoE

- using ethernet and PoE means you don’t have to run one off wires to each device, they can share a bus which results in half the copper being used in a lower voltage car

- moving the voltage up also means reduced heat produced

> using ethernet and PoE means you don’t have to run one off wires to each device, they can share a bus which results in half the copper being used in a lower voltage car

You mean like CAN bus is being used since 1990s? I think that Mr Munro little bit fell asleep and missed whole CAN bus and FlexRay evolution in cars.

CAN bus is still really slow (1Mbps, so bus contention is a problem). Sensors, cameras, AV stuff, etc. can't all live on the CAN bus. Cars are not the same things they were in the 90s.

>cameras

Yes. Post 2021 teslas have nine cameras scattered all over the body. For AV, Tesla would like to get much higher resolution and frame rates out of them.

CAN bus is multi-master access with automatic arbitration between nodes. Something what Ethernet is completely incapable of and that's the reason why CAN bus is here to stay for a long time.

Ethernet needs active switches isolating each branch of the star network from each other. Because Ethernet working in bus mode is absolute joke, slower than CAN bus if you add enough nodes to such network. But when you need to drag all sensors and ECUs to a center of a star where is switch, where is the saving on cables?

Even worse, there is no guarantee that node on such network will be able to deliver message to other node, thanks to CSMA/CD which says Random disconnection if collision. Well guess what? Your wheel just locked during braking and we need to tell that to ABS/ESP unit. When using CAN you can rectify it by using low CAN ID and thus increasing priority in arbitration. When using Ethernet, you are only praying to RNG Jesus.

> using ethernet and PoE means you don’t have to run one off wires to each device, they can share a bus which results in half the copper being used in a lower voltage car

Ethernet isn't a bus, its point to point. PoE over cat5/6 uses 4 pairs of UTP.

so it might be used to join aggregate things together, but it won't be a bus.

Yes, you can increase the datarate, but ethernet is fundamentally unreliable. So you'll need to either strictly manage the bandwidth requirements of attached devices, or put in flow control(expensive) or use the weird "reliable" Ethernet they made for fibre channel replacment ($lol and you need to pay to make it automotive rated)

48v is logical, and a lot of other people are doing it.

PoE is probably stupid

Ethernet makes kinda sense, but firewire would probably be better, its a bus and rated for life critical use.

Ethernet can be used as a bus (see CSMA/CD), but if there are more than 2 nodes, performance of whole bus will go to complete shit and there is no guarantee that an ECU will transmit a single packet during its run, because that CD has no automatic arbitration, it is just random disconnection and try again. Not good for critical things like ABS. That's also whole reason why FlexRay was spawned, because even that FR is inflexible abomination of a protocol it actually guarantees that every ECU on the network will get a time window to transmit its own data.

> CSMA/CD

Lol I'd forgotten about base-T.

I think that's what 10BASE-T1S (standardized in 2019) is for. It has a non-CSMA/CD arbitration scheme. https://www.electronicspecifier.com/industries/industrial/an...

So... you need new PHYs and new Ethernet controllers to use T1S?

A lot of the Googleable information seems to be from chip vendors who want to sell those things :) Yeah it's intended for new designs. Fewer wires than the original 10mbps ethernet.

I work for another EV manufacturer. Good God I would love to switch from CAN to ethernet. We already have way too many CAN buses and we're considering adding more. But it will take decades for our suppliers to even consider the switch. We just paid Bosch $15M for an upgrade to our brakes, they promised the change in six months, it took them two years and quite a few additional millions of dollars, and it's filled with bugs. We can't even run the new brake firmware on public roads it has so many bugs. And we'll have to pay them millions more and wait months or years more for them to fix their own mistakes. This is why Tesla does almost everything in house. I wish my company had the resources to.

Well, then you should maybe ask why do you need such complexity, when cars 5-10 years did not needed to do exactly same task - taking a person from point A to point B.

First of all, there are regulatory issues, that continually demand more both in terms of efficiency and in terms of safety. System that were innovative 10 years ago are not a requirements and new system are recommended and will soon be required. And that is just for minimal compliance. If you actually want to be up to date on safety systems you need even more.

Second, if you are a company you need to actually sell product. And turns out costumers don't want technology from 10-20 years ago. Costumers actually buy stuff with more technology in it. No matter if people on HN rather drive a Honda from early 90s.

So to just tell a company 'just go back in time and that will solve your problem' is simply not gone convince anybody.

Or their architecture is just bad - aka when you need Ethernet for your brakes.

Break-by-wire is pretty standard by now. Unless you have any evidence that the system Tesla uses is worse then traditional automotive CAM and that it is so much worse that there will be lots of Cybertrucks unable to break then I'm just gone go with team of engineers who designed a new system after having decades of experience with the older system rather then some guy on HN.

But doesn't that mean a single point of failure, a single network problem stopping the whole car? I guess there must be a historic reason for mostly direct CAN connections.

It would be great to have 48VDC in homes, for lightning, light appliances, etc. to centralize the whole power factor control in a single big power supply instead of doing it (poorly, or not at all) at every LED bulb.

It'll happen in RV's first, for obvious reasons. I imagine they'll use USB-C as the standard connector even though it's not the optimal form factor for this usage due to its ubiquity. POE would be a better choice.

Doesn't USB-C cap at 20V?

Latest USB-PD standard allows for 48V and 240W. It uses special EPR marked cables.

Replace all power outlets with Ethernet and have everything run over 48V PoE and get network connectivity too

While this sounds great in practice the reality will be far from ideal for the singular reason of security. The cyber issues are compounding at exponential rates as more and more devices that make things "easy" lack even the most basic security protocols and the production targets to generate revenue asap have zero to nil concern around protecting said devices from nefarious actors while in use. When the electrical and data transfer grid become one, as I believe it must for reasons of efficiency, we are certain to witness chaos and losses like never before. What you cannot see matters most! and in time many will pay the ultimate cost for someone else's 'easy'.

More like basically every electronics product uses AC. It’s a two sided market problem - there’s no demand because there’s no supply and no supply because there’s no demand.

The security aspects are solvable through various standards (eg we have LAN over power lines and coax already and they layer encryption on top to build the mesh while balancing UX). The security concerns may be the #1 concern for you but has nothing to do with market adoption.

PoE 802.3bt tops out at 71W. Not even enough to enough to run big USB-C adapter. Also, PoE is pretty lossy which defeats the whole purporse of using DC to save energy.

You would need larger wires to account for the losses at a house scale. Since nothing runs are 48 volts you still have the bad power supply in every LED bulb.

12 gauge wire would work fine for 48v lighting loads; probably 14 gauge too for many of them. Small DC constant-current sources are commodity items now and they're very efficient.

12 gauge is more expensive, and harder to work with.

And it's already in a lot of houses, which was my point.

The Dutch have some homes that are DC. Here's even a paper discussing this[0]. There is also a presentation that mentions DC homes from page 18[1].

[0] - https://www.irbnet.de/daten/iconda/CIB2595.pdf [1] - https://fhi.nl/app/uploads/sites/38/2018/06/10.00-DC-Power-e...

The DC power for LED varies based on the bulb and most are less than 48V. Which means you end up with DC-DC converter in each one. DC-DC is slightly more efficient than DC-AC but not enough to make worth converting.

The same is true of electronics, you are replacing AC-DC charger with DC-DC charger.

The other big problem is that lots of appliances require more power than feasible with 48V. People are fine with the low-power DC right up until they need to plug in a space heater. Are you going to have two kinds of outlets everywhere? Or incrementally upgrade each circuit? Or are going to upgrade the wiring with super thick cable that can handle the current?

> Are you going to have two kinds of outlets everywhere?

People already do, with usb sockets sitting next to mains sockets.

Of course if you standardise on usb-c you are still doing dc to dc (and all sorts of extra things) so not much point as you pointed out.

Golf carts have used mainly 48V for traction for a long time. And there are now great options for 48V LFP batteries for them. So far that usually means also running a 12V converter to power accessories. If the automotive world finally gets their act together on 48V this will be great for all kinds of DIY uses. The batteries and chargers are already here. There are a bunch of off grid and mobility applications that should be made simpler by this. Hopefully the automotive supply chain moves meaningfully around this.

Why would a car need a 48V system for accessories? In general the things a car's 12V system powers have gotten less power hungry over time (LED's, heat pump) and in particular, an EV loses the highest power electrical device on the 12V bus, the starter. The typical equipment used for the entertainment and control systems are going to be much more available with 12V supplies, just because that's the industry standard.

Obviously the traction system is using much, much higher voltages.

The article cites "complexity" of the wiring harnesses, which is nonsense. The wires might get a little smaller, but not by a lot. Like I said, the 12V bus in an EV isn't driving a bunch of high power stuff. (Is it? Am I missing something?)

The one place I can imagine it helping is for driving inverters so you can provide AC outlets for laptops, power tools, etc.

https://de.wikipedia.org/wiki/Bordnetz#48-Volt-Bordnetz_im_A... explains (a bit) why German car makers are using 48V since ~2016 (in addition to the still existing 12V system, which seems to be the difference with Tesla, which went 48V-only).

DeepL translation:

The 12 V electrical system can barely cover the power consumption that modern vehicles need for their comfort systems. The "static" consumers completely overload the alternator, which provides up to 3 kW of power, especially at low temperatures.[12] The battery power is not sufficient for additional dynamic consumers, such as powerful electrically driven compressors.[13]

For this reason, a proposal was made at the end of the 1990s to install a 14 V/42 V electrical system in motor vehicles.[14] From 2001, Japanese manufacturers and General Motors launched hybrid vehicles with this electrical system on the market.[15] Although Daimler-Chrysler was one of the co-initiators of this concept, it was not used in Germany. One reason for this was that it did not appear possible to demonstrate a corresponding utility value to customers for the necessary additional price[14].

Instead, since 2010, German car manufacturers have favoured the solution of providing a second 48 V electrical system to supplement the 12 V system.[9] Since 2016, the first series applications of 48 V electrical system components have been the operation of the electric compressor and the electromechanical roll stabilization in the Audi SQ7 4.0 TDI and Bentley Bentayga. Both are based on the same platform.

Translated with DeepL.com (free version)

A split 48/12 system makes a lot more sense. Run the heater/heat pump, power steering, coolant pump, etc on 48V and keep entertainment and controls on 12V.

Computer chips use ~1.5V or so these days. Why go 48V->12V->1.5V when you can go 48V->1.5V directly? If it's more efficient to use an intermediate voltage, you can choose the most efficient intermediate voltage internally rather than using 12V.

There is a lot of off the shelf 12V equipment you can buy. Plus even more that is sitting in garages ready to be installed in the next vehicle. Cars are manufactured in enough quantity that it would only cost $0.01 per vehicle to design it (plus parts costs which are probably the same), but that is still a few million to the bottom line if they use the same 12 volt radio. Add to that that ICE cars everywhere have 12 volt starters, and you can buy 12 volt jump start kits: when (not if!) a battery fails to start the ICE you better be able to jump start it from a 12 volt battery - this is a safety issue.

Tesla doesn't have ICEs, so the safety concerns are lost on them. Thus all 48 volt makes some sense. They still need something for all the accessories people have.

Because we already have the 12V infrastructure and part supplies in place. You're disrupting things for no benefit. We've been running split 24V/12V systems for decades now in automotive applications. It's not that big a deal to change that to 48V/12V systems as many European car manufacturers have done.

No benefit? I've seen estimates of $1000 in reduced cost due to reduced copper wiring, and more importantly the labor required to string that wiring.

Modern phones charge on 48V these days, so 48V parts are extremely common & cheap.

I'd fully expect other car makers to move to an exclusive 48V setup at some point. They just do it gradually: For the new model a part is replaced by its next-gen successor that is incompatible anyway? Put it on the 48V bus. Repeat until the 12V system is done away with - or force the issue when there are only a few components left, or downstep the 48V to 12V right in front of them, once that's cheaper than keeping the remaining 12V system.

It'd be cheaper to delete the 12V bus entirely and add 48V -> 12V converters in front of legacy components, even if they needed several dozen of those converters.

I expect Tesla to still have a few components like that in the car.

Isn't that the point of the article though? That they run everything on 48V?

I think all the wires/communication are but some of the devices attached are lower then 48V, some very low voltage, and some might be 12V. We will see when its taken apart.

> I've seen estimates of $1000 in reduced cost due to reduced copper wiring

What about aluminum wiring? Lighter, cheaper, though bulkier than equivalent copper. Aluminum wiring got a bad rep back in the day, but it seems with current electrical aluminum standards it supposedly works pretty well.

In sotuations where it is about space you wouldn't choose aluminum. Also afaik most automotive wiring that is certified is copper. Going from copper to aluminum means you will have to put bigger crossections in. This is more weight and more space.

Aluminum is hell to terminate. It basically requires ultrasonic welding; every trade-show has folks hawking various crimp terminals that're meant to break through the surface oxides during the crimp cycle, but not a single automaker has been swayed enough to use it on normal wiring.

The reliability concerns really add up with flexing fatigue, too. It's one thing to put aluminum wiring in a house where its only flex is due to thermal expansion, and it has a hard enough time coping with that it's still a special category in home insurance, to say nothing of a vehicle that's going to spend the next ten-plus years bouncing over the road.

Furthermore, you basically can't modify aluminum wiring. In-line splices and solders are virtually impossible. While that's irrelevant for manufacturing, it hits the aftermarket pretty hard, including dealer mods, and of course, dealer repairs. That can be worked around but it would require communication between branches who don't normally talk, and it just adds friction to any possible aluminum migration.

I've seen aluminum in a single very-heavy-gauge battery cable for a car that put the battery in the back, with ultrasonic-welded terminals on both ends, and that's it. Everything else in that car was copper.

What you may have saved on wiring is going to be offset by the increased cost of the battery (I'm seeing 2x-3x cost) and the fact you now need a much beefier alternator which is going to have its own cost.

You'd think if it were a slam dunk then the bean counters would have insisted on a transition to 48V years ago.

Total current consumption should be about the same (or even less, thanks to lower losses at 48v), so I'm not sure why would you would need a "much beefier" alternator. It will need different windings, but overall it should be about the same size and cost.

Once you've introduced a 48v system engineers will find ways to use that extra power. They've been spending decades carefully managing that power and making compromised. Now they won't have to. So yes, you're going to need a higher output alternator to keep the 48v battery charged due to the increased load.

What modern phone charges at 48V? I'm not aware of any that charge at even 20V, outside of a couple of gimmick devices. No Samsung or Apple phone charges at anywhere close to that, that's for sure.

What modern phone charges at 12v?

Most phones charge at 5v. Modern USB-C chargers can charge between 5v and 20v based on configuration.

Buck converts and regulators are cheap and small these days.

Most phones charge higher than 5 volts these days

Samsung phones can fast charge at 15v/3a (45W).

12V isn't a 'standard' USB-PD voltage, so pretty much none of them. Tons of phones charge at 9V, though. And some use 15V.

The regulators/buck converters you speak of are inside the phones these days. They want a higher voltage even if the battery itself is 3-4.2V, so losses from cabling are lower and you don't need a special 5A cable to handle charging at the fastest rate.

I believe Qualcomm's QuickCharge 5 can use the full 48V of USB-PD. Given it allows 100W, I certainly hope so.

Regardless, QuickCharge 3 is 20V and it's been in a lot of phones since it was introduced in 2016.

You can run smaller wires through the vehicle then down voltage on device.

Like I said, the 12V bus in an EV isn't driving a bunch of high power stuff.

Take a look at the fusebox in any modern car, EV or not. (There will most likely be more than one fusebox.)

You'll see lots of 20A, 30A, 40A parts, some even larger. Running those circuits on 12 volts takes more copper than you probably think it does. More copper and beefier (read: much more expensive) connectors. The move to 48V is frankly overdue.

Just to add the basic idea, the amount of power is amps * volts. So to carry the same amount of energy with a higher voltage, you can you use less amps. The amount of amps impacts how big the wires are, lower amps need smaller wires and that means less space for wires but more importantly less weight of the wires. There is a lot of wiring in a car. Tesla claims this could be 1/4 the amount of copper wiring in an article, below.

This article describes a bit about this, but also says something I never heard, that there were 6v auto systems in the 1960s. https://www.mining.com/new-tesla-low-voltage-system-a-big-de...

6 volt autos were going out of style in the 1950s. They did last into the 1960s, but they were already rare by then.

It may help some also to know what an amp actually is: 6.241x10^18 protons or electrons per 1 second of time passing a certain point. A single Amp is equal to 1 Coulomb and 1 Coulomb has 1 Joule of energy. I share this from my personal documentation in comprehension of understanding the unseen resulting from a device I am building to solve a personal energy storage problem. All open knowledge certainly but graphing these relationships into a visual depiction of the correlation has greatly assisted when talking to others that have ZERO knowledge about energy and power. Humans are nearly all 100% visual so explaining it with pictures presents A LOT of AHA moments for those without such comprehension.

The inverse relationship between amps and volts can also help: 50 volts * 24 Amps = 1200 Watts 100 Volts * 12 Amps = 1200 Watts 120 Volts * 10 Amps = 1200 Watts 150 Volts * 8 Amps = 1200 Watts 200 Volts * 6 Amps = 1200 Watts 240 Volts * 5 Amps = 1200 Watts 360 Volts * 3.333 Amps = 1200 Watts 480 Volts * 2.5 Amps = 1200 Watts 600 Volts * 2 Amps = 1200 Watts

Stay Healthy!

Power steering pumps are electric and have one of the largest wires in my truck. With an EV you also have a heat pump, maybe a heater, coolant pumps now that you don't a constant spinning pulley, windows, lights, headlamps, power doors, seats, radio, amplifier, small PC, etc.

From the article "Switching to 48V architecture alleviates a huge number of challenges automakers are facing with 12V. The biggest one, though, is complexity: You need far less complex wiring harnesses to power all your vehicle systems"

My take is that 12v requires almost a dedicated power line for each part, while a 48v could run to a bus line that gets tapped. 48v might be something that divides easier with the battery pack, and drops the 12v battery.

I hadn't connected the dots that all the various pumps (and fans) have to switch from mechanically connected to the engine via the accessory belt to electrically driven. That's a fair point.

It has been optimal to run accessories electrically for ICE already for several reasons. It has been difficult based on some of the loads on a 12v battery (agm has really helped this)

- Start stop is smoother (and more available) without accessories

- Cooling a turbo after the motor is off - true for the engine as well, heat soak on water pump off can go ~20f over the thermostat

- Brake Boosting without a vacuum (Valvetronic or Hybrid)

- Air Conditioning at idle

> Power steering pumps are electric and have one of the largest wires in my truck.

Most new cars don't have hydraulic power steering systems anymore and use an electric motor for power steering. It improves fuel economy as well but the steering feel is generally worse than a hydraulic power steering system.

Anything drawing over 250 watts is going to need over 12 gauge wire. I put a 2200 watt inverter in my truck and I needed to put 4/0 gauge cables to it which are huge. 48v would mean I could have gotten away with only 8 gauge wire.

Here is an explainer:

https://youtu.be/ky1Z2klPalw?t=573

Transcript:

. . . a little bit about electrical electrical engineering um you don't need to know a lot but just a little bit uh we'll understand that you actually want a higher voltage in order to reduce the resistance losses.

So the heating in any wire is the current is the square of the current. So if you're trying to get a particular power rating through then as you increase the voltage you can decrease the current. Voltage times amperage equals your power. To hold power constant, the heating is is proportionate to the square of the current. So you want to raise the voltage in order to lower the current thus lower the heating in the wire.

And the net effect being that you can have much thinner wires, then as you raise the voltage you can you can drop the the the thickness of the wires. You can have much you can use much less, in a nutshell. You can use much less copper and the wire harness weighs much less as you raised the voltage.

The savings in terms of weight and efficiency are actually significant. This was covered in Tesla's investor day presentation earlier in the year:

The section on electronic architecture (~10min): https://www.youtube.com/live/Hl1zEzVUV7w?si=-Vz0gKT5YDbtrG9V...

The sub section (~4min) on 48V in particular: https://www.youtube.com/live/Hl1zEzVUV7w?si=shfI2vEz9taTLSm7...

Some devices in a car are still pretty power hungry. Eg. The blower motor for the fan (typically 800 watts = 70 amps @12v). Heated rear screen (240 watts = 20 amps). Window motors are pretty powerful too.

End result is you need a lot of fairly chunky cables to power those things.

And the price of copper has been steadily climbing since 1960 - unlike other commodities which have been getting easier and easier to extract with more automation in mines.

Most MOSFETS are 50 volt rated. 50 volts is a sweet spot for switching the most powerful load with the smallest and cheapest switch.

if you're switching 48v, you'd want a mosfet rated for way more than 50v. On a car you'd want 200% headroom at least.

With totally uncontrolled bus capacitance and inductance, sure.

But when you're using the same bus for Comms you need to have control of high frequency spikes, and low frequency spikes are easily handled by a bidirectional DC/DC. Therefore I could imagine peak to peak ripple on this bus to never exceed 1 volt.

> Therefore I could imagine peak to peak ripple on this bus to never exceed 1 volt.

https://www.quanterion.com/wp-content/uploads/2014/09/MIL-HD... disagrees.

Not that anyone is going to stick a plow on a Cybertruck, but holy shit is the hydraulic pump on one of those a huge current draw. It's 4AWG wire on mine. The battery is kind of marginal[0] and when I raise the plow, the volt meter goes down to 7-8 volts if the engine's at idle and the alternator can't supply the needed current. Gunning the engine improves the situation somewhat, but wow, was that an eye opener.

[0] Everything on that truck is kind of marginal, actually. If you aren't plowing for money, plow truck is the last stop before the big parking lot in the sky.

Most of the residential snow clearing outfits around me use plows and blowers on Kubota tractors. Probably part of the reason is so that can use PTO hydraulics...

There are pros and cons. Snow plows beat on a the vehicle - which is why plows are the last thing a truck does before you quit using it. Highway departments will use a dump truck mounted plow because the frame of the dump truck can take the beating (that they can put salt on the dump truck is a very useful side effect). Tractors are designed to pull plows through dirt which also beats on them, and so tractors can stand up to snow plows better than a truck. However tractors are slower and so cannot work for on road work. PTO and hydraulics are useful as well.

You don't use custom-designed vehicles? I'm used to snowplows being these massive, reinforced vehicles that look like they could take on a tank.

I haven't a clue what you're describing. Do you have a picture? Also: where do you live, and how much snow do you get?!

Not OP, but here in park city UT, we average ~21 feet of snow a season and got an epic 51 feet last season!

I normally see dump salting trucks with plows that plow/salt the roads during snow falls and then we have cat bulldozers that later come pick up the snow and move it into dump trucks to be hauled away.

Video of the cats: https://www.icloud.com/attachment/?u=https%3A%2F%2Fcvws.iclo...

Northern Norway. But it isn’t snowing right now — and also I’m in Ireland — so can’t do.

I've never seen that in Minnesota. They are attachments to a dump truck or road grader.

Yup, the tractors are for driveway work. For road work uses the dump truck mounted plows you describe.

In the case of the cybertruck, the windshield wiper motor to drive that massive 4 foot wiper blade is 5hp and would require 300 amps at 12V. That's larger than a starter motor.

Larger in what way? A starter can draw more than 300 amps in some cases. However a starter only needs to run for a few seconds and then get plenty of time to cool off. You can burn out a starter if you crank the engine for too long. By contrast a windshield wipers needs to run for hours when you are driving in the rain, and thus needs to be larger to dissipate all the heat. (starters are also typically series wound DC motors which are also smaller, they work great for starters but not for most other motor applications)

What many people underestimate is all the comfort stuff we have and use in modern vehicles. Most of the utilizes some sort of electric drive. Any electric drive requires power: * Power sliding windows * Power seats * Electric trunk * Power sliding roof * Electric mirrors

Also other stuff: * heated back window * heated front window * heated seats * heated steering wheel

Also the lights, even when they are LED they still draw a lot of power: * front lights, * back lights. * surrounding lights * comfort lights

That is just of few devices. Just look into all the comfort in a modern (luxury) vehicle.

There is a lot more. There is a huge amount of safty equipment and sensors in modern car. That stuff that is not seen but its there as well.

> Why would a car need a 48V system for accessories? In general the things a car's 12V system powers have gotten less power hungry over time

It’s not primarily about delivering more power, is it? I thought the point of higher voltage is that for a given power the wires can be smaller.

It can be both. Higher voltage allows longer small wires, and/or more power on the same wires. Depends on what the car needs. If it is just a few lights on the back of the car you are looking for smaller/cheaper wires. However if you are looking to put something power hungry in back (work trucks have a lot of needs around this) the higher voltage allows the same wires to deliver more power.

Hi, automotive electrical is my job.

There's quite a bit of very thick wiring in a car, not just the starter wire, but boring stuff like audio amplifiers, rear window defrosters, power seat motors. Those things don't draw a ton of power, like maybe just a few hundred watts, but at 12 volts even modest powers require extraordinarily thick wires, especially when you account for bundle derating.

This requires large terminals, which requires larger connectors, and there's the complexity, because MOST of the wiring in the car is just signals, or low-power stuff, which can run over thin wires and small terminals. (Minimum size is limited by mechanical durability rather than electrical conductivity.) Making a "hybrid" connector that has a couple large cavities for large terminals, and a bunch of small cavities for small terminals, is a pain. Having separate connectors for heavy power and for signals introduces more assembly work and negatively impacts testability. The wires have different stiffness and bend behaviors, they exert different amounts of force on weather seals, they have to be terminated on different machines at different points in the assembly process.

By allowing power wires to be nearly as thin as signal wires, you can use simpler connectors with unified terminals. Manufacturing gets simpler, harnesses get lighter, assembly gets faster and easier.

Weight is also a huge deal, every ounce counts. There's upwards of 100 lbs of wiring harness in most cars, more in larger or premium models with a lot of accessories. If half of that weight is signals and won't change with voltage, but the other half is heavy power circuits that'll get 4x thinner at 48v, it's significant weight savings.

Furthermore, switching heavy current means massive relays or FETs and the heatsinks thereon. If you can reduce the current, those components get lighter too. Audio amplifiers get lighter, speakers get lighter (stupid heavy-wound 2-ohm speakers to get reasonable volume out of low voltage drive? Nah, use standard 8-ohm now that you have real voltage at the amplifier!), all sorts of things get lighter.

That's all in addition to the electric power steering already mentioned by others. EPS can easily move 1kw for short periods, and has stupidly huge wiring to do that at 12v. It's still chunky at 48v, but a lot less so, and can use more common terminals and connectors. Replacing a hand-assembled bolted connection with a machine-crimped and clicked-together connector improves reliability or reduces testing process overhead.

It's really significant, and it's embarrassing that the industry fell flat on its face in the late 90s last time they tried. Here's hoping this takes off.

Awesome to hear from an expert. Im looking forward to some teardowns to see how the set this all up.

The rumor I heard was that the higher voltage resulted in lower switch lifetimes. Any truth to that?

Yes, but not meaningfully. The higher the voltage you get, the more arching there is when a relay trips (also depends on if there's any sort of inductive load, think the sparks you see when you unplug a vacuum without turning it off).

But when you think about the impact that has on switches and relays, realize that in your own home you have 120V controlled by switches. Very cheap switches last decades (though admittedly not switched as often as something like a blinker).

Ahh, no.

AC is fundamentally different from DC when it comes to arcing behavior, because it has zero-crossings. If a switch arcs while switching AC, the arc goes out 1/120th of a second later. An arc would have to be pretty enormous to have enough thermal mass to remain ionized long enough for the next half-wave to re-energize it and sustain it. (HV AC transmission and distribution tends to have SF6-filled switches for this reason.) But around the house, your AC switches are really simple because they're not moving anywhere near that much power. And statistically, some fraction of switch openings happen with near-zero instantaneous current anyway.

DC, by comparison, is brutal to switch. It doesn't have zero crossings, so the arc has to be blown out by the design of the switch. That means nice wide contact openings, and on really large ones, magnetic blowouts to divert the arc into chutes that cool it.

If you look at a switch datasheet.... pulling up a randomly-selected one from Digi-Key now.... https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus...

Look at the cycle ratings. It has a bunch of different ratings depending on the contact form (some that're forced apart, some that're sprung apart), but in all cases, the DC rating is equal or much lower current than the AC rating. And the DC ratings only go to 24V, this switch IS NOT RATED for use at 48VDC at all, despite happily going to 250V when switching AC.

So, if you're comparing apples to apples, if you had 48VAC for instance, that would be easier to switch than 120VAC. (At constant current, that is. If you want to move the same power, you need more current at the lower voltage, and it gets harder again.) But DC is oranges.

Yes, switching 48VDC is harder than switching 12VDC, but only at constant current. And it may require _different_ switches than 12VDC. Given that you only need a quarter as much current to move the same power, it's still a net win, but it's not at all comparable to switching AC.

You're correct in all of that in regards to mechanical relays, but none of this matters for solid state devices. I'm not aware of any actual mechanical relays in Tesla's. They do have contactors for the HVDC connections, but that's about as close as you get to relays. Hell, they don't even have fuses; they use self reset-able 'soft' fuses.

You have to worry about shutting down current quickly (i.e., inductor flyback), but that's a pretty trivial problem to solve.

I thought about those, but the 120v AC switches are gigantic beefy things compared to most automotive switches.

Would there actually be switches switching 12 or 48V in a modern car, especially a Tesla? I'd expect the switches to only switch signal voltage/current, and power electronics (MOSFET? no idea, not an electrical engineer) switching the actual loads.

That's right, the switching concern was in older cars where they were switching the 12V straight up, so that is a reasonable point for why they never switched to higher voltages, but yes, in most modern cars (and basically all EVs) buttons and switches would mostly all just be signalling electronic units to do the actual switching.

Is Tesla's design here actually innovative or really just they're the first ones to put together a bunch of stuff that everyone knew and hasn't had the wherewithal to implement?

> or really just they're the first ones to put together a bunch of stuff that everyone knew

Thats what 80% of “innovation” is, with the exception of applied science fields.

I haven't seen the document being referred to elsewhere, but I highly doubt that there's anything fundamentally new under the sun. The industry tried this before but got stuck in a first-mover-disadvantage situation, which doesn't affect Tesla as severely because they have relatively few parts in common with other cars in the first place.

So put me down in the "wherewithal" column.

That's not to discount it at all. There are some real challenges; most automotive fuses for instance, are only rated for 32-volt operation. (Fuse voltage has to do with the length of the gap opened when the element blows, and the structure's ability to withstand or staunch any arcing that may happen.) Telephone fuses would work here but they're not exactly cost-optimized, I'd love to see what they do in this space.

Switch and relay contacts too, may need different or thicker coatings to reliably break 48 volts at the number of cycles needed, but they'll be doing so at much lower currents so I think it's a net win. (Contact wear isn't my field of expertise, though.) However, mechanical switches are decreasingly relevant in the power path anyway, and FETs will definitely do better with the lower currents.

One thing I saw talked about last time, which is completely irrelevant now, is alternator load-dumps. You know, due to the lack of alternators. But in the past, with an accessory belt spinning an alternator, the power produced by the machine was dictated by the current in the field winding. Regulating the output was a simple control loop, sensing the system voltage and servoing the field current accordingly. The field winding has significant inductance so its field can't change quickly, but with a big battery sitting on the bus that didn't matter. However, if the battery lead became disconnected, and the power draw on the system decreased, the alternator would suddenly be producing too much current and unable to rapidly reduce its field, and with no battery there to absorb the overage, the result is the system bus voltage spiking as high as 120 volts, or at least that's what the load-dump test spec says you have to withstand for 400 milliseconds. In practice with incandescent bulbs and some other linear loads around, they'll typically clamp the transient to 40 volts or so, but that's still pretty harsh for stuff that's working at 14-ish.

The concern was that a 48-volt alternator could produce some truly terrifying load-dump transients. (Although I think this is also overblown; it's running at lower current so the field winding would be weaker and should be able to decrease its field faster, no? Hmm. I should do some math...)

But now that the 12v or 48v is produced by an electronic DC-DC converter running from the traction battery rather than an alternator spun by the engine, it's completely immaterial.

Littelfuse makes some nice 58V rated blade fuses.

Doing it first is innovative

Musk said the 48v stuff was not innovative at all; they were only doing the latter things you pointed out.

I've been in the telco/digital communications space for years and all this stuff has run from 48V for decades. So basically plenty of electronic parts are already available with margins suited to 48V already since it's extremely common in other industries like the one I'm in.

Automotive just tends to be a pretty slowly changing industry, but everything is ready for them to adopt 48V that other industries have been using for a long time, someone just needed to take the plunge I guess.

Have you been able to look at the Tesla document? Do you think it'll meaningfully help the EE's at other automakers redesign their architectures?

And to explain why this hadn't been done before/how we got here:

Nothing in a car actually wants 12V DC. Most of the low voltage stuff will run better at 5V or below, while a lot of the higher voltage stuff would benefit from going as high as possible. 12V exists because DC-DC conversion used to be expensive, and you had to make a compromise about the voltage based on losses, wire thickness, and picking a low enough voltage that all the low-voltage stuff doesn't suffer too much.

What's changed is that you can get a single-device DC-DC converter for really cheap these days. Cheap enough that you might as well put it in the light bulbs, and everywhere else that wants a low voltage.

12v exists because 6v was too low; wires were impractically thick for even the early accessories being added in the 1950s. The 6v-12v transition happened in 1955/56 for many cars. Some stuff like lightbulbs could be reused by putting two 6v bulbs in series in a 12v car, so it was a very cheap and relatively straightforward transition.

If they'd just had some foresight and gone 48v in 1955, we would've saved 50 million tons of copper in the years since. It's no harder to make 48v motors or lightbulbs or relays or anything else (and in fact, the telephone network contains plenty of exactly those things, and has, in staggering numbers, for over a century), but the automotive industry isn't exactly known for being forward-thinking.

> If they'd just had some foresight and gone 48v in 1955

How would they have done this without cheaply-available high-speed switch-mode power supplies with low-DCR inductors/MOSFETs?

Why would they need those?

All the stuff that's natively 12 volts now could simply have been made natively 48 volts. You can make a 48-volt lightbulb as easily as a 12-volt lightbulb. You can make a 48-volt motor as easily as a 12-volt motor. Actually, motors for higher voltage tend to be smaller and lighter, which is why industry tends to go straight for 4160-VAC motors whenever 480VAC is inadequate.

What applications cannot be made to work at 48? I'm not aware of any. As I said in the comment to which you're replying, the telegraph and later the telephone network had been running similar DC systems since the 1850s or so at various voltages depending on the length of the telegraph line, with the telephone network taking over and 48 volts firmly entrenched by the 1910s. There was a huge manufacturing base producing 48-volt equipment, including motors and generators, indicator lamps, and a mindboggling array of switches, relays, stepping selectors, and their ilk, and all that was before WWI.

Furthermore, Charles Kettering who invented the automotive starter motor (and made it work at 6 volts), was around the same time making Delco-Light plants for rural electrification, which mostly ran at 32 volts DC. These supported a whole line of 32VDC appliances -- lights, vacuum cleaners, kitchen gadgets, irons, motors that could be attached to other machines in the shop. There was also a less common 110VDC version of the system but I can't find any contemporary literature discussing the differences, although I'm sure they would've quickly discovered that the 32V system was pretty docile while the 110V encouraged extreme care around open contacts.

As for why cars didn't use the higher voltages already in use and superior in many ways, my only guess is that a lead-acid battery with a high number of small cells must've been difficult or expensive to manufacture, compared to one with a small number of large cells. The Delco-Light plant used a large rack of 2-volt cells, whereas the starter motor used a single 3-cell packaged battery that fit easily under the hood. If they'd just figured out how to package more smaller cells together....

> Why would they need those?

To convert voltages to useful levels without suffering massive losses in efficiency.

> What applications cannot be made to work at 48?

Basically every logic-level transistor will not work at 48V. It's nice that these last-century analog devices could be made to operate at different voltages: present-day semiconductors are not so conveniently flexible.

Simple physics dictates that required inductors to step between voltages increase in physical size (and weight, and material cost) as that voltage disparity increases. Capacitance required, etc. all increases with it. Efficiency plays into both of these as a triangle. Heat increases as this disparity increases. These properties are unacceptable for a myriad of use cases.

You didn't have to convert voltages all the time for things you did in a car until relatively recently. All the typical 12V stuff could've run at 48V no problem. By the time we wanted to put computers in cars and charge our cell phones, switching supplies were readily available. The only part of the system now that really benefits from lower voltages are semiconductors.

A 12-volt battery typically has six cells. A 48 Volt Lead-acid battery would have 24 cells - I'm not sure how that would change the constraints on charge balancing and starter-motor stress.

I can say that the 24 Volt deisel vehicles I have used makes buying two batteries expensive.

I think another big part of it is that DC switches tend to get expensive above 12V. Cheap AC switches work fine at higher voltage, because the arc is self-extinguishing as it passes through zero twice per cycle, but DC doesn't do that so you can end up with an arc that doesn't extinguish itself, which, aside from not turning the thing off when you want to, burns out the electrical contacts.

Now we have MOSFETS and IGBTs that can switch DC without sparks. I suspect most DC switching in the Cybertruck is relayed through these. (Except the main contactor and pyro fuse of course.)

And the contactor is usually switched with no current through it. The only time it would open under load is in an emergency, and presumably it only does that once.

Which is to say, yeah, it's a non-issue for pretty much everything. Even in the 12v realm, new BCMs have so few relays anymore, almost everything's done with onboard FETs and software.

And given that this is a Tesla, it wouldn't really have had many mechanical switches in the first place. Maybe the turn indicator? Which could happily run at 5 volts or something and blink the lights via CAN bus messages.

None, unless you count the physical buttons as 'mechanical switches'.

The turn signals on a Tesla don't even make the 'clicking' noise if the Infotainment is rebooting, because it's literally just a noise piped through the infotainment.

Related to the weight of signal wires, Cybertruck also moved to using ethernet instead of traditional canbus, which significantly decreased the complexity of that harness

Thanks for this detailed answer. The chassis is normally grounded. Has anyone tried sending a positive charge through part of it? Combined with a Powerline-style signaling system, some components wouldn't need wires at all.

I already can think of several reasons why this wouldn't work, but I wonder whether there's a good idea in there somewhere.

Compared to ICE vehicles, EVs are expensive and heavy (according to Slate, an F-150 Lightning weighs 35% more than its ICE sibling). Cost and weight reduction are both important factors for any EV maker to optimize.

Why do you assume the 12V bus doesn't drive high-power stuff? Historically, every single electrical component in a car is powered at 12V. Everything. Your alternator outputs 12V to both power your electrical system and charge the 12V battery. Even the starter and ignition system (distributor or coil pack) transforms 12V into the high voltages needed for combustion.

I'm not exactly sure why 48V corresponds to a decrease in "complexity." My guess is that power and data were sent over separate cables, whereas PoE does everything together. That's just a guess, however.

Assuming the same power requirements, a 4x increase in voltage translates to a 4x decrease in current. Looking at [1], a component requiring 8AWG @ 12V can now use 18AWG @ 48V. That's a significant decrease in copper, resulting in cost and weight reductions. A higher voltage is almost always preferred, though the higher electric potential means you need better insulation and safety measures.

Though there's a saying that it's current, not voltage, that kills, high voltage is widely known to be dangerous. For example, consider the US electrical grid, which is actually a 240V system, not 120V. Three wires come to your house from the transformer: -120V, 0V, and 120V. A normal outlet is connected to either -120V and 0V or 0V and 120V, and you can get a 240V outlet by connecting to -120V and 120V. This 120V-by-default setup is much safer than 240V every outlet, like in other parts of the world, and you can still get a higher voltage for high-power appliances (e.g. clothes dryer).

[1] https://en.wikipedia.org/wiki/American_wire_gauge

Compared to ICE vehicles, EVs are expensive and heavy

Expensive maybe, IMHO not really, at least in China. Heavy .. this doesn't sound fair. Are you comparing a cherry-picked, heavy, full battery back EV with an empty tank ICE? Noting the EV has far more torque, and that the same tech is used in UAVs and in a ground vehicle you can arguably move the weight around (lower it) easier in an EV, this casual observer (not a car person) would expect superior mass distribution and lower overall weight (certainly vs torque).

500kg solar EV: https://www.unsw.edu.au/newsroom/news/2022/06/sunswift-7--dr... ... compare Toyota Corolla: 1314kg + 50kg fuel / Toyota Camry: 1360kg + 70kg fuel / Tesla Model 3: 1611kg / Toyota RAV4 average: 1634kg + 55kg fuel / Tesla Model S: 2107kg / Tesla Model X: 2458kg / Your cherry-picked example of an F-150 Lightning: 2948kg / Chevrolet Silverado 1500: 3311kg + 105kg fuel / way more heavier ICE cars follow...

Another potential consideration is that the EV is far better placed to use recovered power from braking, so a small amount of additional mass will have less efficiency impact than in a comparable ICE.

Vehicle weight also affects how much wear the roadways experience. I'm not sure "A Corolla weighs less than a truck" is relevant here, especially considering that the F-150 is the most popular vehicle in the US by sales number. Comparing things to the market leader is generally a useful metric.

Heavy trucks damage roads much more than cars. It depends on the weight but it’s exponential. The weight difference between an EV and an ICE of the same category is not a big concern to have in terms of road damage.

https://en.m.wikipedia.org/wiki/Fourth_power_law

Why not use 48v? I have been designing my farming robot's electrical system and it all runs on nominally 45 volts. The switching power supply you need to downregulate that to 12, 5, or 3.3v (I have all three on one PCB) is tiny and cheap. [1]

No matter what voltage or power level you need, higher voltage will allow for smaller/cheaper wires and connectors that are easier to route and assemble.

[1] You can browse the Kicad PCB design directly in the browser with this handy web viewer. The power section is the top left: https://kicanvas.org/?github=https%3A%2F%2Fgithub.com%2FTwis...

One example is Porsche PDCC. It needs 48V to work so you end up with a car that has both.

Also I think all Mild Hybrids are 48V, so maybe theoretically you could get rid of the extra 12V battery there?

As well as switching to 48V they are going to use Ethernet cables for most of it (PoE). So at the same time they get rid of the CAN bus wiring and have everything running on ethernet for communications and power, which means a LOT less wiring because with CAN bus every device needs its own wire but with Ethernet its much easier to have 'hubs' that channel communications and power on to other devices.

https://twitter.com/cybrtrkguy/status/1731658374775771297?s=...

I think the more important change that Tesla made is the change in the databus. Much higher performance ethernet. They changed the whole architecture of the car where there are now very few point to point connection, and its all essentially routed with a few major modules in each part of the car.

If you look at current cars there are sometimes huge cable bundles, lots of individual cables for everything. Its a nightmare to build up and very hard to install.

I think in their next generation assembly they will have these connection points be fixed and then just plug different sub assembly together at predetermined points. No more huge cable harness installed on completed bodies.

> Much higher performance ethernet.

Depends what performance you are after. Ethernet isn't rated for safety critical stuff. It doesn't provide mechanisms for packet loss detection, and in most cases is pretty shit at flow control.

Ethernet is also shit for small sensors/actuators. There are lots of low bandwidth devices that need power and comms, ethernet isn't designed for that. having to route 2 pairs of cables to everything in a star pattern is really impractical.

Its probably ok for linking different zones, of non critical stuff. But running PoE? for all but specialist things, that sounds frankly stupid.

There has been a lot of work developing standards for reliable ethernet for industrial and automotive applications, resolving most of the issues you mention which apply to 100/1000Base-T. Tesla isn't using your garden variety ethernet or abominations like ethercat.

100/1000Base-T1 is intended to be used with PoDL (802.3bg/cu) and TSN (various 802.1Q)to result in reliable links with guaranteed latency and bandwidth properties. PHY power is a few hundred mw though, and star topologies are limiting to replace CAN/LIN nodes, that's what 10Base-T1S is for though (cheaper, bussed, lower power).

I've been waiting for higher automotive voltage for a long time. Way back I wished for 48V as it's double the 24V standard used in European and off highway trucks as well as industrial automation and -48V is used in telecom. Wires can now carry 4x power. But from memory there was a 50V safe limit that would complicate things as the 48V charging voltage exceeds 50V as does the nominal cell voltage. So instead the industry selected 36V and planned to migrate but it never happened. The reason being LED lighting and small more efficient electronics reduced the need for higher voltages.

With EV's there's no reason to keep 12 V.

The thing is, unless the whole industry moves together to 48V, the cost of this change for a single OEM+Tier1 would be too big.

In cases where they're using a proprietary 48v part I wonder if Tesla would consider becoming a parts supplier to other manufacturers?

This is basically the crux of the matter. Traditional automakers are a complex supply chain that standardises and goes to extra-ordinary lengths to reduce costs. Tesla build a tonne of their own stuff and aren't as price sensitive. The question is "Why don't we just redesign all this stuff" and the answer is "We're Ford, we make tiny margins and we can't afford to redesign our entire car every year and even if we could we get half our components from Bosch anyway". Not to mention the difficulty in convincing FuSa people your arbitrary ethernet network is safe.

You mean like EV cars? :)

It is interesting to think about how an automaker like Tesla which is more vertically integrated and has less in the way of legacy parts/tools/processes can make this change more easily than the established players. From the article:

If you cannot convert all of a vehicle’s systems to 48V architecture, the benefits of using such an architecture start to diminish pretty quickly . . . If an automaker decides to move to a 48V architecture, whatever car it builds must use 48V-ready accessories. But, suppliers aren’t incentivized to build such accessories without sufficient demand.

I'm ignorant and curious: why 48V specifically? Why not 40V? Why not 50V? Is there some ideal ratio that makes DC-DC conversions more efficient or something?

For comparison, Makita (and I think some other power tool makers) have augmented their 12V lineup with a newer 40V platform for tools that need a bit more oomph. I guess there's no need for them to interoperate with other DC voltages, so maybe that explains the "messy" number?

USB, on the other hand, recently grew support for a handful of pleasantly neat voltages:

> Increased power levels from existing USB standards up to 240W. New 28V, 36V, and 48V fixed voltages enable up to 140W, 180W and 240W power levels, respectively.

Does anybody know how these decisions are made?

For batteries it tends to be multiple of the battery cell voltages. So 48v is probably so you could wire 4x12v batteries in series but that is a guess. With tool voltages this tends to be a multiple of the nominal battery voltage (rounded for marketing).

To riff on this, a lead-acid cell is 2.2v. If you look at the 12v battery in your (typical) car, it has six cells. It's less obvious with modern sealed batteries, but super obvious with flooded lead acid batteries in golf carts.

Lithium batteries do not have 2.2v cells; typical li-ion cells are 3.7v. So there's no particular reason why you should stack them to 48v, except that there's already some amount of industrial capacity for 48v components due to the preponderance of 48v golf carts.

Of course, these systems don't work at exactly 12v or 48v or whatever; voltage on the bus fluctuates with state of charge (and state of charging).

This is it, there are many ways to get there. The 48-volt architecture is achievable with four 12-volt lead acid batteries in series, or thirteen lithium-ion cells in series at their nominal 3.7-volts, or fifteen LiFePo4 cells in series at their nominal 3.2 volts. You can ask for any of these to manufacture a 48-volt vehicle.

PoE over CAN bus moves more complexity from EE world into software world. While Tesla currently has best auto software, this is still a very foreign and a different way of thinking/managing for traditional auto manufacturing. This won't be just using a different set of cables, it's going to flip their engineering departments upside down.

Wouldn’t it be PoC instead of PoE?

Power over Ethernet (PoE) is a technique for delivering DC power to devices over copper Ethernet cabling, eliminating the need for separate power supplies and outlets.

Source: https://www.google.com/url?q=https://www.cisco.com/c/en/us/s...

Yes, but afaik CAN is not usually done over Ethernet

Tesla is so cool. Leading not just by example but literally giving patents and designs away for free.

Mild hybrids have been using 48V for a long time. There isn't much new here except that Tesla decided to do every component. That's going to cause quality problems with parts if they remain a tech. island in the industry, so trying to get everyone else on board makes sense.

Doing it for everything is the whole point, it changes the architecture of the car. Yes individual components but those cars had like 1% if connected devices at that voltage and were otherwise exactly the same.

For Tesla ist a replacment of something else, for previous vehicle was it was something additional for a specialized use case.

Could have gone higher. Worth it in copper savings alone. IIRC the cars use AC motors. It needs to go through inverters anyway so there is some flexibility in how high you can go.

Edit: of course the motors are "AC" who would want a brush and commutator based motor in their car?

Most countries have safety rules that apply at 50V, so staying below that reduces regulatory costs significantly.

Good point.

The main motors of an EV are not powered off of the 48V system. EVs generally have 300-400 V main batteries, with discussion of 800 V on the table (someone may have already done it, I haven't been keeping track).

The terminology can get confusing. I many contexts, a "brushless DC motor" is actually a 3-phase AC motor.

The idea is that you can think of the motor and motor controller (often called an inverter) together as a DC motor because the input to the motor controller is DC.

Series-wound DC motors used to be fairly common for EV conversions, and they're still a reasonable choice if you want something that's very cheap and very powerful, and don't care about brush maintenance, efficiency, regen, or being able to reverse easily. (The White Zombie for instance uses a pair of SWDC motors.) Normal people just use AC motors these days.

Am I right in saying this wasn't shared with the public or other (Chinese) OEM's...

Doesn't that raise collusion/anti competitive concerns? Or is Elon relying on the fact no prosecutor will take a case about disadvantaging china?

"shared" in the sense that everyone else was doing it already. In the same way that he's shared the hyperloop, which he got from a 1980s osbourne book of transport.

what I want to know... Is this really what the document looked like? Or was it artistic license for the video?

https://www.rivianownersforum.com/attachments/tesla-48v-jpg....

"How to Design a 48V Vehicle

You incompetent boobs!

Do we REALLY have to do your homework for you?

XXOO, Elon"

I saw this on https://youtu.be/L6WDq0V5oBg

Older Tesla cars have a 12V battery for accessories, until the main high-voltage battery is turned on. So does this mean having a 48V accessory battery? Or what?

I don't know much about the Cybertruck, but in general all modern cars, electrically propulsed or not, have a 12 V system which includes a battery for running electronics and some accessories. Very old cars had a 6 V system. There is a push to move to higher voltages, the battery would also be 48 V to match. https://my.avnet.com/abacus/resources/article/the-shift-to-4...

Yes. Keeping the high voltage battery active is expensive, and also poses a (small) safety risk when the car is sitting.

It's probably a modified version of the '16V' lithium battery in all other Teslas, just with 3x the pack voltage.

If higher voltage leads to benefits, then why 48 and not 120 (US) or 230 (EU)? Or higher? What are the tradeoffs?

48V still counts as "low voltage" for safety purposes. The lower voltage gets them increased safety when working with exposed wiring.

You are mixing AC and DC here.

Please note that all benefits listed in TFA for 48V vs 12V are valid for 220V vs 110V, too.

Does anyone know where a civilian (me) could access a pdf?

Could I have 48V for my GPU power supply as well, please?

Has this document actually been posted anywhere?

is tesla forced to do so because the other automakers are clueless?

Do more stuff like this, Elon. I really don’t like not liking you.

weird comment... maybe we shouldn't feel the need to idolize humans...

It’s ok to like people

did i say it wasn't ok to like people? i used the word idolize, almost like they're different words with different definitions

We humans are all terrible on some level (except my mom, she was a saint), but if you have enormous power, you can help or hurt a lot of people based on your actions. Musk has a lot of power. He must be a terribly lonely person, not knowing if he can trust anyone or they just want something from him.

Nobody knows if they can trust anyone, not just rich people.

Right, but it's a lot easier when you don't have anything someone else might want, much less a billion or more things.

He could give away 99.99% of his wealth, still never have to work another day in his life, and be much less of a target if he wanted to. Boo hoo the poor guy who has more money than almost anyone has ever had in the history of the earth has problems

If he gave away 99.99% of his wealth, that would tank the retirement accounts of millions of people, possibly have his life's work be taken over by some hedge fund ("introducing the Tesla Model V8, now with extra vroom-vroom!"), and then get sued by shareholders for the remaining 0.01%.

True, but it isn't worth a thief's time to steal things from me, so I'm less a target of dishonest people. Not zero target, but not a big target. Rich people because they have money are a larger target. Nobody would seek to marry me for my money - filing for divorce as soon as enough time has past to make it look like that wasn't their goal - a small number of people would do that and they seek out rich people.

Hi, excuse me. Just want to say, don't appreciate you rounding me up with the anti-semites. "We humans". No - those anti-semites, and us reasonable people. Wouldn't like to mix with them thanks. You can make whatever excuses you want for him, but that's what they are, excuses.

This is silly, don't stand on some high horse. If you don't think you have the capability to be unreasonable, you are delusional. Every single person on this planet is capable of evil, but majority luckily see that as a path that ends badly.

I think there's a bright bold line between me and the anti-semites and I think that you're doing the work of the anti-semites to pretend there's not. Everyone is capable of evil. Some people actually do evil things though and some people don't. The issue here isn't what people are capable of, it's what they're doing, and Elon Musk is endorsing crackpot anti-semitism on the platform he owns in the aftermath of the largest attack on Jews since the holocaust.

Is "he's not doing enough cool stuff" really the root of your dislike of Elon?

Don't worry, it will only be a matter of time before he retweets a neo-Nazi and you can go back to hating him.

Some people have way too binary a view of other people. In real life there are rarely outright villains or complete saints. Everybody is a mix of greys. You don't have to agree with everything a person does or says to appreciate their work.

Retweeting neo-nazi content is no shade of grey.

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