Data centers are transitioning from AC to DC | Hacker News Reader

Data centers are transitioning from AC to DC

spectrum.ieee.org

337 pointsjnord415 comments

800V to each rackmount unit, with hot plugging of rack units? That's scary. The usual setup at this voltage is that you throw a hulking big switch to cut the power, and that mechanically unlocks the cabinet. But that's not what these people have in mind. They want hot-plugging of individual rackmount units.

GE has a paper about the power conversion design, but it doesn't mention the unit to rack electrical and mechanical interface. Liteon is working on that, but the animation is rather vague.[2] They hint at hot plugging but hand-wave how the disconnects work. Delta offers a few more hints.[3] There's a complex hot-plugging control unit to avoid inrush currents on plug-in and arcing on disconnect. This requires active management of the switching silicon carbide MOSFETs.

There ought to be a mechanical disconnect behind this, so that when someone pulls out a rackmount unit, a shutter drops behind it to protect people from 800V. All these papers are kind of hand-wavey about how the electrical safety works.

Plus, all this is liquid-cooled, and that has to hot-plug, too.

[1] https://library.grid.gevernova.com/white-papers-case-studies...

[2] https://www.youtube.com/watch?v=CQOreYMhe-M&

[3] https://filecenter.deltaww.com/Products/download/2510/202510...

It is a pretty clever design

> When it is detected that the PDB starts to detach from the interface, the hot-swap controller quickly turns off the MOSFET to block the discharge path from Cin to the system. After the main power path is completely disconnected, the interface is physically detached, and no current flows at this time

> For insertion, long pins (typically for ground and control signals) make contact first to establish a stable reference and enable pre-insertion checks, while short pins (for power or sensitive signals) connect later once conditions are safe; during removal, the sequence is reversed, with short pins disconnecting first to minimize interference.

Yes, I read that. There had better be a backup system. MOSFETs tend to fail ON, and there's a megawatt going into each rack.

Somehow this seems the wrong approach to AI.

Fail spectacularly

Data center workers are gonna need those big yoink sticks and those thick arc-fault bibs that furnace operators wear.

McMaster-Carr has the personal protective equipment required for 800V: Flash protection face shields [1] and Class 0 electrical protection gloves.[2]

It's not that bad. It's just ordinary industrial protective gear.

[1] https://www.mcmaster.com/products/arc-flash-protection-face-...

[2] https://www.mcmaster.com/products/electrical-protection-glov...

I figure the latch-up failure mode is a known failure mode. It's not something totally unexpected.

> Somehow this seems the wrong approach to AI.

One a more ironic level, it's seems on par with the whole AI approach!

The phrase "when it is detected" makes me nervous.

That's why I included the bottom part describing how some pins are longer than others. It's sort of how some hotplugs work in most cases. First ground connects, then other set of pins and so on. So when is detected a physical act of being disconnected.

Or maybe you can require technicians to be in full-protection electrical suits.

As long as you can control for fire, electrical safety seems like a temporary condition as robots and intelligent machines are cheaper and more available long term solution to hot swap blades in datacenter racks.

I think you're being downvoted for speaking of a complex future possibility ("robots and intelligent machines ... solution") as if it was a proven commodity. There will be many twists and turns in the path to the possible reliability, scalability, and cost effectiveness of robots and intelligent machines.

Yea I literally said long term but HN voters have such a hate boner for anything adjacent to AI

But the discussion is about the safety of systems being actively implemented. For now, people are required to maintain data centers. Right now, these centers are transitioning to high voltage DC. Right now the best attempts at fully automated data centers are in progress with unverified status. So, for now we need to keep the humans safe. Future data centers not needing humans doesn't keep the current humans safe. Thus, optimistic future speculation is off topic and not relevant to the discussion of human safety with high voltages.

People are tired of off topic speculation masquerading as relevant to real world problem solving. It's not a hate boner.

EDIT: expanded to make it clearer why I believe the speculation to be wildly off topic for this particular thread.

It is a proven commodity already. Just not in our behind-the-curve country.

Look at NTT Data or SoftBank.

https://www.softbank.jp/en/sbnews/entry/20250917_01

Appreciate your effort to provide reference info. Near the end it says "part of SoftBank’s efforts to implement robotic automation at [one] Data Center scheduled to start operating [no later than April 1 2027]".

They literally speak of preparing for a future that does not yet exist. I am optimistic it will exist, but that's not the same thing as it already happening and having a track record of reliability and profitability. I could find no mention of robots actually doing anything at that link. The article is about prepping servers, not specifically about robotics, in the same sense that planning hoses for gas pumps at gas stations is not about building cars.

Dear downvoters: softbank has been optimizing their datacenters for robotic technicians since 2020.

They are about to have fully human free datacenters by the end of this year.

When you are designing long term goals with datacenters, as I explicitly mentioned talking about, you can't ignore automation.

> Dear downvoters: softbank has been optimizing their datacenters for robotic technicians since 2020.

> They are about to have fully human free datacenters by the end of this year.

What I'm hearing is that they've been trying to build a human-free datacenter for 6 years and they haven't done it yet. What's the betting that that "end of this year" schedule slips further?

An EV fast charger can do 1000V, so with a bit of logic that sounds doable.

EV chargers take a different approach. There is no power on the connector while you're plugging it in. It then locks in place before the contactor closes and power is delivered. Unplugging is the same, power is removed before the plug is unlocked for release.

Do the EV chargers not have an alternative disconnect sequence for when the two sides are forcibly mechanically separated? Either by accident, malicious intent, or mechanical failure of some component.

Yes. See UL 2594.[1] There's a lot of monitoring on those things, plus regular circuit breakers and GFCIs.

[1] https://www.intertek.com/batteries/automotive-battery-ev-tes...

This is effectively how hot swapping is done for may modern systems. It seems counter intuitive to call it hot plugging, but it’s what you’ll find if you look up “hot swap controller”.

The power connectors will be on the far side of the rack from the service side so shouldn’t be a problem for humans touching the third rail so to speak.

With that sort of voltage you should be able to use a capacitive or inductive sensor to activate a relay.

With a power rail that could supply kiloamps of fault current, thus megajoules of energy into an arc, I wouldn't be so sure of that.

Copper vapor inhalation is a definite possibility and a horrible way to die.

Obviously the contact point in the sled will need to be disconnected while not grounded, as the top level suggested, or shorted to ground across a large resistor. It’s not the amperage that’s going to cause problems it’s the 800 volts, backed by the amperage. Small enough capacitance and large enough ground load should let you tap in without frying anything including air.

Wouldn’t the biggest problem will be loading sleds into a hot rack, with all of the sleds powered down? Which probably you shouldn’t do. The parallel loads on a rack that’s half on should sink a lot of the potential.

It's easy to make these 800V systems totally safe. You just have to combine this idea with the extremely sensible plan to put data centers in space and then there will be no worry about when "someone pulls out a rackmount unit" because there not be someone within hundreds of kilometers.

The concern isn't keeping people out of the facility altogether. It's keeping people safe when they are hot swapping dead or outdated rack units.

You could consider a robotized approach, but for now robots aren't very good at this type of task. Whether the robotized system is in space is irrelevant. It's not a "next five years" type of solution.

A high powered EV charger is 800 volts. Totally safe and outdoors in thousands of places.

DC power has been an option for datacenter equipment since I was a young lad racking and stacking hardware. Cisco, Dell, HPE, IBM, and countless others all had DC supply options. Same with PDUs. What’s old is new again.

See e.g. https://www.dell.com/support/kbdoc/en-us/000221234/wiring-in...

48vdc was common in phone exchanges. They filled the basement with lead-acid batteries and to could run without the grid for a couple weeks. In turn the phone was 99.999% reliable for decades.

Not to be _that_ guy, but it was technically -48V DC.

Honestly, that was pretty surprising to me when I had to work with some telco equipment a couple of decades ago. To this day, I don't think I've encountered anything else that requires negative voltage relative to ground.

Check out older English cars.

positive ground used to be in all cars. When they went from 6 volts to 12 the disadvantages became appearant fast and so everyone went negative ground then (mid 1950s). I am not clear why positive ground was bad (maybe corrosion?)

Is that something other than a labelling convention? Is ground actually connected to a earth stake?

Cathodic protection against corrosion was the goal of using -48V, in the telcos' case.

And the telegraph lines before that.

> Is ground actually connected to a earth stake?

Yes, or something similar[1]:

A few of the more efficient grounding electrodes for buildings and structures are:

- Metal Underground Water Pipe

- Metal In-ground Support Structures

- Concrete-Encased Electrode (also known as “footer ground” or “Ufer ground”).

- Ground Ring

As mentioned this is particularly important for telecom and similar systems which have signal wires going literally through the ground.

[1]: https://www.nfpa.org/news-blogs-and-articles/blogs/2021/09/2...

Yes, and that tiny little difference can cost you a lot of expensive gear if you run it off the battery and plug in a serial port or something like that. You'll also learn first hand what arc welding looks like without welding glass.

Lots of amplifier circuits need a bipolar supply: both positive and negative voltages with respect to ground.

RTL and DTL both needed negative-voltage relative to ground, as do many analog circuits.

Some old guitar effects used -9V DC.[1] And the convention with guitar effects power adapter is the barrel is center negative (which is motivated with facilitating easy wiring of the socket's switch to connect to a 9V battery inside).

[1] https://www.analogisnotdead.com/article26/what-is-going-on-w...

Can you explain why it's -48 VDC as opposed to 48 VDC with the + and - inputs mislabeled?

In short, ground.

Because the chassis is connected to ground (as in, a literal grounding rod hammered into the soil) and by definition your 0V reference point.

The crucial difference is the direction in which the current is flowing: is it going "in to", or "out of" a hot wire? This becomes rather important when those wires are leaving the building and are buried underground for miles, where they will inevitably develop minor faults.

With +48V corrosion will attack all those individual telephone wires, which will rapidly become a huge maintenance nightmare as you have to chase the precise location of each, dig it up, and patch it.

With -48V corrosion will attack the grounding rod at your exchange. Still not ideal, but monitoring it isn't too bad and replacing a corroded grounding rod isn't that difficult. Telephone wires will still develop minor faults, but it'll just cause some additional load rather than inevitably corroding away.

Do you also happen to why this is not more common? Must be useful for more than just telephone wires.

Most large scale systems are AC because transformers are relatively cheap, low maintenance, and efficient. When the system is AC ground makes no difference.

With DC systems you generally think about the issues - which is why modern cars are negative ground. However other than cars most people never encounter power systems of any size - inside a computer the voltages and distances are usually small enough that it doesn't matter what ground is. Not to mention most computers don't even have a chassis ground plane (there are circuit board ground planes but they conceptually different), and with non-conductive (plastic) cases ground doesn't even make sense.

> When the system is AC ground makes no difference.

With AC it's about where the ground is attached along the length of the transformer secondary. In the EU they ground one of the ends of the secondary, in the US we ground the center point.

I don't get to say this very often ... but the US way is objectively safer with no downside: 99% of human shocks are via ground, and it halves the voltage to ground (120V vs 240V). A neutral isn't required if there aren't 120V loads.

I agree that the US voltage is safer (with the tradeoff of lower output powers available at your outlets). However, I suspect this is more than negated by the US plug design, which carries a much larger risk of shocks than almost all EU plug designs (Schuko, British/Type G, etc...)

- uninsulated metal pins make contact with supply while partially exposed - much smaller distance between metal pins and the edge of the plug

100% agree the US plug designs are terrible.

But there's no inherent power tradeoff: you can have 240V outlets in the US, with the two prongs both 120V to ground. They're just really uncommon in residences.

Dryers and Stoves/range outlets are very common in US houses. Of course they are generally hidden behind the device and so most people are not sure if they have them at not. They are also reasonably common in garages (welders, air compressors, table saws... - if your hobby needs them you install them, otherwise you won't have them).

In the EU it is quite common for houses to have three-phase power. If you squint a bit, the grounded neutral of the Y transformer isn't entirely unlike the grounded center tap in the US. The voltage is a lot higher, of course!

> If you squint a bit, the grounded neutral of the Y transformer isn't entirely unlike the grounded center tap in the US.

Yes, but you only get the safety benefit on three phase equipment.

In the US there aren't a lot of 240V plugs, but if you get some installed you can get the safety benefits with plain old consumer goods.

> but you only get the safety benefit on three phase equipment.

The wye ground is beneficial even if there are no three phase loads, because the line-ground voltage is 1/sqrt(3) and you can use cheaper switchgear.

The 3-phase alternative to a wye ground is a corner ground (grounding a live phase of a delta secondary), which isn't done in modern installations because ground faults are full line-line voltage and you need more expensive switchgear.

Line-line faults are always interrupted by two breakers on a wye grounded 3 phase system. But with a corner ground, one breaker potentially has to break the full line voltage for a line-ground fault (you can't fuse the grounded phase).

I'm not talking about the safety of different ways of doing three phase. I'm taking it as a given that three phase is wye ground and optimal for safety.

My point is that in the context of a 230V single phase circuit, your ground is no longer in the middle. The ground is on one end of your single phase. If you want a safer single phase, you need to rebalance it to +115 and -115.

I thought they meant a "two phase" service where the two phases are 120 degrees out of phase instead of 180, like an apartment fed with two poles of a 208V wye with 120V to neutral/ground, which is balanced. If it's just a single phase, you're right.

EU power is ~230V on a single phase and ~400V between phases. So a house usually gets three phases, but the only appliance where the voltage to ground is less than the total voltage is probably the oven.

> because transformers are relatively cheap, low maintenance, and efficient

And because that problem of galvanic corrosion the GGP talked about, and the mirror one of material aggregation don't happen. And it also makes switches more reliable.

Both are less dangerous on telephone lines. But are very important on electricity ones.

1 - It won't break your posts, but can easily short small contacts.

It is! Look up "impressed current cathodic protection": you apply a small DC voltage to, say, pipelines to prevent corrosion.

I ran into a guy at a hardware store who ran just such a power supply attached our city's water (or was it natural gas?) infrastructure. I was incredulous, but the idea that it helped prevent corrosion did make sense.

So, there is a true value for 0?

Does that mean when you have electronics and use multiple dc-dc converters all the inputs and outputs share the same ground, it's not just the values for that pair of wires?

And if I want to use a telephone on an incorrectly wired 48dc circuit, I could switch the positive and negative wires, as long as the circuit in the telephone is isolated and never touches ground?

Thanks. Somehow I got in my head that all circuits were just about the delta from neutral and therefore nothing outside them mattered.

There is a true zero potential. You can detect this because two charged objects with zero delta between them will still repel each other.

I think a circuit should mostly care about the deltas, but when you’re talking about things like phone lines, the earth becomes part of your circuit. You can’t influence its potential (it’s almost exactly neutral because any charge imbalance gets removed by interaction with the interplanetary medium) so everything else is going to end up being determined by what you need for their relative potential to that.

Voltage is _always_ relative; you only ever measure differences between two points. Voltmeters have two probes. Ground is just a convenient reference, not a universal zero. And while Earth can act as a reference or return path in some systems, it’s not perfectly neutral or fixed...it’s just large enough to approximate that in practice. (The interplanetary medium aka aether doesn't exist)

Objects don’t repel because they’re at the same potential. Electrostatic force comes from electric fields due to charge. If two objects truly have zero potential difference and no field between them, there’s no force.

You’re correct that circuits care about voltage differences. After all, all work requires a force gradient of some kind.

Can't you define zero as the limit of the potential at infinity? And neutral charge bodies in empty space are generally close to that.

The interplanetary medium absolutely exists. I'm not talking about aether. I'm talking about the soup of dust, gas, and particles that fills space in the solar system. It contains a lot of charged particles, which is what keeps Earth extremely close to neutrally charged. Any deviation from neutral starts attracting positively charged particles and repelling negative, or vice versa, which equalizes the charge.

I didn't say objects repel because they're at the same potential. I said that objects at the same potential will still repel each other if that potential isn't zero.

Seriously, what is this reply? Aether? Objects repelling because they're at the same potential? You seem to have read a comment very different from what I wrote.

Yeah, I did mistake what you were trying to say. We’re just coming at this from two different sides... physics does have the convention that absolute zero potential is defined at infinity. I was looking at it strictly from a practical circuit perspective, where 'zero' is just wherever we stick the ground probe, and we only ever calculate for the relative deltas. And we generally don't have wires that can make it to the interplanetary medium or the edge of the infinite ground plane :)

Space is only ~60 miles away, that's not that much wire. Getting one end up there is left as an exercise for the electrician....

I think it all ties together. Ground potential as in sticking things in the actual ground is in practice pretty much the same as that theoretical potential at infinity, because space has enough charged particles flying around to equalize the imbalance. But it doesn't really matter from a practical perspective when making circuits.

> all the inputs and outputs share the same ground, it's not just the values for that pair of wires?

No, it depends on the converter. There are converters that leave 160V on the DC power rail for a 110V AC input, and 155V on the DC "ground" rail.

They are economic and you could find then when galvanic isolation is at least in theory not important, but they're terribly unsafe when used on PCBs that people might muck with.

If you have some "normal" converters and some of this kind, sharing the ground would be quite dangerous.

I have done some projects that needed some generic dc-dc converters from aliexpress (eg stepping down 12v to 5 or 3.3) I alway treated the output of each step down as a pair of wires that share no ground. It sounds like that would be overkill if they were reputable but it's probably best to not try tying the grounds together.

I figured any happenstance from the multimeter that the grounds match was transitory and not to be trusted.

I am STILL designing hardware for -48v telco standard. The first thing we do is convert -48 -> 48v. That's 4 square inches of PCB space we waste.

What do you need +48V for?

Well if it's negative 48V the electricty flows out of your circuit and back to the grid, so you need to make it positive to have the electricity come in.

Likely as a basis for converting to other useful DC voltages.

We go -48 -> 48 -> 12 -> 3v3,1v8 etc etc. If you went 48 straight to POL voltages then you would have horrific converter performance.

> If you went 48 straight to POL voltages then you would have horrific converter performance.

What's horrific converter performance in numbers?

An isolated flyback (to 12V) should be able to hit >92% and doesn't care if it's fed -48V or +48V or ±24V. TI webench gives me 95% though I'd only believe that if I'd built and measured it. What's the performance of your -48V → +48V?

[with the caveat that these frequently require custom transformers... not an issue with large runs, but finding something that can be done with an existing part for smaller runs is... meh]

-48 to 48 claims something like 97% (load dependent of course). It also needs to arbitrate between two input supplies for glitchless redundancy, plus have PM bus and other spec mandated stuff. There is no technical reason why you cant go -48 -> 12 as you state with good efficiceny, but we cant get hold of a part that ticks all the boxes.

Horrific performance by my definition would be 48v to say 1v. We only realistically use buck topologies for POL supplies. Such a ratio is really bad for current transients, not to mention issues like minimum on times for the controller.

I'm just surprised that either input isolation isn't on your spec, or it still somehow works out better with isolated to +48V than straight to 12V... but I guess if your spec requires other things, it makes sense.

(Thanks for the info!)

I was just looking at these funny parts: https://www.vicorpower.com/products?productType=cfg&productK...

130A, 48V -> 1.2V @ 94% efficiency! Except:

- $100 ea.

- Fixed 1/40 voltage ratio, regulation done by upstream regulator.

- Look at the minimum specs for efficiency…

This is a very strange part, what with the upstream regulator circuit.

My guess is that their efficiency stats dont include losses in the upstream regulator.

100 usd per unit doesnt seem that excessive.

> I don't think I've encountered anything else that requires negative voltage relative to ground

Automotive collectors can probably still relate to cars from the 1920s-50s having a "positive ground."

With positive ground the traditional more-sacrificial spark plugs lasted longer.

Interesting, so this is why the phone line still worked when power was out across the whole town.

Yeah, it used to be that you could still make calls (particularly to emergency services) even in complete power outages, for as long as your local exchange has batteries for. (AFAIR that tended to be on the order of hours, but probably differs quite a bit across locations and regulatory domains/countries.)

Another thing we lost in the age of VoIP landlines, but then again mobile towers also have batteries. Just don't be unlucky and have a power outage with 3% battery on your phone...

Luckily, phone batteries and phone power consumption seem to have improved a lot in the last half-decade.

Yeah I always heard that the phone lines carried their own power, and in Florida the phones did keep working when the power went out, but I never knew why.

So the grid was always charging up the lead acid batteries, and the phone lines were always draining them? Or was there some kind of power switching going on where when the grid was available the batteries would just get "topped off" occasionally and were only drained when the power went out?

Grid charging batteries, phone draining them as I understand. Of course there were switches all over the us so I can't make blanket claims but from what I hear that was normal.

The phone grid predated the electrical grid. There was no other choice for power.

Actually, there was one. Even earlier phones had their own power. A dry-cell battery in each phone, and every 6 months, the phone company would come around with a cart and replace everyone's battery. Central battery was found to be more convenient, since phone company employees didn't have to go around to everyone's site. Central offices could economize scale and have actual generators feeding rechargeable batteries.

It's a pretty decent chunk of power down a POTS cable too, as it was designed to ring multiple big chunky metal bells in the days of yore.

I was wiring in a phone extension for my grandma once as a boy and grabbed the live cable instead of the extension and stripped the wire with my teeth (as you do). I've been electrocuted a great number of times by the mains AC, but getting hit by that juicy DC was the best one yet. Jumped me 6ft across the room :D

The teeth. Yikes! But yeah, I remember having the rotary phone disassembled and touching the wires adjusting something when a ring came. Gave me enough of a jolt to remember.

I discovered the same exact thing wiring a second phone line to my bedroom as a teenager. I jumped into a pile of fiberglass insulation! :/

The batteries and phone lines were one system at -48v with power supplies converting AC power to DC while grid / generator is up.

The batteries are floated at the line voltage nothing was really charging or discharging and there was no switchover.

This is similar to your cars 12v dc power system such the when the car is running the alternator is providing DC power and the batteries float doing nothing except buffering large fluctuations stabilizing voltage.

Neither.

The batteries, the grid/generator-supplied power supplies, and the telephone switch equipment are all connected in parallel -- as if the entire DC power infrastructure consists of only two wires, and everything involved with it connects only to those two wires.

1. In normal operation, the batteries are kept at a constant state of charge. The switches are powered from the same DC bus that keeps the batteries charged.

2. When the power grid goes down, the batteries slowly discharge and keep things running like nothing ever happened (for hours/days/weeks). There is no switchover for this; it's just the normal state, minus the ability to juice-up the batteries. (Remember: It's just one DC bus.)

3. When the grid comes back up (or the generators kick in), the batteries get recharged. There is no switchover for this either; nothing important even notices. (Still just one DC bus.)

4. If the grid stays up long enough, go to 1. Repeat as the external environment dictates. (And as you might guess, it's still one DC bus and there's also no switchover here. Things just continue to work.)

You can play with this at home with a capacitor (which loosely acts like a battery does), an LED+resistor combo (which acts as a load), and a small power supply that is appropriate for LED+resistor you've chosen (which acts as the AC-DC converting grid input).

Wire them all 3 parts up in parallel and the light comes on.

Disconnect the power supply, and the light stays on for a bit -- it successfully runs from power stored in the capacitor.

Reconnect the power supply, and the light comes on and the capacitor ("battery") recharges -- concurrently.

Improve staying power by adding more parallel capacitance. Reduce or eliminate it by reducing or eliminating capacitance. Goof around with it; it's fun. (Just don't wire the capacitor backwards. That's less fun.)

I still have a bunch of 48vdc comms gear in my powerplant.

Why do you have a powerplant?

Power plant is the convention for any large company that has backup power. A few UPSes for the server room - they are the power plant. A backup generator - power plant. Sometimes even just the room with all the break boxes from where the grid comes in is called the power plant (though normally power plant is reserved for backup power). It is extremely common for commercial buildings to have their own power plant. Most of their power comes from the grid in all cases, but they have a power plant. At commercial scale you can often save money by buying a backup generator powerful enough for your whole building so you disconnect from the grid when grid power is in highest demand (see your utility, then your accountant: for details if you can afford a generator this large)

Because I am an electrical engineer in a powerplant and I am responsible for those systems.

I don't own it personally, I say it in the same sense someone says 'my building' when they mean 'place my apartment is at'

-48V! :-)

I'm working on stuff in that market, it's still largely is. DC Power System Design For Telecommunications is still a must read and it doesn't even cover the last 15 years or so of development, notably lithium batteries and high efficiency rectifiers.

I will say that this is a surprisingly deep and complex domain. The amount of flexibility, variety and scalability you see in DC architectures is mind-boogling. They can span from a 3kW system that fits in 2U all the way to multiples of 100kWs that span entire buildings and be powered through any combination of grid, solar and/or gas.

You need thick cables if you want to power a rack with 48V.

This reminds me of the early google data centers that directly soldered those massive duracell lantern batteries directly to the motherboards as a primitive battery backup. I'm struggling to google examples of it, this would have been back around 2008, but i have a vivid memory of it.

edit: found it https://www.cnet.com/tech/tech-industry/google-uncloaks-once...

Obviously 48VDC has been around and internally they will probably still step down to 48V. But these 48V islands are nowadays inter connected by regular AC grid. They want to replace that interconnection with a 800VDc bus. I kind of assume they chose 800vdc because there are already bunch of stuff available from EVs which also have 800vdc battery packs now.

They chose 800VDC because it's a convenient multiple that is the peak possible with a two-level 650V (probably GaN) FET arrangement.

And why is 650V special?

Historical, physical, engineering reasons.

Much of the world's mains-voltage electronics run at 240V (historical) and have PFC circuits (which are essentially just boost converters) that run at ~400V DC link voltages. 650V gives you enough headroom to tolerate overshoots and still have an 80% safety margin with a single level topology.

This voltage also coincidentally is a convenient crossover point where silicon MOSFETs start to become inefficient and GaN FETs have recently become feasible and mass-produced.

800V DC is definitely not "old".

I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC. Straight from the UPS as DC would work much better, and as I was teaching myself more about networking equipment, I was surprised to learn that most of it isn't DC input by default (i.e., each piece of equipment tends to come with built-in AC-DC conversion).

Then I started routing ethernet with PoE throughout my house and observed that other than a few large appliances, the majority of powered devices in a typical home in 2026 could be supplied via PoE DC current as well! Lighting, laptops, small/medium televisions. The current PoE spec allows up to 100 W, which covers like 80% of the powered devices in most homes. I think it would make more sense to have fewer AC outlets around the modern house and many more terminals for PoE instead (maybe with a more robust connector than RJ45). I wonder what sort of energy efficiency improvements this would yield. No more power bricks all over the place either.

I think we're slowly, slowly coming around to the idea of domestic DC distribution. The vast majority of consumer electronics would be perfectly happy to consume 12v. It's cheaper, safer, more efficient. Less design work and certification on inbuilt AC adapters.

I think it's highly unlikely we'll see mass scale retrofits, but if enough momentum builds up, I can see it as a great bonus feature for new builds.

I got lucky with my house and every room has a dedicated phone line meeting at a distribution panel (a couple of 2x4s with screw terminals) built in the 50s. I'm in the process of converting it to light duty DC power. The wiring is only good for an amp or two, but at 48v that's still significant power transmission.

> I think it's highly unlikely we'll see mass scale retrofits, but if enough momentum builds up, I can see it as a great bonus feature for new builds.

I imagine rooftop solar could also source DC for the house directly (or via a battery), before hitting the inverter... ?

The main problem I see is educating consumers. Maybe that starts with a standard for DC outlets and plugs that can't be confused with AC... ?

(Now I'm imagining desktop computers with much simpler power supplies; but you'd presumably have to wire for dozens of amps incoming...)

48v is what most home battery/solar systems run off. Also coincidentally POE, IMO it makes a much more sensible candidate as it is still 'safe' while carrying 4x as much power for a given cable gauge. Consider laptops are 19 or 20v so you would essentially /need/ a minimum of 24v.

"... throughout my house and observed that other than a few large appliances, the majority of powered devices in a typical home in 2026 could be supplied via PoE DC current as well!"

We installed 120 LED ceiling lights in our home circa 2020, all of which were run with high voltage (romex) and accompanied by 120 little transformer boxes that mount inside the ceiling next to them.

Later ...

We installed outdoor lighting with low voltage, outdoor rated wiring and powered by a 12V transformer[1] and I felt the same way you did: why did we use a mile of romex and install all of those little mini transformers when we could have powered the same lights with 12V and low voltage wire ?

I then learned that the energy draw of running the low-volt transformer all the time - especially one large enough to supply an entire house of lighting - would more than cancel out energy savings from powering lower voltage fixtures.

You don't have this problem with outdoor lighting because the entire transformer is on a switch leg and is off most of the time.

So ... I like the idea of removing a lot of unnecessary high voltage wire but it's not as simple as "just put all of your lights behind a transformer".

[1] https://residential.vistapro.com/lex-cms/product/262396-es-s...

> I then learned that the energy draw of running the low-volt transformer all the time - especially one large enough to supply an entire house of lighting - would more than cancel out energy savings from powering lower voltage fixtures.

That's not a constraint of physics, you can absolutely build a DC power supply that is efficient in a wide load range. (Worst case it might involve paralleling and switching between multiple PSUs that target different load ranges.) But of course something like that is more expensive...

> But of course something like that is more expensive...

More expensive than an inefficient unit, but it should still be a lot cheaper than 120 separate units, right?

And I expect one big fat unit to do a better job of smoothing out voltage and avoiding flicker than a bunch of single-light units. Especially because the output capacitors are sized for the entire system, but you'll rarely have all the lights on at the same time.

Though for efficiency I'd think you'd want 48v and not 12v.

Plus you save money on the conductors running to the lights.

These days, you should not be using transformers to power small loads at all, you should be using switching power supplies. They have negligible power draw when there's no load attached.

> I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC.

With double-conversion, generally yes.

I recently ran across the (patented?) concept of a delta conversion/transformer UPS that seems to eliminate/reduce the inefficiencies:

* https://dc.mynetworkinsights.com/what-are-the-different-type...

* a bit technical: https://www.youtube.com/watch?v=nn_ydJemqCk

* Figures 6 to 8 [pdf]: https://www.totalpowersolutions.ie/wp-content/uploads/WP1-Di...

The double-conversion only occurs when there's a 'hiccup' from utility power, otherwise if power is clean the double-conversion is not done at all so the inefficiencies don't kick in.

> Lighting, laptops, small/medium televisions. The current PoE spec allows up to 100 W, which covers like 80% of the powered devices in most homes.

I find it a little hard to imagine that those devices outnumber things like stoves, dishwashers, washers/dryers, kettles, hair dryers... by 4:1.

Unsure why PoE would be better for LED lighting than the standard approach of screwing a bulb directly into AC, either. How many lumens do you get out of strip lights these days? And you still have AC-DC conversion for whatever's sourcing power onto the Ethernet link.

PoE is also fairly bulky, requires large connectors, and either requires a wholly isolated PD or what's basically a class 2 DC/DC converter. That's why PoE-powered stuff usually has that big transformer cube in it with a lot of clearance, slotted PCB, 2-4 kV capacitors etc.

In practice PoE will have lower efficiency than mains powered, since it'll usually be at least double conversion, often three converters in series, plus the losses of the thin network wires, and the relatively high idle losses / poor low-load efficiency of the necessarily over-dimensioned PSE.

I think Ubiquiti (makers of the UniFi wifi products, as well as some of the most popular managed PoE switches) also make a ton of other PoE products such as the usual stuff like cameras, ip phones, network switches, access card readers, door locks, and, now, ceiling lights (presumably due to the latest PoE standards delivering significant wattage).

It's super nice because you only need to put the UPS/ATS at the PoE switch and then you get power redundancy everywhere you have ethernet running (i.e. the phones don't go down).

> maybe with a more robust connector than RJ45

USB-C could be that connector, using USB-PD instead of PoE. Though I'm not sure I'd want to need that much smarts for every single power outlet.

Considering the number of times I've sheared off a USB-C connector vs ethernet, I wouldn't consider USB-C to be more robust than RJ45. YMMV.

How often do you unplug RJ45s versus USB-C, though?

I'm not talking about unplugging. Normal use.

USB-C devices tend to be mobile. Flexing and disconnecting are much more common.

And in normal use, how often do you handle or cycle an rj45 vs a usb?

Even when it's your job the usb are still handled and cycled way more often. You might handle 100 ethernet jacks today, but it won't be the same one 100 times. You plug it in and don't touch that one again for 5 years.

You mean the ethernet cable in my laptop? Couple of times a day. The box under my desk? Often? How about the hundreds of devices I work with that have RJ45 connectors for serial access? All the time? Are you seriously telling me you hold up a (decently made) ethernet cable next to a USB-C connector and think "yeah...the one a fraction of the size of the other is obviously mechanically stronger". Is this some Apple shill campaign to try and get people to think "no, no...the smaller, thinner, narrower and shallower the connector is the better it will be someplace where people bump it all the time"?

No, but looking at the two side by side, I do think that the one with a fragile clip that shears off every time somebody trips on it is going to be more of a problem than the friction fit one that will just come off.

As opposed to the one that has no clip to hold it in, and shears off the whole connector when you trip over it. And I can use the ethernet cable without the tab.

Some people will embrace any absurdity to pretend to be right.

The problem is that all of those DC devices don't operate on 48V either. The vast majority of chips require a 5V or lower input, so with a 48V DC supply you're still going to need a per-device PSU to do DC-DC conversion. In other words: no getting rid of power bricks.

Efficiency isn't as straightforward either. You're still being fed by 120V/230V AC, so you're going to need some kind of centralized rectifier and down converter. It'll need to be specced for peak use, but in practice it'll usually operate at a fraction of that load - which means it'll have a pretty poor efficiency. A per-device PSU can be designed exactly for the expected load, which means it'll operate at its peak efficiency.

We also don't use 5V DC grids because the wire losses would be horrible, so a domestic DC grid should probably operate at pretty close to regular AC voltage as well. In practice this means the most sensible option would be to have a centralized rectifier and a grid operating at whatever voltage it outputs - but what would be the point?

As to PoE: I personally really like the idea, but I don't believe it'll have a bright future. For its traditional use the main issue is that there doesn't seem to be a future for twisted-pair beyond 10Gbps. 25GBASE-T might exist as a standard on paper, but the hardware never took off due to complete disinterest from the datacenter market, and it is too limited to be of use in offices and homes. I fully expect that 25G will arrive in the home and office as some form of fiber-optic interconnect - with fiber+copper hybrid for things like access points.

On the other hand, for a lot of IoT applications PoE seems to be too complicated and too expensive. It makes sense for things like cameras, but individual lights, or things like smoke sensors are probably better served in office/industrial applications by either a regular AC supply or a local DC one, plus something like KNX, X10, CAN, or Modbus for comms: just being able to be wired as a bus rather than a star topology is already a massive advantage. And for domestic use the whole "has a wire" thing is of course a massive drawback - most consumers strongly prefer using Wifi over running a dedicated wire to every single little doodad.

What if all homes had battery storage and or solar? You could then simply use it's rectifier as needed or direct 48v from the solar panels. That would be even more efficient than 230v.

We live on societies, switching from AC to DC because your low-power home appliances doesn't need AC makes no sense. Home power usage is dominated by heating and cooling not by your 45w laptop charger.

DC infrastucture makes sense in highly specialised environments.... Like new gigawatt AI farms

Large home appliances probably mostly need DC power these days too. Look at clothes washers: they all have variable-speed reversing motors, so they're probably using brushless DC motors (which use motor drives that are fed with DC, and output variable-frequency and variable-amplitude sinusoidal waves to drive the motor). HVAC seems to be similar, with variable-speed motors and compressors.

I don't think that much stuff is left which actually needs AC power (usually to run an AC induction motor).

[HVAC] true for the fans and controllers but surely you wouldn't DC feed a compressor.

Aren't compressors these days usually variable-speed?

That'd be neat. But there's no standard for voltage for home solar: The batteries might be 12, 24, 48v, 60v, or even much more. Meanwhile, the panel arrays commonly output anything as low as 0V and up to ~600V. There's not much for rules and norms here.

Even if we were to standardize a low (<50V) voltage for DC distribution within homes, we'd still need ~120/240VAC to power big stuff, or we'd instead need even-larger conductors (more copper) than we use today to do the same work with low voltage.

But, sure -- we can play it out. So let's say we have an in-home 48VDC distribution standard and decide that this is the path forward and we enshrine it in law.

We need to convert whatever the solar system has available to 48VDC. Then, we need to distribute that 48VDC using a completely separate network of cabling. Finally, we still need to convert 48VDC to whatever it is that devices can actually use.

That's not representative of a reduction in steps, or an increase in efficiency.

That is instead just an increase in installed infrastructure expense, and a decrease in device compatibility. It takes what we have, which is simply universal (at least within any given geographical area) and adds complexity.

And for what? What's the perceived benefit?

Almost all home batteries are 48v, I think it would be reasonable to standardise on that.

So 48v it is.

Is the juice worth the squeeze, though? Two sets of home wiring voltages? Substantially bigger copper wire inside the walls instead of existing copper, in order to do the same work? Two sets of appliances (of all sizes) on shelves at the store? More adapters?

Billy now needs to bring 2 wall warts to make sure he can charge his portable gear at a friend's house instead of just 1, because he's never sure until he gets there if they've got a 120 or 240v house like they all used to be, a combination house, or if it's one of those solar-only places that only has the weird plugs.

What we have now is 1 cable plant connecting the rooms of a home, and an increasing number of hybrid solar inverters that -- on a sunny day -- cheerfully convert solar power directly from whatever the panels are outputting to the 120/240 VAC wiring that both existing and future appliances know how to use. At night, these hybrid systems do do the same thing from whatever voltage the battery uses and convert that to AC. There's only 1 voltage, and only 1 plug; Billy brings 1 wall wart and knows he can charge his stuff.

To be sure: What we have not strictly ideal, but then neither is changing things without a clear positive benefit.

Again: What's the qualitative advantage of changing this, other than change for the sake of change?

DC might feel nice and neat, but in reality it doesn't seem to be shaped that way at all to me.

I'm not sure converting the solar and battery to 48V, distributing it around, and converting it to the needed voltage at the point of use is any more efficient than inverting it into 230V and distributing it around.

Also, you'll need wires that 5 times thicker. Instead of needing a reasonably 1mm^2 for a normal 16A line, you'll need 5mm^2 for the same power.

Solar and battery are already at 48v in most cases, so you are avoiding converting it to AC.

I agree, it's unserious to suggest a cooker or something high power is going to run off of 48v. But for loads like lights, PC/Laptop/TV/Audio 16a at 48v is ~770W which is adequate for these devices.

Both solar and batteries voltages vary wildly and require a converter to use.

One of the main problems is conductor size. I wish we could access 22AWG copper in cheap and cheerful cat5e/cat6 format cable. 24AWG cat5e, sometimes CCA is not great for doing large amounts of POE.

22AWG Cat6A is actually what I used (cheap it was not however).

It's fun to think about. There's advantages both ways, but I think it leans most-heavily towards keeping AC.

1. One of these is simplicity. With AC, one single home run of cabling (eg, Romex) can feed a whole room full of stuff, like a bedroom or a living room. At one end of the run is a circuit breaker (a fairly simple electromechanical device) and at the other end is a series of outlets (which are physically daisy-chained, but are functionally just wired in parallel with eachother).

Since one single run of cable can feed many devices, it is easy to accomplish.

2. Another advantage is that it is universal. Anything can plug into these outlets. Whatever a person brings into the home to use, they can plug it into an outlet and it works. It works this same way in every home.

3. And there's quite a lot of power available: A common 20A 120v branch circuit cabled up with 12AWG Romex is stated to supply up to 16A continuously, or 1920W. For intermittent loads, it can supply 20A -- or 2400W. That's tiny by European standards, but it's still quite a lot of power. It's plenty to run a space heater when Grandma visits and she complains about the guest room being cold (even as you start to sweat when you cross the threshold to investigate) and a big TV and a whole world of table lamps, all at once. And you can plug this stuff into any outlets in a room, and it Just Works.

4. But, sure: Lots of devices want DC, not AC. So there's a necessary conversion step that is either integral to the device being plugged in, or in the form of the external wall warts we all know very well.

So let's compare to power-over-ethernet.

1. It's also simple, but only tangentially-so. One home-run cable per outlet, whether that outlet is used or not, is something that can be rationalized as being a simple topology. A PoE switch at the head-end instead of a central box with circuit breakers is a simple-enough thing to transition to. And a lot more individual cables are required, but they're relatively small and are generally easier to install.

2. It's standardized, but it's not universal at all. I've got a few PoE widgets around the house, but I'm pretty friggin' weird when it comes to what I do with electricity. I can't go to Wal-Mart and buy more PoE widgets to use at home, and when people visit they aren't bringing PoE adapters to charge their phones and other electronics. My computer monitor doesn't have a PoE input. I can easily imagine a table lamp or a fan that connects to PoE, and also uses it as a network connection for automation, and that sounds pretty sweet in ways that tickle my automation bones in the most filthy of fashions... but that's getting even further into the weeds compared to how regular people expect to do regular things.

3. There isn't a lot of power available. 802.3bt Type 4 is the highest spec. And within that spec: While switch ports can output up to 100W, a device being powered is limited drawing no more than 71.3W. Now, sure, that's 71.3W per port, but in a room with 10 ports that's still only ~700W -- at most -- in that room. And Grandma's space heater won't run on 71.3W, nor her electric blanket. My laptop wants more than this. The list of useful, portable things that we casually plug into a wall that only draw less than 71.3W is pretty short and most don't benefit from the main advantage of PoE, which is a combination of [some] power alongside high-speed Ethernet data.

4. We still need wall warts since PoE is nominally ~48VDC. For example: Phones use less than 71.3W while charging, but they don't run on 48V. That means 120V AC comes in from the grid, gets shifted to 48VDC for distribution within the dwelling, and then gets shifted yet again to the produce the power (5, 9, 15, and 20V are common-enough in USB PD world) that devices actually want. That's more lossy conversion steps, not fewer -- and we still get to keep the extra conversion (wall warts) as punishment for our great ideas. This is not the path towards increased energy efficiency.

---

PoE is great for the things we use it for today. A camera, a wireless access point -- you know, fixed-location stuff that uses networked data as its primary function and also requires power.

Installed PoE light fixtures (like, say, task lights in a kitchen) also sounds neat -- unless they die prematurely and no PoE replacements are to be found. (Now, you have not just one or two problems, but many: The lights aren't working in that space and they can't be replaced with a trip to Lowes because the Romex that would normally have been installed was deliberately deleted from the plan. It could have been a 20-minute DIY fix that costs less than $100, but now it involves drywall and paint and retrofitting new cabling. Or maybe PoE replacements do exist, but it's now 2035 and the new ones don't talk the same network protocols as the old ones did.)

But there are other upsides: I've got an 8-port PoE-powered network switch that works a treat. It's a dandy little thing. And it sure would be neat to plug my streaming box in with PoE and kill two birds with one cable; I would like that very much.

But most people? Most people don't give a damn about ethernet (PoE, or not!) these days, or streaming boxes, and that trend is increasing. They just plug their lamp into the regular outlet on the wall like they always have, and deal with whatever terrible UI is built into their smart TV, and use wifi for anything that needs data.

And when they buy a home that is filled with someone else's smart infrastucture, their first task (more often than not) is to figure out who to call to erase those parts completely and put it back to being normal and boring.

90% of the power in our academic data center goes 13.8kV 3-phase -> 400v 3-phase, and then the machines run directly from one leg to neutral (230v). One transformer step, no UPS losses, and the server power supplies are more efficient at EU voltages.

But what about availability? If you ask most of our users whether they’d prefer 4 9s of availability or 10% more money to spend on CPUs, they choose the CPUs. We asked them.

There are a lot of availability-insensitive workloads in the commercial world, as well, like AI training. What matters in those cases is how much computing you get done by the end of the month, and for a fixed budget a UPS reduces this number.

> and then the machines run directly from one leg to neutral (230v)

And then every machine has a switching power supply to convert this to low-voltage DC, and then probably random point-of-load converters in various places (DC -> AC -> DC again) for stuff like the CPU / GPU core, RAM, etc. Each of these stages may be ~95% efficient with optimal load, but the losses add up, and get a lot worse outside a narrow envelope.

Yes, but it's not like any other layouts avoid those issues.

You could feed your servers off fat 12/24/48 volt supplies but with how much power a modern server can pull you're already converting in bulk even if you don't do that, limiting the potential advantages. For running CPU/GPU/RAM, there is no other option. When you need hundreds of amps at 1-2 volts, you convert that centimeters away if at all possible.

A datacenter using DC distribution is still using high voltages and stepping them down in layers. The hassle it avoids is in other aspects of power delivery.

Really you're down for over an hour a year? Unscheduled?

I was part of an electrician team renovating a three-letter agency's main data center (adding UPS to an archaic government renovation). As part of this process, we had to isolate the Emergency Power Off system/buttons.

Unfortunately, the EPO ended up having been installed differently than the plans indicated [0] — there was definitely more than an hour of unexpected downtime figuring out how to "unrig" its decades of faithful misconfiguration.

During this same months-long modernization, a separate facility decided to install a temporary tap off our already-temporary taps (no engineering consultation attempted) — with resulting Megawatts of melting disaster. More hours downtime.

tl;dr: shit happens

[0] EPO's main neutral was tied into a general lighting circuit's j-box, some bullshit jerryrigging from an 80s sparkie; our apprentice was tasked with taking out old fluorescents... ended up taking out entire facility (through no fault of his own).

I've been hearing this line for over a decade, now. "Immersion cooling will make data centers scale!" "Converting to DC at the perimeter increases density!"

Yes, of course both of those things are true, and yes, some data centers do engage in those processes for their unique advantages. The issue is that aside from specialty kit designed for that use (like the AWS Outposts with their DC conversion), the rank-and-file kit is still predominantly AC-driven, and that doesn't seem to be changing just yet.

While I'd love to see more DC-flavored kit accessible to the mainstream, it's a chicken-and-egg problem that neither the power vendors (APC, Eaton, etc) or the kit makers (Dell, Cisco, HP, Supermicro, etc) seem to want to take the plunge on first. Until then, this remains a niche-feature for niche-users deal, I wager.

Those vendors all have DC power supply options, to my knowledge. It’s hardly new; early telco datacenters had DC power rails, since Western Electric switching equipment ran on 48VDC.

https://www.nokia.com/bell-labs/publications-and-media/publi...

That’s just it though, telco DCs != Compute DCs. Telcos had a vested interest in DC adoption because their wireline networks used it anyway, and the fewer conversions being done the more efficient their deployments were.

Every single DC I’ve worked in, from two racks to hundreds, has been AC-driven. It’s just cheaper to go after inefficiencies in consumption first with standard kit than to optimize for AC-DC conversion loss. I’m not saying DC isn’t the future so much as I’ve been hearing it’s the future for about as long as Elmo’s promised FSD is coming “next year”.

I think the real reason is because battery power didn't have to be converted twice to be able to run the gear in case of an outage, so you'd get longer runtime in case of a power failure, and it saves a bunch of money on supplies and inverters because you effectively only need a single giant supply for all of the gear and those tend to be more efficient (and easier to keep cool) than a whole raft of smaller ones.

Surely if it makes sense for the big players, they will do it, and then the benefits will trickle down to the rest? Like how Formula 1 technology will end up in consumer vehicles.

At least for servers, power supplies are highly modular. It just takes 1 moderately sized customer to commit to buying them, and a DC module will appear.

Looking at the manual for the first server line that came to mind, you can buy a Dell PowerEdge R730 today with a first party support DC power supply.

These are GigaWatt data centers. For a single one they buy equipment by the container ship. Nothing is niche about it.

As seen on HN a few days ago, immersion cooling is dead: turns out the risks of getting sued to oblivion due to widespread PFAS contamination isn't worth it. [0]

DC doesn't have such a killer. There are a decent bunch of benefits, and the main drawback is gear availability. However, the chicken-and-egg problem is being solved by hyperscalers. Like it or not, the rank-and-file of small & medium businesses is dying, and massive deployments like AWS/GCP/Azure/Meta are becoming the norm. Those four already account for 44% of data center capacity! If they switch to DC can you still call it "specialty kit", or would it perhaps be more accurate to call it "industry norm"?

It is becoming increasingly obvious that the rest of the industry is essentially getting Big Tech's leftovers. I wouldn't be surprised if DC became the norm for colocation over the next few decades.

[0]: https://thecoolingreport.com/intel/pfas-two-phase-immersion-...

They poison water supplies, knowingly, for decades, and it only takes $12 billion dollars to finally get them to stop?

Fucks sake.

Immersion cooling was/is so fucking impractical it is only useful for very specific issues. If you talk to any engineer who worked on CRAY machines that were full of liquid freon, they'll tell how hard it is to do quick swaps of anything.

Its much cheaper, quicker and easier to use cooling blocks with leak proof quick connectors to do liquid cooling. It means you can use normal equipment, and don't need to re-re-enforce the floor.

A lot of "edge" stuff has 12/48v screw terminals, which I suspect is because they are designed to be telco compatible.

For megawatt racks though, I'm still not really sure.

We had a cluster of liquid cooled CDC Cyber mainframes. One of them developed a bad leak and managed to drain itself into the raised floor. This was a Very Bad Day for many folks in the computer center.

Edit: s/have/had/

It is weird to me how far from the state of the art mainstream server equipment is. I can't imagine anything worse than AC-AC UPS, active PDUs, and redundant AC-DC supplies in each rack unit, but that's still how people are doing it.

I recommend reading these two:

https://developer.nvidia.com/blog/nvidia-800-v-hvdc-architec...

https://blogs.nvidia.com/blog/gigawatt-ai-factories-ocp-vera...

almost everybody in the industry is embracing 800V DC mostly because of Vera Rubin and the increased electricity requirements.

How is DC better than a three phase delta 800Vrms, at 400Hz?

- Three conductors vs two, but they can be the next gauge up since the current flows on three conductors

- no significant skin effect at 400Hz -> use speaker wire, lol.

- large voltage/current DC brakers are.. gnarly, and expensive. DC does not like to stop flowing

- The 400Hz distribution industry is massive; the entire aerospace industry runs on it. No need for niche or custom parts.

- 3 phase @ 400Hz is x6 = 2.4kHz. Six diodes will rectify it with almost no relevant amount of ripple (Vmin is 87% of Vmax) and very small caps will smooth it.

As an aside, with three (or more) phase you can use multi-tap transformers and get an arbitrary number of poles. 7 phases at 400Hz -> 5.6kHz. Your PSU is now 14 diodes and a ceramic cap.

- you still get to use step up/down transformers, but at 400Hz they're very small.

- merging power sources is a lot easier (but for the phase angle)

- DC-DC converters are great, but you're not going to beat a transformer in efficiency or reliability

>- no significant skin effect at 400Hz -> use speaker wire, lol.

What are you talking about? There's a very significant skin effect at 400Hz. Skin effect goes up with frequency. These datacenters use copper busbars, not cable, so skin effect is an important consideration.

At 100 000 A for a 100 MW data center at 1000 V, speaker wire is a joke.

You obviously need at least a dozen stands in parallel!!

Clearly skin effect scales with frequency but, 400 Hz is still low, only 2.5x lines frequency (the scale is by the root); so the skin depth is 3mm. 3mm on each side makes for a pretty hefty rectangular cross-section.

If you could get that 100,000Amps flowing through your speaker wire, the vaporised copper and the plasma channel would probably keep your 100MW flowing, at least until your building caught fire.

Even your monster cable? ;)

Well, it'd still vaporise, but it'd sound smoother and more musical as it did it, and the soundstage from the plasma arc would be _stunning!_

It's almost worth the experiment and your cables are a sacrifice I'm willing to make. For science, of course.

You're _so_ right!

I'm pretty sure you have my delivery address from when I bought sorted Lego from you about 10 years back.

Let me know when to expect the 100,000Amp test equipment!

I shall make sure I wear better PPE than just my reading glasses.

:-)

This would be the funniest thing to do. 100K Amps is doable, the question is for how long. That would be one very impressive bank of capacitors. And to turn a 00 into plasma would have some spectacular side effects, such as raining molten copper across a sizeable area. Just your reading glasses would indeed not be enough, there probably isn't any PPE that I would consider entirely safe other than sufficient distance from ground zero. But now I'm really curious. I have a spot welder that will do bursts of 5KA and that will happily throw the breaker every so many welds. 100KA sustained will be a fair engineering challenge.

Ah, that lego project... that was one I always wondered if I should have industrialized it but sourcing enough lego was a real problem.

Ho ho ho, you asked for it:

https://www.youtube.com/watch?v=OC7sNfNuTNU

See also (as posted elsethread): https://www.youtube.com/watch?v=RoGbrgOhPes

Holy crap. That's a whole series of bad ideas extremely well executed. That guy probably has never seen what a lead acid battery can do when it explodes. He keeps hiding away from the hot metal but in the path of ~half of those batteries. Ignorance is bliss.

That's low voltage lightning :)

He was gifted an arch flash suit by the guys from Lightening on Demand :D

"The gift of life". Complete madness.

> no significant skin effect at 400Hz -> use speaker wire, lol

now run that unshielded wire 50 meters past racks of GPUs and enjoy your EMI

> The 400Hz distribution industry is massive; the entire aerospace industry runs on it

nothing in that catalog is rated for 100kW–1MW rack loads at 800Vrms

> 3 phase @ 400Hz is x6 = 2.4kHz... Your PSU is now 14 diodes and a ceramic cap

you still need an inverter-based UPS upstream, which is the exact conversion stage DC eliminates

> large voltage/current DC breakers are.. gnarly, and expensive. DC does not like to stop flowing

SiC solid-state DC breakers are shipping today from every major vendor

> DC-DC converters are great, but you're not going to beat a transformer in efficiency or reliability

wide-bandgap converters are at 95%+ with no moving parts

"now run that unshielded wire 50 meters past racks of GPUs and enjoy your EMI"

Multipole expansion scales faster than r^2.

Also, im not in the field (clearly) but GPUs cant handle 2.4 kHz? The quarter wavelength is 30km.

"nothing in that catalog is rated for 100kW–1MW rack loads at 800Vrms"

Current wise, the catalog covers this track just fine. As to the voltages, well that's the whole point of AC! The voltage you need is but a few loops of wire away.

"you still need an inverter-based UPS upstream, which is the exact conversion stage DC eliminates"

So keep it? To clarify, this is the "we're too good for plebeian power, so we'll transform it AC->DC->AC", right?

"SiC solid-state DC breakers are shipping today from every major vendor"

Of course they do. They're also pricey, have limited current capability (both capital costs and therefore irrelevant when the industry is awash with GCC money) and lower conduction, and therefore higher heat.

They're really nice though.

"wide-bandgap converters are at 95%+ with no moving parts"

transformers have no moving parts. Loaded they can do 97%+ efficiency, or 2MW of heat eliminated on a 100MW center.

An advanced AI rack might use 100kW = 800V 125A, requiring gauge 2, quarter inch diameter---this isn't your lol speaker wire. Actually, I apologize, I realized I may be talking to a serious audiophile, didn't mean to disrespect your Monster cables.

The skin depth by the way is sqrt(2 1.7e-8 ohm m / (2 pi 400Hz mu0))=~3mm for copper---OK for single rack, but starts to be significant for the type of bus bars that an aisle of racks might want.

As for efficiency, both 400Hz transformers AND fancy DC-DC converters are around 95% efficient, except that AC requires electronics to rectify it to DC, losing another few percent, so the slight advantage goes to DC, actually.

As for merging power, remember that DC DC converter uses an internal AC stage, so it's the same---you can have multiple primary windings, just like for plain AC.

> I realized I may be talking to a serious audiophile, didn't mean to disrespect your Monster cables.

I am a recovering audiophool.

I do own a pair of 2m long Monster Cable speaker cables (with locking gold plated banana plugs). I am fairly certain I've used welders with smaller cables.

(In my defence, I bought those as a teenager in the late 80s. I am not so easily marketed to with snake oil these days. I hope.)

(On the other hand, I really like the idea of a reliably stable plus and minus 70V or maybe 100V DC power supply to my house. That'd make audio power amplifiers much easier and lighter...)

I stg if I see the kids talk about Westinghouse being batterymogged I'm leaving the Internet

Ok, this is just plain nuts.

800 volts DC, at the megawatt power supply levels, implies fault impulses of more than a megajoule. Google tells me that's about 2 hand grenades worth of boom. That's an optimistic lower bound.

The resulting copper plasma cloud is a burn and inhalation hazard, along with the overpressure.

Let's say you get a 10 kiloamp fault current, this will then induce voltages everywhere you don't want it to go. If all the interconnects are fiber, that's really not a problem, but you have to have everything EMP shielded if you don't want boards popping randomly after such an event.

The "efficiency" of removing the extra power conversions also removes filtering and surge suppression. It's entirely possible that one power supply over-voltage takes out half of your racks. The MOSFETs used tend to fail closed instead of open, making failures far worse than a simple outage.

Very smart people are making very smart mistakes.

The datacenter I built in 2007 was DC.

Many datacenters I'd been to at that point were already DC.

Didn't think this was that new of a trend in 2026, but also acknowledge I did not visit more than a handful of datacenters since 2007.

It just seemed like a undenyably logical thing to do.

It's obviously not new. ±400VDC architecture was presented at Open Compute last year, which is a fair indicator that the presenter had put it into practice at least 5 years prior to disclosing it. 48VDC distribution within a rack, and 48-to-1V direct regulators for CPUs, were both contributed to OCP 7 years ago, at which point they were both old hat. And 48VDC telco junk is, of course, totally ancient.

I don't understand why new houses don't just have one high quality AC/DC converter so you can just use LED lighting without every bulb needing its own AC/DC converter. I imagine the light bulb cartel wouldn't really like that.

It wouldn't work. leds need low voltages, meaning massive wires. you can run the voltage change on ac or dc. Ac just needs a few capacters to smooth the wave out.

> I don't understand why new houses don't just have one high quality AC/DC converter so you can just use LED lighting without every bulb needing its own AC/DC converter.

IEEE 802.3bt can deliver up to 71W at the destination: just pull Cat 5/6 everywhere.

* https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i...

* https://www.usailighting.com/poe-lighting

And pay $60 per Ethernet POE+ light bulb.

> And pay $60 per Ethernet POE+ light bulb.

In the commercial/industrial space this may be worth it: how long do these bulbs last? how much (per hour (equivalent)) do you pay your facilities folks? how much time does it take for employees or tenants to report an outage and for your folks to get a ladder (or scissor lift) to change the bulb?

Do you want your house to burn down? Lower voltages for LED lights mean higher current.

That's traded off against the increase efficiency of LED lighting, at least compared to incandescent lighting. An LED "equivalent replacement" for a typical incandescent globe is down around 1/10th of the power. A 7Watt LED bulb is typically marketed as "60W equivalent". If that configured as a bunch of LEDs in series (or series/parallel) that need 12VDC, it's right about the same current draw as the 120V 60W incandescent equivalent. (Or perhaps double the current for those of us who get 220VAC out of our walls.)

(Am I just showing my age here? How many of you have ever bought incandescent globes for house lighting? I vaguely recall it may be illegal to sell them here in .au these days. I really like quartz halogen globes, and use them in 4 or 5 desk lamps I have, but these days I need to get globes for em out of China instead of being able to pick them up from the supermarket like I could 10 or 20 years ago.)

With modern technologies, that's power over ethernet or USB-C. Other comments in this thread point out that the telephone service also routinely used 48V for the ring signal.

However, higher DC voltage is riskier, and it's not at all standard for electrical and building code reasons. In particular, breaking DC circuits is more difficult because there's no zero-crossing point to naturally extinguish an arc, and 170V (US/120VAC) or 340V (Europe/240VAC) is enough to start a substantial arc under the right circumstances.

Unfortunately for your lighting, it's also both simple and efficient to stack enough LEDs together such that their forward voltage drop is approximately the rectified peak (i.e. targeting that 170/340V peak). That means that the bulb needs only one serial string of LEDs without parallel balancing, making the rest of the circuitry (including voltage regulation, which would still be necessary in DC world) simpler.

because shorts and voltage loss are a real issue at that scale.

LED light bulbs exist exclusively for compatibility with Edison sockets. Every LED fixture I have seen had a single transformer for the entire fixture; and that transformer was reasonably separate from the LEDs themselves.

What voltage do you use? Most DC stuff wants low voltage (5-48V), but appliances need higher voltage like AC-level to get enough power over existing wiring. The result is DC-DC converters every place that have transformers now.

The gain from DC-DC converters is small and DC devices are small part of usage compared appliances. There is no way will pay back costs of replacing all the appliances.

Every decent LED would then need … a switching power supply. LEDs are current-driven devices, and you get the best efficiency if you use an actual current-controlled supply. And those ICs are very, very cheap now.

The part that would genuinely be cheaper is avoiding problematic flicker. It takes a reasonably high quality LED driver to avoid 120Hz flicker, but a DC-supplied driver could be simpler and cheaper.

Waiting for home DC.

It is silly to have AC to DC converters in all of my wall connected electronics ( LED bulbs, home controller, computer equipment etc )

Not going to happen. For the same reason that the US never converted to a higher domestic voltage even though there are many practical advantages. The transition from one system to another at the consumer level would be terrible, even if there would be some advantage (and I'm not sure the one you list is even valid, you'd get DC-DC converters instead because your consumers typically use a lower voltage than the house distribution network powering your sockets) it would be offset by the cost of maintaining two systems side by side for decades.

You could wire your house for 12, 24 or 48V DC tomorrow and some off-grid dwellers have done just that. But since inverters have become cheap enough such installations are becoming more and more rare. The only place where you still see that is in cars, trucks and vessels.

And if you thought cooking water in a camper on an inverter is tricky wait until you start running things like washing machines and other large appliances off low voltage DC. You'll be using massive cables the cost of which will outweigh any savings.

I suppose that still begs the question somewhat, since the US does have 240V (2 phase) already driving many appliances. Why hasn’t it ever become standard for luxury kitchens to have a European-style outlet for use with a European kettle? I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?

Well, as you say, it would not be according to code and the insurance company might have something to say about it. It's also single phase but not quite the way you do it in the USA, it would be a neutral and a phase whereas in the USA I think it is 2x110. Finally, it's 50 Hz rather than 60 which would work fine for resistive loads but not so well for inductive ones such as transformers and motors.

In all likely not worth the trouble. When I moved to Canada I gave away most of my power tools for that reason and when I moved back I had to do that all over again.

> In all likely not worth the trouble. When I moved to Canada I gave away most of my power tools for that reason and when I moved back I had to do that all over again.

If you ever have to do it again, you can probably get a transformer rated high enough for power-tools for cheaper than replacing all of your power tools.

Of course you can. That's kind of obvious. It is also highly impractical. Besides the frequency delta you end up having to lug a heavy transformer along and then you have to alternate it across your tools so you don't end up frying the transformer.

The line frequency tends to screw with things with motors too. Moved from the US to Belgium back when compact cassette was a common format for music.

Killed a few tapes with a transformer on a US tape deck before buying a 220V 50Hz unit. No, I don’t remember if the pitch was grossly off, but I’m guessing it wasn’t.

You can run 240V circuit to kitchen for kettle and put in NEMA 6 outlet. But few people care about fast boil and importing European kettle. Most people use the microwave or stovetop, and 120V kettles are fine in most cases. It will never become a standard thing.

> I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?

How expensive would a proper AC->DC->AC brick for that power level be?

Not so simple, you'd have to use a 'drier' or 'welder' socket for that otherwise you won't have enough power. A single circuit in Europe is 240V 16A or 3840W!

A pure sinewave inverter for that kind of power is maybe 600 to 1000 bucks or so, then you'd still need the other side and maybe a smallish battery in the middle t stabilize the whole thing. Or you could use one of those single phase inverters they use for motors.

I wired a UK kettle to an unused 240V range outlet in the US once. It was amazing, boiled a liter of water in just under a minute. Obviously kinda sketchy.

That's more like it :)

"Wired"?

...There was some kind of switch involved, I hope?

I just meant I spliced the line cord, adapters don't exist. It was an easily accessible NEMA 10-50 outlet, so we simply unplugged it when we weren't actively using it, because of the obvious fire hazard of a 16awg line cord on a 50amp breaker (which is why adapters don't exist).

Gratuitous disclaimer, don't try this at home kids...

Most important comment here!! I would love to buy like a 6kw battery induction kettle for the states. As far as I can tell, they don’t exist.

Ahckhually US residential is split single phase, not two phase. https://en.wikipedia.org/wiki/Split-phase_electric_power

I think the answer to your question is that it mostly doesn't matter for personal mug size quantities of hot water and if it does matter to you there are readily available competing options such as dedicated taps for your kitchen sink.

Perhaps the biggest reason is that a traditional kettle on any half decent electric range will match if not exceed the power output of any imported electric kettle. Many even go well beyond that with one burner marked "quick boil" or similar.

I use an induction stove on maximum to boil water as I get irritated at the time it takes to boil water with 240v.

I’m surprised that American exceptionalism can tolerate half powered sockets.

The induction stove boost function is glorious. Using twice the power temporarily is such a timesaver!

> but surely someone wanted hot tea faster

No one in the USA drinks hat tea. The choices (and it tends to be regionally-based) is sweet or unsweet tea. No need to boil a kettle quickly for that.

What? Plenty of people in the US drink hot tea.

> No one in the USA drinks h[o]t tea.

There are dozens of us.

Perplexingly I was traveling in one of the iced tea regions of the country in need of a cup of hot tea, and they had no way to make it. Like, you have a commercial coffee maker and hot cups, the coffee maker has a hot(ish) water tap. All you need is a $4 box of teabags that’ll last until the heat death of the universe. Nope.

As a counter argument, things like pour over coffee is getting to be more popular in the US and older drip coffee makers seem to be getting slightly less popular.

Still though, I don't seem to see most of those people seriously clamoring for the electric kettle to go a bit faster. The cost for the wiring difference and dealing with odd imported kettles just isn't worth it generally.

> The choices (and it tends to be regionally-based) is sweet or unsweet tea.

... Unless you're buying it pre-made, does this not still start with making hot tea the regular way? Or what exactly are you doing with the tea bags and loose tea from the supermarket?

Technology Connections did this with an EV battery charger:

https://youtu.be/INZybkX8tLI

>Why hasn’t it ever become standard for luxury kitchens to have a European-style outlet for use with a European kettle? I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?

I've heard of Americans getting EU plugs for things like this, but it's extremely uncommon. The simple answer is: Americans just don't drink tea very much, and the ones who do aren't going to go to this much trouble and expense just to be able to boil water for their tea twice as quickly.

If speed is the issue, Japanese water boilers keep water at or near boiling so there's less of a wait, and they operate on 110v.

These make absolutely no sense and are extremely wasteful if you're only making 1 or 2 cups of tea per day. They make a lot of sense if you're in an office full of tea-drinkers though. Home users are more likely to be in the first group.

I'm not sure it's likely, but I could see DC lighting start to happen in new construction. Have a single AC-to-DC converter off the main service entrance that powers hard-wired LED lighting fixtures in the house. Would probably be better than running the individual (and usually very low quality) converters in dozens of standard LED light bulbs. Would need to be standardized, codified, etc. so probably not happening soon.

Would be more practical to have a single 50-300W AC-DC 24V PSU per room or group of rooms, then pull relatively short DC cables to each light. A multichannel light controller could also be placed nearby, and then if you need fully-featured brightness and color control, only a small PWM amplifier could be placed at each light if distance from controller to each light is too long to transmit PWM power directly.

I just wish I could run my air conditioner and my desktop computer at the same time without flipping the breaker. The RTX 5090 is a space heater and will easily peg at the 600W it’s rated for, and so with that and an air conditioner window unit, I have to run a long cable from another unused room if I want to do anything that stresses the video card.

You can use nvidia-smi to reduce the powerdraw of the card to just below what will trip the breaker.

If you're running an air conditioner and a "space heater" at the same time it might be worth reconsidering your priorities.

I can watch 1080p video on YouTube and it runs in an up-to-date web browser using less than 50% CPU on 12-year-old hardware with 8GB of RAM and a graphics card that was a budget option at the time (my searches indicate it draws at most 80W, though it expects a 500W PSU for some reason).

> Not going to happen. For the same reason that the US never converted to a higher domestic voltage even though there are many practical advantages.

It would be relatively easy for the US to go to 240V: swap out single-pole breakers for double-pole, and change your NEMA 5 plugs for NEMA 6.

For a transition period you could easily have 240V and 120V plugs right next to each other (because of split phase you can 'splice in' 120V easily: just run cable like you would for a NEMA 14 plug: L1/L2/N/G).

What would be the real challenge would be going from 50 to 60Hz.

> What would be the real challenge would be going from 50 to 60Hz.

Other way around, no? The US is already 60Hz.

Edit: I mostly remember this because the SNES games I used to buy in the US and brought back to Europe ran noticeably slower.

... or we could have both sets of wiring, and use what's appropriate for the task/appliance?

The lesser-known instance of this is RV power. When you're running off small batteries and solar, you want to make the best use of the watt-hours you have, and that means avoiding the DC-to-AC-to-DC loop wherever possible. So you run 12V (or in newer models, higher voltage) versions of everything, upconverting as necessary.

I am really skeptical that 12VDC power distribution in RVs actually saves power compared to a high-quality (hah!) higher voltage AC or DC system. 12V is absurdly low and you can’t easily lose quite a few percent in resistive losses even with fairly large cables, and those large cables are quite unpleasant to work with and rather dangerous.

I tried using a microwave off the RV batteries, your inverter needs 4/0 cable. Very "fun".

The vast majority of what you're running from RV DC are things like lights, fans, phone chargers, and other cigarette-plug-adapter type devices. My RV has a 12V DC fridge. For anything more - particularly air conditioning - you need AC for sure.

My inverter-charger is connected to my batteries with 4/0 cable. That wasn't fun to run.

Well, having spent some time operating a 12VDC system last year when I moved into some shacks, I will say that I find it a lot more convenient to run 120VAC.

I end up converting stuff anyhow, because all my loads run at different voltages- even though I had my lights, vent fan, and heater fans running on 12V I still ended up having to change voltages for most of the loads I wanted to run, or generate a AC to to charge my computer and run a rice cooker.

Not to mention that running anything that draws any real power quickly needs a much thicker wire at 12V. So you're either needing to run higher voltage DC than all your loads for distribution and then lowering the voltage when it gets to the device, or you simply can't draw much power.

Not that you can't have higher voltage DC; with my newer system the line from my solar panels to my charger controller is around 350VDC and I can use 10awg for that... but none of the loads I own that draw much power (saws, instapot, rice cooker, hammond organ, tube guitar amp) take DC :D

Catch me wiring my house with 20V USBC ;)

Do you have a website with your system on it? I have an off-grid building I need to add solar to in the next year or so. After I fix the foundation and roof, of course. Naturally I’m exploring options for item 387 on the todo list instead of think about how I’m going to jack the building up.

It's a pretty simple system:

4KW of panels, 400W 48V EG4 6000XP charge controller/ inverter 3x EG4 LifePower4 48V batteries a raspberry pi running solar assistant

I feels like a bit overkill, and there is still a whole mppt unused on the 6000xp so I could still double my panel input. Also solar assistant tells me that I rarly go below 75% battery storage. If I just wanted to run my fridge and assorted convenience loads (and ran things like table saws off a generator) then I could get away with a lot less of a system.

But I'm operating a recording studio, and there were a couple days this winter where I had a full-band session and a couple days of storms and got down to below 50%.

home appliances have lower voltage, like 12V or 5V. The wire loss and heat would be a problem.

It's called USB power delivery

Assuming you live in a "large" western home, it's impractical. Remember, Edison's first power grid operated at 110/220v DC to the home. If there was lower voltage (IE, 12 volts) going from the street to your walls, the line loss would be significant. It only works in RVs and shacks because the wires are short.

Thus, even if you had DC in the walls, it would be 100+ volts, and you'd still have conversion down to the lower voltages that electronics use. If you look at the comments in this thread from people who work in telco, they talk about how voltage enters equipment at -48V and is then further lowered.

Is there anything left in a modern home that really needs or is better on AC?

We have some old ceiling and exhaust fans, but I know those can be replaced. Our refrigerator is AC, but extended family with an off-grid home has a DC refrigerator that cycles way less, probably due to multiple design factors but I’m sure the lack of transformer heat is part of it. I’m not as sure about laundry machine or oven/cooktop options but I believe those are also running on DC in the off-grid home without inverters.

Most of these AC appliances also have transformers in them anyway for the control boards. It seems kind of insane to me that we are still doing things this way.

Of grid homes are vastly more concerned with the energy efficiency of their appliances and thus DC refrigerators generally have more insulation. Most AC customers prefer more internal volume for food over slightly increased efficiency.

AC motors are using way more power than the puddly control boards in most home appliances. So you lose a little efficiency on conversion but being 80% efficient doesn’t matter much when it’s 1-5% of the devices energy budget. You generally gain way more than that from similarly priced AC motors being more efficient.

I agree with everything you said, except it seems like a false dichotomy. We can clearly build DC refrigerators with more or less insulation. We can clearly build them large or small. If you want to prioritize volume, then surely you could do that with DC. Right?

I know that a long time ago DC-to-DC voltage converters were very large in size, which meant AC would win on space efficiency. But unless I’m mistaken, that’s no longer the case. Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator?

> Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator?

Sure, but it’s important to separate what could be built from what is being built based on consumer preferences and buying habits. The average refrigerator could be significantly quieter, but how often do people actually listen to what they are buying? People buying Tesla’s didn’t test drive the actual car they were buying so the company deprioritized panel gaps. And so forth, companies optimize in ways that maximize their profits not arbitrary metrics.

Any appliance with strong motors should be more efficient with AC supply. But almost anything else can be regarded as a heater that doesn't care much as long as it is fed with the correct voltage. Which is actually the core issue.

A DC household would have to choose a trade-off between multiple lines with different voltages or fewer voltages that need to be adapted to the appliances. And we're right back at the AC situation, but worse since DC voltages are more difficult to change.

But consumers like datacenters can very well plan ahead and standardize on a single DC voltage. They already need beefy equipment to deal with interruptions, power sourges, non-sinus components, and brownouts, which already involves transformers, condensators, and DC conversion for battery storage. Therefore almost no additional equipment is required.

What qualifies as a strong motor here? Are you comparing to a brushed DC motor? Do you think a washer/dryer would have worse overall efficiency with a BLDC in a DC home compared to what we have today? If so, that’s news to me. Where can I learn more about that?

The trade-off between, say, one (relatively) high voltage DC bus throughout the home vs many branches with lower discrete voltages is indeed a problem. With AC, we took the bus approach, running 120v everywhere (in the U.S., higher elsewhere). I’m inclined to say we should keep doing that for flexibility and predictability. But it’s a trade off, like you said. It would obviously help if regulatory and standards bodies came out with official recommendations.

Probably 90% of my devices run 5V DC or similar, but you can't run that through a home so you're back to needing AC. If you're going to have AC and DC then you might as well just have AC.

> Probably 90% of my devices run 5V DC or similar,

Indeed. And that’s quite normal. Our electrical system should serve our modern needs.

> but you can't run that through a home

5V might be too low for that length of wire. But you could most definitely have a low voltage line in your house that we could design around, maybe 12V. Electric vehicles are moving towards 48V for accessories. It seems like lack of a standard is holding us back more than anything else.

Or we could just keep doing 120V in the walls, with a DC supply. Modern DC-to-DC voltage converters are very efficient and small. But maybe I’m wrong. A lot of people seem to believe they are still not good enough yet for such a change to make sense.

> If you're going to have AC and DC then you might as well just have AC.

I arrive at the opposite conclusion. Most things are natively DC. So therefore, power in the walls should be DC and we should covert it to AC near the endpoint where necessary.

Things like washing machines, dryers, dishwashers, air conditioners, or fridges spend a lot of energy by running powerful electrical motors, which should benefit from AC.

Everything else I can think of in a typical household is basically a mere heater that in principle works equally well with AC and DC of the correct voltage. Even computers can be said to mostly care about the correct voltage since AC->DC conversion is vastly easier than voltage conversion.

>Things like washing machines, dryers, dishwashers, air conditioners, or fridges spend a lot of energy by running powerful electrical motors, which should benefit from AC.

No, they don't, not at all.

Most modern appliances have variable-speed motors these days. You can't do that by just connecting AC to a motor; you need a control board to generate the waveforms necessary to make the motor turn at the speed and direction you want. That control board has to be fed with DC power. (Source: I used to design BLDC motor control systems)

Only really simple appliances, like old-fashioned horribly-inefficient clothes dryers, still use AC induction motors, and those are mostly being phased out. (Bathroom fans also need AC; they're usually cheap synchronous reluctance motors.)

So it really doesn't matter much whether the incoming power is AC or DC these days, unless you have a bunch of ancient appliances that still use induction motors. If it's AC, it's going to be rectified and fed into a DC-to-DC converter to create the lower DC voltages needed. If it's a higher DC voltage, we can skip the rectification step and not worry much about ripple.

They're still converting from AC to DC at the datacenter, it just isn't being stepped down at the perimeter. There is no transmission of HVDC going on. This isn't really Edison's revenge, more like his consolation price, ha!

I wonder how much of the benefit is simpler redundant power equipment. For AC, you have standby UPSes and line-interactive UPSes and frequency and phase synchronization. And everything needs a bit more hold-up time because, in case of failure, your new power supply might be at a zero crossing.

For 800V DC, a simple UPS could interface with the main supply using just a pair of (large) diodes, and a more complex and more efficient one could use some fancy solid state switches, but there’s no need for anything as complex as a line-interactive AC UPS.

  Hard as a rock!
  Well it's harder than a rock!

its really wild at all the AC to DC changes. for those non electric engineers / hardware hackers (like myself) one of the biggest "examples" I've seen of this has been ceiling fans.

Installing a ceiling fan used to be treacherous and so heavy. Also loud and buzzy after installed. Now the fans in these things are so lightweight and easy.

seeing the same in many more areas (lighting, etc)

Would love to see more mainstream DC lighting options and an updated code to match. I just finished a remodel of my workshop and blew over a hundred bucks on 14/2 for a 15 amp lighting circuit that is unlikely to ever see more than a 1 amps load.

The irony is all the recessed lights I picked out are DC, they all have little AC-DC boxes hanging off them using a proprietary connector. If I hadn't needed to pass a rough-in inspection going all DC would've been trivial.

Well they're kinda transitioning back. When I grew up most DCs (and telecom facilities) were running on 48V DC. Easy to back up with a big room full of lead acid batteries (just keep an eye on that hydrogen gas lol)

Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.

I've worked overseas a lot and one thing that's really different from 2 decades ago is that I simply don't need a step-down transformer anymore because every single thing I plug in converts to DC (or otherwise accepts dual-voltage) anyways. So I have a giant collection of physical plug adapters because every device I use just needs to fit into the socket and takes care of it from there.

(My stand mixer is the lone sad exception)

Agreed!

I spent a few years getting flown out around the world to service gear at different datacenters. I learned to pack an IEC 60320 C14 to NEMA 5-15R adapter cable and a dumb, un-protected* NEMA 5-15R power strip. While on-site at the datacenters, an empty PDU receptacle was often easy to find. At hotels, I'd bring home a native cable borrowed from or given to me by the native datacenter staff or I'd ask the hotel front desk to borrow a "computer power cable," (more often, I'd just show them a photo) and they generally were able to lend me one. It worked great. I never found a power supply that wasn't content with 208 or 240V.

Example adapters: https://www.amazon.com/dp/B0FD7PHB7Y or https://www.amazon.com/dp/B01IBIC1XG

*: Some fancier power strips with surge suppression have a MOV over-voltage varistor that may burn up if given 200V+, rendering the power strip useless. Hence, unprotected strips are necessary.

Something to consider, and something I got a vivid demonstration of while playing with solar panels, DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe.

My understanding is that DC breakers are somewhat prone to fires for this reason, too.

Heh - I vaporised a fairly large soldering iron tip (probably 4mm copper cylindrical bar?), when I fucked up soldering a connector to a big 7 cell ~6000mAHr LiPo battery and shorted the terminals. Quite how I didn't end up blind or in hospital I don't know. It reinforced just how much respect you need to pay to even low-ish voltage DC when the available current was likely able to exceed 700A by a fair margin momentarily. I think those cells were rated at 60C continuous and 120C for 5 seconds.

heh man, I'm glad you got out of that easy, I definitely wore safety glasses 100% of the time after my experience. I think a lifetime of experience with dangerous wall outlets and harmless little 1.5V/9V DC cells teaches us the wrong lessons about DC safety. I've since heard stories of wrenches exploding when they fall across EV high voltage battery terminals. Wrenches aren't supposed to be explosive.

The electricians I was working with also told me stories about how with the really big breakers, you don't stand in front of it when you throw it, because sometimes it can turn into a cloud of molten metal vapor. And that's just using them as intended.

Amps - the old 48vdc telco data centers vaporized wrenchs once in a while.

Those harmless 9V DC cells can do a lot of damage if you use them right.

This reminds me of the sailor who [decided](https://darwinawards.com/darwin/darwin1999-50.html) to measure his internal resistance by pushing probes through the skin on his thumbs and electrocuted himself with the 9V multimeter battery.

Mythbusters time. Salty fluids can be remarkably conductive. Blood qualifies. What's interesting though is that you have to wonder if there isn't some contributing factor here, as a kid I did this quite a few times, so that's one more for that list of stuff that could have killed me. At the same time: I didn't have nice insulation piercing tips back then (I do now) and that may be what saved me. I will definitely not try this again.

Another story in the same line is that I heard that a horse got killed by contact with a lantern battery, but I don't have any reference for that, just a story by a family member that collected coaches.

A bunch of those big breakers require two people. One person in a flash suit and another with a 2m long pole around the first person. That way if an arc flash happens, the second person can yank the first person to safety without also getting hurt.

Why don't they use the pole to flip the breaker from 2m away?

Ruins the fun and interrupts instilling respect deep into the bones of interns.

Allegedly

While on "work experience" from high school I was put on washing power lines coming straight out of the local power station near the ocean - lots of salt buildups to clear.

Same deal, flashover suits and occasional arcs .. and much laughter from the ground operators who drifted the work bucket close.

You got super lucky.

Yep. Super super lucky. I suspect my reading glasses are the only reason I can still see anything.

I have a couple of those narrow escapes one of which led me to put a significant chunk of Eastern Amsterdam out of power. Another involved Beryllium oxide. 9 lives are barely enough.

I would read that book...

'Stupid stuff I've done and survived'...

Ah! Perhaps you are a member of the gigawatt club? Eligible for entry once you have accidentally tripped off 1000 MW of load or generation! No sweeping that under the table

I'm the idiot that sent a fairly high voltage spike into the grid setting off a cascade. Even years later I do not fully understand how it could happen, you'd think the grid would be low impedance enough to absorb a spike like that. But it set off a cascade on a part of the local grid that was known to be weak.

Somehow I simultaneously desperately want to be in that club, and never want to be responsible for an event that would let me join that club...

You brought back a memory, a second hand one, but still a great story. A guy I knew long ago had emigrated from NZ to NL. His main claim to fame in NZ was that one day he showed up drunk for work. In itself this wouldn't have been memorable, if it wasn't for his job, which was to manage a relatively small hydro plant on one of three shifts. On that particular day the plant had to be brought back online after being out for service and since it was really old the synchronization was manual. You had to control the flow of the water, monitor two concentric spinning wheels with the one driven by the grid and the other driven by the local genny and when the phase markings were lined up 'just so' you had to engage this frankenstein level switch to couple the grid to the generator and from there on inertia did it's thing so you could open up the gate to allow more water so the generator would start leading the grid effectively generating power.

Any kid could do it. Probably. But not a drunk one and instead of waiting long enough for both wheels to stay synchronized indicating there would be only a small jump in phase he just said f* it and connected the two anyway. Predictably, this led to a serious disturbance to the grid which in turn caused a whole lot of other stuff to disengage. Since his chances for re-employment on account of his new-found fame were somewhat minimal he decided to emigrate instead :)

> DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe.

It would have self-extinguished if you waited long enough for the probe to vaporize.

> My understanding is that DC breakers are somewhat prone to fires for this reason, too.

I think its that DC breakers are more expensive, so people use AC rated breakers instead. They are both rated for 400v @10 amps, its the same thing right?

It turns out they are not, and most people, even electronics types rarely play with 200v+ of DC.

Yeah, I think this array was pushing 350-400V

That’s actually a recent phenomenon. Before the age of electronics most household appliances either worked with AC or DC equally well (like incandescent bulbs) or worked well with AC only given the technology at the time (think anything with a motor, fans, HVAC compressors etc).

Taking it to an extreme, the house I lived in while in grad school had wall lamp fixtures that doubled as electric and gas lamps. At some point I imagine it would have been possible to choose between using electric or gas by either flipping the switch or turning a valve. They said "Edison Patent" on them. We could have lit the house on AC, DC, or gas.

Thinking about the failure modes gave me the heebie jeebies, but the gas had been disconnected ages prior.

It’s kind of fun that light switches predate electricity. I think you used to turn a key, I guess you were turning a valve? Now that I think of it using a key to operate a valve makes a lot of sense but you don’t see it too often, well, I guess you want to turn things off without needing to find a key…

I lived in a 19th century house in San Francisco that had gorgeous plaster work medallions on the ceilings - think cherubs and fruits - in the middle of which were the light fixtures. One day my dumb-ass flatmate made an ill-advised attempt to DIY his light fixture and cracked the still-active gas line embedded in the ceiling. Sometime in the 1920s - the date was printed on a sticker in the electrical panel - when they electrified the house, they'd wrapped the electrical wires around the gas pipes, and left them otherwise in situ. Crazy stuff.

I've had discussed with people familiar with the matter, and they convinced me its really not worth it for many reasons, the main one being safety - DC arcs are self sustaining - AC voltage constantly goes to zero, so if an arc were to form, it gets auto extinguished when the voltage drops. With DC this never happens, meaing every switch or plug socket can create this nice long arcs and is a potential fire hazard.

Really depends on what we're talking about. A lot of electrical safety equipment has a DC rating, usually something like 90VDC/300VAC. Also, most DC equipment just isn't going to have the stored energy to generate a big arc. Well, except batteries, and we're already piling them all around us.

I mean it depends, but for dual rated stuff has both a voltage and current limit, both of which are way lower. Like typically a 230V/20A AC switch can switch 24VDC/2A. And the energy is not in the equipment, its in the mains (or batteries like you said, or PV panels)

Right, but that's why I mentioned safety equipment. Your common DIN-mount UL-489 branch circuit breaker will be rated for the same trip current, same short circuit current rating (SCCR), but lower voltage. So you can use the same wiring and breakers as you might have with AC and your 48V battery bank won't vaporize the $5 hardware store toggle switch that somehow became a shunt.

I mean, most AC circuit breakers use electromagnets to trip on overcurrent (as well as bimetallic strips using thermal methods for sustained high current).

Electromagnets dont work for DC, so your breaker will never trip. For thermal protection, you need current, so that checks out, and it would make sense for it to be rated under 50V as thats considered the highest voltage thats not life threatening on touch.

PV Batteries in general have a very high current (100s of A) at ~50Vish volts, so I dont think there's a major usecase for using household breakers for them.

Im still not getting your point BTW, switches and breakers are two separate things, with different workings, and household (and datacenter) DC would be I think around 400ish V, which is a bit higher than the peak voltage of AC, but still within the arc limits of household wiring (at least in 230V countries).

The advantage of DC is that you use your wiring more efficiently as the mean and peak wattage is the same at all times. Going with 48V would mean high resistive losses.

> Electromagnets dont work for DC, so your breaker will never trip.

If electromagnets don't work for DC then what am I supposed to do with this pile of DC solenoids and relays? ;)

> PV Batteries in general have a very high current (100s of A) at ~50Vish volts, so I dont think there's a major usecase for using household breakers for them.

That's what the SCCR rating is for. When there's a fault you're going to have a LOT of current flowing until your safety kicks in. Something like the grid or a battery bank will happily provide thousands of amps almost instantaneously. Breakers designed for protecting building wiring are rated for this. Now, most household breakers aren't dual DC/AC rated, but you can actually buy DC rated breakers that fit in a home panel (Square D QO series).

> Im still not getting your point BTW, switches and breakers are two separate things, with different workings, and household (and datacenter) DC would be I think around 400ish V, which is a bit higher than the peak voltage of AC, but still within the arc limits of household wiring (at least in 230V countries).

My point is that there isn't any material reason why DC can't be as safe as AC, all the proper safety equipment already exists. Extinguishing a DC arc during a fault is a solved problem for equipment at household scale.

> The advantage of DC is that you use your wiring more efficiently as the mean and peak wattage is the same at all times. Going with 48V would mean high resistive losses.

I just mentioned 48V because it's a common equipment voltage for household DC systems. 400V would be good for big motors and resistive heating loads.

Regarding DC vs AC and wiring efficiency, talking about mean vs peak wattage just confuses the issue. 1 volt DC is 1 volt RMS. It is an apples-to-apples comparison. If you want to say "we can use 170VDC or 120VAC with the same insulation withstand rating, and at lower current for the same power", then that is absolutely true. But your common 600V THHN building wire won't care if you're using 400V AC or DC, so it's mostly immaterial.

The 'what is safer' question for DC and AC at the same effective current and power has a mixed set of answers depending on conditions. For instance, DC is more likely to cause your muscles to contact and not let go (bad), but AC is more likely to send your heart into ventricular fibrillation (sp?, also bad).

AC arcs are easier to extinguish than DC arcs, but DC will creep much easier than AC and so on.

From a personal point of view: I've worked enough with both up to about 1KV at appreciable power levels and much higher than that at reduced power. Up to 50V or so I'd rather work with DC than AC but they're not much different. Up to 400V or so above that I'd much rather have AC and above 400V the answer is 'neither' because you're in some kind of gray zone where creep is still low so you won't know something is amiss until it is too late. And above 1KV in normal settings (say, picture tubes in old small b&w tvs and higher up when they're color and larger) and it will throw you right across the room but you'll likely live because the currents are low.

HF HV... now that's a different matter and I'm very respectful of anything in that domain, and still have a burn from a Tronser trimmer more than 45 years after it happened. Note to self: keep eye on SWR meter/Spectrum analyzer and finger position while trimming large end stages.

> DC will creep much easier than AC

Can you say more about "creep"? Is the resistance changing? Or is material actually migrating?

Also curious why it's worse using DC.

https://www.eevblog.com/forum/beginners/understanding-high-v...

Thanks Jacques. So creepage is when current flows/arcs across the surface of an insulator, vs through the air. And it's worse with DC due to its unidirectional nature. Worsens when pollution builds up, or the surface degrades.

Indeed. And it's a really nasty thing to properly protect against because that pollution, especially with stuff that is unattended for a long time has a habit of ending up much worse than your worst fantasies. I've taken more than one electrocuted mouse out of the HV section of older color TVs for instance. Up to 250V or so it is manageable, above that you can get the weirdest problems including completely invisible arcing where the only giveaway is the ozone smell and the occasional click. Looking at HV circuitry in the dark or by putting a flame near a suspect spot is a great way to spot these kind of issues.

Sure, maybe?

If your house gets 800V DC you're still gonna need "bricks" to convert that to 5VDC of 12VDC (or maybe 19VDC) that most of the things that currently have "bricks" need.

And if your house gets lower voltage DC, you're gonna have the problem of worth-stealing sized wiring to run your stove, water heater, or car charger.

I reckon it'd be nice to have USB C PD ports everywhere I have a 220VAC power point, but 5 years ago that'd have been a USB type A port - and even now those'd be getting close to useless. We use a Type I (AS/NZS 2112) power point plug here - and that hasn't needed to change in probably a century. I doubt there's ever been a low voltage DC plug/socket standard that's lasted in use for anything like that long - probably the old "car cigarette lighter" 12DC thing? I'm glad I don't have a house full of those.

There are niches where DC makes sense - low-voltage lighting, USB/LED ecosystems.

Once you get into higher power (laptops and up), switching and distribution get harder, so the advantages fade.

For bigger appliances (fridge, etc), AC is fine + practical.

Your modern fridge is probably going to have an inverter-driven motor, so you're right back to using DC.

All modern appliances and HVACs are using inverter drive motors for efficiency. Brushless DC motors are more efficient though.

"Brushless DC motors" are actually just AC synchronous motors.

Having a single big DC converter at a home would help a lot with power factor (LED lamps connected directly to AC have terrible power factor).

Modern bricks really aren’t that inefficient though. An Apple charger is like 90% efficient. A DC to DC converter is about that efficient or worse.

The power adapters became so efficient that we have to transition to wireless charging to keep it down

The irony...

I'm renovating a house, and have been considering 24V or 48V DC outlets in a few rooms. Semiconductors become more expensive above ~32V, so 24V might be the sweetspot.

However, there's also PoE (24 or 48V!), so maybe that's the right approach. It's not like each outlet is going to run a heater anyway.

Lower voltage makes voltage drop across the line proportionally worse. Depending on the purpose PoE is probably the way to go since the wiring and hardware is all standardized and safety certified.

Unless you mean running AC and installing inverters in the wall? What is this even for? All my electronics are DC but critically they all require different voltages. The only thing I might benefit from would be higher voltage service because there are times that 15 A at 120 V doesn't cut it.

No, I meant running separate DC wires. I'm Europe, so it's 240 VAC vs 24/48 VDC. For small devices, 24 V would be useful in that you don't require an isolated SMPS, so cheaper endpoints are possible. Slightly less risk of burning down the house with some cheap Chinese AC/DC. 24 V is still high enough to use USB PD/PPS at 20 V, and I doubt I'll run enough current that the losses due to lower voltage would be a problem.

For PoE, I thought it was standardized at 48 V, but I see lots of cameras run at 24 V, and I think I've even seen 12 V. Seems a bit of a mess.

It does make a whole lot is sense. The amount of energy you loose to convert AC to DC can be humongous . And useless if you produce your own power (normally already in DC).

I’ve always wondered about these new High-Voltage DC (HVDC) transmission lines.

I always thought AC’s primary benefit was its transmission efficiency??

Would love to learn if anyone knows more about this

https://en.wikipedia.org/wiki/High-voltage_direct_current

AC is less efficient than DC at a given voltage. The advantage of AC is that voltage switching is cheap, easy and efficient. Switching DC voltage is way harder, more expensive, and less efficient. However the switching costs are O(1) and the transmission losses are O(n) so for some distance (currently somewhere around 500 km) it's worth paying the switching cost to get super high voltage DC. The big thing that's changed in the last ~30 years is a ton of research into high voltage transistors, and fast enough computers to do computer controlled mhz switching of giant high power transistors. These new super fancy switching technologies brought the switching costs down from ludicrous to annoyingly high.

> AC is less efficient than DC at a given voltage

To expand on this, a given power line can only take a set maximum current and voltage before it becomes a problem. DC can stay at this maximum voltage constantly, while AC spends time going to zero voltage and back, so it's delivering less power on the same line.

this iirc is the smallest of 3 problems. the other 2 are skin effect (AC wires only store power on the outside of the wire) and capacitive effects (a write running parallel to the ground is a capacitor and AC current is equivalent to constantly charging and discharging the capacitor)

That’s true, but my understanding is the main contributor is skin effect, since AC travels only on the surface of the wire, while DC uses the whole area, resulting in lower resistance loss (https://en.wikipedia.org/wiki/Skin_effect)

Maybe if by "same voltage" we mean DC voltage the same as AC peak voltage. When we talk about AC voltage we are referring to root-mean-square (RMS) voltage. It's kind of like saying the average, though for math reasons the average of an unbiased sine wave is 0. Anyhooo, 1 VRMS into a load will produce the same power as 1VDC. If AC delivered less power than DC at the same voltage then life would be very confusing.

The primary benefit of AC is it's really easy to change the voltage of AC up or down.

The transmission efficiency of AC comes from the fact that you can pretty trivially make a 1 megavolt AC line. The higher the voltage, the lower the current has to be to provide the same amount of power. And lower current means less power in line loss due to how electricity be.

But that really is the only advantage of AC. DC at the same voltage as AC will ultimately be more efficient, especially if it's humid or the line is underwater. Due to how electricy be, a change in the current of a line will induce a current into conductive materials. A portion of AC power is being drained simply by the fact that the current on the line is constantly alternating. DC doesn't alternate, so it doesn't ever lose power from that alternation.

Another key benefit of DC is can work to bridge grids. The thing causing a problem with grids being interconnected is entirely due to the nature of AC power. AC has a frequency and a phase. If two grids don't share a frequency (happens in the EU) or a phase (happens everywhere, particularly the grids in the US) they cannot be connected. Otherwise the power generators end up fighting each other rather than providing power to a load.

In short, AC won because it it was cheap and easy to make high voltage AC. DC is comming back because it's only somewhat recently been affordable to make similar transformations on DC from High to low and low to high voltages. DC carries further benefits that AC does not.

Important factor is that AC at given nominal voltage V swings between 1.41V and -1.41V, so it requires let's say 40% better/thicker insulation than the equivalent V volts DC line. This is OK for overhead lines (just space the wires more) but is a pain for buried or undersea transmission lines; for that reason, they tend to use DC nowadays.

BTW, megavolt DC DC converters are a sign to behold: https://en.wikipedia.org/wiki/File:Pole_2_Thyristor_Valve.jp...

> I always thought AC’s primary benefit was its transmission efficiency??

There are many factors involved, and "efficiency" is only one. Cost is the real driver, as with everything.

AC is effective when you need to step down frequently. Think transformers on poles everywhere. Stepping down AC using transformers means you can use smaller, cheaper conductors to get from high voltage transmission, lower voltage distribution and, finally lower voltage consumers. Without this, you need massive conductors and/or high voltages and all the costs that go with them.

AC is less effective, for instance, when transmitting high power over long, uninterrupted distances or feeding high density DC loads. Here, the reactive[1] power penalty of AC begins to dominate. This is a far less common problem, and so "Tesla won" is the widely held mental shortcut. Physics doesn't care, however; the DC case remains and is applied when necessary to reduce cost.

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

Have a solar system at home and from the panels it is DC into the batteries but then the inverter needs to convert it to 220V/50Hz AC for home use.

The large brick you have on all your tech when you plug it in is the converter. AC works great for some applications, none of them really technical in nature.

Anyone notice that 400V and 800V are also used in EV battery architecture? I wonder if there's any sharing of technology?

I guess we've come full circle. It was just 20 years ago that my datacenters gutted DC in favor of AC.

This article seems to imply that 800V DC is high-voltage DC, but that seems quite low.

Quite low compared to a power utility's HVDC, but quite high compared to the 5/12/24 V output of most AC/DC converters used for electronics.

I think there'a a regulatory "Low Voltage" definition of "below 50V", which has implications around whether you need to be a licensed electrician to install it or not. Anything above that is - for at least some purposes - considered "High Voltage".

Other people, of course, have other definitions of high voltage:

"This resonant tower is known as a Tesla coil. This particular one is just over 17 feet tall and it can generate about a million volts at 60,000 cycles per second."

and:

"This pulse forming network can deliver a shaped pulse of over 50,000 amps with a total energy of about 1,057 times the tower primary energy"

https://www.youtube.com/watch?v=RoGbrgOhPes

They were Thunderstruck?

Transitioning? It already happened decades ago. Only smaller scale/generic or less proficient "we bought all Dell and HP" use AC. At large scale it's been a ton of DC for literally decades. And for 70 years in telco and network gear.

Soon they will replace all the iron railings with maiden.

AC is also waaaay safer for households: since the power drop to to zero 100x (50Hz) per second switches are cheaper and safer, and electrocution is less likely to happen.

"How can we turn this technical story into a story about people and their conflicts?"

I somehow made it to middle age without making the connection from AC/DC to electricity. Or I never thought about it till now.

It is absolutely stupid to talk about this as edisons revenge. If Tesla had the modern high power transistors needed to get high voltage dc out of the ac produced from a spinning turbine he would be all for high voltage dc too. Tesla understood that high voltage was needed for efficient long range transmission. He also understood that transformers were the inly remotely efficient way to climb up to and down from these high voltages. And transformers only work with ac. So he designed an ac system and even designed some better transformers for it.

If there was anything like a high power transistor back then he would have used that. High power transistors that are robust enough to handle the grid were designed inly recently over 100 years after the tesla/edison ac/dc argument.

Also, if anything would have been Edison's revenge it would have been HVDC, where they're sending power long distances with DC. (But as you said, even there it wouldn't make a ton of sense, since they were arguing in a different era).

The two primary reasons to do that are to allow the intertie of two AC grids that are not otherwise synchronized, and to take advantage of "earth return" paths when necessary to double the capacity of the line. The latter you may need to consider just to make the line cost effective over an equivalent AC span.

Tesla also design the modern induction motor which needs ac. Though these days we often run them on a phase generator which has a dc step.

Agreed, for the IEEE to go down this route is more than a little weird.

It's just a fun title, you are overthinking it

the internet really needs to stfu about tesla and get over that oatmeal comic that spawned a billion internet myths. dude was a decent inventor but suffered from chronic mental health issues and, in his lifetime, wasted so much time/energy/money and burned so many bridges with his horrible attitude. there's a reason most people didnt like him in his day, he was a depressed asshole who alienated everyone around him, and yes I know he was likely gay in a time when that wasn't cool. the fact still remains; his inventions are massively overblown by internet nerds.

the podcaster Sebastian Major from "Our Fake History" did a looonnngg patreon episode on tesla and debunked most of the weird myths around tesla. Sebastian doesn't have a vendetta or anything, it's just amazing how much of the Tesla stuff is just nonsense or is viewed through a very weird bias nowadays. Major also briefly touches on the weird Edison stuff and how the internet has twisted Edison into a villain.

Tesla was an outstanding technologist, but a poor businessman. He had a "vision" (actually more than one) about how his ideas could transform the world. Some of his ideas were amazing, but he was swindled out of his patents because the investors knew he had a passion and wanted to see them in use. The polyphase AC motor or fluorescent light bulb could have made him millions.

IMHO, the vision he had about universal free electricity (transmitted wirelessly) was the dumbest. It was a novel idea, and he invested a lot (his time and other people's money) in it. The problem with his idea is that there was no way to monetize it (and profit from it). (There were also the technical issues of the power loss over distance (1/R^2), the harm to the environment, and the interference with radio communications.)

Edison was quite a villain. He stole many of his "inventions", and orchestrated a PR campaign against Tesla touting the "evils" of AC power. AFAIK, the electric chair was either invented or inspired by him.

I know these things because I've read many books on various topics related to Tesla, and all of this knowledge predates the Internet.

Edison did not invent the electric chair. When the inventors were trying to choose between using AC or DC he helped them decide on AC as part of his PR campaign.

These (and many other) sources cite Edison funding a campaign to use AC to electrocute animals, to show that it was more dangerous than DC.

https://www.energy.gov/articles/war-currents-ac-vs-dc-power

https://www.discovermagazine.com/the-cruel-animal-testing-be...

Essentially none of this is true. The war of the currents was between Edison and Westinghouse, not Tesla. Tesla's downfall was that he turned into a crackpot who rejected modern science, such as Maxwell's equations, and started defrauding investors. Edison was an outspoken opponent of the death penalty, and the electric chair used AC simply because it is much more deadly.

> The war of the currents was between Edison and Westinghouse [...]

Thank you for quashing the gross misinformation. I was going to post this, but searched and found your comment. `\m/`

(I learned of the "Current War" in the 70's, since the Edison Museum was in my "backyard" -- and was a common destination of local school field trips.)

Westinghouse was using Tesla's patents. Get your facts right.

Every so often, I see or hear a new narrative of history that does not align with reality. I used to wonder how this could happen, but one of my sons explained to me that in his college history courses (in multiple accredited universities), the professors would teach their version of history, using their notes as the course material. They circularly cite other like-minded revisionist material, and most of their students just accept what the professor says as fact. He has seen this again and again in both lower and upper division courses.

This is a disturbing trend, and aside from "woke culture" indoctrination, I don't know what's behind it, or why these professors are not held to basic academic standards.

https://geekhistory.com/content/george-westinghouse-used-tes...

We’re talking about Nikola Tesla, not Elon Musk, and I don’t think Musk is gay.

I think you need to read the post you are responding to again.

People need heroes. It's like the Keanu Reeves or Musk era, all the ""badass"" stories about this or that soldier / local hero / w/e that are very often overblown and get further and further away from the initial facts every time they resurface. No hate here, just noticing there is a weird visceral need to distill stories to their most essential, good vs evil, and the Tesla v Edison thing embodies this perfectly I think.

Keanu Reeves and Nikola Tesla to a degree as well, are decent figures.

Aside from all the cult classics Keanu is part of like john wick and the matrix, even discounting that, he is a good person in it of itself who is genuinely humble and might be one of the best persons within hollywood.

What I feel pissed about is that people like Andrew Tate and others like them took the concept of Matrix and the contributions Keanu did within that movie and tried to capitalize on that cult classic decades after in the most toxic form that might be the issue if we are talking about an era

To be honest, Nikola tesla is also a great person within the context of his time. GGP's comment is still true but Tesla's contributions can hardly be reinstated and I'd much rather people believe these to be the heros (Keanu/Tesla) rather than Tate/Musk etc.

If I take anything from Keanu, I would like to take his humility/humbleness.

Tate is just attention hungry. It’s pretty obvious. If you feed no attention to him, he will go back to where he crawled from.

Whilst I agree that Keanu is a most excellent human, he was hardly responsible for the concept of the Matrix. In my opinion, Philip K Dick was a major influence (I'm a fan and consider him the prophet of the modern age), though Gibson's Neuromancer was likely a big influence too. (Also, there's the old Doctor Who episode "The Deadly Assassin" which features the Matrix).

It always seems to me that the far right are bereft of original ideas and always co-opt other pre-existing concepts. There's exceptions, but I always find that right wing works are always lacking humour or irony (c.f. Ayn Rand's works).

> the far right are bereft of original ideas and always co-opt other pre-existing concepts.

That's not unique to them: Good artists copy; great artists steal.

Yes, but I'd have difficulty in pronouncing Andrew Tate as a good or great artist. Maybe con-artist would be the highest that I'd go.

"It is only the unimaginative who ever invents. The true artist is known by the use he makes of what he annexes. And he annexes everything."

- Oscar Wilde

Except for Keith Moon. All the stories about him are true and if anything underplay the truth. :-)

I mean yeah, but it's not like the guy's 'horrible attitude' came from nowhere. He naiively romanticised migrating to the US thinking the game was about scientific progress rather than capital, and so he got repeatedly screwed over by almost everyone around him for decades.

If I was in his position I'm not sure I'd have taken it as well as he did.

There’s no way he suddenly developed autism or whatever mental illness plagued him upon arrival to American. Like most absolute geniuses he struggled in other areas. He said he had visions as a child.

But there is: his neurotype suddenly became considered "whatever mental illness" upon arrival in Eugenicsland.

> he was a depressed asshole who alienated everyone around him,

enough Edison bashing!

Look, Tesla was a weirdo, but, he was a very good inventor who actually invented shit.

Edison was an industrialist, who knew the price of everything, and wasn't above spending a lot of money to destroy a rival.

Do I idolise Tesla? no, but I respect his understanding of high frequency electronics with really primitive tooling.

Do I despise Edison? also no, but he is a massive prick. Excellent buisness man, but an abrasive prick never the less.

Software engineers idolize Tesla because they see themselves as the Tesla (a selfless devotee of the abstract idea of technology) against evil Edisons (businessmen who only care about money and steal other people's ideas). They've basically projected the Jobs/Woz divide back onto two historical figures who, in reality, barely interacted.

The funniest part is that The Oatmeal comic didn't invent this concept, but drew on pre-Internet narratives put forward by The Tesla Society, who were mailing busts of Tesla to universities around the country since the 70s at least. And that organization is explicitly nationalistic and religious, tied to other Serbian-American heritage organizations, and doing events with the Orthodox church.

> And that organization is explicitly nationalistic and religious

So are many Serbs (more so if emigrants from atheist-socialist Yugoslavia, or descendants of folks who moved before WW2) as well as many other nations and organizations (America itself lol). So are many Something-Or-Other-American individuals and communities.

I presume that the organization(s) sending Tesla busts, being American-rooted, have had no illusions about which matters will forever remain impossible to communicate to Americans. (Such as anything not reducible to paperclip optimization.)

Instead, I consider it more likely that the point of promoting Tesla was not to impress anyone in America, but to uplift Serbia and generally the South Slavs of the Balkans who'd only gained national sovereignty in Tesla's day: "look, our heritage has already produced an honest-to-god American inventor half a jebani vek ago, so you guys have zero excuse to act as if you're stuck in the middle ages - do join the cargo cult of mordorn civilization instead, will ya - we got value to extract from ya!"

>They've basically projected the Jobs/Woz divide back onto two historical figures who, in reality, barely interacted.

I'd rather say this has been projected for them, but by whom is anyone's guess; not like there's a shadowy cabal operating. Besides said Serbian-American heritage promoters and whatever their game is, I guess - but here we're not talking mid-XX century Serbian diaspora any more, but a "culturally nonspecific" audience.

Much safer to call it "a hivemind situation" when nobody knows where some idea comes from, and nobody is accountable for rebroadcasting it either, since it comes pre-tagged as Good and True and Useful and it is wrongthink to doubt those. Especially when the idea is so obviously Useful for excusing nonaction. ("I can't be bothered to learn the first thing about electricity, even the history of why I have access to it in the first place - but now that Tesla guy I've vaguely heard of, he was the great genius of the people! What better reason to Experience a Positive Emotion!")

Did he also not fall in love with a pigeon ?.

>It is absolutely stupid to talk about this as edisons revenge. If Tesla had the modern high power transistors needed to get high voltage dc out of the ac produced from a spinning turbine he would be all for high voltage dc too.

This!

The soon people realized these facts the better. The pervasive high rise buildings did not happen before the invention of modern cranes.

Exactly twenty years ago I was doing a novel research on GaN characterization, and my supervisors made a lot money with consulations around the world, and succesfully founded govt funded start-up company around the technology. Together with SiC, these are the two game changing power devices with wideband semiconductor technology that only maturing recently.

Heck, even the Nobel price winning blue LED discovery was only made feasible by GaN. Watch the excellent video made by Veritasium for this back story [1].

[1] Why It Was Almost Impossible to Make the Blue LED:

https://youtu.be/AF8d72mA41M

I've heard the EV charging has played a big role in the maturation of GaN / SiC.

Yes, EV and high frequency electronics (microwave, mmWave, photonics) that require very fast switching capability.

And military radars love GaN

https://shrunk.ai/research-journals/f/cranes-skyhooks-and-it...

Does that mean when we run out of Ga there are no more LED TVs?

Why would we run out of Ga?

There's a component of modern culture that trains and expects people to be extremely pessimistic about long term human development. It results in situations above, where without any further information people just assume by default that were going to run out of a thing and are on some collision course with not just a disaster, but every single conceivable one.

(Gallium is a byproduct of aluminum production. We aren't going to run out.)

My understanding of most elements is if we want more it’s either pretty easy to make from something else we have a lot of, or we need to redo the Big Bang, the latter being, in my opinion, a bit of a disaster scenario.

Even synthesizing helium is prohibitively expensive. Unless you want whatever heavy decay products we have from nuclear waste, synthesizing elements at industrial scale probably isn’t happening.

Unless by “make from something” else you mean extract the element from existing chemical compounds found in Earth, in which case we’re still just using existing deposits on Earth.

On the other hand, it is possible to run out of a metal when all of it is either somewhere in some device or scattered among landfills (i.e. not concentrated in a place like a mine).

That’s still not running out. It’s still there, just more effort to get.

"At 10 parts per quadrillion, the Earth's oceans would hold 15,000 tonnes of gold", says the Wikipedia page on gold.

I'm inclined to think we've lost that gold.

Practically speaking, sure. It's obviously not cost-effective to extract it. But it's there if someone can get it. I don't expect anyone to be extracting gold from ocean water, but there are other source of other elements that may not be cost-effective now but could be in the future or may simply become necessary despite the cost.

Effort high enough to consider that material lost to any practical purpose like a tv.

Cost scales with refinement effort, so it just results in more expensive TVs. That said, pretty sure we'll have drowned the planet in landfilled TVs long before this becomes a serious issue

If prices of certain metals were high enough I bet people would stop throwing out TVs and dig up old ones from the dump.

It's a byproduct of aluminum production.

The earth's crust is 8% aluminum.

We will have bigger problems before hitting this one.

That is true, but gallium is present in the aluminum and zinc ores only in minute quantities.

We will not remain without gallium, but it is impossible to scale up the gallium production to a higher level than provided by the current productions of aluminum and zinc.

So there is a maximum level of gallium that can be used per year and it would not be possible to increase the production of blue and white LEDs and of power transistors above that level.

Fortunately, the amount of gallium used per device is very small, so it is not likely that we will hit that level soon. A much more serious problem is the associated consumption of indium, for which the resources are much less.

Thanks for providing a real answer.

Its concentrated in a place like a landfill that already has access for large vehicles.

> On the other hand, it is possible to run out of a metal when all of it is either somewhere in some device or scattered among landfills

The metal isn't going to disappear, but it won't be concentrated enough to be as easily retrievable.

Sidenote: Whenever someone tells you that (vital) reserves of some ressource are going to run out soonish (implying drastic consequences), you should be extremely skeptical:

Such predictions have an abysmal historic track record, because we tend to find workarounds both on the supply side (=> previously undiscovered reserves) as well as flexibility on the demand side (using substitutes).

This applies historically for oil, lithium, rare earth metals and basically everything else.

edit: I'm not saying we're never gonna run out of anything-- I'm just saying to not expect sudden, cataclysmic shortages in general, but instead steadily rising prices and a somewhat smoothish transition to alternatives.

> Such predictions have an abysmal historic track record, because we tend to find workarounds both on the supply side (=> previously undiscovered reserves) as well as flexibility on the demand side (using substitutes).

That's a classic example of the "preparedness paradox" [1]. When no one raises the alarm in time or it is being ignored, resources can go (effectively) exhausted before alternatives can be found, or countries either need to pay extraordinary amounts of money or go to war outright - this has happened in the past with guano [2], which was used for fertilizer and gunpowder production for well over a century until the Haber-Bosch ammonia process was developed at the start of the 20th century.

And we're actually seeing a repeat of that as well happening right now. Economists and scientists have sounded the alarm for decades that oil and gas are finite resources and that geopolitical tensions may impact everyone... no one gave too much of a fuck because one could always "drill baby drill", and now look where we are - Iran has blasted about 20% of Qatar's LNG capacity alone to pieces and blocked off the Strait of Hormuz, sending oil prices skyrocketing.

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

[2] https://en.wikipedia.org/wiki/Guano

I don't see the Guano industry as a straight counter-example, it even illustrates my point:

If you had made predictions/scenarios in 1850 based on Guano deposits running out within a decade or two, you would have mispredicted completely, because a lot of the industry just transitioned to sodium nitrate (before synthetic fertilisers took over). Nowadays media landscape would've gladly made such doom-and-gloom predictions for global agriculture back then.

I completely agree that quickly depleting reserves often indicate non-sustainable pricing for ressources (which is obviously bad long term), but that is very different from sudden collapse.

I've seen articles from the 1880s claiming oil will run out by 1890. 140 years latter...

Yes we can run out of oil, but nobody really knows if or even when that will happen. Right now I'm guessing we won't run out because wind and solar is so much cheaper for most purposes everyone is shifting anyway - this will take decades to play out.

> Yes we can run out of oil, but nobody really knows if or even when that will happen.

We can run out of cheap and accessible oil very, very fast if the shitshow in MENA continues to escalate. Qatar already lost 20% of their LNG capacity in a single strike.

The US may have enough domestic oil production to sate its domestic demand, but the prices would still skyrocket even for them. Europe meanwhile, we're straight fucked here. Technically the oil hasn't run out, it's still in the oil fields of the journalist-butcher country and other sheikdoms, but that doesn't matter if it cannot be pumped out any more because the wells got blasted to pieces or if it cannot be transported thanks to Iranian mines, Europe is still running out of oil in practice.

What does "Europe running out of oil" mean to you? Gas at the pump for >10€/l, potentially with some rationing scheme? Do you honestly think that's gonna happen?

It is easy to get infected by the media narratives that are notoriously biased towards maximum drama, but I firmly believe that we are not gonna escalate into such a scenario.

There's always options; sorting priorities because of price, radical electrification of transport, or, at the extreme end, picking up coal hydration again (worked well enough to keep the Nazi war machine running for quite a while, with much worse access to crude).

For comparison: Copper prices did increase by 500% since 2000, but people barely even care, and that's how I would expect "shortages" to typically go.

I always add "cheap" to the sentence. It seems they are always talking about the cheap version of anything. Going to run out of water? Or are we running out of the "cheap" version of water that does not have to be processed?

This is a valid point: quickly depleting reserves often indicate that pricing is not sustainable. Which is bad.

But non-sustainable pricing is very different from "cataclysmic collapse", and too many people expect the latter for too many things, which is just not realistic in my view (and historical precendent makes a strong case against that assumption, too).

A society where water prices gradually increases to "reverse-osmosis only" (instead of "pump-from-the-ground-everywhere") levels is very different from a society where water suddenly runs out.

"Reserves" are the name of something that exists only at a set price. Change the price, and the reserves change too.

The people that rush to tell you that reserves are running out tend to omit what price they are talking about. That way of expressing oneself is normally called "a lie".

Except for gaseous hydrogen and helium, and some spacecraft, all other atoms remain on the earth and are recoverable with enough energy and effort.

One more exception: uranium. It actually splits into smaller atoms when it's used as fuel.

Gallium is expensive to extract because it is extremely diluted in the environment.

It accompanies in very low quantities aluminum and zinc, so it is extracted only in the mines of aluminum or of zinc, as a byproduct.

However, the abundance of gallium is similar to that of lithium, while gallium is used in smaller amounts, so there is no risk to not have enough gallium in the near future.

On the other hand, all semiconductor devices with gallium also use some indium. Indium is used in even greater quantities in all LCD or OLED displays, to make transparent electrodes.

Indium is an extremely rare element in the entire universe, comparable with gold, so for indium there is a much greater risk that its reserves will become insufficient.

This could be mitigated by extracting such critical elements from the dumped electronic devices, but this is very expensive, because only small amounts of indium are used per device, so very large amounts of garbage would have to be processed in order to extract a sizable amount of it.

What are some novel processes or technologies you see becoming more important in the next 5-10 years?

> The pervasive high rise buildings did not happen before the invention of modern cranes.

yyy! if we're going to wander off-topic :-) then I should mention elevators, water pumps, fire suppression including fire truck ladders and more! :-)

sure, and also Montezuma didn't actually plan on diarrhea ruining people's vacations, but vernacular usage being what it is we have the phrase Montezuma's revenge.

I only found Edison in the headline, I didn't find it anywhere in the body, nor did I find Tesla. Glancing through the article it almost seems like someone tried to make a catchy headline to get clicks.

It was Westinghouse who pushed the AC grid against his rival Edison's DC approach. Tesla was a minor figure working for both of them for a bit.

> If there was anything like a high power transistor back then he would have used that.

Mercury arc rectifiers were used long before his death.

Yes, but a rectifier only rectifies. That's not going to give you DC-DC conversion - let alone converting it to a higher voltage for long-distance transmission.

DC-DC before the transistor was difficult to do at scale. Vibrators and relays existed but were not reliable long term.

But there was an equivalent: a mechanical switch. Or an electromechanical relay. Or a spinning wheel with electrical contacts.

Title is clickbait. Edison is not mentioned anywhere else in article. I am okay with it.

Yeah this isnt an argument. It was far simpler to wrap some copper wire around a chunk of metal than it was to fire up a mosfet fabrication plant in the 1800's.

You can have the best idea in the world, but if you cant manufacture it you're SOL.

Agree, clickbait.

yes, this! thank you good post

Note that one could email the mods to de-clickbait/enrage the title, especially with such a concrete point as this comment’s. (I haven’t done so as TIL is a poor basis for such an argument.)

Ok, we've deposed Edison from the title above.

That is about like aying the band AC DC had its revenge.....

can we stop vibe generating headlines?

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