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Comment by Corrado | Hacker News Reader

I didn't even think about non-silicon based chips being viable, let alone more efficient. The article mentions that SiC (Silicon Carbide) chips can be 50% more efficient. Diamond based chips can reduce energy loss by one-50,000th of that of Silicon chips.

If we can get these chips manufactured at a reasonable cost it would really help EVs get longer range. And it might even give us multi-day use out of our smart devices (phones, watches, etc.)

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> If we can get these chips manufactured at a reasonable cost it would really help EVs get longer range.

How much longer though?

The motors that move the wheels consume way more energy than the microchips on board the car. Even when a car is standing still, the AC or the heating system are also quite energy-hungry compared to a few CPUs.

Yeah but in most EVs you need to transform the battery DC current to AC for the motor.

I was under the impression the Model 3 uses permanent magnet DC motors, with the increased efficiency accounting for some of the range gains.

No electric motors are really DC driven. They do differ how the AC is derived, though, mechanically or electrically.

To say a word about the physics: The fundamental force at play is the electromagnetic force. If you run a current in a coil in the magnetic field, it will rotate so that the coil’s field comes into alignment with the outer field.

Once it’s there it is happy to stay. You’ve got to change something to get the motor running continuously. AC is quite clever about it because it just changes the field electrically and this is much more reliable than changing it with moving parts.

I've got an idea for a DC electric motor that has no apparent AC. Can anyone spot any hidden AC here?

Take a disk on a shaft. Use a ratcheting mechanism on the shaft so that it can only rotate in one direction. Attach permanent magnets around the rim of the disk.

Attach more permanent magnets to bimetallic strips positioned outside the rim of the disk. Near each bimetallic strip place a resistor.

The angular spacing of the bimetallic strips and magnets around the outside of the rim should not be that same as that of the magnets on the rim.

Turn the disk by moving one or more of the outer magnets closer to the rim to create asymmetrical torque on the disk. You move the outer magnets by using the resistors to heat the their bimetallic strips. You move an out magnet back to its original position by letting it cool back down.

Why would you use bimetallic strips instead of, say, a solenoid? The whole point of the discussion is to avoid thermal losses...

The comment I was replying to said DC motors actually use AC internally. My comment was an attempt to design a DC motor that definitely uses no AC.

Solenoids have an inductor with a changing magnetic field that stores energy and eventually gives it back. I want to avoid the possibility that that changing magnetic field will induce a current somewhere that is in the opposite direction of the normal current in that place thereby producing AC.

By just using the DC input to make heat, there is no chance of inadvertently getting AC.

> You move the outer magnets by using the resistors to heat the their bimetallic strips. You move an out magnet back to its original position by letting it cool back down.

You are switching the resistors on and off with a pulse pattern that will look a whole lot like you're driving a stepper motor. That's what we call AC.

DC means that the voltage stays constant over time. AC means it changes. Switching DC on and off creates AC.

DC is any current that flows consistently in one direction. AC is current whose flow direction switches back and forth.

That sounds like a https://en.wikipedia.org/wiki/Stepper_motor with extra steps.

You could argue that a stepper motor is also just pulsed DC, though it starts looking more like AC as you increase the drive efficiency.

When the resistors are heating, there must be more power going through them then when they’re cooling, right?,

The voltage driving the resistors? Just terribly slow, matching the terribly slow speed of the motor.

That would be variable DC, not AC.

Your resistors would still need a varying voltage applied to them in order to spin the rotor. If you view your "pulsed DC" as not being AC then a simple brushless DC motor would meet the same definition. I believe if you want a truly DC motor without a commutator generating AC like a brushed DC motor you would need a homopolar motor.

https://youtu.be/TzsUhiOej-s

Model 3 uses two types of motors in the dual motor model and performance model. AC in the front and DC in the rear.

I think you're confusing induction versus synchronous reluctance permanent magnet motors with AC versus DC.

The motors Tesla uses are all AC, but you could also call them DC if you're referring to the whole motor/inverter assembly, which inputs DC from the battery.

DC motors aren't used much in EVs because the brushes require periodic maintenance and doing regenerative braking or running in reverse are both rather difficult whereas with a motor that runs off of 3-phase power, those features can be implemented in the software of the motor controller. They tend to be rather low efficiency, too. That said, there are some really powerful and cheap series wound DC motors that have been used to great effect in vehicles like the White Zombie.

Articles refer to the rear motors as DC similar to the DC motor used in the leaf. Here's an example:

https://www.motortrend.com/news/electric-cars-explained-gear...

I'm pretty sure the author of that article is just confused. The synchronous reluctance motors in the Model 3 run on AC just like an induction motor, but can be thought of as a DC motor if you consider the whole inverter/motor assembly, just like an induction motor.

I think Tesla has been migrating from induction motors to permanent magnet motors (which usually have higher efficiency and produce less heat), but they all run off of 3-phase AC from the inverter.

Sometimes the inverter/motor combination is referred to as a brushless DC motor because it takes DC as input before converting it to AC for the motor to use.

The power electronics in an electric drive train also have transistors. That's where you can make real efficiency gains in an electric car. Not in some microcontrollers.

That's certainly true, however the cooling required for the microchips also typically takes a lot of energy, as well as the microchips themselves. Reducing the energy usage, reduces the heat output, and thus also the cooling requirements.

> And it might even give us multi-day use out of our smart devices (phones, watches, etc.)

Not going to happen, they'll just find a way to use more power instead. You probably noticed that for years now, phones and the like have had a fixed battery lifetime of about a day of medium use, even though battery and chip technologies have improved. I'll admit that in terms of efficiency - performance per watt - things have increased, but the goal of the phone manufacturers is not to make things last longer, it's to min/max and find a balance between battery life and power.

With current day technology you can easily make a phone that lasts for a month on a single charge, but it'd be bulky compared to what you can do with it.

Once we all own nothing and are happy though, perhaps it will be in the phone company's interest to make their phones last longer so they can get more rental income off one asset.

Yes, you're probably right. For proof we just need to look at RAM & CPU requirements for most software. As both of those components increased, the software grew to consume them. sigh one can wish, can't one?

SiC is not a good fit for anything under ~100-200V, it's just not what it is designed for.

GaN makes more sense for consumer electronics, that's why it's popping up in a lot of devices, even if prices right now are too "high end" for most users.

As for phones, watches, etc..:

1- These technologies won't be as dense as standard silicon for quite some time (if ever.

2- We've had big swings in both efficiency and battery capacity several times already, but it works in the same way internet speed works. Power-hungry features grow with increased efficiency in the same way websites grow in size with increased internet bandwidth.

Silicon Carbide is extensively used in Power Electronics. It's just that there is a very small group of people that are having to deal with kilovolts on a daily basis, so I suppose it is not perhaps widely known.

For some strange reason, my high school had a subscription to the EPRI journal [1]. For this budding nerd, reading about SCRs the size of hockey pucks, with optical fiber triggering, was quite entertaining.

[1]: https://eprijournal.com/

As far as I understand it, these SiC chips are things like discrete MOSFETs designed to work at hundreds of volts and handle huge power running through them. I think the likelihood of this scaling down to millivolts is quite unlikely. The more likely applications for this are power stations and hooked up to solar power plants rather than in your iPhone I would expect.

You're correct that SiC is for medium to high voltage. But there's also GaN, which is for low to medium voltage, and already works in the millivolt range. Both GaN and SiC will have wider ranges in the future as the technology continues to improve.

All EVs are already highly efficient, any further increases is going to be extremely marginal.

There is still plenty to be gained from squeezing that last 1% out. Tesla is probably cell limited right now, so if your car is 1pct more efficient you can pull less cells in it and mthen make 1pct more vehicles.

EVs tend to be efficient at high power. They can be 94-98 percent efficient at 100kW but normal driving is something like 4kW at 45mph.

If you reduce loads by 40 to 50 watts, you can gain a mile of range. With inverter losses in the 1-2 kilowatt range at high power there is room for improvement.

For pure range, sure. But think about things like heat sinks or other cooling devices. Or the weight of these components themselves. Swap over to this new SiC, you get more direct efficiency, AND you don't need to carry as much supporting hardware!

Presumably you mean to rather than by?

> And it might even give us multi-day use out of our smart devices

I don't think you understand how software development works. Q: How much hardware do you need? A: How much you got?

The latest generation only gets the battery longevity because software developers still have to support the previous generation. As soon as enough e-waste happens, the gains disappear.

I might be a cynic but there sure seems to be a lot of empirical data to support my disorder.

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