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Comment by Koiwai | Hacker News Reader

I'd like to point out this is not about increased range, for example, if the ECU already works at 95% efficiency, that's not a very high number for brushless ECU, just for example, so 5% of energy is wasted, if we can reduce that in half, the efficiency will only increase to 97.5%, that's a very small improvement on range. BUT, now the ECU only needs to dissipate half wasted heat, this could be a big net win.

A more close to everyday life example would be chargers for notebooks, we now have smaller chargers thanks to GaN FETs, SiC is like GaN.

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This isn't quite right...

In a car which can accelerate up to speed and brake again every 30 seconds while going through a city with a lot of stop lines, the efficiency of the power components really matters.

If you loose 5% in the motors, 5% in the power electronics and 5% in the battery in each direction, then each accelerate-brake cycle is losing you ~30% of the energy you started with. At town speeds, friction and air resistance losses are tiny, so that 30% is probably actually most of the energy you are using!

Add that to the fact that certain motor control techniques such as field weakening involve every Amp of real power that comes from the battery passing many times though the inverter, since there is a higher circulating current between inverter and motor coils.

> If you loose 5% in the motors, 5% in the power electronics and 5% in the battery

You realize SiC is not the savior for all your problems right?

I'm not saying efficiency doesn't matter, I'm saying this is not gonna improve range significantly, there is a difference.

The GP's point is that this is not about maximum range, it's about increasing range in city transit that is normally much smaller.

Both gains seem relevant to me.

EVs typically have more range in city transit than on the highway.

Totally! X^n with 0<X<1 quickly goes to zero as n increases. You get about 6 of those cycles if X=.9 before you lose 50% of what you started with initially.

You're going to lose a lot more than 5% in the motor. You will also lose more to rolling resistance, various hystereses, etc...

Even assuming 100% inverter efficiency you will lose at least 20% in the regen part of the cycle alone.

Motors can get well above 95% efficiency, even at a wide range of speeds and torques.

Eg. See https://cdn.motor1.com/images/mgl/y83JG/s3/tesla-motor-effic...

They can when they are being used to produce kinetic energy. Using a motor as a generator however has much lower efficiency.

Absolute nonsense. Motors are do not care whether they are generating or consuming electrical power. It is a fundamental fact of induction that rotation in the motor creates a reverse voltage- motors literally would not work if they did not have very similar efficiency as generators.

The only differences between a motor and a generator in practice are cost optimizations and fixed-frequency optimizations. Industrial generators run at fixed speeds, unlike EV motors, so they can be built more cheaply. EV motors are not any less efficient when used to recapture power.

That is true in theory. In practice, when using the motor as a generator, the operating conditions are different, and so are the efficiencies. The load side is also different, the motor controller will not act the same way as the inertia of the car.

For example, even the simple inductance and resistance of the motor means that at the same speed and at the same load angle you will see a lower voltage at the poles of the motor when acting as a generator. When your motor has high efficiency, these differences can lead to a large absolute difference when running as a generator.

You could say the same thing about how speakers/microphones are equivalent. But it should be clear that some of those devices are tuned for outputting sound vs inputting sound, or vice versa.

You mean ESC, not ECU.

Generally cooling ESCs is not that big of an issue, just stick them in the same cooling system as the batteries.

arguably the same thing. If you want to get pedantic, "ESC" refers to a specific subset of drive topologies that are all fairly lossy on the D axis, meaning the efficiency drops at low speeds or under heavy acceleration.

"Drive controller" or "motor controller" are common terms, and while I have seen acronyms like DCU, nothing really sticks. MCU is already taken as an acronym, which doesn't help.

ESC doesn't have any connection to efficiency as a function of load. All circuits will be less efficient as you output more amps, ie, at low speeds where the voltage is low but the power stays the same, or under heavy acceleration.

Nowadays ESC simply refers to any circuit you attach to motor and provide with a target speed/torque/power. In common practice yeah ESC/drive controller/motor controller are used interchangeably.

ECU is specifically something else. It's "Engine Control Unit". It refers to the controller for a combustion engine, not a motor.

To make things more confusing, ECU can also stands for Electronic Control Unit

I'm pretty sure Tesla refer to them as ECU.

Trust me, I'm more customed to use the term ESC since I play RC models and I don't drive a electric car, or any car.

This is the key observation - hitting breakpoints in efficiency that let us remove active cooling, silicon area or heatsinks reduce weight, cost & complexity.

Yep. High efficiency is also the key to the crazy high performance we see in high end EVs these days. Going from 96% to 98% drivetrain efficiency only gives you 2% more battery life but it doubles your power output.

You are absolutely right there. I first read that in an article an EE wrote. He said what you care about with power inverters isn't the efficiency but the inefficiency. Small gains in efficiency you wouldn't care about translate in to large reductions in heat and smaller cheaper power devices. Power devices don't follow Moore's Law and aren't cheap.

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