Hacker News Reader

Comment by sunstone | Hacker News Reader

Electric motors are remarkably good already. Even if it doubled the power for half the weight you still need lug along all those batteries.

View on HN

Right, look at the size of the motor versus the size of the batteries in an electric car. Efficiency is already well over 90%, too.

If you managed to create an idealized electric motor that was 100% efficient, had no limits on power, torque, or RPM, weighed nothing, took up no space, and cost nothing, it would be a nice improvement but I don't think even this would revolutionize electric cars. Batteries are the key.

According to people on the TMC forums (so take with a grain of salt) Tesla's motors only cost $350-400. If that's true, they're basically perfect already. It's the batteries which drive cost and weight.

They are mostly iron so it seems plausible.

Is that the Model 3 motors? I've heard that the Model S motors had a surprisingly high failure rate, many owners of the earlier models having had 5+ drive unit replacements. I'm guessing the Model 3 drive units are more reliable?

The early Model S motors had problems like that. They got a lot better over the years. The Model 3's is great, and the Model S/X front motors are now the same as the Model 3's, while the rear motors are something else that's still a lot better.

Any clues what exactly within the motors fails?

There’s usually a funny noise long before any catastrophic failure, so I think it’s the bearings or the gears, but concrete information is hard to find.

I actually had my motor replaced due to this noise. It was a high pitched whining, kind of like a jet engine spooling up. Not real loud, most noticeable in a parking garage with the roof open, and I wasn’t even sure if it was abnormal, but I took it in and they replaced it. It’s easy to swap out, so they just put in a new one and then fix the old one at their convenience and give it to the next victim.

Incidentally, I had another weird noise sometime later which was a distinct clunking sound when accelerating from a stop. That turned out to be a bolt that wasn’t tightened properly. Oops!

Thanks for clearing it up!

Amdahl’s law of EVs.

Wouldn't that be with multi-motor EVs? ;-)

If you had a motor like that you wouldn't need batteries. You'd power the car with the motor :)

While motor efficiency is 90%, drivetrain is less than that because of gearbox. This motor claims to remove this inefficiency.

Tesla claims that their drive unit (which includes the motor, inverter, and gearbox) efficiency on their latest models is 93%.

Average or peak?

Making something that performs well at freeway speeds, yet also is efficient when manuvering round a parking lot is hard.

Most companies just hope you don't care about only getting 5% efficiency round the parking lot, because that isn't a large fraction of your energy budget, even when it's so inefficient.

No idea! Would it be expected for an electric motor to lose so much efficiency in that scenario, though? I though the variation was small.

Motor efficiency aside, a total “energy spent for distance moved” accounting will look bad at such low speeds, just because the car has to power non-motor systems and they use energy at the same rate no matter how fast you’re moving. Peak efficiency in a Tesla is at around 25MPH.

It must be peak. You could see how an electric motor efficiency map looks like here:

https://x-engineer.org/automotive-engineering/vehicle/electr...

A reduction gear is really not all that much of a loss, wind on the other hand-- that's a big one.

Airflow losses in big AC generators are solved by having the whole motor sealed in helium. The helium gas is used as a coolant too.

It would be hard to design such a system with a big enough supply of gas to survive leakage for the whole life of the motor though.

Airflow losses for a car will be dominated by the outside air. Surrounding the car with helium seems impractical, and hard on the occupants.

I thought these mostly used hydrogen instead of helium?

(and as an aside, hydrogen detecting sensors is an area of astounding complexity and cool effects which are worthy of an HN post all on their own)

I doubt hydrogen would ever be used because it makes metals brittle.

I'm pretty sure large generators used hydrogen at one point. I seem to remember reading about them using a palladium membrane to purify the hydrogen used to cool generators.

I am not sure why we are focused on the electric car angle. Assuming this motor design is legitimate and practical, I feel the implications for commercial/industrial prime movers and power generation are far more substantial. Hypothetically, if we were to replace all existing HVAC compressor and blower motors with this technology, where would that leave us in terms of power consumption reduction? How much wider do the applications become due to the variable speed capability of the motor design?

HVAC systems are far from theoretical peak efficiency. For example, notice how they all have a 'capilary tube' to restrict the flow of liquid coolant between the hot and cold sides of the system? That's like using your brake to go slowly round town rather than letting off he gas...

A small turbine rather than that capillary tube would instantly increase system efficiency...

It would be crazy loud.

Reply on news.ycombinator.com