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What motor for a high efficiency car alternator?


100 mW
May 2, 2022
Hi guys

I have been reading up on how cheap alternators waste a lot of fuel:

So was wondering:
What motor and 'controller' would you use as an alternator if you wanted a really high efficiency alternator with thin laminations, high copper fill etc.

I note that the higher the voltage the alternator produces; the more efficient it is.
So a 48V+ system and DC/DC converter..?

If you're going high efficiency, crankshaft coupled, 48V+ you may as well do:
Motor during acceleration and generator during braking? (unless the battery's below a certain voltage/charge level)
What ctlr would be best for that or could be modded?

This is all stuff I plan to swat up on when time allows, but thought I'd put it here in the mean time.
What makes alternators great is that they can keep their output voltage constant with changing speed. To do so, they effectively change KV.

An alternative approach would be to use a PMSM motor/generator and then a buck/boost converter in series to keep the voltage where it needs to be. It might be more efficient if done right, but probably also more expensive.
There are some 48v hybrids. Valeo has a few versions of their 48v starter generators and axle assist. Some is versions as well.

The 48v hybrids are typically belt assist but all seem to have their own names.
Hyundai has the hsg but it runs at a couple hundred volts.

It would be great to have the option to add a hybrid system. It could probably listen to the can bus or just the throttle pedal and rpm and decide what to do.
You could probably add some code to VESC and have pretty much any VESC controller work.

I was looking for a controller to be able to run something like a mild hybrid. The most I found was a guy doing one as a starter in some project car. It didn't seem open source. There were a few others trying to hack oem systems, I'm not aware of any that are functional yet but haven't looked in a while.

Driveshaft / axle coupled could work too - if it had a decent reduction.