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aitchnyutoday at 9:55 AM3 repliesview on HN

Tangential, how much regen can this system support?

For example, can a car with 200kW propulsion have a 400kW regen (Tesla has upto 65) and are cost effective like friction brakes?


Replies

superxpro12today at 1:31 PM

All motors are generators. It's only a matter of how you are creating the magnetic field with the stator windings.

In order to generate a higher regen, you'd have to somehow get more energy in the motor first... and since its only rated for 200kW, good ol' physics limits you, IF thats all the energy you put into the system.

If you roll it down a hill, or do something exotic like inverting the magnetic fields .... you can exceed the motor rating. But thats usually not recommended because the motor driver itself isnt rated to handle that power.

masklinntoday at 11:02 AM

> can a car with 200kW propulsion have a 400kW regen

At the motor level it should be the same, in propulsion you’re converting current to torque and in regen you’re converting torque to current, with the same hardware. The high voltage wiring is the same and will set the same limit on current regardless of direction.

I believe bidirectional inverters are generally symmetrical as well, so that should not be a factor.

Which I reckon leaves two factors:

1. Battery C rates, afaik pretty much all chemistries have a higher discharge rate than charge rate, especially when trying to maintain them for a long time, so by that account regen power would at most be the same as propulsion (if the entire power train is sized for the battery’s charging rate).

2. Artificial limitations, obviously you could always artificially under-prop, though that seems unlikely outside of niche applications.

tldr: I don’t think so, except on a technicality (that you can artificially hobble propulsion).

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wjnctoday at 10:17 AM

Am I reading you right that breaking power (that you want to regenerate in the system) >> speeding power? Obvious now I come to think of it, and still pretty nifty new thing learned if true!