Comment by distortedsignal
5 years ago
> Regen braking has no physical cost associated - it's pure software/firmware.
I think this is a slight exaggeration.
The way I understand regenerative braking is that you (effectively) run your AC generator in reverse of what you would in order to accelerate in the direction of motion and then take the current generated by that, rectify it to DC, and use that current to charge a battery. The energy in the system is provided by the back EMF induced in the stator by the magnetic field generated by the motor rotor. I agree that the AC generator is going to stay the same, but I think there's specialized hardware needed for the rectification and charging cycles. At the minimum, you need a more specialized battery and battery management system to make sure that you're balancing the charge across the cells in your battery.
I think you are overestimating unique requirements of typical car engines. They are usually DC powered AC engines, where the DC->AC converter (generating 3-phase AC of controlled power and frequency) can probably run backwards (AC->DC) with at most a few minimal hardware changes, if any.
If you're not overdoing regen, you probably don't need additional balancing. Even if you wanted to charge the EV by towing, you could probably use the normal charge balancing circuitry, again minimal if any HW changes. Non-wimpy batteries and cells should be fine - if they can fast-charge, they can take regen. Might have some limitations on acceptable power vs. temperature, charge state etc.