Capacitors and regenerative braking

[RedBaron]

Clearly a Li ion is not actually a capacitor, but their dynamic impedance is not that different during short current pulses where the V is assumed to be more or less constant, after all both are used as "short term" voltage sources. Now I'm comparing large electrolytics to Li ions, not something like a film or ceramic where you can get v low ESL.

Also its quite reasonable to model a Li ion as a capacitor with the right esr/esl and the capacitance value being determined by the energy stored in the battery between Vfull and Vempy.

Paralleling capacitors to a battery for short bursts would make sense if the battery source impedance is "slow" vs your application or you have very large inrush currents that might damage them (eg the starter batteries in the links above), but you would have to measure how much the volt dip is during said pulse at the inverter terminals to determine if this has any value. Keep in mind that any motor drive is already going to have some pretty high quality capacitors on its internal DC bus to deliver the xkHz PWM current and keep that HF current local to the inverter. Basically for transient current its an impedance matching game and the capacitors would have to approach the source impedance of the batteries for them to have any worth while effect.

To me the OP is not pushing his batteries (rated 150A and only pulling 100A) and unless the voltage dip is significant at the inverter terminals a capacitor would likely have minimal effect for transients and would need to be huge to provide noticeable energy storage increase.

IMO determine if there is even a problem with the set up as is by measuring before adding more stuff to it, if its a hobby and you just want to have the caps then fine but in any sort of product development there'd have to be a pretty compelling case to add them to warrant the cost.

This made me understand so much better what's going on and what to look for. Thank you.