Originally Posted by
Roelof
The cap is not for the power but to save the ESC.
Several functions are done with the caps:
- filtering out the high frequencies of the swtiching ESC
- filtering out voltage peaks produced by induction on the wires and motor coils.
- take the high current peaks to prevent the voltage drop goes to low and with that keeping the voltage on a better level so the FET's are getting enough to get fully opened.
With no caps it is known the ESC can produce more heat which is not good for its life.
That ^.
Here's another nice explanation, stolen from:
http://www.rcgroups.com/forums/showt...php?t=1753720:
Ripple is the difference in voltage the fets see when they turn on - turn off ( load, no load).
Now since some of the components inside the esc need to see certain voltages to operate properly mfg's put capacitors on the incoming line to basically smooth this difference in voltage out. If we didn't things would go boom pretty quick. The biggest thing that will happen if the ripple is to high is the caps will charge & discharge at such a high rate they will eventually be damaged or they simply won't be ably to supply the demand & could cause failure of the esc.
Acceptable ripple is normally 5% of total pack voltage ( 50v - 2.5v Ripple) 10% & things will still work but you can expect a short life from the esc. Over 10 - get better batteries if they are old & weak or add inline caps if the power system is just a monster.
In addition, here's some nice info from MGM COMPRO (the guys making those fancy expensive HV controllers) on the effects of braking on ESCs:
https://sites.google.com/site/planbp...g-beim-bremsen (German),
https://www.google.de/url?sa=t&rct=j...82001339,d.bGQ (English pdf). While caps are not the main focus of the article, it is mentioned that caps do in fact absorb part of the (potential ESC damaging) energy that is generated by braking:
... Another distorting part are filtering capacitors on the inputs of the controller, which do absorb a part of the energy during braking current pulses.
Adding additional caps to keep ESCs happy is very common in high power applications (speed-runs, high-power bashers). I'm not a racer, but I'm guessing for typical racing, Power throughput is low enough for the stock caps to be sufficient.