In general as Jay mentioned you want to keep the ripple voltage low as a percentage of the total pack voltage. The sensitivity to ripple voltage increases dramatically the closer you get to the caps voltage limit. For example, if you run a 8S rated ESC at 8S and the caps are only rated for 35V it is quite easy for the bus voltage plus ripple voltage (30V +5V ripple=35V) to exceed the maximum voltage of the caps. This is often why user's or companies recommend never running an ESC at it's rated voltage. Some companies match the Cap voltage levels too close to the ceiling voltage level in my opinion. It's a compromise between ripple voltage performance and capacity. One might assume it would just be better to add 100V caps on a 50V system, but then you only have 50% bus voltage utilization from the caps.
The type, capacity and quantity of caps also make a difference. I will also point out that actual ripple voltage tends to be higher than what is logged by our hobby ESC's. I have conducted tests on professional level 3 phase controllers where measured ripple current from the datalogger was 45% of the actual peak as measured with a specific scope and current probe. So although you are logging 4V ripple's, in actuality the ripple is closer to 10V.
Adding capacity helps to some extent, but placing the extra caps away from the board does not gain as much as if the caps were directly mounted on the board. The extra lead length can in some cases causes a resonance which can actually be more detrimental than beneficial.
I'm going off on too much of a tangent here, but good rules to follow:
Use heavy gauge short wire with good connectors (this assumes good solder and soldering skills as well)
For high current applications, leave some headroom between the operating voltage and the rated voltage of the ESC.
If extra caps are deemed necessary, use the same type and voltage level. Keep the caps as close to the board as possible and avoid long length of wire to remote mount them.
View attachment 51248
Here is a shot from a SAW pass running a 6S1P, Note 400A peaks and ripple is around 4V peak. ESC ran perfectly with no extra caps, just short wires, a stout battery and good connectors.
TG