# Low ESR capacitors



## CaptConan (Jul 12, 2010)

I saw on here once that when selecting capacitors for use, whether that be to smooth out pack voltage to lengthen it's useful life, or what may be the case, that one should select capacitors with low equivalent series resistance (ESR).
What would be considered "low" in this case? I've seen several large caps with approximately 50mOhm of esr. Is that "low" enough?


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## samborambo (Aug 27, 2008)

The DC bus link capacitor ESR is driven mainly by the power dissipation of that capacitor. The power dissipation of the capacitor is the ripple current ^ 2 x ESR. Unfortunately the peak ripple current of a DC chopper (DC motor controller) is very high - by definition it is the peak motor current.

ESL of the DC bus link is also very important. The capacitor may have the peak current ability but if it's ESL is high, it won't clamp the voltage spike at gate turn-off.

Film capacitors usually offer the best ESR and ESL but are relatively large for the capacity they store.

Ask Tesseract what he used in the Solution 1.

Sam.


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