EVH Tech: Controllers: Capacitor Precharge

Updated by Bill Lofton 12/30/15

Courtesy of Elithion

Precharge circuits are used to precharge the load capacitors in motor controllers before the contactor is closed to fully energize the motor controller. Without a precharge circuit, upon closing the contactor, the resistance of the circuit connecting batteries and load capacitors is so low that a near short-circuit condition occurs.

The resulting in-rushing current is well above the peak current rating of the installed batteries, contactor, and load capacitors. Bad thing!

How To Precharge Capacitors

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