Relay, In-Rush Current Reduction: Operation

In-Rush Current Reduction relay is used on Engine Stop Start (ESS) equipped vehicles.

Prior to the starter motor solenoids contact closure, the In-Rush Current Reduction relay contains a shorting bar that opens the contacts routing the starter motor current through a resistor bar. The increase in series resistance reduces or eliminates the initial current spike (in-rush current) and reduces the consequent voltage drop. After a set time, the power to the In-Rush Current Reduction relay is cut, the shorting bar closes the contacts, removing the resistor bar from the circuit and restoring full power to the starter motor. At this point, there is a rebound of the current surge and subsequent drop in voltage; however, neither is as intense as they would be would be without initial jump in resistance.