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- Add a precharge resistor across main contactor RS. It is typically a 200 to 1000 ohm power resistor (a 60 watt 120v light bulb will do). Close negative contactor MS first, and wait a second or so for the precharge resistor to charge up the capacitors inside the Curtis 1231C controller. Then close RS and you are ready to drive.

Without a precharge resistor, a huge surge of current flows into the controller when RS closes. This damages the contacts of RS, and shortens the life of the controller.
 
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