How to Calculate Motor Controller Amps for DC Motors

Inspect the DC motor and locate the motor's specifications plate. The DC motor's information plate will divulge the motor's required voltage and its resistance rating.

Record the DC motor's resistance and voltage, based on the information on the DC motor's specifications plate. Ohm's law -- usually expressed as I = E/R, where "I" is the current, "E" is the DC voltage and "R" equals the resistance -- states that the current in a DC circuit, measured in amperes, equals the voltage divided by the resistance.

Divide the DC motor's voltage by the resistance. The result is the current, measured in amperes, required by the motor under normal conditions. Since the motor controller and the motor form a single system, the amp rating for the motor equals the amperage required for the motor controller.