How to Test DC Motors

Learn how to test DC motors.
••• wires and hoses image by Victor M. from

DC motors draw power from deep cycle (DC) batteries. If you have a DC motor that is malfunctioning or drawing and bleeding power through the wires, there are tests that can be done to test the efficacy of the DC motor. This test can be done in your own workshop using simple hand tools and a specialized electric testing device.

    Remove the wire connections leading from the motor to the DC battery. Use the Phillips screwdriver to unscrew the set screws of the connections. Check to make sure there are exposed wire ends on the wires, as you will be using them to complete a test circuit.

    Make sure the motor is not attached to any machine connections. If the motor is attached to any part of the machine, disconnect the DC motor. Use the sockets and ratchet or a screwdriver to disconnect the motor, if necessary. Check to make sure the DC motor's rotor can turn with no impediments.

    Switch the voltmeter to "Ohms". Attach one end of the red lead wires to the DC motor and run the DC motor's red wire to the battery. Attach the clip of the black lead wire to the DC motor and run the black motor wire to the battery. Attach the red and black lead wires to the volt meter on the red and black terminals respectively.

    Look at the display on the voltmeter and check for the ohm reading. With the complete connection (battery-voltmeter-motor) your motor will also be running off the battery's juice. The first reading you see will be a quick surge reading between 10 to 100 ohms. Let the motor run for five seconds and then take another voltmeter reading.

    Look at the DC motor's specifications for volt ohms. Compare your reading to the voltmeter reading. If there is a difference of 10 or more ohms, there is a problem with the motor.

    Things You'll Need

    • Voltmeter
    • Set of red and black lead wires with clips
    • Phillips screwdriver
    • Socket and ratchet

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