DISCOVER
×

How to Check an Electric Motor Capacitor

Updated February 21, 2017

The purpose of coupling a capacitor with an electric motor is to increase the efficiency of the electric motor. A capacitor stores power that would normally be wasted by an electric motor and redelivers that power during the negative power cycles of the motor. When a motor capacitor looses capacity, the motor can overheat or fail, as most motors are now designed and manufactured in such a way that they will not operate without a capacitor in place. You can ensure your motor is running safely and at peak efficiency by checking the motor's capacitor regularly.

Switch the circuit breaker powering the motor to the "Off" position.

Remove the wires connecting the capacitor to the motor or power supply.

Set your voltage meter to test for continuity. The continuity setting delivers a small DC voltage through the circuit being tested. You can use this small DC voltage to determine if the capacitor is functioning; however, you will not know the amount of capacitance.

Place the two voltage meter leads on the two wire connection points on the capacitor. Leave the leads in place for about thirty seconds and then remove the leads. This charges the capacitor with a small voltage.

Set the voltage meter to test for DC voltage. Place the two voltage meter leads on the two wire connection points on the capacitor. The voltage should spike rapidly then fall to zero. The voltage level is not important. You only want to know if the capacitor stored the DC voltage from the continuity tester and then released it when you checked for voltage. If no voltage spike is present, the capacitor is defective and should be replaced.

Reconnect the wires to the capacitor and restore power.

Tip

Some voltage meters come with a setting for testing capacitance. If this is the case, you can simply disconnect power, remove the wires and test the capacitance of the capacitor using the voltage meter.

Warning

There is always a danger of electric shock when working with high voltage. Only certified electricians should attempt this procedure.

Things You'll Need

  • Voltage meter
Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

Joey Butler began writing in 2006. His work has been published in "The Index Journal" and in "Review: Lander's Literary and Visual Arts Magazine." He has written everything from investigative news articles to a study guide that was published by I.B.I.D. Books. Butler holds a Bachelor of Arts in English from Lander University.