Today, direct current (or DC) electric motors are used in a wide range of applications, such as moving windows and seats in your car. Due to the hidden nature of these motors, it can be very difficult to complete any repairs or maintenance on them without having to separate whatever it is you are powering. That’s why, once you’ve managed to get to your DC electric motor, you should always give it a quick check to see if it has “gone bad” and needs to be replaced.

Begin by removing the DC motor from its mount, making sure that you have also removed any sources of electrical power that could cause it to accidentally start spinning. You may need to follow the manufacturer’s instructions for doing this, as some motors are very stuck in position and could present an electrocution hazard.

You can then test the continuity (or connection) of the electric motor by connecting it to a voltmeter. Make sure the meter is in the “ohms” position, then put the red and black wires into their connections (the red wire should be connected to the “ohms” and the black wire should be connected to the “common” point). Test that the meter is working properly by touching these two leads – the display should read zero ohms (or full continuity).

To test your DC motor, touch the ohmmeter leads to the motor leads. The meter display should indicate a low resistance (between 10 and 30 ohms), but if it reads infinite ohms or an open circuit, you should turn the final shaft of the motor. The ohmmeter should give different readings as this shaft is rotated (which is an indication that the electric motor itself is OK, but there is a problem with the electrical circuit. If the meter still reads as an open circuit, the ohmmeter conductive brushes may have gone “bad”.

Use a screwdriver to remove the brushes from the end of the electric motor (you can find them under the plastic caps on the opposite end of the motor from the drive shaft). Carefully inspect brushes for signs of surface cracking or breakage – the area of ​​the brush that sits against the conductor or commutator should be smooth and curved. If there are broken wires or springs, the motor will fail. If the brushes seem fine, then the problem may be with the commutator.

Take the screwdriver again and use it to remove the cover from the rear end of the DC electric motor (removing the two screws that run the length of the motor). Inspect the boards that include the switch assembly; there should be an opening between each one. If you notice any broken wires or burnt varnish, the switch has failed and its damaged parts will need to be replaced.