How Would You Use a Meter to Check a Motor?

By James Stevens
Multimeters are used to measure voltage and amperes.

Electric motors operate by converting electrical energy (voltage and amperes) into rotating mechanical energy using a system of magnets and wire windings. The magnets remain static and electricity passes to the windings on the electric motor's armature. The flow of electricity into the windings creates an electro- magnetic field which the magnets try to repel and the motor starts to turn. You can use a multimeter to check the voltage and amperes your motor is using.

Check the label on the electric motor to determine the voltage and amperes it needs to operate. Note the two figures so you can check them against the multimeter readings.

Locate the two terminals on the motor. They are labeled “+” and “-“ indicating positive and negative, respectively. It’s also likely that the wires connected to the motor are colored red and black, making identification easier.

Turn on the multimeter. Adjust the settings so it measures voltage. Turn on the motor.

Place the prong on the end of the meter's red wire onto the positive terminal on the motor. Place the prong on the end of the multimeter's black wire to the negative terminal. The meter will them measure the voltage the motor is using.

Read the meter. It will always read the same as the voltage noted on the motor’s label. The voltage always matches the label, as it relates to the electricity flowing from the power source to your motor.

Adjust the meter to measure amperes. This check determines whether the motor is operating correctly. Amperes relate to the current the motor uses.

Read the meter. If the motor is operating correctly, the amperes are the same as the motor’s label. If the amperes are less, the motor is not operating correctly and needs checking, as it probably has worn brushes. Turn off the motor.

Tip

The label on the motor may tell you the voltage and the wattage instead of the amperes. Wattage is the amount of energy the motor uses in one hour. For example, a 60 wattage motor will use 60 watts per hour. You can calculate the amperes your motor is using by dividing the wattage on the label by the voltage you noted from the multimeter. If you measured 12 volts and the label stated 60 watts then 60 divided by 12 equals 5, which is the amperes.

Warning

If your motor operates on high voltage electricity, such as the same or similar to your domestic electricity supply, it's sensible to wear protective rubber gloves to protect you from getting an accidental electric shock.

About the Author

James Stevens has been writing articles for market research companies in the U.K. since 1990. He has written various country profiles for inclusion in comprehensive market reports including Vision One Research and Investzoom Market Research. Stevens holds a General Certificate of Education from Chelmsford College of Further Education.