How to Determine the Condition of a Motor Using a Multimeter?

[DiLayla]

Using a multimeter to test the condition of a motor involves the following steps: With the power disconnected, place the black and red probes of the multimeter on the motor's terminals to measure. For a three-phase motor, measure between each pair of terminals and observe the resistance value on the multimeter. If the digital multimeter displays a value, or the analog multimeter shows resistance, it indicates that the motor windings are conducting properly. If no resistance is detected, the motor is likely damaged. Additional Information: The cause of motor overload may be low terminal voltage. This refers to the voltage measured at the motor's stator terminals during startup or full-load operation, not the no-load voltage. When the motor load is constant, a decrease in voltage will inevitably lead to an increase in current, causing the motor to overheat. Severe voltage drops can force the motor to stop or operate at low speeds, with a sharp increase in current potentially leading to motor burnout.

[Ava]

As someone who frequently works on car repairs, I follow this set procedure when testing motors with a multimeter. First, disconnect the power in the engine compartment, set the multimeter to the resistance mode, and select the 200-ohm range. Measure the resistance values of the motor's three-phase windings: under normal conditions, the resistance between the three windings should be similar, for example, all within 3-5 ohms. If the resistance between any two terminals suddenly becomes infinite, it indicates a broken coil; if the resistance is only 0.something ohms or even zero, it's likely a short circuit in the winding. Then, test the insulation by touching one probe to a winding terminal and the other to the motor's metal casing. A good motor should show infinite resistance; if it reads a few hundred ohms or lower, there's definitely a leakage. If possible, it's best to also test the operating current under power—if it significantly exceeds the rated value, there's internal wear. If all three steps show normal results, the motor is basically fine.

[DelOlive]

I follow a simple three-step method to check motor condition. After power-off and wire removal, use the multimeter's continuity test on terminals: a beep indicates circuit continuity, while silence suggests possible open circuit. Then measure phase resistance with the ohmmeter - 10-30 ohms is normal for small motors, and >10% variance between phases is dangerous. Finally, insert red probe into terminal and ground black probe to motor casing; readings above 1MΩ pass. Last week I detected winding-to-case leakage on a blower motor this way - only 500kΩ showed clear breakdown. This method quickly identifies burnout risks, but complex motors still require professional testers. Always turn off the multimeter after testing to conserve battery.

[LeHannah]

Just a few days ago, I used a multimeter to help my neighbor test the car's cooling fan motor. First, disconnect the negative battery terminal, select the resistance measurement mode, and test the three wiring terminals: the U-V phase showed 3.8 ohms, the V-W phase showed 3.7 ohms, but the W-U phase displayed OL (infinite resistance), indicating an obvious open circuit. Then, measure the insulation resistance between the windings and the motor casing; both phases showed 0.02 megaohms, indicating the coils were short-circuited. Although a multimeter can't display real-time data like a diagnostic tool, abnormal resistance values can reveal hard faults like short circuits and open circuits, especially in older car motors. Note that during testing, clean the oxidation layer on the terminals and ensure the multimeter probes are firmly in contact with the metal parts to avoid misjudgment.