How to test a dc motor with a multimeter？

How to Determine the Condition of a Motor Using a Multimeter

You can determine whether a motor is working properly by measuring the resistance of its windings, the insulation resistance between the windings and the motor housing, and the current flowing through the motor. Today, we will mainly introduce the following three methods. The specific measurement steps are as follows:

Method 1: Measuring the Resistance of the Windings

1. Disconnect the power supply to the motor and remove the connecting wires. If possible, disconnect the power cables from the motor to avoid interference.
2. Set the multimeter to the ohms (Ω) mode. For digital multimeters, you may choose the continuity test mode. For analog (needle-type) multimeters, it is recommended to select a range of 20k or higher.
3. Measure the resistance values between each pair of the three-phase windings (U, V, W phases). Under normal conditions, the resistance values of the three phases should be equal or very close. If there is a significant difference among the three readings, it may indicate a fault in the motor, such as a short circuit or open circuit in the windings.

Method 2: Measuring Insulation Resistance Between Windings and the Housing

1. Set the multimeter to the megohm (MΩ) mode (insulation resistance mode).
2. Connect the red probe to the winding terminal of the motor and the black probe to the metal part of the motor housing.
3. Observe the multimeter reading. Under normal conditions, the insulation resistance should be very high (typically above 2 MΩ). If the value is significantly lower, very small, or close to zero, this indicates poor insulation between the windings and the housing, which may result in leakage current.

Method 3: Measuring the Motor Current (More Complex)

1. Set the multimeter to the lowest DC current range (below 5mA).
2. Connect the red and black probes to the two terminals of each motor winding respectively.
3. Manually rotate the motor shaft and observe the current reading on the multimeter. If the maximum reading is close to that of the other two windings, the motor may be functioning normally.

In addition to the above, it’s also important to check whether the power leads of the motor are conducting properly, to ensure that power can be supplied to the motor correctly.

Reminder:

The above steps are only preliminary diagnostic methods and may not apply to all types of motors or multimeters. During the measurement process, always follow relevant safety regulations to avoid accidents such as electric shock. If you suspect serious issues with the motor, it is recommended to use professional testing equipment and methods for more comprehensive diagnostics.