Brushless DC motors (BLDC motors) are widely used in electric vehicles, drones, robotics, HVAC systems, and industrial equipment because of their efficiency and durability. However, like any electrical component, they may face performance issues over time. One of the most practical ways to check the health of a BLDC motor is by using a multimeter.
In this article, we will explain how to test a BLDC motor with a multimeter, covering resistance checks, winding integrity, and insulation quality, so you can identify faults before they lead to bigger problems.
Why Use a Multimeter for BLDC Motor Testing?
A BLDC motor consists of three-phase windings and a permanent magnet rotor. Over time, problems like short circuits, open windings, or insulation breakdown can occur.
Using a multimeter allows you to:
Verify the continuity of windings.
Check for resistance imbalances between phases.
Detect shorts or open circuits.
Ensure proper insulation resistance against the motor housing.
This method is quick, affordable, and reliable for troubleshooting.
Step 1: Prepare for Testing
Before you begin testing your BLDC motor with a multimeter:
Disconnect the motor from its power supply and controller.
Set your digital multimeter to the resistance (Ω) mode.
Identify the three-phase wires of the motor (often marked as U, V, W).
Step 2: Test Phase-to-Phase Resistance
Place the multimeter probes between U–V, V–W, and W–U.
The resistance values should be very close to each other, typically in the low ohm range (e.g., 0.2–2Ω depending on motor size).
If one phase shows significantly higher resistance or no reading, it indicates a broken or open winding.
If resistance is extremely low (close to zero), there may be a short circuit.
Step 3: Check for Phase-to-Ground Insulation
Set the multimeter to continuity mode or use a high-resistance range.
Place one probe on a motor phase (U, V, or W) and the other on the motor housing (ground).
A healthy motor should show no continuity.
If the multimeter beeps or shows resistance, there is likely an insulation failure, which could lead to dangerous short circuits.
Step 4: Test Hall Sensors (If Applicable)
Many BLDC motors include Hall sensors for rotor position feedback. To test them:
Connect the motor’s Hall sensor wires (often 5V, GND, and 3 signal wires).
Power the sensor circuit with 5V DC.
Rotate the motor shaft slowly by hand.
Use the multimeter (set to voltage mode) to check each signal wire; the voltage should switch between 0V and 5V as the rotor turns.
If one signal does not change, that Hall sensor may be faulty.
Step 5: Rotate the Motor Manually
Finally, turn the shaft by hand:
The rotation should feel smooth with slight cogging from the permanent magnets.
If there are rough spots, scraping, or excessive resistance, mechanical damage or bearing failure may be present.
Testing a BLDC motor with a multimeter is a simple yet powerful diagnostic method. By checking phase resistance, insulation integrity, and Hall sensor output, you can quickly determine if your motor is in good condition or requires repair.
For best performance and safety:
Always disconnect power before testing.
Compare resistance readings carefully.
Address any anomalies immediately to prevent further damage.
With regular testing and maintenance, your BLDC motor will continue to provide high efficiency, reliability, and long service life across applications from drones to industrial automation.