Motor phases - measure

BLDC (Brushless Direct Current Motor) motors are very robust. Electrical faults are rare as long as the motor control electronics are not housed in the motor itself.

From the ST2 onwards, current motors have outsourced the controller, i.e. only the stator, the rotor, the three Hall sensors and the thermistor for temperature monitoring are still in the motor.

Defects in the windings are rare. Detachment of one or more permanent magnets is a known but also rare fault.

If you do not want to or cannot open the engine, e.g. due to a lack of special tools, you can also test the function of the engine from the outside.

A very good tutorial with illustrations can be found in the 'elektricbike.com - Forum' in the post by 'tommycat' - 'Testing BLDC motor's Phase Wiring - Hall Sensors and Wiring.'

Based on this article, the Youtuber 'High Tech \ Low Life' has created a video that also explains the procedure visually > 'How To: Ebike Hub Motor Hall Sensor Testing, Diagnosis, and Fixes (Display Error 10, Error 30)'

If you only want to check the correct function of the motor phases, you can stick to these 3 points:

• Disconnect the 3 phase cables (thick wires) from everything without moving or turning the motor. Test the resistance (ohms) between each two phases and compare the resistances of all three phase combinations. All three readings should match.
  Note that this is only a general test with a digital multimeter. The resistance readings are very low (below 1 ohm) to be truly accurate. It's not so much about an exact match of the values, but whether they are all comparable.
• Then check the resistance between the individual phase wires and a metal part of the motor, e.g. the motor axle. It should be infinite - no short circuit or very low resistance to ground. If this is the case, the motor must not be used until it has been repaired.
• Then connect two phase wires together in different combinations for a total of three tests. For each combination, a similar magnetic resistance (also known as "cogging") should be felt when the wheel is turned by hand. If no phases are connected, there should be no resistance.

If you want to make things easier, you can also buy an e-bike tester with which the main functions of a BLDC motor can be easily tested.