BLDC motors (Brushless Direct Current Motors) are very robust. Electrical failures are rare, provided that the motor control electronics are not located within the motor itself.
Stromer motors have had their controller outsourced starting with the ST2 – the motor itself only contains the stator, rotor, three Hall sensors, and the thermistor for temperature monitoring.
Defects in the windings are rare. Detachment of one or more permanent magnets is a known, but also rare, failure pattern.
If the engine cannot be opened, for example, due to a lack of special tools, its function can also be tested from the outside.
A very good tutorial with illustrations is available in the forum electricbike.com in the post by „tommycat“: „Testing BLDC Motor's Phase Wiring – Hall Sensors and Wiring“.
Based on this post, the YouTuber „High Tech \ Low Life“ has created a video that visually explains the process: „How To: Ebike Hub Motor Hall Sensor Testing, Diagnosis, and Fixes (Display Error 10, Error 30)“.
Anyone who only wants to check the correct function of the motor phases can follow these three points:
- Disconnect the three phase wires (thick wires) from everything without moving or rotating the motor. Measure the resistance (Ohms) between each pair of phases with a multimeter and compare all three phase combinations. The readings should be consistent. The resistance values are very low (under 1 Ohm) - it's not about exact matching, but whether all values are comparable.
- Check the resistance between the individual phase wires and a metal part of the motor, such as the motor shaft. 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.
- Connect two phase wires together in different combinations for a total of three tests. With each combination, a similar magnetic resistance (also known as „cogging“) should be felt when rotating the wheel by hand. When no phases are connected, there should be no resistance.
For those who want an easier time, you can also get an e-bike tester... with which a BLDC motor can be easily tested in its main functions.
