I recently was riding my e-bike (with a bldc hub motor) and decided to cool the motor (it -the stator- was approx 100-150 celcius I think) in the river.

The controller is on the top of the bike and definitely stayed completely dry. The motor has cooling holes drilled in its housing through which the water can flow in.

cooling holes in motor housing: enter image description here

This method was very effective for cooling but the drive train (motor/throttle/controller/battery started acting up after riding it again after cooling...)

Note: after the motor had dried/warmed up again the issues were gone (not sure what caused the issues so not sure if the water or the sudden change in temperature or something else caused the issues).

Symptoms: -weird wining noises from motor when accelerating (much higher pitched and louder than normal) -when the motor reaches a certain rpm (above this rpm) it appears as if the coil groups are misfiring (motor vibrates/shakes and appears to be braking rather than accelerating). The severity of this braking effect appears to be random, sometimes it's worse but not sure why.. The issue appeared to mostly start occurring when a certain rpm was exceeded but sometimes (less often) the issue also occurred at much lower rpm. -the issue was gone after approx 30 minutes of riding when the motor was approx 60 celcius (motor housing)(stator was probably approx 80 Celcius).

There is no temperature sensor from the motor connected to the bldc motor controller (the controller does not have this feature).

What might cause these issues?

  • Can the water entering the motor mess up the signals coming from the hall sensors? If so what causes this?
  • could the sudden temperature change cause issues similar to this? If so please explain how
  • Is there another explanation which I did not think of?

video: https://www.youtube.com/watch?v=l2dHn89Dvso&feature=youtu.be

Thank you!

  • $\begingroup$ Never cool electronics or motors with water unless specifically designed for it (as in, it already has its own water cooling) $\endgroup$ Apr 14, 2020 at 17:08
  • $\begingroup$ Are you sure it was an electrical issue? Sounds a lot like you just had something in your bearings (whining noises, vibration) that got washed out. Contamination in your bearings makes your system less efficient, requiring more power input for same output, excess power is dissipated as heat. $\endgroup$
    – jko
    Apr 14, 2020 at 18:33
  • $\begingroup$ @jko yes quite sure it's an electrical issue since it only occurs above a certain rpm and the symptoms are very similar to when one of the phase wires is disconnected.. $\endgroup$ Apr 14, 2020 at 19:54
  • $\begingroup$ @jko also when the throttle is released the symptoms disappear (immediately as soon as it is released) regardless of the rpm.. so that also makes me think it's some sort of electrical issue.. $\endgroup$ Apr 16, 2020 at 11:20
  • $\begingroup$ @Maarten-Monicaforpresident interesting. Sounds like you may have had debris somewhere in the motor/electrical connections and managed to clean it out $\endgroup$
    – jko
    Apr 16, 2020 at 11:29


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