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!

  • 1
    \$\begingroup\$ Don't use dirty water that can carry particles into the motor. Also rust. \$\endgroup\$
    – DKNguyen
    Sep 5, 2020 at 15:35
  • 1
    \$\begingroup\$ You probably want to start saving up for a new BLDC motor hub. If it is not specified as being suitable for total immersion in water, then it will be corroding inside. \$\endgroup\$ Sep 5, 2020 at 15:36
  • \$\begingroup\$ @AndrewMorton yes you are right it is not good practice. luckily I have an aluminum center of the stator (so no steel parts in motor apart from the bearings and the 'motor laminations' which shouldn't rust I think since they are covered with insulation), bearings might suffer though.. As mentioned in the question the issues luckily go away once the motor has warmed up again to approx 60 celcius \$\endgroup\$ Sep 5, 2020 at 15:41
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    \$\begingroup\$ @Maarten-Monicaforpresident There is also the problem of different metals being in contact with a conductive liquid around them: galvanic corrosion. It will affect aluminium, copper, and solder joints too. \$\endgroup\$ Sep 5, 2020 at 15:44
  • \$\begingroup\$ @AndrewMorton Good point regarding galvanic corrosion, i had not considered that. Thank you \$\endgroup\$ Sep 5, 2020 at 15:49


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