Help with seized/shuddering front hub motor


New member
Local time
8:05 AM
Apr 6, 2022
Help! I think I might have killed my ebike motor and/or controller. Don't know where to begin thinking about diagnosing this. It's a generic chinese front hub kit from carbonspeedcycle ( I have a 1000w front hub 20" wheel on my bullitt cargo bike.

I was riding to work this morning and hadn't made it half a mile from my house when the battery indicator on my (fully charged battery) ticked down to 3/4 - usually that doesn't happen until at least mile 3. Then I hit my first moderate uphill and I noticed that power/speed was only about 3/4 of what I used to. Then before the end of the hill the wheel began alternately stuttering and losing power, and the power indicator on the display started showing weird readings - 1999 watts (never shown more than about 1300 watts previously) while off the throttle, 0 watts while under power, etc. I tried limping home on power but it was too unnerving to be constantly shuddering, losing power and accelerating - I was sure I was going to make whatever's wrong worse. I was able to ride home analog without any noticeable extra drag.

I had left the bike outside in the light rain for a couple hours last night while I helped a friend rebuild his sailboat winches in my garage, so my best guess is the problem is caused by moisture in the system.

How can I triage this down to figuring out whether this is a problem with the hub motor or with the controller/something else in the system? I guess I'll open it up and try to dry it off and if that doesn't fix it, give it a few days to dry out? What else can I do to start?
Check the phase wires going into the motor. Should be a total of 8, 5 thin, three thick. Might be just the three thick ones. Check VERY, VERY carefully and closely for nicks or breaks in the insulation, generally close to the axle entry point. Thick ones are phase, thin ones are for Hall sensors.
Flex the wires in different directions, a fine cut may not be easily detectable at first.

You CAN open the motor, carefully. Search for and watch the "CLANG" video. Powerful magnets. Trace the Hall wires and make sure the sensors are firmly mounted and not loose. Opening the motor would be the very last thing to do, a PITA and mildly dangerous to your fingertips. CLANG.
It happens when putting the cover back on.

Might also be water inside the controller. Less problem here to open and dry off. Look and smell for signs of burnt electronics, dry THOROUGHLY, then test. Bag of rice works well here, just make sure and get it all out.

The symptoms of high power usage, shuddering, wildly varying power usage, etc. are common indicators of a short between two or more of those phase wires, they carry power to the motor in high multiples of amperage. Kind of like spark plug wires, with careful timing. Short could occur in wires themselves, inside motor, or inside controller. Water inside the motor itself does not usually cause this kind of short, unless there is a cut in the insulation, which usually occurs at the axle entry point.

Also put a voltmeter on the battery, wait a few hours, test again, charge, repeat. Ideally put a load on the battery, and test repeatedly. Could be an issue here, but symptoms not generally caused by a battery problem.

I would start with the axle entry point, then the controller.

Good job describing your symptoms, and the weird or unusual thing (rain) which happened right before the problem started.
Thank you so much! I dried off the controller and display and the motor began working fine, though the varying power usage (at least as reported on the display) and battery life indicator continued for a few minutes. Then those also both resolved themselves after a couple minutes of running the motor without any load. This was all before I read your comment, I'll check the phase wires next. I'm pretty sure it's just 3 thick ones.
You may want to look into filling the controller with potting compound, basically epoxy fill, does not help with heat dissipation but does make the controller essentially waterproof.

My controller is fully potted, something I enjoy myself, though mine is very low power and does not generate much heat. I live in an extremely rainy area though, and it has worked well.

if you have only the three phase wires, then your motor is sensorless, or at least your controller is and the motor works OK with it. Sometimes a bit of a rough start but once rolling works OK. No real downside other than that and one less thing to potentially go wrong.