36V Electric Bike Motor Short Circuit Issue

[listende-elg]

Hello everyone,


I’m having an issue with an electric bike I recently purchased as a “defective” unit, and I’m hoping someone here can help diagnose the problem.

Bike and Components:

• The bike has a 36V lithium battery that provides around 40V when fully charged.
• It's powered by a front wheel hub motor of 250W
• Bike is probably from around 2019 as far as I can tell from google
• It's a "whitelabel" bike sold by a Danish supermarket chain. I have not been able to look up any tech specs, as it's not being sold anymore.
• Controller is a WZKD3615KA-BD29-Z6 from Tianjin Santroll. Rated volatage: 36V and maximum current 15A. Rated current is 7A. See attached photo.
• Display is a LCD03U 4K36 BD1.3
• Motor casing is severely corroded, but the motor is conneced using this 6-pin Julet connector (see attachment)

Issue Description:
Bike is completely dead (electrically) even though battery is powered on and confirmed working. It works absolutely fine as an "analog" bike. If I disconnect the front motor, the display starts working.


Troubleshooting Steps Taken:

1. Battery Test: I confirmed that the battery is providing the correct voltage (40V).
2. Voltage Drop: When I connect the battery to the controller, and try to measure the voltage across the battery terminals, the voltage drops to 0.0V. This behavior was consistent with both the original battery and a second fully charged battery I tested.
3. Controller Test: I isolated the controller by disconnecting all components except the battery and measured the voltage. I connected components one by one and measured again. Measured voltage is approx 40V as expected. As soon as I connect the motor, the voltage drops to 0.0V.
4. Motor Test:
   1. I measured the resistance (ohms) between the three phase wires (thicker wires) leading to the motor. The resistance between all three phase wires is 0 ohms.
   2. A couple of times I felt a short jerk in the bike when I connected the battery. I guess this could only originate from the motor.

Questions:

• Is this motor likely to be beyond repair, given that there’s a 0 ohm reading between all phase wires?
• Could there be an issue with the controller that I’m overlooking, or does the evidence point directly to a motor failure?
• Has anyone experienced a similar issue, and if so, what was the resolution?
• I've found a similar wheel/motor for sale, but for a newer model bike. It has a 9-pin connector in stead, but otherwise have the correct specs. Could I make it work with the same controller somehow?
  • If not, could I simply change the controller to one of the cheap ones available on Aliexpress or Amazon?

Any advice on further testing or whether the motor is salvageable would be greatly appreciated. I’m considering whether it’s worth attempting a repair or if I should look for a replacement motor, but I haven't been able to find any motors with a similar 6 pin connector.


Thanks in advance for your help!


Best regards,


Kasper

 

[docw009]

Phase wires are low resistance circuits, just tenths of an ohm. They're just a length of wire wrapped around forms. With a meter, you really have to look hard to tell the difference between a short and normal. Your connect motor, kill battery test does suggest something is shorted, but it could just as likely be a fault in the controller in my opinion.

A motor connector with three large pins (for the three phase wires) and three small pins suggests a sensorless motor and controller. You need five pins for three hall sensors. That would be three hall signals, +5V power and ground. With three pins, that suggests a speed sensor which is power, ground, and speed signal.

That would mean you want to find a sensorless controller in your bin of spare parts and see if it runs the motor or find a friend/shop in Denmark willing to do that, I guess you have to buy one. At least a sensorless controller will run a sensored motor,

 

[listende-elg]

Aha! So I can’t be certain that it’s the motor yet.
It seems almost impossible to find a replacement sensorless motor, and I’ve got no spare parts bin, so I guess my best bet would be to find a 9-pin motor and a new controller. I see there are several controllers available on Amazon/Aliexpress that seem to fit that bill with a price tag of less than 15 EUR. Could I just swap the current controller for one of those and install a new 9 pin motor, or do I have to buy something closer to 50-60 EUR if I want something usable? I guess that would also mean that I’d need a new display, right? I find it extremely hard to figure out which parts go together. It seems there are multiple different 9 pin motor connectors, quite a few displays ranging from 12 to 80 EUR with a green Julet connector etc.

The bike was 130 EUR and the aim is to keep costs at an absolute minimum. I’ve found somebody willing to sell a brand new front wheel with a 9 pin motor for 55 EUR, so if I could buy a controller and a display for 30 EURs in total, that wouldn’t be too bad. But it’s a 5 year old bike so I don’t want it to get much more expensive - otherwise I could just have bought something brand new for 650 EUR.

 

[TommyCat]

Hi Kasper,
And welcome to the forum!

I would first encourage you to check the resistance between the motor’s windings and the motor‘s metal case/stator.
You should see NO connection at all. Then go from there.

For more tips and tests/observations to make on your BLDC motor, see this thread…

Testing BLDC motor's Phase Wiring - Hall Sensors and Wiring. - Electricbike.com Ebike Forum


Regards,
T.C.

 

[listende-elg]

Thank you very much! I’ll definitely check that out!
When testing the connection (or lack of) between windings and case, could I just use the multimeter to measure the resistance between the phases in the connector and the motor housing? Or do I have to disassemble the wheel/motor to do so?

 

[TommyCat]

Yes, use your multimeter with the motor assembled first.

 

[listende-elg]

No connection between the phases and the casing.

 

[TommyCat]

Might as well check all 6 pins... but for now, that sounds good.
Try the other recommended tests with the motor disconnected next. Like tying a couple phases together and checking for resistance/cogging. (see the thread)

 

[TommyCat]

That casing looks really corroded… clean off a shiny place to test from just to be sure.