PSA: How a faulty third-party display burned my Bafang Ultra M620/G510, and then my BBS02

nimpol

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TL/DR:

If your bike shut off during ride and display went black, you might have burned both your controller and display. Then, if you replace the controller/motor and plug in the same old display, that new controller will be burned immediately.

You can test your display before reusing it, though.

Post:

I have found a similar problem on forums in just three cases:
Bafang ultra m620 controller burnt
Bafang Ultra G510 - error code 11 & burnt controller
M620/G510 burnt controller issues

People there burned two-three motors in a row before seemingly giving up on electric transport entirely. That’s sad, so I hope this experience will help someone.

This happens with the M620 and third-party displays (Eggrider in posts and 500C in my case).

I have not found confirmed cases with other motors or stock DP C18 displays. That makes me think that though the UART M620 works with any UART display, it may be a bad idea to use it. If someone shares the same issue with the stock DP C18, well, then it doesn’t matter what you use and you just hope for the best.

Before, I had a 48v BBS02 with a Luna Mini 500C display. When I switched to a 52v M620, I hated DP C18 from the first sight and bought some version of the 500C from eBay.

For about 700 miles, everything was fine, then I suddenly lost power during a ride, and the display went black. I took apart the motor to see the same burn damage as in the first post above.

Also, my bike has two batteries with a diode balancer, as my previous BBS02 setup had. This might be the cause too, but I never had any problems with this before. Though, Eggrider does not advice to use their displays with two batteries setup.

I ordered a new motor and a replacement controller to fix the burned one and have a spare. Normally, I would just replace the motor and see if it works. Luckily, the posts above gave me the idea that something is wrong with the display. So, I took one of my very old BBS02s and immediately burned it with that 500C just by plugging the green connector into the motor. Darn. I might have sold it, but it’s much better than burning a new M620.

I tested the 500C with a multimeter, and it surely shorted between “P+” and “Ground” - zero ohms. A working display shows some resistance, and that resistance changes when pressing the power button. Then I tested that working display with the motor again, just in case, to see if testing itself could damage it. And it’s fine.
 
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