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Smoked BMSbattery motor

Posted: Jan 14 2020 9:49am
by smaua
Hey everyone, I'd like to ask for some help about my bike

Last night I over exerted the motor.. Was going up a very big hill with a lot of weight and when the battery was almost empty I tried to squeeze the last bit from it. And then there was smoke. I got a bit confused where it came from but this morning I had a look at the back wheel and even without power it's not spinning smoothly anymore. Feels clunky/bumpy at best, inside the motor Hub, and can kinda hear a noise too. It still spins when I plug it into the battery but I'm not sure if it's a good idea to use it anymore. As in whether it's safe to use until I get a new one?

The kit I have is from BMSbattery : Q11 48V1KW REAR Driving E-Bike Conversion Kit.

There's nothing that looks any different from the outside.

So yeah I would like to know how dangerous it is to keep using it for now,
if there's any not super difficult fix ideas
else what good not too expensive 48v motor could I get instead?
Hopefully with quick ish postage because I need to travel daily and it's kind of limiting not having a working ebike.
I am based in the UK.

Thanks a lot for any suggestions.

Re: Smoked BMSbattery motor

Posted: Jan 14 2020 11:20am
by pwd
Sounds like blown controller and/or damaged phase cables. If you disconnect the motor from the controller does the wheel spin smoothly again?

Re: Smoked BMSbattery motor

Posted: Jan 14 2020 11:25am
by smaua
pwd wrote:
Jan 14 2020 11:20am
Sounds like blown controller and/or damaged phase cables. If you disconnect the motor from the controller does the wheel spin smoothly again?
Thanks for reply pwd.
Do you think that if the battery is detached and its still not smooth it could be the controller?
Like, I dont understand how it is different with or without controller as long as battery is detached.

Re: Smoked BMSbattery motor

Posted: Jan 14 2020 11:49am
by pwd
Yes, even if the battery is disconnected, it still could be the controller if the wheel doesn't spin smoothly. The motor is basically a generator. If any of the phase cables (three large cables from the motor) touch, it will make the wheel harder to spin; even without power. A blown controller will usually result in two of the phase cables shorting out. There are many good explanations if you search for "blown controller" or "shorted phase". Here is a good troubleshooting page:

https://www.ebikes.ca/documents/BlownMosfets.pdf

you will see at the very end, it mentions that the motor will not spin freely if the phases are shorted.

Re: Smoked BMSbattery motor

Posted: Jan 14 2020 1:07pm
by smaua
Ahh actually maybe u have a very good point. Just checked closer and there are some melted wires near the motor so maybe that's the problem. Will try to replace them and see!

Re: Smoked BMSbattery motor

Posted: Jan 17 2020 6:50am
by dogman dan
FWIW,, you did melt the motor. If the big wires contacted, it could have also damaged the controller.

Overload, and then ride up the steep hill, will do in hub motors every time. You have to keep that thing rolling at 15 mph or so, or the motor makes excess heat at lower rpm under that much load. Typical kits have a practical load limit of about 300 pounds on steep hills. That's you, the motor and battery, the bike , and the cargo. Easy to overload, unless you weigh less than 150 pounds.

But the motor may be fixable, and if you have luck, it didn't damage the controller.

Often what happens inside a melted motor, is the hall sensors get cooked. they are cheap, and can be replaced. Then your wires need repair as well, if the insulation melted enough to short.

An inexpensive motor and controller tester can save you a lot of time, as you try to make repairs. It can confirm your controller is ok, or not, and then it can help you see if your motor repair is complete. it might be all you need is to fix the melty wire.