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Upgraded Fat Tire bike stopped running, something seems Burnt!!

Posted: Jun 10 2021 9:24pm
by banshee28
Hey guys, need some help here!!

So, I upgraded my fat tire bike with all new components: 52V 21Ah battery, 35A controller, Color LCD, 750W Bafang rear Hub, throttle, etc. Everything was working good for a month or more across all terrains, no issues!

Last ride, I rode in some heavy beach sand areas and had some low speed areas where I used full throttle at very low speed. I think this may have really been a bad idea, but it seemed to handle this fine on previous rides.

I did look down at the LCD at times and notice 1200-1500 or so watts showing so i know at brief times it was working hard.

Anyway, during this ride the motor and LCD eventually turned off and would not turn back on. I peddled home and let it cool down. Still no power. Nothing seemed hot or burnt at the time. I disconnected the battery to the controller and let sit overnight.

The next day, I try to plug things back in and quickly heard a sizzle and seen the battery terminals turn black while plugged in to the controller!! I also notice while pushing the bike backwards there seems to be a slight more resistance in the motor.

So I would like some help here on the possible issue. Did I overload or burn out the motor, controller, battery, hopefully not ALL of them, LOL

Any suggestions on how to check things out?

Re: Upgraded Fat Tire bike stopped running, something seems Burnt!!

Posted: Jun 11 2021 7:39am
by pwd
It's likely that you burnt up the controller and/or have damaged the phase cables from the motor to the controller. Is it a geared or direct drive hub motor? I'd start by inspecting all your connectors and cables for damage and then move on to controller troubleshooting:

https://ebikes.ca/documents/BlownMosfets.pdf
https://www.youtube.com/watch?v=lTssCn5YyTw

Re: Upgraded Fat Tire bike stopped running, something seems Burnt!!

Posted: Jun 11 2021 8:17am
by banshee28
Thanks, its a geared hub. It was originally the 350W version, but I swapped in the "guts" of a new 750 into the case, which is a perfect fit. I will check the cables but I don't think any are burnt or damaged enough to see on the outside, but will disconnect and check today.

Not sure how to troubleshoot the other stuff? Can I use a volt meter and check battery and things to make sure its still ok?

Re: Upgraded Fat Tire bike stopped running, something seems Burnt!!

Posted: Jun 11 2021 12:08pm
by fechter
Unplug the motor from the controller and see if the abnormal resistance to pushing backward disappears. If so, the controller is shorted. You can also check the controller with an ohmmeter once the motor is unplugged. Measure resistance from each phase wire to B-. Reverse the meter probes and measure again. Repeat measuring to the controller B+ wire. If any of these measurements show near zero ohms in both directions, the controller FETs are shorted.

Re: Upgraded Fat Tire bike stopped running, something seems Burnt!!

Posted: Jun 11 2021 2:06pm
by banshee28
fechter wrote:
Jun 11 2021 12:08pm
Unplug the motor from the controller and see if the abnormal resistance to pushing backward disappears. If so, the controller is shorted. You can also check the controller with an ohmmeter once the motor is unplugged. Measure resistance from each phase wire to B-. Reverse the meter probes and measure again. Repeat measuring to the controller B+ wire. If any of these measurements show near zero ohms in both directions, the controller FETs are shorted.
Thanks will do this next!

Re: Upgraded Fat Tire bike stopped running, something seems Burnt!!

Posted: Jun 12 2021 11:24pm
by banshee28
fechter wrote:
Jun 11 2021 12:08pm
Unplug the motor from the controller and see if the abnormal resistance to pushing backward disappears. If so, the controller is shorted. You can also check the controller with an ohmmeter once the motor is unplugged. Measure resistance from each phase wire to B-. Reverse the meter probes and measure again. Repeat measuring to the controller B+ wire. If any of these measurements show near zero ohms in both directions, the controller FETs are shorted.
Update: I think good news, I unplugged and it DID seem like the motor spins easier now! So does this mean its shorted and needs to be replaced or do I need to test further? It would be nice if it was only the controller and both motor and battery are OK.
Thanks!

Re: Upgraded Fat Tire bike stopped running, something seems Burnt!!

Posted: Jun 13 2021 11:18am
by fechter
If the motor spins easily with the controller unplugged, then the motor is probably OK. You need a new controller.

Re: Upgraded Fat Tire bike stopped running, something seems Burnt!!

Posted: Jun 14 2021 10:23pm
by banshee28
fechter wrote:
Jun 13 2021 11:18am
If the motor spins easily with the controller unplugged, then the motor is probably OK. You need a new controller.
Great, hope so!! I will run a quick test on the battery ASAP, hope it is ok too. If so will order a new controller soon. Any suggestions on which model, maybe there is a better one than what I had here (35amp 36-52v KT Controller).