Temporary power outages and motor noise

[Victor Dupont]

Hi there!

My partner’s electric bicycle is no longer working properly.

The symptoms evolved, but to summarize today’s situation, when riding it after stopping to pedal, motor often won’t turn back on, unless we bring the bike to a standstill. And when motor is on, it makes a lot of noise.

Here’s a video:

Complete history of the symptoms​

For the complete history, my partner purchased it second hand, from someone who seemed very trustworthy and very careful with the bike. The bike didn’t have a scratch and was working perfectly for a week.

The only event we can think of between the moment when it was working and when it stopped was a time when we put the electric bike in the trunk of our car, together with my bike, and at some point my bike tipped and fell on her electric bike. But it wasn’t a big shock really.

After that, the motor didn’t work at all. The display lit fine, but the motor never.

I tried to mess with it, unplugged and replugged every cabled, tested a lot of things. While doing so I got the bike to fall from shoulder height when it was hanging from a low tree.

After all this fiddling, now the symptoms are what I described: when we start riding it the motor starts, when we stop pedaling it stops, and when we start pedaling again it often won’t restart, not always though, .

If we then stop the bike, meaning bring its actual speed to 0, without doing anything else, not changing any controller setting or whatever, and start pedalling again, most of the time it kicks back in instantly.

Conversely, if I keep riding the bike without the motor kicking in, even if I'm going downhill for a few seconds and not pedalling, the motor will not kick back in when I start pedalling again.

It will only kick back in after bringing the bike to a standstill.

Also, when motor runs it makes a lot of grinding noise and big vibrations. The whole back of the bike shakes.

When I hang the bike on the tree again and try to reproduce the issue, the motor noise is significantly lower, I wouldn’t notice that it is wrong. Also it always starts back, I couldn’t reproduce that behaviour when bike is hanging from the tree, basically with no real load. I move the pedal by hand, motor starts, I stop pedalling, it stops, I move the pedal again, it restarts, etc. Basically normal behaviour. Here's a video:

Tests I made​

I did all the tests listed here, except for those that require a device to turn the wheels at constant speed: https://electricbike.com/forum/foru...-motor-s-phase-wiring-hall-sensors-and-wiring. All the other tests I did, and they all passed successfully.

I opened up the motor, suspecting loose magnets. Although I didn’t manage to separate the rotor from the stator, looking at them together I didn’t notice anything weird. This is my first time trying to repair an electric bike, but everything seemed normal. The bike is a foldable Megamo Park and I think it’s a Shengyi DGWX2 motor.

I also checked for broken teeth from the planetary gears but didn’t find anything.

The casing where the gears meet with the wheel had a very slight bit of slightly rusty colored stuff, but very little, and nowhere else.

Hypotheses​

The noise made me suspect a problem with the motor, but intermittent power outages don’t seem to me to be related. Power outages would have made me think of a controller issue.

I would also tend to rule out a battery problem, since the display is always lit no matter what.

Does anybody have any idea what the cause could be?

Thanks a lot in advance for your help!

 

[docw009]

Instead of a multimeter, connect an appropriate 5V LED's across the output of each Hall sensor. Much easier to see the pattern.

 

[Victor Dupont]

Instead of a multimeter, connect an appropriate 5V LED's across the output of each Hall sensor. Much easier to see the pattern.

Thanks for the reply, and for the tip!

It's a good idea, I'll keep it in mind next time.

You seem to have experience with these things. Do the numbers I measured and shared in this other discussion seem normal to you?

Thanks again for the help!

 

[docw009]

Thanks for the reply, and for the tip!

It's a good idea, I'll keep it in mind next time.

You seem to have experience with these things. Do the numbers I measured and shared in this other discussion seem normal to you?

Really don't have any interest in debugging ebike controllers or gaining a detailed understanding on how to spin a motor. When my controller breaks, I have a spare.

 

[Victor Dupont]

Hi guys!

This bike is fixed!!!

Turns out it was the bootstrap capacitor of the yellow phase wire gate driver circuit which had blown. Replacing it, and the resistor it had taken down with it, fixed it.

I'll write a retro on this to give more details into the whole process.

Already, I would like to thank you a lot for your help.

In particular, @amberwolf, you've been absolutely instrumental in helping me from the start. I couldn't have move forward to the end without you.

I saw that your signature includes a link to a patreon page or something. Is that still a good way to thank you? Are there other ways too? Money is a resource that is not too abundant with me at the moment. If there are other ways to thank you that are at least as good, let me know. Otherwise I'll still be happy to chip in what I can.

Again a huge thank you for all the help

 

[Victor Dupont]

@amberwolf , just wanted to touch base with you, to know how I can thank you. I really mean it.