Help! Bafang BBS02 shutting down

[AVMontari]

Bafang BBS02 500W 48V mid drive
2 months 500km
Hailong 48V 17.5ah

I’ve done a lot of reading and tried every search string I can think of.

The above mentioned ebike conversion has changed my life and I want it back.

Worked fine for 2 months. All of a sudden after 7km display and motor shut down. Volt meter on battery shows no lights. Battery had plenty of charge.
I charged the battery, took off and same thing happened after 10km. Battery Volt meter was showing no lights.
Next I plugged the charger in for 2 minutes. I unplugged the charger, the bike turned on and was showing full charge.
I have repeated this a few times, I have noticed each time the bike hits 500W it shuts off.

I have also noticed the bike seems to speed up for no reason before shutting off e.g on a flat pulling 200W, all of a sudden ramps to 500W for 1 or 2 seconds before shutting off.

I made a video (3 mins) showing the what happens.

Video 1 just shows the battery lights not working

Video 2 shows me recreating the shutdown issue on a bikestand.

I think it is the battery. I was thinking to get a 2nd battery while I work on a fix for this one. Happy to have a spare. Before I do that I’d like to know the motor isn’t the fault and is somehow damaging the battery.

What do you think?

 

[vfr400]

If it were just shutting off when it reached 500w, I'd say that your battery was worn out.

I don't quite understand what you're saying about the current going up by itself, nor what you were doing in the video. Were you holding the wheel back with the brake to force the current up? If so, what do you mean by it goes up by itself?

Assuming that the current does go up by itself, that would point to a number of possibilities why you're getting cut-offs, but that would normally make the bike slow down, not speed up.

it would help if you give a lot more details about what's going on, how and when. What happens with the PAS? What setting power levels does it happen on?

 

[AVMontari]

If it were just shutting off when it reached 500w, I'd say that your battery was worn out.

I don't quite understand what you're saying about the current going up by itself, nor what you were doing in the video. Were you holding the wheel back with the brake to force the current up? If so, what do you mean by it goes up by itself?

Assuming that the current does go up by itself, that would point to a number of possibilities why you're getting cut-offs, but that would normally make the bike slow down, not speed up.

it would help if you give a lot more details about what's going on, how and when. What happens with the PAS? What setting power levels does it happen on?

In the video I am applying the rear brake with the brake sensor unplugged. Just for demonstration.

Happens on any PAS. Happens sooner on 4 or 5. I never really take it higher than that.

It has happened 5 or 6 times on the road. First couple of times at PAS 5/9. More recent times I have been trying to be gentle on PAS 2 or 3.

The very first time it happened I was on a flat and stopped suddenly, then took off in the high gear. About 30 seconds later it shut off. A few mins later I was able to switch it back on.

On a few occasions after shut off I have been able to get it back by switching it off then on again after a few mins. Other times I have to plug it in before I can turn it back on.

I don’t understand the ramping speed either. It didn’t happen in the video demonstration. One time I noticed the motor whirring louder, I looked down and saw it ramp from 200W to 500w, then it shut off. I was on a slight incline at a steady 17km/h on PAS (from memory). A few times since then I have heard the louder whine immediately before shutoff.

 

[ljmail321]

My bafang bbs02 mid drive 750w rear 17.5 amp hour rear rack battery doing the same thing.
Works fine untill I'm down to about 50 percent battery. After that any accessive battery drain of anything over 500 w causes battery to cut out. Battery indicator says no charge. After a few minutes I can cycle the battery off and on again to get it to power up. But as soon as I give it any significant juice again it just cuts back out. Over and over. If I charge to full I'm fine for a bit untill I'm down to 50 or 60 percent battery again..
I don't think it's the bms concidering the indicated on the battery itself indicated it is dead even though it is not. Also the tail light attached to the battery cuts off as well untill battery is cycled off and on again

 

[soundwave]

the capacity in the batt has gone and what you are getting now is voltage sag and why it shuts down and comes back on but as soon as you pull the amps out of it the voltage drops again and cuts off.

 

[ljmail321]

the capacity in the batt has gone and what you are getting now is voltage sag and why it shuts down and comes back on but as soon as you pull the amps out of it the voltage drops again and cuts off.

Yeah looking more into it, I am assuming I have a low voltage cell. I will measure the voltage across all the calls and make sure ther are ballenced

 

[Fordulike]

Although not an ideal solution, you could use a programming cable to limit the maximum current drawn from the battery.

This may extend your ride time until the battery cuts out, but will blunt performance somewhat.