How do I diagnose my battery (random shutdowns)

Voltron said:

Nice probe hack.... what kind of displays do you have, i.e. when it shuts off do all the displays or voltage LEDs go dark too, or does the power just cut out but leave power indicators lit?

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I just have a basic twist throttle as a display.

Yeah, when it happens, my throttle indicator (which displays the voltage ) drops down to 20 or 30 volts. That's when I'm in motion. Sometimes, it happens when I'm just taking off or sometimes I haven't even mounted the bike and it happens. In that case, it drops down to something like 19v. I never paid too close attention to the figure in both cases. I just know it tells me a number that's way lower than I'm used to see.

Touch wood. Since replacing both extension wires I use to bridge the distance from battery to controller, I've been riding free of any random shutdowns.

I'm hopeful that this was indeed the cause. The wires I was using were not the best. I had spliced 2 shorter wires for each together and added some solder to ensure that they didn't pull apart easily. My soldering skills really sucks and the join was the narliest thing you'd ever seen. But it did the job for the past 6 months or so.

I aslo added a butt splice recently to make more length with a thin 16 AWG wire. I had to do the same thing on the battery positive. Maybe butt splicing such thin cables (even though they only spanned 5-10 cm all up) creates a sag in voltage and could have been responsible for these random shutdowns. Is that possible?

Anyway, I not only replaced the extension leads with 10 AWG wires but I also changed the splced extension on the battery's positive with a piece of 10 AWG just to be on the sure side.

Hopefully, I'm not jynxing myself by saying this but if it turns out that this problem is solved, I'd like to thank everyone for helping me figure it out. Especially thanks to whoever it was that mentioned wire corrosion. That made me question those extension wires.

Quick update on the situation. Since changing those extension leads, I've had no problem.... Until today.

I decided to do a non stop 37 km journey (I've been holding off since my good charger blew and my back up charger is slow and under charges to 53v)

And about 5 km away from my destination (maybe a little more), it happened. At first I thought it was just an lvc. I was getting low and seeing my indicator drop down to 45v (un-throttled). Which surprised me because I usually make that journey with at least 46v left at the end.

When it happened, I assumed it was an lvc but when I looked down to the numbers of the indicator, it was floating at around 13v. Usually, when I get an lvc, I see a nice static 42.5-42.7.

I pulled over to check all my connectors. I unplugged and plugged. And I didn't get a spark or any power again. I had to mostly pedal the rest of the way (lucky I was just about there). I did manage to make it work intermittently by unplugging and plugging a few times but every time, 13v after 30 seconds or so.

I can't say that this cropping up again rules out the quality of the wires I replaced as the cause of the issue initially since I've been shutdown free for nearly 2 weeks But considering that it happened after a long 30 km ride and with a drain down to pre-lvc levels, I think voltage sagging might be part of it. I tested my wires for continuity and checked the connectors. They were fine. I'm hoping that after a 3 hour charge, I won't be running into this again.

Bro I feel your pain its infuriating with this stuff.

Quick tip if you want to probe the balance leads just grab a single strand wire used for hobby electronics and shove it in the jst connector for easy probing.

From what I can gather from scrubbing lightly through your ordeal, it seems that your battery is 6 months old plus. So considering is probably one of these cheap Chinese crap (of which I own one, never again) I'd put into mind cell degradation especially if you were using every day.

My chiniese pack at the end of a 30km round trip starts to sag a lot and the BMS starts cutting out.

This however should happen constantly if its the case, however for you it seems very intermittent so its unlikley.

If I were you Id just change the BMS