Strange ebike shutdown

[drebikes]

Hi all,

I was wondering what your thoughts are about this fault. The ebike electrics have ran since 2014 just fine, with no issues outside of dodgy connectors that had to be swapped along the way.

Some data:
*Battery 14S5P Samsung 22F 2.2Ah cells (state of the art in 2013 )
*Infineon inverter from EM3EV
*9C motor until 2019, Q128C since
*Yearly usage ~ 6000 km / 4000 miles
*Average consumption measured 5.5Wh/km // 8.5Wh/mile - it's an almost EU-spec pedelec, power a bit over 250W, top speed assisted 25kph/16mph
*estimated number of cycles for the battery ~380 - you know it's hard to get an accurate number, take this number with a grain of salt 8)

The issue - yesterday I was running it a bit low, but the battery voltage was just above 46V or 3.28V per cell when it just cut. Like complete shutdown, onboard computer, everything. 1st time it ever did that in 6 years. Pedaled up the hill to home and measured battery HV - no voltage on DC. Shit. Did I grill the battery pack? About an hour later, DC is back at around 47V OCV, very weird.
Then I put the bike on the stand and let it run with the wheel in the air (no load), taking about 25W. After a while it cut again, same sympthoms - no DC at all. It came back after several hours, but not before I physically disconnected the inverter from the pack.
Once DC came back, it could be charged overnight, and now it seems fine.

So wfh happened yesterday, why a full systems shutdown? Battery voltage seems an obvious culprit, as it was running low, but not that low. A dodgy cell may lead to this, but how? The BMS does not report cell (P-row I guess) voltage in a way I can see without dismantling the pack. I'd like to diagnose as best as it can be without cracking open the battery. The culprit may be somwhere else (controller?) though I don't see how; that's why I'm bouncing the question to you. The conversation in my head ran out of steam this morning.

Thanks for reading the long prose.

Cheers

D

 

[john61ct]

Sounds to me like nothing wrong, just the capacity of the battery is reduced, resistance higher from wear.

Did you really get 7 years' use out of it? That's amazing, try to replace it from the same supplier! How many cycles total do you think?

Better longevity would be achieved by stopping at a higher SoC% each cycle.

Depending on the C-rate an LVC set at say 3.5Vpc, if high amps a bit lower, at low current a bit higher.

Resting voltage should settle at 3.55V or even 3.60V after cutoff.

Letting it get drawn much lower accelerates wear reduces lifespan, avg DoD is a huge factor in that, along with C-rates, temperature, charge termination point.

 

[john61ct]

Adding a CAv3 will give good insight, help you manage the LVC and actual C-rate get even longer life out of your next pack.

 

[Hwy89]

That battery has had an incredible lifespan. You really can’t fault it for getting a little weak in it’s old age. My guess is that one or more of the cell groups are faltering and the BMS is shutting down. It isn’t unusual for the voltage to come back up a little when the battery is at rest and reset the BMS.
You could open the battery and measure the voltage of each group and possibly manually balance them but after that much use I would suggest just replacing it.