Ok home now. Lights on vesc/metr/remote are behaving normally.
Pack tests 38V
Weird, it was fully charged when I left.
Leads on charge port on BMS read 10.5V
VESC works perfectly on another battery.
Issue seems to be the BMS but I don’t have another 12s BMS with the same balance header to swap and test
I would take that BMS off even if you don’t have another one, and not ride that battery yet.
Unless you find the root cause, how do you know the BMS didn’t drain your whole battery. Although without anything getting hot, that’s not possible.
How long was it sitting? Are you 100% sure it was fully charged or only 99.99% sure?
Done and done. I fully agree. BMS balance plug is disconnected and the whole pack is sitting alone not connected to anything. Will be tracing balance leads later to look for crosses or shorts.
Charged overnight at 1.6A. LLT showed 50.2V and all groups balanced. Put it in an Uber for a 30 minute trip, waited at a spot for ~20 minutes then rode about 5 blocks, it cut out while riding, while at rest.
I made a jumper from a an extra wire harness i had and a jst female connector plugged into a jst male pcb mount connector to test a pack with a suspicious bms. Use any jst connector with the correct pitch, probably 2mm. I dont have a pic of the 13pin version on me but here is an old pic of the 2pin i made to test and balance a low p group on a 10s6p that was out of balance when i built it and I didn’t want to wait for the bms to do it’s thing.
Edit: removed wrong pic
Maybe that’ll help if you have enough junk lying around
I can make all that but idk what exactly to do with it yet. I’m really wanting to avoid tearing off nickel, anything I can do to avoid as much of that as possible would be great.
If you can get the to the balance connector you should be able to manually test the voltage. What you find will tell you what to do from there. If you can make an adapter (do not fuck up the phasing) and plug in a know good smart bms you can use it to check the pack
Solid print tpu would be my recco.
That’s something I’m lacking right now, I have one on the way but it’s not in yet. Do you think it’s dangerous to leave the pack disconnected until the new BMS comes in? I have a backup pack to use in the meantime (dumb BMS)
Least dangerous thing would be to have the pack disconnected. No load = safest
Yes it’s disconnected but should I do more? Should I desolder series connections and free up the p-groups? I would prefer to avoid a fire while I’m not home…
Do you have a multi meter? Test at the pins, carefully not to short them, and it will get you your voltages. Cheap meters at harbor freight work good enough If you’re in the states. You can probe at the small metal retaining pins on one face of the connector. They are very close together so use sharp pin type probes with tape covering all but the very tip if you don’t have steady hands
All cells are just above 4v testing each group. I feel slightly better but still worried I messed something up.
No load = no electrons moving about. Should be fine. But grab a multi meter and measure voltages between p groups. See if it’s still balanced. Might find a bad group in there. Even still, not too bad for danger. I mean, maybe don’t store inside until you can get to the bottom of this.
Your batt is likely fine if they’re all the same volts. Probably lost the bms. You said the esc works fine with a diff battery? Not much else to check then right? Bms really looking like the imposter here. Sus as all hell…
Now the big question is why?
LLT is supposed to be the go-to smart BMS, and this one has less than a year of use (2 different packs of identical cells and config)
How could a BMS go bad like this?
Great explanation! Gotta have the sharp pins. Never taped em before, but a damn good idea!
I HATE bms’ for this reason. I dunno man. I’ve had nothing but problems with them.
I’m currently putting in a flexi for the battery I’m building. I hope this one will be the first one I’ve owned that didn’t fail.
How do I join team #FuckBMS
Smarter folks than myself could answer this better, but the poor bastards get pretty hot when trying to balance cells all the time. Many smd components and I dunno if they were ever really designed to be in warm enclosures with heavy vibrations attacking them all the time. Electronic shit fails. Likely for reasons haha
