I built a 12s3p pack with Samsung 25r cells with a LTT/Xiaoxiang 10-15s bms wired as a middle man for charge and discharge
I had my belt break and school was starting so I put it aside for a couple of months. one day I decided to check in on it to make sure everything was good… The first cell was at ~0.15v the second was at ~2.5v while the rest where at ~3.7v! Screenshot_20200621-020100|236x500
I tried to leave it plugged in for a couple of days to hopefully fix the issue but no luck. Maybe the bms takes parasitic power from just the first cell? I dont think the bms draws that much power but maybe I’m wrong? I have a video of the wiring, I could upload it if that would help with diagnosis. Thanks for the help!
Edit: The multimeter confirms most of these readings, however the first cell shows 5.7mv and the second shows 3.8v
Do you remember with which voltage or put away your board. As min if it was fully charged or after a longer ride without charging it?
In general it’s never good to leave your board connected to escs, antispark, discharge bms or other electronics which have a current draw alone for some weeks or even months without monitoring.
Yeah I know it’s not good practice for bare batteries but I figured with a bms it would be ok, also the power line to the esc/receiver/etc. Is interrupted with a xt90 key so they weren’t being powered during the absence. If I remember properly it was near full charge but not all the way there, maybe 3.8v per cell?
It’s exactly the other way around.
For bare cells or packs it doesn’t matter. With bms it matter (there are exceptions for sure depending on the bms)
How ever the bt module of the smart bms is always switched on as long as the balance wires connected. Means it does drain your pack over time.
Omg I didn’t even think about the BT module that makes sense, and I guess if it’s always trying to balance that’d take a bit of power as well but shouldn’t it take it from the whole battery not just one cell?
Why only the first two cells are drained so much I can’t tell. If you didn’t set your bms on active balancing than there shouldn’t happen any balancing without a charger connected.
The bt module by the way doesn’t draw current because it balance. It draws current because it’s just switched on and always try to connect to your phone or computer.
Yeah I understand that the Bluetooth module doesn’t balance I meant along with the module drawing current the constant balancing done by the bms would draw current as well. Anyways I do believe it was set to actively balance but again why just the first cell? Still stumped on this one, I’ve seen other LTT boards that had the reverse wiring for the balance port maybe something got mixed up?
I wasn’t locking it, I thought that only cut off the main power which was already cut by removing the xt90 key. Maybe if I switch out the bad cells with good ones and set the bms to static balance it’ll be ok?
I’m trying to trickle charge the first P group until my new cells get in but you bypassed your bms for discharge? I was thinking about doing that but didn’t think I’d surpass 60A what’re you running?
I just don’t trust a bms for discharge. The only reason I wanted a smart bms was for the bluetooth cell voltage, to ensure my Pgroups were balanced.
Im running a 12s4p molicel p42a pack. Planning on running the vescs at 70a each, knowing that I’ll never hold full throttle for more than a couple seconds
