I will get straight to it: I let my 10s8p battery pack sit for close to 2 years. I went to charge it up today and this was the graph shown in the BMS app:
I was told to not charge below a certain delta but unsure of if this pack is past a saving point.
Any help would be appreciated.
if it’s been 2 years, i wouldn’t
that group being .4V off from the rest could mean a very unhappy cell/more and it likely is forever going to be unhappy
It’s probably safe to charge assuming group 3 drained because of a cell that has higher than average self discharge, BUT this pack will probably never be happy again since it’s evident there’s at least one questionable cell here.
Appreciate the help
Thanks for the help
Follow up even though it isn’t the right topic: would this be ok to put for sale on the parts market?(unfortunately getting out of the hobby) I would of course stipulate that it has one bad cell.
Probably not worth it
I’m no expert here but it’s one group that’s out of balance after possibly draining for years and it’s way above the “dead cell” voltage. I’d probably try to charge it in a very safe environment and see if it 1. balances up and 2. discharges evenly after that. If not, scrap it.
But on the other hand if it’s just to sell it, maybe scrap the battery and sell it without it. I wouldn’t wanna pass on a potential problem to a new owner.
though it may be above the “point of no return” voltage, the evidence of one of those cells self discharging much more/faster than the rest is a telling sign it’s not as healthy. it might be ok but it won’t last long at best
I’d still stick it up for parts . That’s still at least potentially 72 cells that are fine. It can be dismantled and used to build a new pack
I’ll charge it and report back on where it balances out
it would take a lot of cycles to balance out. In the bms settings, there’s a way to turn on static balancing, I just dont know how to do that in your version (ios) of the app
I was able to turn that on right now, I can see where it balances out after that.
Two years is a long time, it doesn’t take a lot of differing self discharge to get that level of imbalance, as such the cells are likely still okay based on this information alone.
Assuming the BMS is bypassed, the risk of using it unbalanced is that the lowest cell group could go to zero during discharge as the vesc doesn’t know it’s lower than the other cells, it only sees pack voltage. Then, after this event is where charging becomes an elevated risk of fire.
I would balance the pack manually with a bench DC power supply, or an 18650 charger if you’re not well equipped.
I screwed a wire to each end of a block of wood 60mm long, and soldered pins at each end. The block of wood fits into the 18650 charger / capacity tested, and the pins slide neatly up a balance connector. Works great, and doesn’t take long - unlike waiting for a BMS passive balancing circuit, which could take days.
I’ve also balanced with a 12v halogen light bulb the same way, but this took way more admin so I don’t recommend it.
If the battery goes out of balance soon after, that’s when I would bother thinking about building a new pack /repairing. A cell with a high self discharge is advertising the fact it wants to drain it’s buddies’ energy, potentially making fireworks happen.
