BMS fails pack

[mxer]

Apologies first off as it's a hoverboard battery (i know I know, but it's my kids). Same principle as an ebike battery hence the help here I need.

Take a look at the picture to see cell voltages at present.

HVC/LVC is present hence battery shutting down and charger saying its full, so battery and board is useless atm.

I have removed the bms to eliminate any board issues and it works flawlessly.

So I need to balance the pack up again to stop the bms shutting down detecting imminent danger!!..

I do have medics for Lipos but wrong connections which tells me I shouldn't be using these to balance the cells so give that a miss.

I have heard/read about draining down certain cells but trying to get my head round doing this is hard as all batteries are connected in series or parallel?? Surely draining down one cell is not possible without pulling down others in the string?.

I hope you guys can help and hopefully I've explained what I would like to do.

Thanks all in advance, and apologies again for not being a ebike.

 

[Deleted member 4366]

Presumably, the BMS is doing its job correctly. If you charge without it, there's a fair chance you'll damage something. You need to balance it before you go any further. Drain down the high one to about 3.9v with a 3v or 4.5v torch bulb. The low one needs to be charged to the same with a single cell charger or any USB charger. When charging, you must keep an eye on it to stop it at 3.9v.

 

[mxer]

Thanks d8veh, I've managed to get the 4.15v down to 3.9v using a 12v bulb.

Your an absolute genius, never knew about 5v usb charger to bring the low cell up to 3.9v fantastic, cheers.

My balance charger has died so was puzzled how to raise that cell, cheers

I have ordered a bestech 10s bms in case this one's duff, but will monitor and report back..

Really really appreciative of your help, thanks

 

[mxer]

Does this look right?, 1 draining 1 charging

 

[Deleted member 4366]

Looks OK to me.

 

[mxer]

I'm getting really close now to all cells at 3.9v which thanks to you d8veh is fantastic, thank you

Once I reconnect and solder the bms back on am I best to charge the battery (via it's correct charger) or run down the battery on the board using it?.

Cheers

 

[OldBob1]

Welcome I would check the output voltage of the original charger and if thats OK charge with that, but leave on after charger has stopped charging to allow BMS to balance the cell pack.
Good luck
Bob

 

[mxer]

Great advice thank you Bob.

I put on the charger as soon as all cells matched 3.9v after an hour or so charging stopped (green light) one cell hit hvc 4.18v while others resting around 4.0.

I have left it green light and slowly the high voltage cell is lowering 4.15 now while others are rising. So I'm guessing the key is to just leave it and monitor.

I'm off to bed now and reluctant to leave overnight so will terminate balance charging which is a shame, but I don't trust the pack yet (its in the oven atm, lol) so will continue tomorrow.

Thanks again all for your quality time and help,


Cheers

 

[Deleted member 4366]

Once I reconnect and solder the bms back on am I best to charge the battery (via it's correct charger) or run down the battery on the board using it?.

Cheers

Correct.