Troubleshooting Dead or Damaged P Groups. (SMART BMS)

Hello all,

Ive got some 10s4P Packs laying about that are in perfect condition balenced ready to go besides 1 P group being dead in each pack.

3 Packs

Groups 5 , 6 , and 10 respectivly.

My objective is to if possible revive cell groups (that mitght be between 2.3-3V)

Avalible to me in terms of BMS are the following:

Bestech80a discharge bms

Does anyone have any tips tricks or advice on the best way forward - without replacing the groups.
Ideally im trying to determine if the location of the group itself impacts the abblity for the BMS to preform its function.

EG. it would seem if group 10 dies, things charge no problem. if its the mid section of the pack, balecing struggles to occur. takes much longer but does eventually balence out.

Open to ideas - hoping for a contructive platform that others can use later down the line to solve such situations.


i will ping some expert battery builders to help out:

@ZachTetra @Skyart @MrDrunkenMobster @JoeyZ5

sorry if i missed someone, there are too many names to remember, please forgive me :cry:

Batteries balance by draining the highest voltage one, I would manually bring the lowest group to above the rest then let it balance. LTT is an easy one to use since you can see what’s happening live

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Yea if you have a lipo charger that can do 1s, connect just that group up (5, 6, or 10 and double check polarity) and charge it slowly until it is above the average voltage on the other cells. Then go into the smart BMS setting and set “Balance only when charging” to off. It will then balance all the cells to an equal voltage, but might take a while.

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He might also have to set the Start Voltage a touch lower than the voltage of any cell and to whatever voltage he wants to balance to.

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You can also just use a regular 18650 charger and some fuckery


Fuckery indeed


Perfect example :ok_hand:


So I’ve got most of the cells charged balenced overnight playing with a lower charge 1a hopefully for less vdrop. Found using balence while charge on and off and changing the start value for it to slow down the 6-10 groups that are well balenced from reaching overcharge.

It’s a bit tedious though to constantly do it delta now less than 0.6v

Could I prehaps just unplug the postive lead of that group? I’ve had weird BMS backlash on me doing that before. Wasent well designed in general though in fairness

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From the BMS?

Delta of 0.6V is definitely not balanced. You should aim for at least 0.1V, preferably 0.03V or lower.

And do not disconnect the BMS wire permanently, they should all be connected.

What are the voltages of the cells? (A screenshot of the BMS screen would help)

I’ll trry and screenshot each pack with the LTT and with the FlexiBMS

This is exactly what I do lol

This was before I wrapped them lol

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This is probably my worst pack - had it for over a year it’s been my abuse pack for extreme testing (it’s seen water damage and eveyrhing under the moon) recently lost group 10 fully and 9 is only recently acting up (discovered on the oringinal enertion bms that was delivered with this pack that the pgroup 9 pin broke off (the BMS side)

Plugged into LTT to check and see the above.

(Two other packs in question are new. Never used or used 1-2 cycles. But I shorted one of the groups trying to remove the pins to swap them to a 13s connector for the flexibms) I now know how to remove pins correctly lol… will add screenshots.

It does seem to me that a BMS that has direct access to + - and also the positives of the balence wires is much more capable than one that only has postive from the balence s and is otherwise charge only…

In the case of the LTT BMS seeing as it technically is a discharge bms but only connects to the negatives (other than balences) seems to work most of the time but has shortcomings.

Aka if you have 1-10 and group 5 is unreable/dead/ or something is wrong.

Groups 1-4 will balence and 6-10 will balence. But getting 1-4 to balence with 6-10 seems near impossible as it seems to try to push all the current into the faulty group (probably to revive it)

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IMO, something else is going on.
These “passive” balancing BMS’ just discharge each cell, when required for balancing, using a resistor and don’t move charge from one cell to the other. They can’t bring any cell’s voltage up, just drop it down.

Some BMS controller chips do divide their cells into groups of five though. But the BMS setting will apply to all cells so even if there are separately monitored groups of five they should all be brought to the same range of voltages. Unless that BMS is all software controlled, via a MCU, and doesn’t use one of the BMS controller chips

Weird what that BMS is doing though.
What are your balancing voltage threshold and allowable balancing voltage delta settings?

I’m not a pcb expert but this BMS seems to be on par with flexi lite. Flexi seems better both can do the “active balence feature both during charge and outside of charge.

But I can say for sure watching it do what it does. It literally is taking say 10-30mv from a high group and feeding it into a weaker group which seems to work well. On my perfect pack this BMS needs only a minute or two to make sure eveyrhing is within 10mv or less

Again though I think there’s something to do with if a BMS has that + - main lead access. And of course is software controlled (which the LTT is)

Just took out that really old pack. Still can’t get group 9 to go above 3v for very long. Did manage for once to see it hit 3.078v. ( but it required me to have 4.35 as cell overvoltage which then the cooldown is 4.15. )

Once I got over 4.20on all cells the last group finally started to rise

I’m still wondering how to use these features correctly

Is this happening during charging?
If so then the charge is not being shifted from one set of cells to another. Charge is being drained from one set while the other set is still being charged up (increasing its voltage).

No it happens outside of charging, in addition I can do it during charging as well. (As in there’s nothing at all connected besides a BMS and A Pack

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