Can I bridge over a dead cell?

[Number21]

I have a bunch of 8s li-ion packs. I need to use them to build a 14s battery by putting 2 in series.

That leaves 1 extra cell per battery pack. I don't want to destroy the pack and heavy plastic enclosure, and I could not remove that extra cell unless I saw it out. Instead of that, would it be possible to drain 1 cell down to zero volts, and bridge across it making a 7s pack out of an 8s? Will that one dead cell cause a problem?

 

[stok]

yes it will cause a major problem. rather electrically disconnect the cell in the pack and "jump over" the cell or you can connect it in parallel with another cell, so that you have only "7" cells in series and balancing issues.

 

[Quattrohead]

Just move either the + or - wire over 1 cell.
Adjust the BMS to the new cell count otherwise you will get an error.

 

[stok]

Just move either the + or - wire over 1 cell.
Adjust the BMS to the new cell count otherwise you will get an error.

this is the best solution +1

 

[MrSparkle]

or you can connect it in parallel with another cell

I think this might also cause different problems.
The only way I would do is bypass it completely.

 

[yabert]

I have a bunch of 8s li-ion packs. I need to use them to build a 14s battery by putting 2 in series.

Umm! you drop 12.5% of capacity by removing 1 cell.
Why don't you build a 16S battery and simply reduce max voltage a bit? 4V x 16 is 64V.
I know Victron and some other can be use at 66-67V.

 

[MrSparkle]

build a 16S battery and simply reduce max voltage a bit? 4V x 16 is 64V.
I know Victron and some other can be use at 66-67V.

From 4.2 down to 4.0 (/cell) also reduces capacity.
Though if both alternatives are about same reduction, then I agree this suggestion sounds better.
If all components can safely handle up to 64V (48V nominal) then I see following benefits:
1 - no need to alter cell-connection to bypass.
2 - better for health of the cells, thus longer life span if charging only up to 4.0V instead of 4.2V.

 

[TM48]

3: And no fire