Charging Lipo batteries in series

[J-Dogg]

Hi, so i have these batteries that operate on 11.1V and i want them it to be 18v But after pulling them apart they seem to be wired in a way that each battery or "cell" has its own wire between one another. What i want to know is weather or not i can remove all those inbetween wires add the extra 2 batteries on the end to get the required voltage and just charge the batteries from the end facing positive and negetive.

 

Thanks,

 

 

 

 

[mahyar]

does your bms support 18 volts?

[WereCatf]

11 minutes ago, J-Dogg said:

What i want to know is weather or not i can remove all those inbetween wires add the extra 2 batteries on the end to get the required voltage and just charge the batteries from the end facing positive and negetive

Technically you could, but it's a bad idea. If any of the cells in the series is more worn-out than the others, for example, they'd be unbalanced and you might overcharge them. You really should either just disconnect them from one-another or use a proper balance-charger for charging cells in series.

[J-Dogg]

The charger only support the original configuration so i think i'll just have to get a bit fancy with connecting the batteries that way when they are depleated they can be put back to the chargers specs.

 

Thanks for the help.

[Hackentosher]

The wires on each cell junction are balance wires. When you charge a series battery such as this one, you charge the whole pack to its full charge voltage, then drain the cells that are too high, bring up the whole pack back to full, drain the high ones, and repeat until all cells have the same voltage across them. You'll need to add balance wires to the additional two cells you add and get a 5s BMS or balance charger in order to charge properly.

[mariushm]

No you can't charge from one end to the other, lithium batteries don't work like that. 

 

The charging circuit has to detect the number of cells in series and adjust the charging voltage accordingly. In your case, the batteries are around 3v completely discharged, and around 4.2v fully charged, so the charger detects there's 3 cells in series and configures the charging voltage to around 3 x 4.1v..4.2v = 12.3v

 

To make a 18v battery, you would have to add 2 more cells and make it a 5S battery, which means the charger would have to supply up to 5 x 4.2v = 21v to charge the batteries, and also support to more wires between those extra cells, to detect them and balance the charge between the cells.

 

A charger that can charge a variable number of cells in series figures out how many cells are in the series by measuring the voltage of each cell using those wires between the cells. In your 3 cell battery, the charger reads voltage on the blue wire, and reads voltage on the white wire, so it knows there's 3 batteries.