Balancing 2 LG Chem Solar modules in series

[wer2000]

I've seen a couple of videos of people reusing LG Chem modules such as https://www.ebay.com/itm/LG-Chem-So...a=1&pg=2060778&_trksid=p2060778.c100290.m3507 and was wondering if it is really possible to connect two of these modules in series with a singular bms? Having built 18650 battery packs before, I understand the general theory but fail to see how one can reliably connect two cells which may have slight imbalances in a safe and efficient manner. Anyone have any ideas on how this could be done or why it cannot?

 

[jonescg]

As long as you can access every cell terminal you can apply any BMS you like. Just make sure the cell count matches.

 

[JackFlorey]

. . is it really possible to connect two of these modules in series with a singular bms? Having built 18650 battery packs before, I understand the general theory but fail to see how one can reliably connect two cells which may have slight imbalances in a safe and efficient manner. Anyone have any ideas on how this could be done or why it cannot?

In theory you can; but practically it's going to be somewhat difficult. The wires brought out to the balancing connector are very skinny (20 ga? Something like that) and if you do get a cell fault you can see a lot of current flowing through those tiny leads - which could lead to a fire.

You could do something more complex, like using a resistive divider between the two sets of cells to limit current, but if you do that you won't get very much balancing current via the BMS.

 

[amberwolf]

The wires brought out to the balancing connector are very skinny (20 ga? Something like that) and if you do get a cell fault you can see a lot of current flowing through those tiny leads - which could lead to a fire.

if the modules are in series, as proposed in this thread, where would the current come from?

if they were in parallel, i could see the potential problem, because a cell failing shorted in one module would then pull current thru the sense wire from it to the bms to the other module's equivalent cell.

but in series there are no connections at cell level between two modules, only at the main + terminal of one, and main - terminal of the other.

 

[amberwolf]

I've seen a couple of videos of people reusing LG Chem modules such as
<snip> and was wondering if it is really possible to connect two of these modules in series with a singular bms? Having built 18650 battery packs before, I understand the general theory but fail to see how one can reliably connect two cells which may have slight imbalances in a safe and efficient manner.

if you connect modules in series, there are no connections between cells from one module to the other (only main + terminal of the most negative module to the main - terminal of the most positive module), so there is nothing for an imbalance to cause a problem with, in the manner you're speaking of.

if you connect them in *parallel*, *then* you would want them to be in balance before connection at cell level.

 

[JackFlorey]

if the modules are in series, as proposed in this thread, where would the current come from?

Ah, sorry, I misread. Yes, as long as you have a 32s BMS then no problem putting them in series.

 

[999zip999]

Do balance before installing BMS . The BMS is to keep a balance pack balance. So balance first.