I took apart the first of the defective 25.9V LiPO packs I got recently to try and see what was happening inside. If you just want to find out, then watch the video below. If you want to know the gory details then check out the pictures below the video.
First outer wrap of plastic and tape removed. Feline creature checks out the wiring.
What I thought was a dent in the outer casing of the pack was actually the first cell! This could be very dangerous if it should short out.
Close-up of the damaged cell.
Close-up of the BMS with the individual leads going to the cells.
The BMS leads connected to each cell under the cargo tape.
Double-sided tape holds the BMS to the pack. You can also see the black plastic foam pieces separating the tabs.
The black foam pieces are supposed to hold the tabs in place to prevent them from shifting and shorting out.
The BMS leads are soldered to the tabs which are folded over each other and then soldered in series.
The solder quality isn't great. But it did seem to work.
You can see the globby look of the solder. It should be smooth and rounded.
Uneven and inconsistent soldering.
More of the same.