In this video, I'll show you how I tested the two dead cells I found in the C3 battery pack I tore down in the previous video:
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http://youtu.be/C9zqho7Bk5kThis pack seemed to have 3 good cells at 3.9 - 4.2 volts and then 2 dead cells at 0 volts. So I soldered on some charging leads onto the battery management system (BMS) board after testing continuity between the cells and the BMS board.
I set my bench power supply to 4.2 volts and 0.1 amps and connected to each dead cell in turn. The #2 cell would rise up to around 0.5 volts but not above and after disconnecting, it dropped back to 0. Cell #3 would not move off 0.0 volts.
So, I determined that those two cells are not useable and need to be replaced. I ordered a pair of new Samsung 18650 cells, rated at 20 amp discharge and for power tool use. When those arrive, I'll see what it takes to get the old cells removed and the new ones installed. Stay tuned for that repair video.
This pack could cycle between charging and disconnected when connected by the pack terminals to my bench supply. This must be the signal they send to the charger to indicate a "defective" pack.
The BMS must turn on for a bit, then check the 5 cell voltages and if any are out of spec. it'll disconnect the cells from the charging current. I showed this in the previous video. This is likely done to protect the cells damage. In this case, the dead cells present an almost dead short to the charger and if 20 volts were applied across the 3 good cells, they would over charge and could explode.
This BMS board is really quite sophisticated from what I can tell. I handles charging, cell balancing, battery protection from over and under voltage and has a fuel gauge function.
I'll do some testing of these other aspects in some other videos, so be sure and check those out.
If you have any questions or have done any research into these battery packs, post that in the comments section below.
Thanks for watching!
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https://www.youtube.com/watch?v=SVGc3ks22zI