If you have been following my Shay restoration thread you know that I needed to separate my 4 cell pack to two locations. This was a good idea, but caused me a bit of grief. Fortunately it tuned out well. I thought I should share what I learned.
My mistake was to assemble, charge and test the pack then dissemble to remote mount one cell. The protection PCB sensed the removal of one cell from the pack and registered a fault; thus shutting off the output power. Re-connecting the external cell was not enough to bring the pack back to life.
When I could get no output I suspected a broken connection or dead cell, so I completely dissembled the pack and cut the PCB free of the heat-shrink I used to cover it. I found no broken wire, no shorts and all of the cells were within .01V of each other. WTF, over!!!
Time to hit the net in search of answers. There is a lot of stuff out there on Li-Ions. Lots of it speculation or just plain bad information. The light bulb went on when I read the technical data sheet for the TI chip that is the heart of most Li-Ion PCBs. I discovered that by assembling the pack, then disconnecting one cell the PCB’s brain thought one cell had gone bad and shut down.
OK, so the PCB needs to be reset. How to do that? The technical data sheet wasn’t so clear on that. One method mentioned was to present a charge voltage to the pack, but my smart charger sensed that the pack was in failure mode and would not even try to charge it.
Back to the net. I found a sketchy video with a method to revive a laptop pack after changing out a cell. He demonstrated momentarily jumping the PCB + Output to the last cell of the pack’s + terminal for just a moment while under load.
I tried it and it worked!!! Son of a gun. I could have done that without tearing everything apart and saved a few days.
To review; To reset the PCB that has gone into protection mode from a missing or undercharged cell you simply place a load on the pack output, then momentarily jump the + from the last cell (B+ on my PCB) to the PCB Output + (P+ on my PCB).
WARNING - Replacing cells in a pack is not recommended and can increase the fire hazard. Charging an over-discharged cell can also be dangerous. Use this information at your own risk.
@Rooster - Feel free to post your A-Bomb pic here.
