Well, it's quite possible that this high altitude is making me stupid. There has been a recent rash of dumbass maneuvers on my end.
Recently i wired up an cell_man 9FET infineon controller's power leads backwards. A puff of nasty smoke came out of the 10S 5AH 20C turnigy lipo pack i hooked it up to, surprisingly, the controller lived..!
The connectors were quite charred afterwards.. after cleaning them up, i noticed that only one 5s lipo brick was smelly.. and seemed to have 1 cell WAY off..
So i plugged it into my 2x 50w halogen array to see if it would transfer current.. nope. The cell at 0.300V would drop to 0V in an instant. I figured.. i had burned a connection in the lipo.. so i had to investigate.
There's the dark spot, looks like cell #5 got hit.
More gore after taking the tape off..
WOW.. something fried in there didnt it..
The padded tape that protects the top of the pack had solder on it and scorch marks. Looks like the solder leaped off the circuit board!
LOL.. yep, that's exactly what happened. It cut the connection from cell 4 to cell 5 almost completely.
Now i'm wondering if the solder is designed to do this, in order to prevent even worse shorts that lead to a runaway thermal reaction inside.
Perhaps this pack is not toast.
3.98v on this cell looks good to me. Let's rejoin the cell bridge and see what happens.
First, tape off the adjacent cells adequately for the love of god. You don't want to cross-solder any of the cells and have the solder explode / vaporize in your face, killing a cell in the process!
Another thing to note when soldering here, is that the solder used on this pack is a bit different than the standard lead/rosin core stuff. You can definitely blend standard solder in with it, but you can't really solder to the aluminum (???) tabs so well.. you'll have to mix up the lipo pack's solder with yours.. you'll know it's mixed as the solder used on these has a very different smell when heated up..
Bam, there it is.. 10 ga. copper wire soldered between the pit of despair, doing it's job as a bridge
( 10 gauge is fine here since this pack is used in series, if you're doing this same repair to a turnigy nanotech, 45C lipo etc though, you might want to beef it up and go for 8 ga.. )
The CellLog 8S approves of my repair.
..and so does the iCharger! the IR on the bridged cell is actually reading at a lower resistance level than the other cells.
Note: the iCharger is awful at measuring milliohms, it will provide a random variance of +/- 5mOhm, which is why these numbers are all over the board. But it does a good enough job of determining if there are severe anomalies.
A discharge test at 3.85A confirms that the cell
Next: i will do a full discharge test of this pack. But i am quite confident going off the IR that this cell has not received much damage, if any. It hasn't puffed or change voltage.. these are good signs.
If you have a pack that has been shorted, and hasn't puffed.. you may want to inspect it for this exact kind of damage. This repair is not difficult.. definitely one of the easiest lipo surgeries.
Hope this helps