Due partly to my little crash on Monday morning, I didn't get this started until a couple of hours ago. But it might be fixed already.
First I took off the plastic wrap holding the BMS to the pack, and carefully rolled up that plastic to put it back on for shipping back to RTLSHIP when it's done. Then I looked at the duct tape wrapping, peeling up the strips at the corner/edge where all the wiring goes in, to see if it was across the top like mine, or some other way.
It is across the top, but this pack has some foam padding between the inner and outer layers of tape, whereas mine had thin cardboard. The foam will tear to pieces if I try to unwrap the tape like I did mine, so I have to cut the tape very carefully, all the way thru the foam but not into the second layer of tape (don't wanna cut wires by accident, or nick cells). This took some time, but worked, and then I could peel back the top of the pack's wrapping to see the wiring scheme.
That was necessary so I would know which half of the pack the bad group is in, so I would only have to open up that half (and maybe not even that, depending on how the rest of it was packaged).
It was on the "right" half with teh wiring end towards me; you can se the brown marker I used to trace the balance wires on either side of the bad group from the balance connector.
While there, I also noted that the very corner cell has it's shrinkwrap damaged; I can't tell when it might have happened or why, but there isn't anything else I can see wrong with the cell.
I also noticed that the duct tape comes in at least three types, two of which seem to be much better tape than the innermost. I am suspecting at this point that the pack has been apart before, and the tape under the balance-wires' hotglue is the original, and the other two colors are "new".
I split the ducttape and foam all the way thru right at the seam between the pack halves, on both ends and the bottom, so that I could unfold the pack open, after I found the end with the connecting tabs (opposite the pack output end with the wires on it).
Laid open, it has exactly the same cardboard piece and rubber sheet that my Vpower/CammyCC pack does, to separate the two halves. Niether is glued down.
Pulling those off,
I can see there definitely was a repair done, to the lower left cell in the pic, which has been soldered back to the string on the end. (most negative, IIRC).
There was also a popped weldset on the "topmost" cell gropu on this half of the pack, on teh far left end of that group. Easily fixed with the 80W Weller iron, with about 1.5 seconds of soldering. Couldve been popped already, or done so while opening the pack.
There was a bit of solder debris hiding in there on a strip, probably from the factory but possibly from the cell repair.
Close examination of the rest of the tabs on this inside of the pack (rest was left wrapped in it's tape and foam) found at least one blown-out weld, like this:
THe rest are ok, so I guess it's safer like that.
THis is the group that's bad, with the pen on top of it
I hooked up the group to the meter via balance wires via my contraption made up for my own pack's testing.
So next I start cutting the tabs between cells in the group, to do a binary search for the bad one.
To cut them, I just scored them deeply with a sharp blade, then gently lifted the cut with the edge of the blade from underneath. All cuts were made only to the inside ends of the cellls.
I highly recommend AGAINST doing it this way, becuase you could drop the blade onto cells and short stuff out; i was lucky and didn't but I thought about it just as I finished the last cut....
I first cut the two 9-cell groups from each other, hten the side that drops in voltage is cut in half, then next and next.
Instead of used solderwick braid, thie cut tabs on this one will be fixed with strips of metal (either tin or nickel) that came from a big old console tv, formerly used as ground straps for the CRT.
They're not jus tsteel, as they solder very easily.
I put strips of card stock under the tabs to be repaired, so pressure on them with the iron doen'st melt thru the cell shrinkwrap an short anything.
Each group of cells came back up to 2.1-2.2V by this time, without any input from anything, except for the isolated cell, which had dropped to 0.12V by this time.
I soldered the tab repairs on the other cuts, and started charging that group with the Sorenson on 3.65V 250mA, where it will stay until it gets to 3.0V, and then I'll go up to 500mA. That was about 530am, and was at 2.87V by around 6am. (added note: while typing this, it reached 3.11V so I upped it to 500mA, at 704am)
After it has recharged that group, sometime tomorrow or the next day, I'll test the pack as it is now on DayGlo Avenger for a short ride to see how it works. Since it has a different connector, I'll temporarily solder on one of my big Anderson Multipole connectors to the BMS outputs to do the testing with. If it works ok, then I'll see about getting a replacement cell for the bad one.
If it still shows any issues, I'll further troubleshoot it as needed.
Right now all cell groups except the very first one on that side (the one with the soldered-in cell at the pack corner) are 3.48V to 3.51V. That group is 3.25V. Might just not be balanced, or it might have a problem. I'll keep rechecking it after the rest of the pack is working ok, and as I do testing with it.
Now I'm off to take a nap, as I've dozed off several times typing this.