G'day Phil
Having already opened your battery - this test you have completed really outlines the main sections of the battery. The total should be your readings + ~4.1V for the cell block connected directly to the
BMS.
That's why you get the reading of 41.9V however,
Sounds to me that cell block #1 could be faulty/failed. What happens here is your other cells will overcharge and your total reading will and could be within range, however once you draw substantial current through the cell, the voltage lowers to the point of your
BMS cutting out.
If you find your battery is charging quickly, or quicker than normal then your
BMS could be cutting out due to the cells overvoltage - your charger then thinks "oh my job is done, I'm switching off now" and
you "think" you have a fully charged battery - when really it's just a matter of discharging the over charged cells before the
BMS cuts out again.
Considering your readings, it would pay to inspect each cell block individually.
Here's how to do this: [scroll to the bottom to get to the point lol]
The biggest concern here is putting to much heat when soldering. You will need some locking pliers or something to 'hold' onto the nickel battery tangs so you avoid putting any heat into the cells. The nickel heats up extremely fast - and is overlooked alot when soldering.
1. Have a real good look at your battery, take a picture from the top and bottom - so you can re-attach all of your
BMS wiring when you put it back together. Wear some protective glasses, as there is quite a bit of solder, and you may fling some around doing this
2. At the rear end of the pack (non-
BMS side) you will see a big clump of solder. Since there is so much, you have to be really concious of the heat - or you could easily damage your other cells while doing this.
Use locking pliers, or 'helping hands' or a bunch of aligator clips EITHER side of the nickel battery tang. If you have an adjustable heat soldering iron
great - otherwise use a 40-60W iron and prepare your solder tip so it will draw solder away quickly as possible. Touching the battery tang while using solder braid or a solder sucker will also be a good idea. With gentle force, the battery tang will come apart.
3. De-solder all the
BMS wiring from the top of the pack. Remember to mark the wires or positions, the cable will sit back the same way anyway, but at least you will be clear on what goes where.
4. Remove all the red taped protective cardboard, take the sticky tape of both sides of the pack
5. Remove the
BMS - be very careful again with the direct GND connection (
BMS-[D]) as this is another big battery tang with heaps of solder on there. Try drawing the heat away from the cells using your tools like above.
6.
BMS removed and everything else, you should be left with your pack, and a wire that was soldered to
BMS+ you have removed. Starting from the rear (where there was no
BMS) gently pull the pack apart. Again its protected in the middle with the red adhedsive cardboard. You can split the pack enough to test each individual cell block 1 by one. If you get to the front, and you are sure the failed cell is there - then you can decide to de-solder the pack completely. The solder point inside, up the front is the most difficult because the wire is pushed through the battery tangs, then heavily soldered. If you try to heat that part up while attempting to pull it apart - you can easily add too much heat into this and damage the cells.
You should have some work to do with the above.
Once you get the readings of each cell (using your multimeter set to 20V range) post them up here
Hopefully it's just 1 block or just a few cells and you can fix it before any further damage.
Peace out
MM
