We can make up the two discharger cables, as we did for Rush D, so you can build your own discharger, or you can get the thing built and ready to use.
Not sure what the availability of the Lowe's shop lights is, but I grabbed 32 of them while I could. 8 are already spoken for.
The dual 300W bulbs allow series wiring, to handle the 250V max that the charger can put out, and the power MOSFET is rated for 8A max, so at least until we find a good alternative, that is the best shop lite to start with. I was thinking that it may be worth trying to track down the importer and see if we can buy them directly.
The videos will go into plenty of detail and will hopefully explain all of this.
The bottom line is that when a pack gets old and is misbehaving. we would like to get it back into full working order, this involves topping to equalize the SOC, then discharging to measure capacity, and cycling to recover as much capacity as possible.
The charging and balancing takes care of getting all the cells to 100%, but because some cells were only being cycled on the low SOC part of their capacity, they have developed reduced AH capacity.
When the fully charged pack is discharged, and we stop the discharge at the point where the weakest cell runs out of AH, we have found the weakest cell and stopped, just where that weakest cell ran out of juice relative to the rest of the pack.
The higher that drop out point is in voltage, the weaker that cell is relative to the rest.
We run a couple of these cycles, and should see the run time and the voltage where this drop out happens get longer and lower in voltage.
When the drop out repeatedly stops at a voltages over 140V, we can assume that a cell has developed permanently reduced capacity due to possible overheating and venting.
If the pack is on the bench, and the connector board and protective cover on the other side is exposed, we have access to each end of each subpack.
With the addition of a jumper, or a fused jumper across the now exposed center taps for the switch and 100A fuse, we can connect the charger terminals directly to the + and - ends of the pack, and both charge and discharge.
We have a feature in the V2.2 code only accessible via the password protected tech mode where we can prevent the discharge detection from turning off the discharge. It will still beep to indicate that a drop out was detected, but it will continue to discharge.
This is the bad cell identifier mode.
With a simple DVM, we can run down the 20 subpacks, and the one with the weak cell will stand out clearly with nearly a volt lower voltage than the rest.
That is the cell/stick that needs to be replaced.
Manually stop the discharge, and mark the stick as one needing replacement.
Of course that cell is being reversed charged, but it is already bad, so we will be replacing it anyways.
At that point you may have isolated the only bad cell, or there may be another just behind like this pack:
This pack had 5 cells that dropped out between 156 and 144V. It turned out that three of the cells were in the same subpack, so by changing 3 subpacks this pack would be in much better shape, and while still suffering from lower than new average capacity, we will have brought all the sticks into better capacity balance as well as better SOC balance.
I think the best time to do this would have been when the pack was first pulled from the car to do the harness install. Just let it run through 3 full automatic cycles,(the cycle data is stored in eeprom) and simply look at the minimum voltage reached for each cycle, and the discharge run time, to determine if you need to change a stick or not.
If you do, pull the ends off the pack and reconnect the charger/discharger to find the weakest sticks, replace or repair the sticks and your probably going to quite happy with the results.
Yes the source of replacement sticks is a problem, but I was thinking that since I have the equipment to replace a single cell, we could have you guys find the bad stick,send it to me, and I can to set up a repair system where we trace the "bad" stick, on my cell level tester, evaluate if it is toast, or repairable, and I can simply replace the bad cells with used ones that have been fully tested, and binned as to AH capacity, IR, and self leakage.
We can replace only the bad cell, send it back to you, and you will have brought the pack back into a useable state for the minimum cost.
The repaired subpack would come with a graph showing each cells performance under high current charge and discharge conditions, so you will have a hard copy of the final test of the stick, so you can be sure of what your getting.
We happen to know where there are thousands of used subpacks just sitting in a closet, and if the used sticks are separated into cells, tested, and binned, a single pack would yield 120 possible replacements instead of a max of 20 of questionable balance.
I will be rebuilding my cell level tester, so it can both charge and discharge the stick as a whole or on a cell by cell basis, all the while recording the process on a graph for analysis. As usual I can come up with projects faster than I can make them happen, but am thinking that since the weather is getting better, we may want to revive the Saturday workshops, so we can get some help with making this happen, and get a steady supply of packs that need help to better evaluate how well the process works.