So I'm testing~200 cells that I harvested from laptop packs, and I came across some data that I think can be useful to sort bad/good cells out, and I'm planning on getting some feedback from you guys.
So this is it:
step 0) charge to 4.2v, wait for two weeks and take out <4.15v cells.
step 1) Discharge some cells down to 2.9v with a low current, just so that they only bump up to 3v after I stop discharging. This is to "ensure" that all cells were discharged to the same voltage/level, because some cells kept bumping back to 3.4, 3.2, 3.7v after discharging at like 0.5A.
step 2) Charge them up to 4.2v, write down the mAh. For this I am using a Liitokala Lii-S6 (bought by mistake, it's only a charger and will not do discharge tests).
step 3) Do a NOR test on a Liitokala Lii-500, discharging at 0.5A (choosing 1A charge rate at the display)
step 4) Compare the charge and discharge capacity of the cells.
Sample values from some of the cells I have:
Kind of cell discharge |charge | resistance | percentage of charge that went out vs in
Red Sanyo 2236| 2393 | 15 | 93,44%
Pink Samsung 2323 | 2493 | 20[size=small][size=small] [/size][/size] | 93,18%
Red Sanyo 2254 | 2369 |33[size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size] | 95,15%
Red Sanyo 2205 | 2374 | 29 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 92,88%
Blue LG 2207 | 2337 | 38 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 94,44%
Blue LG 2133 | 2442 | 125 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 87,35%
Grey LG 1709 | 2122 |90 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 80,54%
Red Sanyo 1665 | 2293 | 63 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 72,61%
Also, the Lii-500 measures resistance, but in a very unprecise way (same battery gives a lot of random readings if you just keep taking it out and putting it back in, same slot). I also know that resistance is exactly what I'm talking about, the cell needing more charge than it's able to discharge. I see that the higher spectrum of the resistance values tend to be related to these "bad" cells, just not very consistently.
I'm assuming these three last cells will be harmless to a pack, in the sense that they take a lot more charge to reach the same capacity. I am thinking that this can throw down all the "math" on tools like repackr and lead to unbalanced/unmatched packs.
I am planning on using a cell balancer on this 7s pack, with a cheap 7s bms also, but I am not planning on using a balance charger with it, kinda like what a solar charger would do.
Is this a problem, or am I overthinking?
So this is it:
step 0) charge to 4.2v, wait for two weeks and take out <4.15v cells.
step 1) Discharge some cells down to 2.9v with a low current, just so that they only bump up to 3v after I stop discharging. This is to "ensure" that all cells were discharged to the same voltage/level, because some cells kept bumping back to 3.4, 3.2, 3.7v after discharging at like 0.5A.
step 2) Charge them up to 4.2v, write down the mAh. For this I am using a Liitokala Lii-S6 (bought by mistake, it's only a charger and will not do discharge tests).
step 3) Do a NOR test on a Liitokala Lii-500, discharging at 0.5A (choosing 1A charge rate at the display)
step 4) Compare the charge and discharge capacity of the cells.
Sample values from some of the cells I have:
Kind of cell discharge |charge | resistance | percentage of charge that went out vs in
Red Sanyo 2236| 2393 | 15 | 93,44%
Pink Samsung 2323 | 2493 | 20[size=small][size=small] [/size][/size] | 93,18%
Red Sanyo 2254 | 2369 |33[size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size] | 95,15%
Red Sanyo 2205 | 2374 | 29 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 92,88%
Blue LG 2207 | 2337 | 38 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 94,44%
Blue LG 2133 | 2442 | 125 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 87,35%
Grey LG 1709 | 2122 |90 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 80,54%
Red Sanyo 1665 | 2293 | 63 [size=small][size=small][/size][/size][size=small][size=small][size=small][size=small][size=small] [/size][/size][/size][/size][/size]| 72,61%
Also, the Lii-500 measures resistance, but in a very unprecise way (same battery gives a lot of random readings if you just keep taking it out and putting it back in, same slot). I also know that resistance is exactly what I'm talking about, the cell needing more charge than it's able to discharge. I see that the higher spectrum of the resistance values tend to be related to these "bad" cells, just not very consistently.
I'm assuming these three last cells will be harmless to a pack, in the sense that they take a lot more charge to reach the same capacity. I am thinking that this can throw down all the "math" on tools like repackr and lead to unbalanced/unmatched packs.
I am planning on using a cell balancer on this 7s pack, with a cheap 7s bms also, but I am not planning on using a balance charger with it, kinda like what a solar charger would do.
Is this a problem, or am I overthinking?