Due to the fact that salvage cells come from different packs…. And those packs are at a different state of charge…. It’s a wise move to pre-balance any salvage cells by wiring them all in parallel and applying ~3.65 volts.
3.3V chemistry has an almost perfectly flat discharge curve through a huge branch of the capacity…. So just attaching them in parallel is like cutting a 2×4 with a nail file. You really want to apply a voltage that brings the chemistry up into the steep part of the curve…
- 3.2V too flat
- 3.3V too flat
- 3.4V transition
- 3.5V looking good
- 3.6V steep part of the curve
- 3.7V that can work but more than needed
- 3.8V they will tolerate it
- You can go higher, I dont
If anyone tells you some NONSENSE GARBAGE like…. “The cells tend not to drift, so I don’t use a BMS”
- Those are the guys that burn down your boat
- Those are the guys that burn down your RV
- Those are the guys that get catastrophic failures after 3 or 5 years
- Dont be that guy
If you can’t set up a BMS then you really do need to check the cells regularly to make sure they are reasonably in balance. This can’t be done in the middle of the discharge curve, You have to do it while they are empty or full.
See how easy this is with Headway cells? They are stupendous. Compare that to my soldered pouch cells… Sigh.
… The next step is to short the negatives, set the CV/CC power supply to 3.65V, confirm that with the four digit fluke, Set the current to 5 amps, Attach the leads and walk away.
- 5 hours will be done
- 1 hour it will likely be done
8Ah x 4 cells = 32Ah
Get them to +/- 20mV (0.020V) resting imbalance
-Schindler