Thought I'd take advantage of the long sunny days to get the pack nicely balanced before the nights start drawing in again. My pack is 16s EVE 280Ah cells which is working well for nearly a year, but the OCD in me wanted to get the cells better balanced. Have one cell that is a bit below the others in terms of voltage at the top end and then it's the one that drops off first at the bottom end. Don't think it's very far out in terms of SOC %, but I do like to twiddle things to perfection. ??
BMS is a JBD/overkill, so it's not that powerful in terms of its own balancing capabilities - currently set to balance on charge when > 3.4V / cell.
So, I've spend a few hours attempting to discharge the highest cells using an automotive bulb when they're at the top end - when the pack is either charging or fully charged and the cells are above 3.4V. Have experimented with different pack charge currents (8A, 4A and 2A) and also different max cell voltages (e.g. 3.45 / 3.5 / 3.55).
The thing is it only takes 5 to 10 minutes for the most of the cells to get from 3.4V to 3.5V, whilst manually discharging the top one. Meanwhile the lowest cells has gone from something like 3.370 to 3.375V. If I then discharge the 15 cells from 3.500V(ish) back to 3.400V (which takes ages manually) and repeat the process, the lowest cell only goes up from (say) 3.373V to 3.378V. So it appears it's working but it's sooooo slow and impractical to achieve the balancing manually.
Would appreciate anyone's thoughts on whether charging the one low cell instead of discharging the high cells would be a better option. I'm thinking along the lines of charging the pack up to 3.5V/cell first then, off load but still connected together, putting an isolated bench power supply set to 3.5V on the low cell.
?
Would that work? Anyone done it? Any gotchas?
BMS is a JBD/overkill, so it's not that powerful in terms of its own balancing capabilities - currently set to balance on charge when > 3.4V / cell.
So, I've spend a few hours attempting to discharge the highest cells using an automotive bulb when they're at the top end - when the pack is either charging or fully charged and the cells are above 3.4V. Have experimented with different pack charge currents (8A, 4A and 2A) and also different max cell voltages (e.g. 3.45 / 3.5 / 3.55).
The thing is it only takes 5 to 10 minutes for the most of the cells to get from 3.4V to 3.5V, whilst manually discharging the top one. Meanwhile the lowest cells has gone from something like 3.370 to 3.375V. If I then discharge the 15 cells from 3.500V(ish) back to 3.400V (which takes ages manually) and repeat the process, the lowest cell only goes up from (say) 3.373V to 3.378V. So it appears it's working but it's sooooo slow and impractical to achieve the balancing manually.
Would appreciate anyone's thoughts on whether charging the one low cell instead of discharging the high cells would be a better option. I'm thinking along the lines of charging the pack up to 3.5V/cell first then, off load but still connected together, putting an isolated bench power supply set to 3.5V on the low cell.
?Would that work? Anyone done it? Any gotchas?
