coulomb wrote: ↑Fri, 11 Dec 2020, 08:44
nuggetgalore wrote: ↑Thu, 10 Dec 2020, 20:54
with the battery supposedly fully charged at 259 V.
I hope you mean 3
Sorry yes a typo
Max cell voltage at start of charge was 3.71 V min 3.68 V,pack 324.3V.
So you still had probably around 55 km of range left. Turtle for these cells should be around 3.5 VPC.
...until the BMS said at 4.11 V max cell volt and 4.07 min cell volt (pack 459.90 V) battery is full.
I hope you mean 359 V.
I make this type of typo typical....
I think the cells (amongst other things) are not a matched set,the BMS is struggling to balance the cells (the original cells always topped up at 4.1 within 0.02 or better and pack volt 362).
Graeme reported earlier that with the 94 Ah versions of these cells, he had a lot of trouble balancing them, so he had to take all the cells out of the first conversion and parallel them for a week. You might be able to get away with some manual balancing (sets of headlight bulbs with clip leads (I have a box of these) and some dual chargers. Though I'd want to break the pack into at least two pieces before using chargers on them; 360 V is a bit much to trust to the insulation of a cheap charger / power supply.
I had all the cells near perfectly balanced when I installed them into the pack. with the exception of cells 33 and 34 (different reason), both i909 and EvBatMon confirmed this.
As bladecar and zzcoopej posted, the lack of regen was because the high volt cell was not able to take any more charge,after a few more km it did regen again. I am now fairly sure that the relatively big inconsistency in the cell capacity make them nearly unusable. At relatively high pack volt, cell #6 always becomes the high volt cell when I take the foot of the accelerator, and another cell takes that spot as soon as I ever so lightly accelerate again.
With the exceptions of just a few(at the lowest volt cells), all cell balance drives are on all the time, battling to keep the cell voltages in line.
I wish I knew more about those cell balancers, and what it means when they are "on".
I have now been able to cross reference the balance drive [OFF] status with the low(est) volt cells.
So my deduction is that if the drive is on,it bleeds a small amount from the cell,allowing the lower cells to catch up. But it appears the out of balance (resp the capacity mismatch) of these 60Ah cells is too great for the BMS to handle. The original cells even after nearly ten years in service always were able to get to within very close tolerances during charging and of course at the end of charge. On a related topic, the target voltage is always the voltage of the lowest cell, I assume (with caution!) that as long as there is head room for the high cell, the charging continues until the target reaches the top.But if the high cell runs out of space, stiff cheese for the poor straggler cells,it then follows that the pack volt does not reach full voltage resp all the possible Ahs.
Interesting that at the end of charge, the fuel gauge showed 12 bars and GoM 91 km.
12 bars at the end of a charge? That seems strange. Did you perhaps mean 16?
not a typo this time!
I took it for a short (1km) drive,and fuel gauge went to 15 bar and GoM to 96 km.
The RR meter increasing as you drive it a familiar situation.
Never happened before,quite the opposite, just 10 meters driving used to reduce RR by a km.
The real bad news is that when I took the car for short drive, I noticed that regeneration is not working anymore.
I have no idea why that is; I never noticed that. It is probably due to the difference in voltage versus SOC at high SOC.
Edit: it may also be that the 94 Ah cells can take more regen than the 60 Ah cells, since regen current is smaller relative to 1C.
I have a good idea why I never noticed the lack or reduction of regen with the original cells.They are much fatter and evenly balanced, but also just a short moment after end of charging sagged a little bit, enough to take a regen charge straight away.Just talked to a '12 iMiEV owner who had his car from new,he never noticed that phenomenon either (not looking for it,of course).
So this morning I drove off with the above mentioned 15 bars on the fuel gauge ; GoM 94 km; pack volt 357.80; high cell 4.08; low volt cell 4.04 .
Result after driving (no freeway but up and down a small slope) 42.4 km:
Pack v now 331.1 V; high cell 3.79 V;;low cell 3.75V and GoM 25km. Back on charger,wonder how many Ah/kWh it will accept from this position.
[ Edited Coulomb: fixed quoting. ]