LakeHouse
Solar Enthusiast
I'm pretty sure this isn't the case.
As I noted above, I have Aliexpress cells that were supposed to be 280Ah 'Brand New' EVE cells. 15 of them have QR codes ground off, but one has an intact code that indicates it is a CATL 240Ah cell model 6LH3L7, which as far as I can tell CATL produced in 2018 or 2019. I acquired the cells in December of 2022 (so they were either used or warehoused for several years) and capacity tested them with an EBC-A20, and they all came in between 232 and 239 Ah, which is pretty well-matched in capacity terms, I'll agree (also note, I refer above to them being 230Ah cells, which is how I set my capacity because it's about what I actual get out of them, but one of them at least is technically a '240Ah' cell).
These are far-from-perfect cells from a far-from-reputable supplier, and in fact one of them (perhaps not coincidentally, the one with the intact QR code) seems to behave differently from the others in an important way: while charging it rises above 3.4V about 2% or 3% of SoC before the other 15 cells. Initially, I had my balance start voltage set to 3.4V but noticed that the active balancer would start discharging cell#3, and continue to do so from about 93% SoC to 96% SoC, then gradually the other 15 cells would catch up in voltage and then blow right past #3 which had been discharged slightly by the balancer. Then from about 98% SoC to the end of the charge the active balancer would charge cell #3 to force it to catch up with the others.
What was happening was that #3 had a slightly different charge curve than the other 15 cells, and so active balancing too soon was actually causing imbalance. I changed my balance start voltage to 3.45V, and since then the active balancer doesn't really have much of anything to do, even with my relatively not-great cells. So in my particular case, even starting balancing at 3.4V was too soon!
@Steve_S, looking at some of your other posts here and here, you reference starting balancing at 3.30V, and I suspect that this is causing imbalance in your packs. @RCinFLA spells out a reason in a response here, and I think he's correct. Also Andy of Off Grid Garage has documented this phenomena several times. So, if you're creating some amount of imbalance any time the cell voltage is between 3.3V and 3.4V by shuttling energy back and forth between cells that aren't actually unbalanced, it makes a lot of sense that you would then require a significant amount of active balancing (e.g., 1A per 100Ah of capacity) once the cells get above 3.4V to actually get them back into balance.
I'm no expert, and it's possible that I'm just flat wrong about this, but I suspect that if you changed your start balance voltage to somewhere between 3.40V and 3.45V, you'd get away just fine with a smaller amount of active balance capability.
