I am betting he is mistaken. I thought all the cell man packs with a BMS were tab welded 26650's. Unless very very early on you got one of his first couple packs using pouches.[/quote]
[quote="John in CR wrote:This pack is new enough that Cellman should cover it. Was it the same cell that was at 3.48V the cycle before, and then wouldn't charge above 3.33V .John
Paul and I spent a long time discussing my pack prior to his assembly. if my "?" after the pack implied I do not know the difference between a cylindrical A123cell and a prismatic A123 pouch cell, I apologize. Just wasn't certain if A123 manufactured different pouch cells w/different model # designations.
Pack is constructed with A123 20ah prismatic cells.
John, I would like to think he will offer some assistance considering the pack has 30 cycles at 8.8 ah discharge max. I sent him a second email today.
John in CR wrote:If the cell will take near 20ah charge from it's current status, then there's something wrong with that channel of the BMS. If not then that cell is a problem, and needs replacement. If the cell is stable, just lower capacity, and if you're on your own with it (hopefully not the case), then the fix might be as easy as paralleling just one or more 26650 A123 cells with that weak cell to make up the difference...not pretty or elegant, but a fix. I've got a number of those cells at various capacity, so we could get you up and running in a jiffy.
John, thanks for your input and your offer. Seems like the next phase is to try and bring that cell up to 3.65 ~ 3.7 so it can play with the others.
liveforphysics wrote:You need to charge and watch the low cell's voltage relative to the others while charging. If it's first to fall off the cliff and first to reach peak voltage, it's a weak cell group, likely just had a paralleling tab-weld disconnect (and no, this won't change it's voltage, just capacity of that cell group).
So Luke, I need a little help understanding "cell group" - my understanding of the pack's operation is that the BMS controls and monitors charge on each cell via the balance wires. Based on what you have indicated, it sounds like the BMS monitors cells individually and in "groups"?
BTW, based on space limitations in the frame, the 24s pack is constructed of two sub packs - 9s & 15s connected to a single 24s bms.
Thanks agian for all the input guys. As much as I have tried to avoid it, sounds like my battery pack construction and function education is formally beginning.....