rustyrotors
New Member
- Joined
- Dec 29, 2022
- Messages
- 29
ive noticed my 2 year old, diy lifepo4 battery getting out of balance, two cells are out of balance, one SOC is about 10% over and the other is 10% under. 8S eve 304ah on a jk bms with 2A active balancing set at 3.4V. seems like what is happening is when its charging, the weakest cell's voltage is surging, making the bms think that cell needs to be discharged, so it dumps its power into the lowest voltage cell, the one with the least voltage surge. then when charging is done and its floating, the two cells reverse voltage state, the cell the balancer thought needed discharging is now the lowest voltage and works to undue what it just spent 1-2 hrs doing during charge. basically the weakest cell gets dumped into the strongest cell during bulk/abs charge, and effect is reversed in float. if the float voltage is not close to 3.4V, then the effect is never reversed, and the cells get pushed further and further out of balance every day. it seems on a newer battery, if the cells are well matched, they all surge together and this effect does not happen. but as cells age unevenly, the surge/sag overcomes the balancers ability to measure cell SOC based on voltage
problem is i dont really feed comfortable floating the cells at 3.4V for 4-6hrs a day, it degrades cell capacity. ive tried lower charge voltages, but only makesa difference of 20min in charge time, still spends roughly 1-2hrs every day putting the battery out of balance. at this piont i would be better off i disable balancing and just do it manually every so often. if only there was a way to disable balancing during charging, and only enable it during float or low current to eliminate the effect of voltage surge/sag. im looking at external active balancer triggered by victron relay output
problem is i dont really feed comfortable floating the cells at 3.4V for 4-6hrs a day, it degrades cell capacity. ive tried lower charge voltages, but only makesa difference of 20min in charge time, still spends roughly 1-2hrs every day putting the battery out of balance. at this piont i would be better off i disable balancing and just do it manually every so often. if only there was a way to disable balancing during charging, and only enable it during float or low current to eliminate the effect of voltage surge/sag. im looking at external active balancer triggered by victron relay output
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