nlspace wrote: ↑
Thu Oct 10, 2019 6:26 pm
Excuse me, but you still haven't provided any information of how more
energy is added to the lower cells than the higher cells during charging?
If you made a mistake or don't know, then at least be man enough to admit it. Don't imply that i have an attitude problem when i ask about the rationale for statements about charging and cell energy. Nobody wants to read or repeat bad information on the forum.
The same current flows thru each cell of a series string, so if the car is charging at 10 Amps for 3 hrs, then 30 A-hrs has been added to each cell. The only way to correct the OPs issue is for the balancer circuits to activate for a long time to bleed down the higher cells, or to open the pack and put charging current thru only the low cells to bring them up, or replace the low cells with some that are closer in capacity to the rest.
People come here looking for help to solve problems; let's give them solid answers based on facts and data, and not wild-axed guesses.
The BMS has shunt resistors. These are controlled by the BMS and they open to allow a small amount of current to flow between the cells. The greater the voltage difference between the cells, the more current is able to flow. Greater voltage differential, as you stated, exists at lower %SOC.
It definitely makes sense that at low pack voltages, the greater voltage differential would result in a higher current flow across the shunts. Practically speaking, I don't know how much that will accelerate the balancing, but there will be an effect.
Personally, I'd take the car back and say that the new cells are either bad or the pack has not been properly balanced. The repair was simply not done correctly. It's possible that over a few months the problem may work itself out, but that's an awfully long time to wait.
If gary doesn't want to do that, it might make sense to leave the car running with no AC/Heat, etc from 50-5% SOC for hours in the garage, following it with an immediate L1 charge. This would allow for a prolonged period of low-amperage discharge with a prolonged period of charge--maximum balancing time.