Quote:
Originally Posted by hybriddriveguy
The issues with the parallel pairs was needed to help balance the high and low cells. What I would recommend is to separate all cells before any charging and record the static charge on them. Add all voltages together and divide by the total number of cells you have. This will give you a cell average that you are looking for. I would then start matching highs and lows within the cells to match the average as close as possible. This will give you the best pairings for each parallel pair.
The reason we have to do this is because you are charging the whole pack to around 58 volts and the biggest danger to these cells is overcharging. You could have a low cell starting the charge cycle at 2.7v and a high cell at 4.1v.
If they are wired in series they will both continue to receive charge until the total system voltage is achieved. This would in our experience drive the high cell to over 5 volts and damage it before the low cell would be high enough.
Connecting these in parallel, creates a balancer for that high and low cell by using one to balance the other.
We have been fighting this battle since may and my company has been through about 3 complete sets of the batteries, while trying to get all the bugs worked out.
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When all of my cells were shipped to me I tested their resting voltage. They were all within .02V of each other. After that, I put them on the balancers to balance them out even further. IMO charging shouldn't be an issue once they are balanced.
Info I'm getting from other users is that it takes some time to brake in the cells until they will charge/discharge uniformly. This doesn't make much sense to me as I don't believe any other battery chemistry has this problem, but I am a bit new to lithium.