Posted: Sat, 24 Jan 2015, 01:47
offgridQLD wrote: "broken up into sets of 4 and each individually charge controlled "
So Terry, your saying you have two separate 12v chargers on your 24v 8 cell banks?
Your secondary system being cell level motoring with balancing ? what are the voltage limits befor the secondary system kicks in?
The key point I guess is how good is the manufacturing process / consistency of the Calb/Winston cells. That's the one thing we cant change and as long as your interconnections are up to scratch . Most likely the only reason they go out of balance. How much and how long it takes is on average with our kind of assuage is the key bit of info.
The systems use 12v nom. solar panels, the negative for the "B" set (12v to 24v nom) is tied to positive terminal of the "A" set (0v to 12v nom.) By cutting the positive on the "A" solar the "A" battery stops charging, but the "B" battery continues to charge. By cutting the neg on the "B" solar the "B" battery stops charging, but the "A" battery could continue charging if required.
3.6V in any cell in the 4 cell pack sets the secondary system into action, at any other time the charging is left to the primary control.
Mains charging is SOC controlled, start at 20% SOC and stop at 80% SOC, no run-aways within this range, but either secondary circuit can cut the mains supply if a high cell voltage is detected. This was required as a safety in case the SOC was incorrect or lost due to a temp disconnection of the meter.
As far as dirty connections, they show up on a log graph as a quite obvious tell tale, high voltage when charging and immediate low voltage under load equals a high resistance some where within that cell group. We use multiple smaller capacity cells in parallel to build up to the Ah required, then series connect these packs. The advantage is the differences in production tolerance's are balanced out across a number of cells, this really helps with maintaining a balanced pack.