Absorb Time for LiFePO4
I've read snippets here and there but nothing conclusive about absorb settings. If this has been discussed elsewhere on the blog, please point me and I'll see if I can get this deleted.
Anyway, up and running with 800Ah bank and learning about balancing/charging etc.
Originally tried charging up to 3.45V but discovered that at my slow charge rates (<0.05C) the knee at 3.4V is incredibly critical and that if the bank starts edging beyond that knee, the balancers cannot keep up and some super cells just start running away.
With absorb at 3.395V, the charge current fell from mid 30s to about 12A over 3 hours. Difference between high and low cell was less than 25mV throughout the time.
They were pretty well balanced at what the graphs show to be over 95% SOC.
If they are nearly fully charged, why does the current continue to fall as they sit at absorb for 3 hours? I was expecting to see the current stabilize and from that I could decide on a reasonable absorb time but it was still falling after 3 hours.
How can I determine how long to leave them at absorb?
My other conclusion is that a float of 3.35 V seems too low. Unlike my FLA batteries, which fell to float voltage over a very short time, these batteries have such great capacity, that they greatly resisted falling to float. For two hours at the end of the day, some power was coming out of the batteries rather than all from the sun. It seemed like a waste that any was coming out of the batteries during the day when sun was available, just to drop the batteries to float.
I'm thinking of a float around 3.375 might lessen this effect.
Is there a downside to setting the float up this high?
12 * 300 W (10 fixed rooftop, 2 movable pole mount), Morningstar Tristar MPPT 60, Magnum 4448 PAE, 64 200Ah CALB in 4p16s arrangement with 16 LED Balancers and a Choice BMS300 (It is lousy and I don't recommend but it provides high and low voltage cutoff)
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