There's those who say that you can't tell a LiFePO4 cell's State Of Charge (SOC) from the cell voltage.
They're right!
In my previous post I mentioned that cells around 3.3V appeared to only be about 2 to 4AH shy of fully charged.
Well in Pack #9, we have so far put 11AH into a cell that initially measured at 3.28V and it's only just up to 3.5V - so it's nearly charged. The critical voltage at 20 degrees C for reasonably new LiFePO4 Headway cells seems to be between 3.2 and 3.4 V.
I had ideas of logging pack voltage and current and coming up with a SOC indicator that didn't have to measure AH in and out of the pack. The idea was to compensate the pack voltage with the current being drawn from it and assume a particular SOC from the compensated voltage. I think it may be harder than that!
William is at home today and I'm at work, so I am getting cell voltage and current updates from him.
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