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Balancing a troublesome CALB cell
#11
Voltage is not the determining factor for charge termination, tail current is - meaning the cell should be kept in the CV mode until the current has dropped to a level as specified by the manufacturer - typically a few percent of its C rating.

So before you condemn cell 6, make sure it's being correctly, fully charged.



Ignore the voltages depicted, the concept I'm illustrating is the CV phase and decaying current until charge termination.
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#12
And just to finish things off, here's the pic from 7.45am next morning at 46% charge. Looks good again.



Cells all look in perfect condition, no swelling etc. I think I've got a dying cell.
Mike. DIY Offgrid in South East Queensland, Australia. 

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#13
I dropped the CV  charge point to 27.7 and will see if that helps, if so, might even go down to 27.6

Sean, thanks for the advice on charging, especially the graph, I'll take your advice and see how things go. In all honesty, I think my primary concern at the moment is trying to stop cooking the mon!

it's now 10.45am and cell 6 is starting to sneak up, .03V higher.

I have not looked at the WM4 auto balance setting, will have to go and study up how to do that

Bit cloudy here today, so cells are charging a little slower than normal. 11am 63% charge pic:

Mike. DIY Offgrid in South East Queensland, Australia. 

17x250W Trina panels, 2P12S 48KWh / 24 x 2V 1000Ah SLA, 8S 2.4KWh / CALB CA100 LiFePo w/ Battrium WM4 BMS, 
1 x PCM60X + 1 x PIP24 inverter for house, 1 x PIP24 inverter/charger for utilities using LiFePo for trial.

Belt: Autostart 100A 24V petrol alternator/charger, Braces: 3KW genset.
Hydrotherm programmable heat pump 800W/275l storage hot water from solar/battery. ~0.8KWh/day

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#14
What Sean is trying to say, is that lithium batteries have a fairly flat discharge curve. LiFePo4 especially. State of charge is impossible to predict based on voltage alone. It is most likely the cell is simply not reaching full charge. By lowering your float voltage, you are not going to improve the situation.

As for the mon - cook it - its cheaper than a battery. Put a fan on it to help cool it instead. Maybe even buy another. You can put several mons on one cell, to help balance it faster. Perhaps even put a dummy load on it - such as a light globe or a resistor, to help the mon out.

You probably do have a slightly crook battery, but with LiFePo4 cells, it is going to be hard to do much about the situation.
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#15
But if the charge state would have been a problem the cell wouldnt have switched being over voltage and then suddenly under voltage comparing to the other cells just by a little charge or discharge.
That clearly show signs of an issue with the cell or bad contact on cables/junction points.


Auto level as such wont do that much in this case since its passive balancing. It still require that the cell perform the same in most of the work area.

Note that 0.03V is nothing.... Im easily off by up to 0.05V or even more. But its not that off that its an issue. Ie same amount of during load as in during charge.
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#16
My money is the cell is failing - a cheaper stop gap may be to add a smaller LiFePo4 cell in parallel with your cell #6.
While not ideal, it'll postpone having to replace the cell & lighten it's load.
It'll also help to operate the pack so cell #6 isn't being pushed too high or too low, the more that happens, the faster the demise will be.
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