Hi all,
I have the victron LFP 200-a 25v batteries in my system. Recently I've gotten 4 more batteries to add 20kwh to the system.
It seems however that these 4 batteries display the wrong voltages. At first, I thought I was maybe a bad connection, as these 4 batteries (2 sets) added to a new distributor. However, after manually measuring all the batteries, they are all at the same voltage, which is only 0.05v off from the reported voltage of the "old" batch. Even if completely disconnected from each other and the system at rest, this voltage discrepancy exists.
The new batch reports 0.25V lower than what I measure at the battery poles, why the old batch reports only 0.05v lower than what I measure at the poles.
Below, you find a picture of the batteries at 98% SoC. All connected to the same bus bar.
The top 2 batteries are of the "new" batch, and the bottom 2 are of the "old" batch.
I imagine these batteries on their own could be "unsafe" as the cell overvoltage protection would not work correctly (unless I manually set them to a lower max voltage threshold inside the battery settings). But I can also imagine this creating problems with cell balancing, as the cell balancing gets triggered at a certain voltage.
But because the internal sensing of cell voltage is off, this balancing starts far too late and when the charge cycle ends, and it drops back to "float" state, it no longer will be balancing.
As you can see in the screenshot it is right now also balancing, it's just about always balancing when I check because it never has enough time to balance I feel like. Might have to increase the absorption time just to make sure these batteries manage to balance. Might also be that for example in the 2nd picture. cell 8 is actually 3.53V but measures as 3.45V but due to the wrong voltage sense on it, it never actually manages to "balance" it since it's in reality at 3.53v already.
Of course, they always recommend matching batteries and that adding batteries later into the lifetime of a system should be well-thought-out. However, all the batteries are less than 18 months old. The degradation on them is minimal, and the only issue is that the measured voltage internally does not match up with the actual measured voltage at the poles.
Would it be possible to calibrate the cell voltage sensing? Are these just "broken"?
What would you guys recommend?
