diy solar

diy solar

Is this indicative of a problem with this cell?

pralinebuckets

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Jan 3, 2021
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Hey all,
I have a 16S 280Ah 48v battery. I built it and top balanced a while back and recently installed a jk active balancer to get things closer to where they ought to be when fully charged. I have it set to engage when a cell hits 3.45V.

While charging from say 75%-97%, cell 2 will be consistently higher voltage than the rest of the pack, occasionally as high as ~4.45V (though not staying there long if I set the max charge to 56.5V). When the charge is stable and the amperage of the charge starts to drop, that cell then becomes the lowest voltage in the pack by far. Things are pretty far out of kilter in general right now, but while I wait for the balancer to do its thing and pull the rest of the cells closer together, I'm curious about what this behaviour implies about Cell 2.

When not charging, the cells sit pretty close together. Generally within 0.005V of each other while under low load (1-2A). With higher load, the differences in delta v start to show up, which is why I figured adding an active balancer would be wise.
 

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What Tim suggests eliminates balance lead as an issue. That would leave you with the likelihood of a weak cell which does not have the capacity of the others. That was your original assumption and that process might help confirm that.
 
I haven't had chance to do this yet - but the JK app does say that the resistance of each lead is roughly the same. All of the cells show ~0. 059-0.060 ohms (or m ohms? Can't remember the units).

That means that this specific cell is somehow weak? I don't quite understand why it initially increases in voltage, and then while still having a charge applied will drop below the others. What's going on chemically there?
 
Also check that the buss/terminal connections are good both ends of that cell.
 
I have seen some of my cells act like this. I have found on my cells that it is a bad connection or a dirty contact. Make sure that the defective cells contacts are cleaned and that they are all torqued with a torque wrench to the specified specification.
 
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