Cell 1 always lower when discharged and charged

Westtoast

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May 8, 2022
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Hello,
I have a 12v 30ah lithium Iron (eco-worthy) battery. The bms failed so I removed it and connected a cell meter to it. I find when I discharge the battery cell 1 goes down a lot more than the other cells. Is this normal? It gets pretty low 2.6 V others are 3.0V It usually a few volts lower at complete charge. 3.25 vs 3.3 (other cells). Any thoughts and do I need to fix it? Have balanced charged it and cell 1 is always .05 volts lower.
 

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Westtoast

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I tried to balance charge it. One cell always goes down a lot more then the others. Is this normal. Do I need to replace this bad cell?
 

MisterSandals

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I tried to balance charge it.
I am not sure what this means. Can you explain?

Do you have a way to connect all cells in parallel to top balance to 3.60-3.65V?
Or can you charge each cell to 3.65V individually?
This would put all the cells in sync with each other and give you the best chance of having them behave voltage-wise at mid to high voltage.
 

Westtoast

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So to confirm it is not normal for one cell to discharge way more than the other cells when in use?
 

MisterSandals

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I used a balance charger that I believe connects to the individual cells.
Ah yea, good deal, that will do just fine. Did you get all cells up to 3.6V-3.65V (all the same)?
If not, then you should give this a go to top balance the cells - its your best chance of getting your cells to behave.
 

Substrate

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I have one similar to the Tenergy. Does a good job *provided you have good connections* for balance charging. Small bleeders, but then again, you only have 30ah batt so no sweat.

If you want to charge individually, of course you set for 3.6v and "1S" and not use balance leads, just the main positive and negative cable.

*maybe* what took out your original bms also hurt cell #1 a little bit. We don't know.

What I suggest is that you do not let your cells get even as low as 3.0v. Aim more towards 12.5v pack total (3.125v) max under load. Now cell 1 won't be driven so low. And perhaps strive for no more than about 0.3C discharge current. (9A max surges - it'll last longer)

Consider getting a real multimeter, rather than relying on those low-end indicators. What they often *dont* tell you is that their specifications are only at higher voltages, like 12v, and can err significantly in lower ranges.
 
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