lifepo04 280ah eve cells capacity testing are these bad cells?

[Jorvs]

You are 'shorting' current through the bulb to take power out of the cell and lower its voltage. The bulb limits the amount of current.
You need to take care that your 'test probes' on the wires to the bulb are suitable, this could be as simple as a few mm of the cable wire core that you 'prod' on the cell terminations or the buss bars to the cell.
As you lower the charge on the cell one of the others may become the 'high cell' so you switch your attention to that.
It's a bit like 'wack the mole', keep moving the load to the high cell for a few seconds when that cell becomes the cell with the highest voltage.
When working with cells take the usual safety precautions using eye protection, no metal jewelry or rings, insulated tools.

Mike

I mean do do this while its on a 12v series?
and do stop the charging while doing it? or do stop the charging first?

 

[mikefitz]

You do it whilst charging in series with a bms connected. If the cell voltage is changing too quickly reduce the charge voltage or disconnect the charger for a short time. You can apply the load at any time where there is a cell at a high voltage.
The cells will start to diverge in voltage as you approach full charge. This is when you 'play wack the mole'.
If you are able to set up different charge voltage on the charger, carrying out this balance maybe easier in stages, starting at 13.8 volts and increasing in 0.2 volt steps to 14.4 volts.


Mike

 

[Jorvs]

You do it whilst charging in series with a bms connected. If the cell voltage is changing too quickly reduce the charge voltage or disconnect the charger for a short time. You can apply the load at any time where there is a cell at a high voltage.
The cells will start to diverge in voltage as you approach full charge. This is when you 'play wack the mole'.
If you are able to set up different charge voltage on the charger, carrying out this balance maybe easier in stages, starting at 13.8 volts and increasing in 0.2 volt steps to 14.4 volts.


Mike

your advice has been a great help..
I try this..
thanks for your advise greatly appreciated

 

[munsterfan2]

Hi,
Hope it's OK to jump on the thread here, I have 16 200ah batteries with a seplos BMS. The batteries are labeled so appear to be from 2 different batches. They were top balanced until the meter was reading .02a @ 3.65v. As current increases, charge or discharge, 8 of the cells start to diverge

In the second graph here the dotted line is the current.




If I check the voltage differences of the cells vs current differences I get two fairly distinct sets of impedance (R=V/I)

V @ 60.1a	V @ 8.872a	Vdiff	R (mOhm)
3.391333​	3.3314​	0.059933​	1.169933​
3.486​	3.3596​	0.1264​	2.467401​
3.452333​	3.3458​	0.106533​	2.079592​
3.458​	3.3466​	0.1114​	2.174592​
3.457667​	3.3522​	0.105467​	2.05877​
3.400333​	3.3336​	0.066733​	1.302673​
3.453​	3.3446​	0.1084​	2.11603​
3.395667​	3.3322​	0.063467​	1.238906​
3.411667​	3.3374​	0.074267​	1.449728​
3.400667​	3.3352​	0.065467​	1.277947​
3.398667​	3.3336​	0.065067​	1.270139​
3.454667​	3.3492​	0.105467​	2.05877​
3.39​	3.33​	0.06​	1.171234​
3.400333​	3.3312​	0.069133​	1.349522​
3.473667​	3.3572​	0.116467​	2.273496​
3.512667​	3.3634​	0.149267​	2.913771​

At request of supplier going to do a capacity test on one of the cells showing high impedance. I am assuming I need to replace the 8 cells, any other suggestions as to what could be wrong. I have top balanced twice, moved cells around in the array and it is always the same 8 cells, regardless of location.

Thanks,
Ruairi