Is this behaviour correct (SOK 100 Ah 12V System)

[csreades]

I have contacted SOK directly and they have been helpful but I was looking for a second opinion on this. I have two 100Ah batteries wired in parallel for a total 12V system with 200 Ah capacity in my campervan. They run a number of different things and they charge in a number of different ways. The performance I am particularly concerned about is when charging the batteries. One of the two batteries has a single cell that jumps to a higher voltage than the rest and the battery enters charge protect mode.

The picture is from some home automation system I have that is able to plot the cell voltages over time. Eventually what happens is that the cell drops and the protections turns off, then that cell jumps up again. As this is a campervan system the batteries have not been on a prolonged charging stint and typically only charge while I am driving. I have noticed this behaviour since getting a solar panel and the battery is being charged while already at a high voltage.

Is this behaviour normal/concerning any recommendations?

SOK themselves said it was relatively normal and to put the battery on a prolonged charge.

 

[sunshine_eggo]

This is extremely common on brand new batteries, batteries that have been in storage and batteries that are not regularly charged to full.

The cells are never perfectly matched, and they are rarely at identical states of charge.

Their recommendation is typical and correct.

Hold batteries at 13.8-14.4V for 24 hours. This should bleed off about 1Ah from the high cell. You should see some convergence.

However, 3 cells under 3.40V with a cell peaking at 3.70V is pretty notable. It either indicates significant imbalance or a potentially bad cell. After balancing, I would capacity test the battery. If it does not pull full capacity, and cell 4 is also the first cell to drop out, I would seek a return/replacement.

If you do not see significant convergence, and these are brand new batteries, a return may be warranted. Charging for a day or two - fine... charging for weeks... no thanks.

 

[DIYrich]

Charge at 0.05c (10 amps for your 200 ah batteries). Then follow the above advice. The slower charge will help cells stay in balance while charging.

 

[KITROBASKIN]

I have the same setup. It is very similar (one cell would read a little over 4.6V) to what mine did but I followed the charge profile guidelines on the currentconnected website (under the item description for those batteries) and it was self-sorted out after some months. It is concerning that the BMS protection gets triggered but this system is doing fine.

I question Ah capacity estimates from the Bluetooth feature.

The Bluetooth is the weak link with SOK batteries. Many other budget units do not even have that feature so those customers are somewhat in-the-dark, though.

diysolar member sunshine_eggo has previously discussed the option of lowering charge parameters to potentially extend the life of batteries, depending on use. I tried lowering voltages and cell imbalance did increase in time, resulting in going back to the currentconnected suggested settings.

Our application is not pushing performance to the limits; the system is fine.

 

[csreades]

Thanks for the comments and feedback. I haven’t had a chance to slowly charge the batteries until I got the solar, hopefully a few days of sunshine will give me the ~10 Ah for 24 hours - just discontinuous. I will keep an eye on them during this and see if it improves.

It is a relatively new battery, however I have never really charged them except for driving.

 

[sunshine_eggo]

Thanks for the comments and feedback. I haven’t had a chance to slowly charge the batteries until I got the solar, hopefully a few days of sunshine will give me the ~10 Ah for 24 hours - just discontinuous. I will keep an eye on them during this and see if it improves.

That should be fine. Avoid deep discharges. Set absorption to 14.0V and float to 13.8V

It is a relatively new battery, however I have never really charged them except for driving.

This is a contributing factor. The need to spend adequate time above the balancing voltage to stay in balance.

 

[csreades]

I won't draw any conclusions as it has only been a few hours but with the sun shinning there doesn't seem to be any trend towards balancing.


The follow up question, if the other cells are not going to go above 3.385 what real capacity is being lost?

 

[sunshine_eggo]

It's hard to say without a discharge test. Cells that don't get above 3.45V won't get fully charged, and even there, they may not get above 98%.

Given the small amount of current with passive balancing, you may not see much results after only two hours. I'd give it the cumulative 24 hours and then assess. I would pass that info on to SOK. Failure to attain charge voltage is grounds for replacement.