No-matched cells?

[Jeff King]

I have a new battery bank and SBMS0 system. I am using Winston LiFePO4 cells. I have eight cells arranged as 2P4S configuration for 12V RV system.

During charging from a Victron MPPT SCC, one of the cells goes to a higher voltage than the others.
My low cell #1 is 3.270V, my high cell #8 is 3.718V, delta 448mV.

I didn’t have the EXTiO4 connected yet to a DSSR to cut off the solar panels to the charge controller at this time. I am use a Vitron BlueSolar charger, so do not have a remote on/off. I will add a DSSR between the panels the Victron Charger to allow the SBMS0 to cut off charging.

So, my one high voltage cell would cause charging to cease due to single cell cutoff. It is my mismatched cells that cause this problem.

My question is this:
Would it be wise to rearrange the cells? Take the higher voltage cell from #8 2P package and mate it up with the lower voltage cell from the #1 2P package? Would pairing the low voltage cell with the high voltage cell act to cancell each other out?

[Dacian Todea]

Jeff,

You need to connect the Victron MPPT to the SBMS0 EXT IO4 set as type 1 else the SBMS0 can not protect your battery.

If you had the DSSR20 installed then that high cell voltage will not have exceeded 3.55V

You pack may also be fairly unbalanced for some reason as I will have expected the lowest cell to be around 3.35 to 3.4V if that high cell was 3.55V or above meaning fully charged cell.

There will always be a cell to get first to 3.55V and charging will be terminated but the other cells should also be close to around 3.4V if they where to be around 99.x% SOC so almost fully charged.

You can rearrange the cells as a quick way to redistribute the SOC and have a more balanced pack. In time a few weeks with daily solar charging the pack will eventually be balanced by the SBMS0

New cells are usually way more balanced from factory than this so I assume you do not have new cells.

[Jeff King]

Yes, I bought used cells. These are 8 cells from a lot of 26 the guy had for sale.  So, I understand the mis-match.

I was simply asking if re-arranging the pack would help even out the out of balance situation?

And yes, I will get the DSSR20 installed between the solar panels and the MPPT controller. This is brand new DIY installation I have done. So, it has not gone through even one full discharge/charge cycle. At the time of writing.

I now have the DSSR20 installed between the solar panels and the MPPT controller, I still have not charged with solar yet (I am parked in a driveway under an awning and and its raining for a couple days.

But you answered my question: yes, re-arrange the pack is a solution to distribute the SOC and make more balanced. But, also the SBMS0 will handle the mis-match over time with charge cycles. this is good to know.  Once I get the install completed, I can park the rig out in the sun, run the fridge and other full time loads, let the sun charge during the day and loads discharge over night.