Balancing 4x - 12v battery packs all at once?

K8MEJ

Solar Addict
I have a 2x - 12v battery system in my RV that I put together myself. I am using EVE 280Ah cells and Overkill Solar 12v 120A BMSs. Very soon I am going to introduce two new 12v packs built with the same cells and BMSs. I individually top balanced the original two packs and then put them into service in a parallel configuration about four months ago. I will individually top balance each of the two new packs as I did before.

Questions:
  • Should I also top balance the two original packs again?
  • Should I put all 16 cells into parallel and top balance all the cells before the final parallel configuration of all four packs?
    • If so, is this something that should be done periodically?
  • Is it safe to put all four packs into series and top balance the entire pack as one unit once each 12v pack is balanced? I'm not sure if the 4s Overkill BMSs can handle that voltage. The manual simply says "Complete assemblies can be connected in parallel or series." I have a bench power supply that I can program for the higher voltage, but can the BMSs handle that?
It's a lot of effort to take the packs apart, balance all the cells, and reassemble. If that gives me 1-2% of extra capacity, it's not worth the effort. If it gives 5% or more, it's probably worth the effort once a year.

Thanks in advance for the help.
 

MisterSandals

Participation Medalist
Should I also top balance the two original packs again?
I would base this decision on how well your packs stay in balance. Not required if working well.

Is it safe to put all four packs into series and top balance the entire pack as one unit once each 12v pack is balanced?
It is safe but will do nothing for balance.
It's a lot of effort to take the packs apart, balance all the cells, and reassemble.
If your batteries are working properly you are better off not messing with them. If it works, don't fix it.

Make sure you wire your 4 batteries in a balanced manner.
 
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Bubba1

Solar Addict
Have you considered two separate packs and a selector switch? Many don't like my suggestion but I do.
 

K8MEJ

Solar Addict
There's the aspect of having all the cells in a single battery balanced to maximize overall capacity and to even the wear and tear across the cells. In a parallel bank of four battery packs, wouldn't you want to do the same thing to maximize total capacity and to even out the wear and tear on the individual battery banks? I realize a huge assumption is keeping the battery cables and rest of the connection points even.

Right now, the two packs both maintain balance within the cells of each pack and across the two packs. It sounds like you advise I balance each pack individually and insert the two new packs at the same state of charge as the original two. I can do that by charging the new packs to the same voltage as the original and then putting it altogether then keep an eye on them to make sure they maintain a consistent SOC and voltage. That's certainly easier, for sure.

Thanks.
 
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