Can i do this? Spitballing an idea.

Tyler702

Desert dweller, quiet prepper
I have 8x100Ah cells from OKS. Rock solid! I've recently upgraded to 8X200Ah cells for my 24V garage build, so I'm spitballing ideas for these 8 100Ah cells. More specifically, a milk crate build for camping purposes. I've decided to go w a 12V config, and I should be getting the 12V 120A bms from OKS in the next few days, along with a 12V 1200W PSW inverter. My question is: Am I stuck with a 4S 12V 100Ah bank, or is there a way to parallel into a 4S2P bank and still be able to use the 1 bms? Essentially, I'd like to utilize all 8 cells for a 12V 200Ah bank, and at this time, only for a few days of boondock tent camping. Loads only, no charging. The bms would only serve to cut out once the bank has reached its cutoff point, which, according to my calculations, should be about 3 days. Can I parallel 2 cells to act as 1, then series those pair into a 12V? Could I then attach the bms sense leads to the middle of the appropriate busbars of the 2 paralleled cells? So the bms thinks it's just 1 cell? My loads will be low, like 600W at best. Once back home, I can charge the pack back up and be ready for my next outing. Thoughts?
 

MisterSandals

Participation Medalist
or is there a way to parallel into a 4S2P bank and still be able to use the 1 bms?
No, this requires 2x 4S BMSs.

If you wire as DThames suggests (so i think anyway), and configure as 2P4S you can use a single BMS.
I have a big battery in this configuration and it works great. I strongly recommend that you match your pairs so that the pair totals are equivalent. Strongest paired with weakest. Second strongest with second weakest....

If you labeled your cells and have data, this should make the process easier.
 

Tyler702

Desert dweller, quiet prepper
Ok, I think I may have mixed my 4S2P with 2P4S? I'm not sure what you would call pairing/paralleling 2 cells into one, then series 4 of those pairs into a 12v config. Like this is my plan: 2P4S?
 

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A.Justice

Swears he didn't start that fire.
I actually just finished wiring up my 2p4s pack after an upgrade earlier today. Uses one 150 amp, 4s BMS. Picture as an example.
 

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Tyler702

Desert dweller, quiet prepper
I actually just finished wiring up my 2p4s pack after an upgrade earlier today. Uses one 150 amp, 4s BMS. Picture as an example.
Thats it! Thats what I'll be doing. Wish I could procure 3 custom busbars for those long 4 post terminal runs, but other than that, spot on! I also thought I'd drill a small hole in the middle of the + bars to place my sense wires on. My thinking being the bms reading might be slightly off if attached directly to one of the paralleled cells. Splitting hairs? Idk..
 

Tyler702

Desert dweller, quiet prepper
2' x .5" Copper pipe, 2 beers, hacksaw, hammer, .25" drill bit.

I recommend slotting the holes to allow for easier fitting and some cell expansion.
Ha!! Point taken! Hammer to flatten the pipe and beer to cool the bars while cutting and drilling I suppose? Ok to have a vodka/tonic prior to hammering?😄
 

Pyrofx

Flux capacitor builder
Those bars suck. Either jump o. Ebay or makes cables with welding wire. Hammered pipe will never be flat.
 
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