Series and Parallel for batteries

[lokmer]

Setting up my first off-grid system at 48v nominal, and trying to figure out how to wire the batteries in.
I have 2 24v 100AH batteries, and 8 12v 100AH batteries.
I know I need to wire the pair of 24v in series with each other to make one 48v batt.
Similarly, I need to do 2 pairs of 4 12v in series to make 2 48v batts.
The part where I'm stuck is:
How to I hook the resulting 3 48v batteries up to my charge controller? Do I connect the seriealized batteries in parallel at (for lack of a better term) the "head" cell in each bank, and then connect the charge controller to the "head" cell in one of the 3 banks? I have this strange (and probably incorrect intuition) that doing it this way would put extra stress on the cell to which the charge controller is connecting. Is there a place I can look this up? Having pored through the forums here and watched all the youtube videos I can find I'm still lost on this point.

(LiFePO4 chemistry, in case it matters).
Thanks much!

 

[Samsonite801]

You're right, 3 48v battery banks paralleled. It's a good idea to fuse each paralleled 48v battery unit, so if one shorts it can break off the main 48v bus going to the charge controller. Are all the cell groups protected by their own BMSs?

 

[lokmer]

Ah, fusing! Hadn't thought of that. Where can I find info on how to size the fuses?

Rather than these being 3.48v prizmatics, these are batteries (most of them CHINS 12v--can't remember the name of the 24v), and they do have bms's in the individual batteries, but I had not thought of BMSs for the series groups. Is this something I ought to consider? I've been trying to minimize parts so that I minimize points-of-failure, but obviously I don't want to go so far down that road that I actually create big doors for problems.

 

[lokmer]

Follow-up:
If it is something I ought to consider, is there a good brand I oughta look at? I'm seeing a lot of Daly BMSs around at a relatively high price point, and then a lot of others at lower price points. Is there a good resource for what BMSs provide good reliability and value-for-money?

 

[Samsonite801]

Technically, you don't need a BMS on group level (just make sure all batteries are top balanced to start with)... Your cells are all protected by BMSs in each individual battery (for overvolt/undervolt, overtemp/undertemp protection)... You can monitor them, but they should all stay balanced, if not, then could add in a balancer or something. I suppose you could put a BMS on group level if you wanted but I probably wouldn't bother...