24V Large battery build. 24x(3.2v/320Wh) cells and a BMS.

[Dertychai]

Hello!
I am new to building Batteries and the whole solar life. Building an off grid Tiny Home. Wired for 110 throughout. Have an Outback Power FLEXpowerONE 24v 3500watt system. I bought 24 cells ( 3.2v 320Wh) before knowing much of anything. I have heard that I can make a large battery with what I have if I wire in parallel and series using one BMS (100a 8s 24v) from Overkill Solar. My Spidey sense is telling me I jumped the gun and will need to obtain 2 more BMS units to make a total of 3 24v batteries and wire them together. Any advise pointing me in the right direction would be appreciated. I also have a Battle Born 12v that I would like to put in the system as well if possible, but could go in another project if this is unrealistic.
Thanks.

 

[Tonic]

If you are running 24 volt you would need 8 cells in series.
If you would like to make one big battery with the 24 cells you have you have to wire 3 cells in parallel. then you would have 8 batteries of (3.2V 960Wh) now that you have those you would wire those "8" batteries in series to create your 24v battery. and you connect your bms to this "big battery )

 

[Dertychai]

If you are running 24 volt you would need 8 cells in series.
If you would like to make one big battery with the 24 cells you have you have to wire 3 cells in parallel. then you would have 8 batteries of (3.2V 960Wh) now that you have those you would wire those "8" batteries in series to create your 24v battery. and you connect your bms to this "big battery )

I appreciate the input. Time to play some Tetris with the layout and configuration.

 

[HaldorEE]

If I was building a system that big for residential use, I go ahead and build 3 individual batteries, each with their own BMS and wire the 3 batteries in parallel. That way if one of the batteries has an issue, you still have the other two. Plus a 900A BMS is going to incredibly expensive. I don't know what kind of contactor you could use for that.

You can get an 8S, 300A FET based BMS for less than $100.

 

[TankFish]

If I was building a system that big for residential use, I go ahead and build 3 individual batteries, each with their own BMS and wire the 3 batteries in parallel. That way if one of the batteries has an issue, you still have the other two. Plus a 900A BMS is going to incredibly expensive. I don't know what kind of contactor you could use for that.

You can get an 8S, 300A FET based BMS for less than $100.

Hi, sorry to steal the OP. If you did 3 separate batteries and 3 different BMS, how would you wire the parallel? Would the BMS negative output go to the next cell? If so, wouldn't the whole system shut down if any of the 3 large packs went down? Meaning is the cell directly feeding the inverter tripped the BMS for whatever reason, the other two would shut off, or the middle one goes down and the back kicks off. But with them in a parallel, would any shut off with at least one BMS active?

FYI I am not critiquing, I am new to these builds and just ordered 24x3.2v LiFePO4 280ah cells and will be building this same system described by the OP and am just looking how to wire it to a BMS or BMS(s). I am very curious on how to configure this, especially when I'll essentially be creating a 840amp bomb with those 8s and 3p. I do have a few months to plan, since these will be coming from China.

 

[Steve_S]

Batteries in Parallel are most often to a common DC Bus using 2 Busbars.
These batteries will share Load & Charge.
Each battery pack is independent as each BMS controls the cells within its pack. (they should all be fused.)
If any one battery cuts off for any reason, the remaining batteries will continue BUT they divide Load & Charge.
All cabling from Battery to Busbar should be of equal length, to maintain an equilibrium.
All Battery cables should be kept as short as possible AND together as much as possible to reduce EMI/RFI "noise" and voltage ripples.

Refer to this document from Victon, notably from page 17 (related to LFP).

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

Hope it helps, Good Luck