How to build a 48 volt 200ah Lithiom Ion Phosphate battery

[tnt4him]

I have 15 lifepo4 3.2 200ah cells. I have some experience working with batteries in the military, mostly Nicholl cadmium. I want to build a 48 volt 200ah battery for the solar system back up. I'll need to find a battery box and the correct BMS. Any helpful tips much appreciated.

 

[Horsefly]

Ummm, before you can do anything, you need one more LFP 200Ah cell. You can't build a 48V battery out of 15 cells.

 

[rmaddy]

FYI - just to get the terms correct. LiFePO4 is Lithium (Li) Iron (Fe) Phosphate (PO4), not to be confused with the more generic term of Lithium ion. LiFePO4 is a specific type of Li-ion. And NiCd is Nickel Cadmium. Finally, amp-hours is abbreviated Ah so you have 200Ah cells.

 

[TerrySilver]

Lots of videos on YouTube about building your own. watch them. High level, you need matching even number of cells, people get them from eBay, Amazon or Alibaba.com. Some other sites have ready to build components too. Then you wire them up with a BMS. If you run 4 12v in series I believe the recommendation is for each to have a BMS. That adds to the cost.

 

[tnt4him]

Ummm, before you can do anything, you need one more LFP 200Ah cell. You can't build a 48V battery out of 15 cells.

I added one. But please explain your math.

 

[BMcL]

I added one. But please explain your math.

It takes 4 each 3.2V cells to make a 12V battery using LifeP04 cells. So 16 for a 48V system.
I'm a newbie so I can't explain beyond that.
You won't need but one BMS to monitor it.

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[rmaddy]

It may help to understand that while 15 x 3.2V = 48V, you don't actually want exactly 48V. A 12V nominal battery is really 12.8V. So a 48V nominal battery is really 51.2V.

The other thing to understand is that you need your cells in 4S to build a 12V nominal. You need cells in 8S to build a 24V nominal, 12S for 36V nominal, and finally you need 16S to build 48V nominal.

If you wanted more capacity you could double it with twice the cells and then put the cells in 4S2P for a 12V, 8S2P for 24V, etc.

Incase you are not familiar, the "S" and "P" means series and parallel respectively.

 

[MisterSandals]

You need 4S2P to build a 24V nominal, 4S3P for 36V nominal, and finally you need 4S4P (16 cells) to build 48V nominal.

Nope, those are all 12.8V.

 

[rmaddy]

Nope, those are all 12.8V.

Ugh! I wasn't awake enough for that post. I was partially confusing cells with completed batteries. I have fixed my post. Thanks