DIY battery bank build that needs help

[Rocjohns]

Hello all, I am absolutely struggling here and I need some sane guidance…

I have 4 LiTime 12v 100ah batteries connected in Series/Parallel for a 24v 200ah battery bank. I have a single victron battery balancer keeping them balanced.

Here is what I want to do:

I want to open up the 4 LiTimes and take out the 16 3.2v 100/105 ah cells and build a DIY battery banks with a heavy duty JKbms. I also want to buy 8 more 3.2v 100/105 ah cells to expand my array to 300 ah (want more longevity after sundown).

The question:

Based on above, is some sort of 8s3p array with 3 x 8s jkbms able to do anbove and if so, how would I balance power between the 3 strings? I would also want to add 8 more cells later for 400 ah.

Am I thinking this wrong? I do have limited funds and I can’t move to 48v because I have invested in all 24v victron equipment.

 

[boflyer]

Uhm, this seems like a lot of messy work without gaining anything. I wouldn't rip your four existing batteries apart if they are already playing nicely together. They each already have a BMS. So save the expense of a separate BMS. Plus none of your battery cells are matched or bought at the same time, and new ones would also not match your old ones. If you want to add capacity, just buy a LiTime 24v battery. A 100Ah LiTime 24v right now is $420. Add this in parallel to your existing group (likely cheaper than buying cells and a BMS). Or add a 200Ah 24v battery in parallel. You can scale up capacity as budget allows. Parallel the separate 24v groups via bus bars. Series parallel.

 

[Bananaman321]

Uhm, this seems like a lot of messy work without gaining anything. I wouldn't rip your four existing batteries apart if they are already playing nicely together. They each already have a BMS. So save the expense of a separate BMS. Plus none of your battery cells are matched or bought at the same time, and new ones would also not match your old ones. If you want to add capacity, just buy a LiTime 24v battery. A 100Ah LiTime 24v right now is $420. Add this in parallel to your existing group (likely cheaper than buying cells and a BMS). Or add a 200Ah 24v battery in parallel. You can scale up capacity as budget allows. Parallel the separate 24v groups via bus bars. Series parallel.

I say try it if it fails it's just for 12 volt batteries you can always order some prismic cells reuse the bms what better to practice on I've learned more from my failures than...

 

[littleharbor2]

Do the cells in these types of batteries have bolt down terminals or soldered interconnects? If soldered, I would hesitate to disassemble them.

 

[Rocjohns]

Do the cells in these types of batteries have bolt down terminals or soldered interconnects? If soldered, I would hesitate to disassemble them.

I want to say Will opened one of these up in one of his videos. I will check.

 

[Rocjohns]

I say try it if it fails it's just for 12 volt batteries you can always order some prismic cells reuse the bms what better to practice on I've learned more from my failures than...

I am leaning towards this.

 

[Rocjohns]

Uhm, this seems like a lot of messy work without gaining anything. I wouldn't rip your four existing batteries apart if they are already playing nicely together. They each already have a BMS. So save the expense of a separate BMS. Plus none of your battery cells are matched or bought at the same time, and new ones would also not match your old ones. If you want to add capacity, just buy a LiTime 24v battery. A 100Ah LiTime 24v right now is $420. Add this in parallel to your existing group (likely cheaper than buying cells and a BMS). Or add a 200Ah 24v battery in parallel. You can scale up capacity as budget allows. Parallel the separate 24v groups via bus bars. Series parallel.

I have a 24v 100ah LiTime in my cart. I just hate that these batteries aren’t very compact. It’s my backup plan, but I really want to stop paying for premade stuff and start building my own.

 

[littleharbor2]

I have a 24v 100ah LiTime in my cart. I just hate that these batteries aren’t very compact. It’s my backup plan, but I really want to stop paying for premade stuff and start building my own.

Building your own from scratch is very satisfying and, nowadays is cheaper than lead acid in many cases. It's really not very complicated.

 

[boflyer]

Building your own from scratch is very satisfying and, nowadays is cheaper than lead acid in many cases. It's really not very complicated.

I don't think lead acid is even a consideration here for cost or any other comparison, but yes, building your own can be satisfying.

 

[boflyer]

I have a 24v 100ah LiTime in my cart. I just hate that these batteries aren’t very compact. It’s my backup plan, but I really want to stop paying for premade stuff and start building my own.

Battery density, means size and weight can only get so small for a given capacity, but yes, I know you mean the bulk of packaging for multiple batteries, series cabling, bus bars, etc., makes for a more awkward and messy fitment of space. But you also said you were on a budget, so in that vein, simply adding capacity with another 24v battery (which you have?) would be your least expensive option.

Even if you want to rip everything apart and build a battery bank from the existing components, to reduce the footprint, you are doing so with a mishmash of battery cells, none of which were likely of similar voltages, which means fully charging them together will be a pain, as you will likely get one cell peaking earlier and others lagging behind, which will cut off your charging before the bank is actually full. If you want to build a battery bank, I would strongly encourage you to buy new matching cells for the purpose.

Rather than connecting and wiring all those mismatched 105Ah cells to achieve your goal, I would suggest starting from scratch, and buy 8- 300Ah prismatic cells for your 24v mission. Less complexity, and you can get matched cells, and need only an 8s BMS. fewer balance leads, fewer bus bars, fewer connections.

 

[Rocjohns]

Battery density, means size and weight can only get so small for a given capacity, but yes, I know you mean the bulk of packaging for multiple batteries, series cabling, bus bars, etc., makes for a more awkward and messy fitment of space. But you also said you were on a budget, so in that vein, simply adding capacity with another 24v battery (which you have?) would be your least expensive option.

Even if you want to rip everything apart and build a battery bank from the existing components, to reduce the footprint, you are doing so with a mishmash of battery cells, none of which were likely of similar voltages, which means fully charging them together will be a pain, as you will likely get one cell peaking earlier and others lagging behind, which will cut off your charging before the bank is actually full. If you want to build a battery bank, I would strongly encourage you to buy new matching cells for the purpose.

Rather than connecting and wiring all those mismatched 105Ah cells to achieve your goal, I would suggest starting from scratch, and buy 8- 300Ah prismatic cells for your 24v mission. Less complexity, and you can get matched cells, and need only an 8s BMS. fewer balance leads, fewer bus bars, fewer connections.

And this is what I’ve sort of decided to do. I went for 8 x 105 EVE cells and an 8s jKBMS. Will just put this unit in parallel with my 4 x 12v 100 configured for 24v. I have a large enough container for another 8s string and BMS to have a total of 200 Ah 24v diy build. One day I will do the big build once I move to house, but this system just runs pool, shed, hot tub, and other outdoor junk.

 

[Rednecktek]

Rather than connecting and wiring all those mismatched 105Ah cells to achieve your goal, I would suggest starting from scratch, and buy 8- 300Ah prismatic cells for your 24v mission.

And a welder, and a grinder, and some hole saws...