How to build a LiFePo4 battery bank.

[StirCrazy]

A lot of people dont have any idea how easy it is to build a DIY LiFePo4 12V battery so I'll post a deicent video of how to do it so people can decide for themselves if it is in there capability.

this video is pretty decient on how to do it, what is missing is some sort of case. the Prismatic cells like to be clamped togeather slightly if you going to be running high currents. I have seen cases made out of wood with threaded rod providing the pressure, and several other ways also.

also I am not a fan of the BMS he uses, there are lot better ones, but he explains he needed the high capacity one to do a torture test on the cells.

so he builds a 280Ah 12V battery in this video, if you need more you could build 2 and then just tereat them like two 12V batterys and run them in parralell, or just build it all in series and do a 24V set up if you want to do the higher voltage systems.

280Ah LFP build

Steve

[time2roll]

I put the 2x Overkill BMS and some fuses on a small shelf in the box. This is actually two separate batteries. Each has 2 cells in parallel and 4 in series so 8 cells per battery.

I expect to get this into my front compartment next weekend.

[time2roll]

Cells in the box measure 24" long, 15" wide, 12" high. About the same size-weight as my previous 4x GC2. s/b 1000 Ah usable vs 200.

[time2roll]

16 cells on the bench getting an initial charge to verify condition. All seem to be good.

[S_Davis]

Did you get your cells? Any progress?

[StirCrazy]

so got a call yesterday, my buddy just placed an order for sixteen 280AH cells. if the price he paid keeps falling or stays the same I'll probably put my order in around end of july/aug. For his system we are building four seperat 12V batteries using the overkill BMS which will give us a total amp draw capibility of 480Amps if he needs it. he also wants to take the propain furnace and such out and go to a heat exchange system incase anyone is wondering why he wants 1120 usable AH. he has also suckered me into helping him put a bunch of solar panels on the roof, I should have let the phone ring 😉

Steve

[time2roll]

More like three volt cans in this world 😉

[StirCrazy]

pianotuna wrote:
otrfun,

It may be an issue if the batteries are connected in series to create a 24 volt bank. This means using six volt jars may be not recommended.

For parallel they need to be connected in a balanced manner.

a 24V battery is no issue, you would make one battery using 8 cells and a 8S BMS. it is designed for a 24 volt battery. they also make a 12S and a 16S BMS. so if you want to buy the big step down converter you could make a 280AH 48V battery and use that.

Steve

[pianotuna]

FWC wrote:
What is a '6 Volt Jar' in relation to lithium batteries?

I would also agree that how you wire the batteries is not that important, besides using the appropriate wire gauge. No harm in 'balanced wiring' but not something to worry about.

pianotuna wrote:
otrfun,

It may be an issue if the batteries are connected in series to create a 24 volt bank. This means using six volt jars may be not recommended.

For parallel they need to be connected in a balanced manner.

Tell us about your system. Then I'll answer your question.

[FWC]

What is a '6 Volt Jar' in relation to lithium batteries?

I would also agree that how you wire the batteries is not that important, besides using the appropriate wire gauge. No harm in 'balanced wiring' but not something to worry about.

pianotuna wrote:
otrfun,

It may be an issue if the batteries are connected in series to create a 24 volt bank. This means using six volt jars may be not recommended.

For parallel they need to be connected in a balanced manner.

[time2roll]

pianotuna wrote:
For parallel they need to be connected in a balanced manner.

I am thinking this issue goes away with LFP. Cycle life is so long combined with low resistance and increased efficiency this balance matters so little nobody is concerned.

[pianotuna]

otrfun,

It may be an issue if the batteries are connected in series to create a 24 volt bank. This means using six volt jars may be not recommended.

For parallel they need to be connected in a balanced manner.

[otrfun]

FWC wrote:

otrfun wrote:
Even if you used the same BMS and cell configuration for =>two parallel battery packs (to increase overall current), wouldn't you potentially run into charge/discharge balance issues between battery packs after a certain number of cycles? Talking about the same balance issues the BMS's are supposed to help prevent from occurring between the individual cells in each battery pack. If this did happen, one should be able to resolve it by top balancing the battery packs themselves, right?

No. The two packs are in parallel, so they will always see the same voltages and will be inherently balanced (just like the 30 or so cells in parallel inside a battleborn stay in balance). Within the packs, the cells are in series and could get out of balance, but the balancer in each BMS will keep them in balance.

Thx for clarifying. Makes sense.

[FWC]

otrfun wrote:
Even if you used the same BMS and cell configuration for =>two parallel battery packs (to increase overall current), wouldn't you potentially run into charge/discharge balance issues between battery packs after a certain number of cycles? Talking about the same balance issues the BMS's are supposed to help prevent from occurring between the individual cells in each battery pack. If this did happen, one should be able to resolve it by top balancing the battery packs themselves, right?

No. The two packs are in parallel, so they will always see the same voltages and will be inherently balanced (just like the 30 or so cells in parallel inside a battleborn stay in balance). Within the packs, the cells are in series and could get out of balance, but the balancer in each BMS will keep them in balance.

[otrfun]

Even if you used the same BMS and cell configuration for =>two parallel battery packs (to increase overall current), wouldn't you potentially run into charge/discharge balance issues between battery packs after a certain number of cycles? Talking about the same balance issues the BMS's are supposed to help prevent from occurring between the individual cells in each battery pack. If this did happen, one should be able to resolve it by top balancing the battery packs themselves, right?

[FWC]

time2roll wrote:
I plan to use two Overkill BMS on two parallel batteries. 240 amps continuous. I believe Overkill will surge 130 to 150 amps for a few seconds.

You can program the max current and duration on the LLT/Overkill. 150A for a few seconds should be fine as the problem is heat dissipation in the MOSFETS. You could even add a better heatsink if you need to do higher currents often.