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

[drgslayr]

What I did was wire this to a switch directly to the battery. I bypassed the BMS since it has low temp cut off.

the tank heater has its own thermostat, so if it starts to get too cold I flip the switch and go on with my day.

https://www.amazon.com/gp/product/B07GW8ZX7X/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

[BFL13]

Looks like you can handle whatever happens--well thought out set-up!

You need to do your hot water line trick again to put a hot water line by the battery bank, and heat that water from the furnace exhaust now being wasted to the outside air. 🙂

[time2roll]

BFL13, wish I had all the answers. I don't.

Heat pads will be controlled with a thermostat relay and powered from the battery.

https://www.mpja.com/Digital-Temperature-Controller-FAHRENHEIT/productinfo/32764+MP/



Thermostat has a display. BMS gives data through the BT app. Worst case the BMS prevents charging and discharge at low temperature.

Generator or solar would provide for heating even if the BMS had cut power. Not sure the solar will work with no battery connected. I don't expect to get in that situation. If it looks like trouble I would adjust as needed.

The 700w generator will put a lot of power in the battery on a 30# cylinder. Shake down cruise will be in Yosemite in two weeks. Only a small chance of getting to freezing. Not all is even connected yet.

The heat pads will be wired in 2 in series for about 60 watts. I have drawn up potential plans for a second thermostat and DPDT relay that would switch all pads to parallel for 240 watts of heat in extreme cold. I will be doing that if I plan to be in your area in winter 😉

[BFL13]

Time2roll, very classy job!

Just curious how you plan to operate it while camping when it gets cold at night in some scenarios. I know you are a minimalist for monitoring stuff.

How do you operate the heat pads side of it all? How do they get their power? More than one way?

Do you figure on a slow charge if under 5C and then you can crank up the charging rate? Or just wait till at 5C?

How do you know the batt temp so you know what charging rate to use?

If starting from cold, how long to warm up the batts enough with those heat pads? Will the little propane generator run that long so solar can then charge them, or is that not in any camping scenario where you go, so it doesn't matter?

Very nice job, and it looks like you can move it to your next rig when that time comes too, so that's clever.

[S_Davis]

My 12 EVE 280ah cells showed up today, building three 12v 280ah packs. I am going to run two in the truck with a spare on the shelf.


EVE 280ah

[Itinerant1]

Yes, very nice and welcome to the world of lfp. 😉

[pianotuna]

Time2roll,

I guess that is totally the end of dragging around a generator for you! I hope it works wonderfully well.

[time2roll]

Installed and working....

[time2roll]

Heat pads: 50 x 100 mm fit nicely on the 70 x 200 mm cell edge.
I am gluing them on with Permatex high temp red silicone gasket maker adhesive.

https://www.aliexpress.com/item/1005001620200397.html

[StirCrazy]

time2roll wrote:
I plan on minimal compression with two zip-ties around the box. The straps are temporary to hold the cells in place to fit the bus bars. If using ratchet straps I would re-thread them to eliminate the hooks.

ok perfect, I dont think with that size of a bank your going to get anywhere near the charging rate that would require more compression anyways haha

time2roll wrote:
I decided to skip the separators. They are wrapped nicely in the standard blue vinyl. Easy to overthink everything. Have not really read any issues with skipping the separators even though some insist something is needed. Not intended to be a bulletproof off-pavement design.

ya the only reason I ask, is a lot of people have been putting something thin in that will prevent that vinal from getting scratched or worn off exposing the metal under it and a possible short, but I don't know how tough that vinal coating is and if it is nessasary

time2roll wrote:
The box wall next to the fuses is floating (movable). There will also be heat pads, one per cell, on the outside controlled with a thermostat. They are 15w silicone pads. I will run two in series for maybe 4 watts each, 64 watts for the entire block.

Member Pianotuna will be pleased to see my battery wiring will finally get balanced 😉

that looks almost exactly like mine is set up haha. so I imaging you are self powering the pads from the battery bank? I was thinking of doing some sort of heating pads but make them so I could power them directly from the solar controler (load termanals I believe, have to read up and see how that works) so as I am driving the batteries will be kept warm. I am also going to move them into the empty space under the stairs of the 5th. right now the cold air returns for the furnace are in the steps so the warmed air will always flow through there and there is room for 4 battery packs under there easy. do you have a link to the heating pads your using?

Steve

[pianotuna]

time2roll,

Hurrah!

[time2roll]

I plan on minimal compression with two zip-ties around the box. The straps are temporary to hold the cells in place to fit the bus bars. If using ratchet straps I would re-thread them to eliminate the hooks.

I decided to skip the separators. They are wrapped nicely in the standard blue vinyl. Easy to overthink everything. Have not really read any issues with skipping the separators even though some insist something is needed. Not intended to be a bulletproof off-pavement design.

The box wall next to the fuses is floating (movable). There will also be heat pads, one per cell, on the outside controlled with a thermostat. They are 15w silicone pads. I will run two in series for maybe 4 watts each, 64 watts for the entire block.

The lid will come later. The sides will most likely stay open. More pictures in a week assuming I make progress.

To be installed into this space:



Member Pianotuna will be pleased to see my battery wiring will finally get balanced 😉

[StirCrazy]

time2roll wrote:
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.

I like that setup. only questions I have is the use of the rachet strap and the potential for the hooks to damage the side of the battery cell. and I cant see any isolater between the cells. if the rachet strap is temporary how do you plan on compressing the cells to get better life out of them or are you, not worring about it as the charge rater will be lower than .25C and no risk of any heat?

Steve

[StirCrazy]

FWC wrote:

otrfun wrote:
Overkill BMS's seem to have a very good rep; however, to my knowledge they don't make BMS's larger than 120a. For those who have 2000-3000w inverters with 200-300a current requirements what options do they have? Daly makes a few 150-250a models, but they have a somewhat sketchy rep. I suppose one could parallel multiple Overkill 100-120a BMS's and LifePo4 battery packs.

Running several in parallel is not a bad idea, it would be the same as running several drop in batteries in parallel. It spreads the load (and heat) across multiple devices, and provides redundancy as well. On the down side, you would need to look at several screens on the app to see what each pack is doing, but that is not a huge deal. If you are handy you could also merge the data from each BMS into one stream as the protocol is open source.

To give credit where credit is due - these are not Overkill Solar's BMS, they are just retailing/rebranding LLT powers BMS.

yup and if you go to there site you can get a 200amp version.

https://www.lithiumbatterypcb.com/product/3s-12-6v-4s-16-8v-or-4s-14-6v-lifepo4-battery-bms-with-120...

Steve

[pianotuna]

time2roll,

Exciting times for you I'm sure.