DIY 200 Amp-hr LiFePO4 Van house Battery with steel compression and thermal

Posplayr

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I have just completed the complex part of building a steel compression fixture for my Van application. That is it with the cells still need to be wired to the BMS but all the mechanical is done except for the actual mounting in the Van. The assembled unit with the light grey Hardy board cover is pretty much ready to mount.
After much reading on the subject and having purchased some somewhat bloated but full capacity cells (8x 100 Amp-hr) , I decided to go with a metal compression fixture (to meet the 12-18 psi load range) using SSB.012.014 compression springs that would allow for the possibility of excessive expansion of the cells. I would also use various spacers materials (G4 fiberglass and ABS sheet) and some fireproof Hardy Board material from Home Depot.
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https://www.zoro.com/raymond-iso-d-...nsactional_None_All_None_1&smtrctid=111257197

The springs are fairly long 3.5” which allows for a full 1.5” of compression. With the side by side battery pack design (63 inch^2 area), 12 psi corresponds to 759 lbs. Using 8 springs, I need 95 lbs per bolt which is 0.75” of compression each (126.2 lbs/Inch). In the arrangement below using 1”x2"x 11 GA rectangular steel tubing, it is easy to set the compression by measuring the spring compression with a depth gauge. The springs are recessed into the side structures and so the overall outside dimensions of the battery pack are kept to a minimum. Total outside dimensions are 10 1/8" (wide) x 17 1/2" (length) x 6 1/2" (height) for the 200 Amp-Hr unit.

I used a wood clamp to assist holding the fixture together while I tensioned all the all-thread/springs. You can also see plastic coved steel cables with wooden handles that I can use to carry the battery. It weighs 58 lbs without the cabling. I plan to only use 4 bus bars to bridge the end to end gaps (length wise) everything else will have 4 awg cables and crimp ends.

The idea for the cables comes from thinking through the scenario where this battery pack were on fire and I need to get it out of the van. Because everything is metal, nothing should fall apart but it may be too hot to handle. So hopefully the wooden handle would not be burned and would provide some insulation to lift it out of its mounting spot under the bed on the drives side rear wheel well.

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Because I live in Tucson and it gets hot where 110 DegF (43.3 DegC) is the summer is not unusual and we can have freezing weather in the winter although not typically a lot, I’m going to try and also do some thermal controls and have installed a surplus ebay cooling plate https://www.ebay.com/itm/113722337224 and will use thermostatically controlled a heating pad.

Inside this steel compression cage is a 3/16” aluminum cooling/heating plate. The idea is to split the 4 inline cells so that the maximum expansion relative movement is for two side-by-side cells. I assume no length wise expansion. This split is achieved with a vertical 4” plate that helps to remove heat from the inside of the battery pack. The liquid cooled cooling plate is screwed with thermal pad to the bottom of the cold plate and the whole assembly will rest on a thermostatically controlled heating pad.
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There is also a vertical end plate for the 4S 120A Overkill BMS with Bluetooth and the and 4S active balancer.

https://www.aliexpress.com/item/4001013797039.html?spm=a2g0s.9042311.0.0.5cb74c4dCVmSVO

And the cells are paired to minimize stacked cell imbalance.

https://diysolarforum.com/threads/parallel-cell-capacity-balancing-pccb-procedure.26301/

The liquid cooling will be provided by chilled water from a 120VAC dorm fridge or room temp water on a low power pump.

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