DIY LiFePO4 build
so this started because I gave away my first DIY build (280amp) to a good friend, because I also wanted to upgrade the 5th wheel but standardize the batteries between the 5th and truck camper so I ca...
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so the hard part is deciding how to mount this in the camper. when I had the two 6V batteries in it they were in a outside storage space, when I built the 280ah lifepo4 I put them in a smaller one that was originally made for a single car battery. this one I want to move them into an interior closet.
this is where the new home is going to be. the bottom shelf that covers the furnace will be the base and I will take the bottom 12" of the cabinet and move the solar charge controller down also, so all the power stuff is mounted in the bottom. then I will add shelves as we never use it as a closet, just a place to pile stuff into so I will add a few shelves so we can pile stuff a little neater haha
So with that in mind I decide to make something up on the go and see how it turns out, keeping in mind it has to be able to provide compression to the cells, act as a support for the first shelf, and provide mounting places for all the electrical bits.
bottom, back, and one side on. glued and screwed togeatherused construction adhesive and screws.other hard side installed, the front panel is floating and will be used to provide the compression.rubber mating on the bottom of the battery and both endsclear vinal tubing over the threaded rod so it can't scratch the cellsrods installed and slight compression applied. I may switch out to longer rods and use springs on it once I figure out which springs to use. the chunks of vinal tubing are just to protect my hands while I am working on it.. I have a bad habit of cutting my self on anything that I can hahajudging approximate location of BMS, and hole drilled to tape the temp sensors to the side of the battery cellsso that's where I got to on Friday, have to see what I am doing today, I have to rip some parts out of the camper, well the shunt anyways, to finish working on this. so I will have to shut down the solar panels, take out the 6V batteries that I put back in for the last half of last season after I gave the old Lifepo4 to mu buddy.
I also have to decide if it is worth it for me to take this all apart again just to paint it, or just leave it natural, your not going to see much when everything is installed so I am not sure if it is worth it right now. maybe I'll just get it in for this season and do that as a winter project if that's what I decide.
I'll post more as I get more done.
Looks good great job so far. I doubt I would paint the boxes as they are inside an interior cabinet.
Do you mind expanding on the compression of the cells? Is the compression just to keep them from moving around in the box? Or is there a engineering advantage to putting pressure on the cell cases?
ya, I am leaning towards not painting it also, then I don't feel bad if I screw something new to the sides haha
there is an engineering aspect to them also, plus the added benefit of them not moving around. when they charge at higher rates the casing can expand and swell, so by putting between 4000nm and 7000nm (min/max) of compression on the battery pack, it serves to enhance the lifespan and performance of the battery by preventing internal components from delaminating. It also helps to manage swelling that can occur due to internal pressure during charging and discharging cycles.
so do you need it, its debatable, the cycle life is based on test of cells than are under compression, so by not having them in compression it stands to reason that it will be affected, and eve recommends compression. For the average rv use though, where our charging is 55amps at max, then on one 100Ah battery it will make a lot of difference in my opinion, but if you have 900ah like my 5th wheel and your only charging at 55amps then you are only charging at 0.06C and that is pretty gentle on the battery. so the bigger worry would be from vibration of traveling. there are also people who claims that most of the damage from swelling is done in the first 5 to 10 cycles so you only need compression for that..
then there is exactly how much cycle life do you lose uncompressed, some claim that instead of 4000 cycles you might get 2500, that sounds like a lot, but it is still 24ish years with two cycles every weekend, which is why the cheep batteries don't worry about it as it is going to outlast their 5 year warranty unless you abuse it which then the warranty won't cover it anyways..
for me the benefits far outweigh the extra work, as I do a lot of off roading to get to places so holding the guts of the battery together with compression just makes sense. I still have to figure out how to do it in the 5th wheel, what I might just do is make the compression fixture the battery hold down under the steps so I just drop the battery into it and tighten the end down. I have to get under the stairs and see what I have to work with and come up with a game plan for when I put those ones together.
