RV Battery Build – looking for advice and such…?

Zbugsii

Solar Enthusiast
Joined
Aug 20, 2021
Messages
24
I am looking for answers, thoughts and comments on my RV battery project.

Summary:

I have a metal battery box welded on the front frames of my travel trailer. It has a hinged cover and though not water proof, water would not splash directly on the enclosed components. The size of the box is 15”W x 13”L x 11 ¾”H.

I have looked for a plastic box/enclosure for trying to make two new 12v 200+ Ah LiFePO4 batteries to place into my metal RV battery box. I have found nothing suitable. I was considering just getting 2 SOK batteries and putting them in there…. BUT, they just will NOT fit. So, now I am in the planning stage for making my RV metal battery box be my battery enclosure for 8 cells and 2 BMS.


My Planning:

Put two rows of 4 cells side by side on top of a cushioned rubber mat. Put something (???) between the rows and between each battery. That something is currently an unknown and I am looking for suggestions on this…?

I will then mount two each surface mount battery terminals (+ and -) on the side of the metal enclosure for connecting the BMS’s and wires to the RV.

I will try and find a flat plastic box to fit one each or both of the BMS’s and mount them on top of the two rows of cells. Provided I find a decent box, I can make it very water resistant.

Questions?:

I have seen it said, cells should be “compressed” together to prevent bulging. Should I do so and is it really needed? If so, thinking of using some closed cell foam tape around each group of 4 cells and stainless steel hose clamps all the way around to hold them together. Thoughts on this?

What should I put between the cells and the rows of cells? I will not have much room between the rows of cells, since cells are just under 7” wide for each row and my enclosure is 15”. I am planning to put something on the outer sides of the cell rows to help keep them in place and insulate them from vibration and such.

BMS mounting… maybe just use double sided sticky tape in the plastic box and the same for plastic box to the top of the batteries? Or just leave it loose on top of the batteries?

Thoughts, comments and whatever… ? Are most welcome. Thank you
 

K8MEJ

Solar Addict
Joined
Nov 23, 2020
Messages
275
Location
Central Ohio
Do you really need to put the batteries on the front frame of your RV? I put all my LiFePO4 batteries under the bed in my travel trailer. This keeps casual thieves from stealing them, protects them from the weather, and most importantly, helps keep them from getting too hot or too cold. I was willing to do major rewiring in my 2018 travel trailer to convert it to work completely off-grid. But, even if you don't want to do major rewiring, it should be pretty easy to relocate the batteries inside a storage area somewhere.
 

Zbugsii

Solar Enthusiast
Joined
Aug 20, 2021
Messages
24
I would have considered that... but the boss is unwilling to give space. I can lock my battery box, so that helps. As far as temps go... yes, but at different times it gets hotter inside than outside. Cold is not a problem. If it becomes so, I have a DC warming pad that I can place in the battery box to keep it out of the danger zone.

Thanks for your comments... hopefully I will get more.
 

K8MEJ

Solar Addict
Joined
Nov 23, 2020
Messages
275
Location
Central Ohio
Make sure you have a way to deal with water that condenses inside the metal box. If there is enough air movement then it likely won't be too much issue. You can buy inexpensive flexible plastic cutting "boards" to separate each cell from each other and between rows. You can use thicker plastic to put on top of the cells and put your BMS's on top of the plastic board. As for compression, I got all wound up about that when I built my packs but from a practical standpoint, I just don't think it matters too much to get it exactly right. I think stress on the cell terminals is the bigger issue from cell movement. Today, I'd use fiber reinforced packing tape to hold the cells together. Do this when the cells are approximately 50% state of charge. Will had a recent video where he used foam tape between the cells that allowed a little movement in the middle of the cell to expand and contract, but kept the cell terminals stable.

I don't want to get into the middle of your domestic relations, but what happens if you find that you want or need more battery capacity? You'll be limited to what you can put on the tongue of your trailer.
 

Zbugsii

Solar Enthusiast
Joined
Aug 20, 2021
Messages
24
Well, should negotiations fail with the boss, I can quit being the driver and the boss goes nowhere. So, I pick the battles based on weapons on hand.

Based on what I think, with the capacity I am going to.... I think I will be good for a long while....

I have found a flat waterproof box that should work very nicely for the BMS's and they will fit on top of the batteries.

Thanks K8MEJ for your comments.
 
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