Please Check 2 X 8S Lithium Cell Build

[chrisski]

Welcome comments on my diagram prior to assembling these 2 X 8S 214 volt total of 560 ah build for my RV. I am putting these in a slide out battery tray, so this limits how to place the cells. 8S will fit in the 24 1/4" Wide 24" tall picture, but once compression and material between cells is taken into account, the cells don't fit.

-Drawn to scale: the Brown Box is a slideout battery tray; Eve 280 cells are black boxes
-Not drawn to scale are the Class t fuse holders (7" X 2"), busbars (7" X 2" long), and Overkill BMS (Oddly enough, don't see dimensions, but will fit in the space shown).

 

[BuffaloTrace]

At 24" you could just do a straight side by side 8s with similar positioning of negative and positive terminals at either end of the pack. I'd imagine it would make compression, layout, and bus bars, to be much simpler.
280ah cells are approx 2.9" thick. Could still have 3/4" to spare and over an inch in the 24.5 direction.

 

[chrisski]

At 24" you could just do a straight side by side 8s with similar positioning of negative and positive terminals at either end of the pack. I'd imagine it would make compression, layout, and bus bars, to be much simpler.
280ah cells are approx 2.9" thick. Could still have 3/4" to spare and over an inch in the 24.5 direction.

Trying to avoid what you mentioned for spacing requirements. Looking for a second set of eyes to see that how I have the terminals set up on the batteries is indeed 24 volts.

That 3/4" you mentioned turned out to not be enough. I got my reasons as odd as they may sound for this odd configursation. Once I take into account Building a cover, how tight the already installed battery box is, the amount the nuts stick out on the compression rods, the width of the plywood for compression, turned out to be too much. Moving the battery box is a huge pain in the but and a 1/4" off on the drill when I do so makes a punctured black water tank.

 

[Horsefly]

@chrisski - Looks to me like the diagram does give you an 8S pack on each side. I agree with @BuffaloTrace, but if you have some mysterious reason for that configuration, it's all good.

 

[NwCali]

I see why he wants this layout, why does no one else?

 

[chrisski]

I appreciate the help. Actually took a few iterations to get an 8S. Found it so much harder setting these cells up when they were not in the normal side to side config.

These are a couple of the other configurations I considered, and the batteries and box are to scale, but the 1/2" on each side of the plywood for compression and the 2 mm of spacing between each cell added up:


I will lay the batteries out in the tray the 8S way first, and I do hope it fits. Right now, in Arizona we are having a rare 2 days of rains and I'm not going to do this install in the rain. I have the RV back from the collision repair shop but stored several miles away. I've got 24 volts set up on FLA batteries, which took about three days to swap the stuff out from 12 volts and work out the kinks. Just have to get the lithium battery in and swap the main ANL fuse to a Class T fuse.

 

[BuffaloTrace]

That 3/4" you mentioned turned out to not be enough. I got my reasons as odd as they may sound for this odd configursation. Once I take into account Building a cover, how tight the already installed battery box is, the amount the nuts stick out on the compression rods, the width of the plywood for compression, turned out to be too much. Moving the battery box is a huge pain in the but and a 1/4" off on the drill when I do so makes a punctured black water tank.

I get this. There is something to be said for wiggle room. The configuration you have will give the most squared up centered pack, basically giving up room in one direction for room in the other. But it would fit in the straight 8s config depending on the thickness of compression box which could be pretty thin depending on what you use (1/8 alloy plate). Bottom could be setup so that only compression rods are needed at the top...either way you got a 24v battery bank, all nicely fused.

 

[BuffaloTrace]

I do the same thing you're doing myself and always try and take simplicity of cell arrangement and try and make it work over complexity/space. Of course you gotta lay them out in every config you can think of on paper as you dont have to physically move anything, than if what you choose doesnt work, you got all the work done on paper. There is a lot to be said for ease of install and access as well, but once its installed and working well do you really want to access it or even think you'll work on it much again.

 

[chrisski]

But it would fit in the straight 8s config depending on the thickness of compression box which could be pretty thin depending on what you use (1/8 alloy plate).

Do you have a recommendation on plating?

I could not find plating locally on the shelf of a home depot or lowes, and metal sheets look too pricey for me to order several times until I get it right. Most of my projects like that end up with some extra stuff where I ordered what doesn't work.

If I knew what to order, that would help tremendously. I have the tools to cut it, just don't know what to order.

 

[chrisski]

Looks like 6061-T6 aluminum four sheets or cut to 8" X 9", 1/8" thick would work.

What type of metal have you used for cell compression?

 

[HRTKD]

To add to your options, the end plate of the compression fixture doesn't have to be plate. It could be a piece of unistrut or anything that is sufficiently rigid. I was eyeballing one of my wife's cutting boards for an end plate. It's about 3/8" thick plastic. She told me to buy my own.

 

[Horsefly]

To add to your options, the end plate of the compression fixture doesn't have to be plate. It could be a piece of unistrut or anything that is sufficiently rigid. I was eyeballing one of my wife's cutting boards for an end plate. It's about 3/8" thick plastic. She told me to buy my own.

Yeah, my wife doesn't seem to share my enthusiasm for this stuff either.

 

[BuffaloTrace]

To add to your options, the end plate of the compression fixture doesn't have to be plate. It could be a piece of unistrut or anything that is sufficiently rigid. I was eyeballing one of my wife's cutting boards for an end plate. It's about 3/8" thick plastic. She told me to buy my own.

Yes, dont have to use plate or wood. Could even use a couple aluminum/metal long bar stock to go across the center ends of the cells using double sided adhesive foam mounting tape to insulate.

If a box is going around it for protection than a cell size end plate isnt needed. The center large flat area of the cell is what needs to be kept from bulging and is what carrys the stress of the interior cell pressure. Lots of space saving options for compression. Being lined up, side to side makes compression so simple.

 

[BuffaloTrace]

Cant wait to see how this turns out. My neighbor had a a few Class A rv friends that we have done small upgrades for, and now they are finally moving onto electrical including solar installs and the goal is to ditch the LA in their slide out racks for something else. I've heard them talking about all sorts of ideas, but I've been trying to convince them to Lifepo4. The climate here on the California coast is extremely mild, and a conversion would be pretty straight forward.