EVE-280 cells should these be clamped tight or spaced for expansion?

NEWYORKHILLBILLY

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I working on my 4s 280ah battery plans.
I thinking of my battery box. should these cells have a air space between them or be bonded tight together with a hose clamp or something similar.
 

Ampster

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I am doing a 2P17S pack and I am using a 1/16 inch by 1 inch wide spacer on the edge of each cell in my pack. I am making custom buss bars so I don't stress the cell posts. Then I am clamping each column of 10 cells. the short column of 4 cells gives me room for my BMS, contactor and fuse in my cabinet. My cells will be on their sides in a cabinet on a wall next to my inverter.
 
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Dzl

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I working on my 4s 280ah battery plans.
I thinking of my battery box. should these cells have a air space between them or be bonded tight together with a hose clamp or something similar.

Personally, I would opt for securing them tightly, or some combination of the two. The data I've seen suggests that unless you are dealing with continuously higher C-rates (like 1C and above or 0.5C if you want to be conservative), cell temperature will be within a few degrees of ambient, in this case a little extra airflow would be (1) not necessary, and (2) probably not that effective.

I think your application and environment is probably important as well.

There is also this bit from the EVE datasheet @Steve_S uploaded to the resources section:

Screenshot_20200529_232014.png

Which seems to imply a substantially greater cycle life if pressure is applied to the cells, but I'm not 100% sure I'm reading that right. I don't own EVE cells so Its not something I've spent much time thinking about, and not something I've noticed in other datasheets.

My guess is for low C-rates, moderate temperatures, and stationary or gently used mobile systems neither airflow or pressure is that important but that's just a guess (on the second point at least).
 
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Ampster

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I had planned on using a spacer based on another thread that said the cells had some expansion. Based on the above I may abandon that idea and focus on clamping them. I had read that section and was not clear about what "fixture" implied.
 

solardad

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Personally, I would opt for securing them tightly, or some combination of the two. The data I've seen suggests that unless you are dealing with continuously higher C-rates (like 1C and above or 0.5C if you want to be conservative), cell temperature will be within a few degrees of ambient, in this case a little extra airflow would be (1) not necessary, and (2) probably not that effective.

I think your application and environment is probably important as well.

There is also this bit from the EVE datasheet @Steve_S uploaded to the resources section:

View attachment 14253

Which seems to imply a substantially greater cycle life if pressure is applied to the cells, but I'm not 100% sure I'm reading that right. I don't own EVE cells so Its not something I've spent much time thinking about, and not something I've noticed in other datasheets.

@Dzl I believe you are correct on the compression, that is what "Fixture" relates too. I plan on applying compression with my upcoming build, 16s4p , LF280a cells. I project my C rate at the highest discharge will be .17 (200a) or .05 (60a) during the majority of the day so I am planning on no heat issues caused by the demand given these are well within the testing values.
 

Steve_S

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WORD:

Compress does not mean put under pressure ! In this context, it means snug & tight but not under pressure or force. You can "strap" them together (protecting the corners so they do not crush). Many pack builders use commercial strapping made with that nylon-mesh, even BYD & CATL do this with LFP packs. I myself used Commercial Fibre-mesh "tape" to tightly bundle my cells together.

Make sure your "sets" (I do mine in blocks of 4 cells) are square and tight together, you can even clamp them (lightly) to ensure they are nice & snug then run 4 circuits of tape at the top & bottom, then install your busbars. see below how I bundle my cells. The strings are Nylon and there to allow me to pull 4 cells out of the casing should I have to do maintenance for some reason. Makes it easier to pull the "block" out of the box. FYI: I built my own battery boxes with 3/4" Plywood and they are "snug" for the cells. Image for the wood cutting below for the box as well. in case it's helpful for anyone.

cell-bundling.jpg

280AH-Battery_Box.jpg
 

Ampster

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I will have 34 cells in a 2P 17S configuration. I plan on stacking them in four columns on their side in a 30 X 30 metal cabinet. I plan on using thread rod to secure them vertically. I am sure the inspector will want to see some seismic constraint since I am in California.
 

solardad

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I will have 34 cells in a 2P 17S configuration. I plan on stacking them in four columns on their side in a 30 X 30 metal cabinet. I plan on using thread rod to secure them vertically. I am sure the inspector will want to see some seismic constraint since I am in California.

@Ampster sounds like a good plan. Will it be similar to this layout?
 

NEWYORKHILLBILLY

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WORD:

Compress does not mean put under pressure ! In this context, it means snug & tight but not under pressure or force. You can "strap" them together (protecting the corners so they do not crush). Many pack builders use commercial strapping made with that nylon-mesh, even BYD & CATL do this with LFP packs. I myself used Commercial Fibre-mesh "tape" to tightly bundle my cells together.

Make sure your "sets" (I do mine in blocks of 4 cells) are square and tight together, you can even clamp them (lightly) to ensure they are nice & snug then run 4 circuits of tape at the top & bottom, then install your busbars. see below how I bundle my cells. The strings are Nylon and there to allow me to pull 4 cells out of the casing should I have to do maintenance for some reason. Makes it easier to pull the "block" out of the box. FYI: I built my own battery boxes with 3/4" Plywood and they are "snug" for the cells. Image for the wood cutting below for the box as well. in case it's helpful for anyone.

View attachment 14257

View attachment 14258
I like the tape better than hose clamps. Do you know what the wood box weight was? In my case weight is a concern . mine would only be 4s so 1/2 the weight
 

zorlig

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WORD:

Compress does not mean put under pressure ! In this context, it means snug & tight but not under pressure or force. You can "strap" them together (protecting the corners so they do not crush). Many pack builders use commercial strapping made with that nylon-mesh, even BYD & CATL do this with LFP packs. I myself used Commercial Fibre-mesh "tape" to tightly bundle my cells together.

Make sure your "sets" (I do mine in blocks of 4 cells) are square and tight together, you can even clamp them (lightly) to ensure they are nice & snug then run 4 circuits of tape at the top & bottom, then install your busbars. see below how I bundle my cells. The strings are Nylon and there to allow me to pull 4 cells out of the casing should I have to do maintenance for some reason. Makes it easier to pull the "block" out of the box. FYI: I built my own battery boxes with 3/4" Plywood and they are "snug" for the cells. Image for the wood cutting below for the box as well. in case it's helpful for anyone.

View attachment 14257

View attachment 14258
What does the "300kgf force" mean then? Are you thinking that is a 100% charged pressure and no pressure at low charge?
 

Airtime

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What does the "300kgf force" mean then? Are you thinking that is a 100% charged pressure and no pressure at low charge?
I had the same question and asked Amy earlier, she checked with an engineer but I got an answer to a different question... translation issues. I have asked again, trying to make it simpler and more clear, hopefully . I'll report back on anything I learn.

The spec certainly reads as though applying 300kgf force to compress the cell will extend life from 2500 to 3500 cycles. That could be done with some plates and compression springs, if it was worthwhile. Of course, even 2500 cycles is more than I'll ever use.
 

Dzl

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I had planned on using a spacer based on another thread that said the cells had some expansion. Based on the above I may abandon that idea and focus on clamping them. I had read that section and was not clear about what "fixture" implied.

Yeah to be honest, I'm not 100% sure what it means either, but my best guess is they are referring to applying a uniform light force/pressure to the cells or maybe just to the long side of the cells, but i'm not entirely sure.

Compress does not mean put under pressure ! In this context, it means snug & tight but not under pressure or force.

This might be two ways of saying the same thing. What you call snug and tight, could also be described as light pressure/force being applied, no?

kgf = kilogram force which (best I can tell) is a unit of force (equivalent to 9.8 newtons, or the force exerted on one kilogram of mass by earths gravity). How that translates into usable information for us I don't know. kgf wasn't a unit that I had heard of before yesterday, and it seems to be a fairly obscure unit.

I would like to get to the bottom of this
 
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Dzl

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on thing seems to be clear is you don't want to have a space between the cells.

You would think that a logical takeaway from EVE recommending a force be applied for longer life is that you wouldn't want space between the cells, but then you have brands like fortune that actually design for cell spacing (then again they are much smaller cells and designed for higher C-rates I think), so I really don't have much clarity on this issue.

I still think its possible that neither cell spacing or compression are crucial for health cells at low C-rate's, but I wouldn't take my word for it, just a guess.

I guess the prismatic cells want to be smashed into each other so the packets don't buldge?

Seems plausible, IDK, I wish EVE would provide more of an explanation. It could have to do with bulging, it could have to do with mechanical (internal) strength, or we could be misinterpreting the datasheet.
 

Airtime

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kgf = kilogram force which (best I can tell) is a unit of force (equivalent to 9.8 newtons, or the force exerted on one kilogram of mass by earths gravity). How that translates into usable information for us I don't know. kgf wasn't a unit that I had heard of before yesterday, and it seems to be a fairly obscure unit.
kgf is just kg, but clarifying that it is force not mass. On Earth with 1g gravity, kgf=kgm=kg=2.2lbs. So 300kgf is 660lbs, not what I would call light pressure.

I’m trying to get clarification from EVE on the “fixture” and how the 300kgf force is applied.
 
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