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

chrisski

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I finger tightened my cells when I did the top balance for the first time. Perhaps 30%-40% SOC after removing the cells from the shipping container when I hand tightened them. I needed a wrench to get the bolts off when the top balance was done.

I’m not positive a torque is as important as sandwiching the battery between two pieces of something that won’t bow out. 1/4” plywood will work on my Tiny 25 ah cells, but not for the bigger 280 ah cells.

I think the nuts need to be tight enough not to fall off when the cells get to a low SOC.

I think a XXX ft LBS would not be correct.
 

Diysolar123

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I think you misunderstood that part (but really nice post otherwise BTW ;)), the +/- 1 mm is just a manufacturing tolerance, the expansion will be around 0.5 mm between 30 and 100 % no matter what.

The typical cell will be 71.5 mm @ 30 % and 72 mm @ 100 % but for example you can have a cell that is 70.8 mm @ 30 % then it'll be 71.3 mm @ 100 %.

I guess the datasheet should have been clearer and said 71.5 mm +/- 1 mm @ 30 % and +0.5 mm @ 100%. But I think we're quite lucky with what we have, I've seen datasheets much worse than that...

I have updated my posting above as your interpretation of the spec including manufacturing tolerances and SOC tolerances is certainly different than what I was thinking they were trying to say.
I have several cells I guess I could take them out of the fixture and run them thru a discharge cycle while watching with my mitutoyo dial indicator. From the initial cell I did a test cycle on I have more than 20thou of expansion when charged to 100% because of how it felt (not a huge bulge but it definitely did grow so I could easily feel the difference).
I could put the battery on a surface plate to keep things stable; I hate lugging that thing around, even the small one weighs a lot hehe...
Not sure how to handle the fact that the growth is not uniform, maybe if I secured one side of the battery, then use my surface plate height guage with a large plate attached to it and put the dial indicator on the back of that...hmmm, that should work, maybe???
 

Diysolar123

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I think you misunderstood that part (but really nice post otherwise BTW ;)), the +/- 1 mm is just a manufacturing tolerance, the expansion will be around 0.5 mm between 30 and 100 % no matter what.

The typical cell will be 71.5 mm @ 30 % and 72 mm @ 100 % but for example you can have a cell that is 70.8 mm @ 30 % then it'll be 71.3 mm @ 100 %.

I guess the datasheet should have been clearer and said 71.5 mm +/- 1 mm @ 30 % and +0.5 mm @ 100%. But I think we're quite lucky with what we have, I've seen datasheets much worse than that...
well I did a test and carefully measure the expension of an EVE brand new cell from 50% to 100% SOC...this was NOT in a fixture, just free standing.

The answer is that I measured an expansion of .762mm so that is much less than what I thought it would be however it is certainly more than 0.5mm... so an 8cell fixture would need at least 0.24" of room.
I wonder if the 0.5 expansion is when the cell is compressed with the 300kgf???
 

BiduleOhm

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Interesting. I'm not sure about if the spec is with or without the 300 kgf tho.
 

cinergi

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No, my expansion under compression is less then 0.5mm per cell on average.
 

100 Proof

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No, my expansion under compression is less then 0.5mm per cell on average.
That's consistent with my results too, but I budgeted for .5mm in my spring selection and fixture design.
 

Vonglick

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New member here. I’ve been reading a lot about cell compression using springs. All the packs I’ve seen are using the springs on the outside pushing the end supports toward the cells using four springs. Am I right at assuming these springs should compress at 165 lbs to achieve the 12 psi goal.

Could I use four springs to pull the end supports together using threaded rod with eyelets on the end? I recently salvaged the seat springs out of my old Toyota. I found they started to stretch at about 160 lbs. I’m not an engineer, what do you think? 4S 280 ah cells

6372B530-96F7-4E67-BCE1-1447B94A4227.jpeg
 

100 Proof

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New member here. I’ve been reading a lot about cell compression using springs. All the packs I’ve seen are using the springs on the outside pushing the end supports toward the cells using four springs. Am I right at assuming these springs should compress at 165 lbs to achieve the 12 psi goal.

Could I use four springs to pull the end supports together using threaded rod with eyelets on the end? I recently salvaged the seat springs out of my old Toyota. I found they started to stretch at about 160 lbs. I’m not an engineer, what do you think? 4S 280 ah cells

View attachment 71866
An arrangement like that could definitely work. I considered doing something like that, but abandoned the idea as I felt springs in compression with rods was just going to be simpler for my use.
 

Vonglick

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An arrangement like that could definitely work. I considered doing something like that, but abandoned the idea as I felt springs in compression with rods was just going to be simpler for my use.
Thanks 100 Proof, I’ve got eight springs out of the two seats. I thought I’d give it a try since the springs were free. I’ll use 1/4” eyelets with 3/4” plywood ends. I’ll post pictures after the build.
 

100 Proof

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Thanks 100 Proof, I’ve got eight springs out of the two seats. I thought I’d give it a try since the springs were free. I’ll use 1/4” eyelets with 3/4” plywood ends. I’ll post pictures after the build.
If you can, try to hang 165 pounds off of one of your springs and then measure its extension. Use that same extension measurement to dial in your force.
 

Vonglick

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If you can, try to hang 165 pounds off of one of your springs and then measure its extension. Use that same extension measurement to dial in your force.
That’s exactly what I did. I put a hook into a ceiling stud, hooked the spring to it, made a loop with a rope and stepped into the loop. I weigh 170 lbs and had all my weight on the spring. Reached up with some calipers and measured the length of the spring. I figured, close enough!
 

Zjohn

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Did anybody do compression on a larger bank of e.g. 8S4P cells? I mostly saw builds of only low-cell units but may have missed a pic or two. If somebody did it, do you compress all cells with one and the same mechanism or is there an advantage to compressing each (4P or even 2x4=8P) parallel stack by itself? I imagine so but it might not be very practical or nice looking when doing it with springs. So that's why I'm also interested in knowing if there is a final verdict on the spring vs foam issue ...?
 

cinergi

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Did anybody do compression on a larger bank of e.g. 8S4P cells? I mostly saw builds of only low-cell units but may have missed a pic or two. If somebody did it, do you compress all cells with one and the same mechanism or is there an advantage to compressing each (4P or even 2x4=8P) parallel stack by itself? I imagine so but it might not be very practical or nice looking when doing it with springs. So that's why I'm also interested in knowing if there is a final verdict on the spring vs foam issue ...?

Mine is two compression structures of 16 cells each. Just have to account for X cells times 0.5mm of variance when sizing your spring.

 

Zjohn

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Mine is two compression structures of 16 cells each. Just have to account for X cells times 0.5mm of variance when sizing your spring.

Definitely a very nice setup cinergy! Unfortunately I do not have space for a 2x16 setup like that and will need to do a 4x8, complicating things a little... Also, I am a little surprised to notice the springs compressed to just about 100%, am I seeing that right?
 

cinergi

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Definitely a very nice setup cinergy! Unfortunately I do not have space for a 2x16 setup like that and will need to do a 4x8, complicating things a little... Also, I am a little surprised to notice the springs compressed to just about 100%, am I seeing that right?

Yes almost 100% at 100% SoC gets me the PSI specs I was looking for. They're long springs so even the 16*0.5mm of movement that could occur still gives me great compression at 0% SoC
 

conquistador

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I went through the whole compression thread, and I have a question:
Each cell is supposed to expand 0.5mm which makes it at least 2mm for a pack of 4 cells. Now these 0.5mm go in some direction, one cell pushes the other a little bit further.
In your installations: like this one I see 4 cells connected by a solid copper bar.
Where does the movement go here? My theory is that there must be a lot of strain on the rods where the solid bar is screwed on. So after a few (hundred) movements, the rods might become lose or might push something inside the cell.
Sorry for my ignorance, but I just received my cells 3 days ago and I wonder how this all works.
 

cinergi

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I went through the whole compression thread, and I have a question:
Each cell is supposed to expand 0.5mm which makes it at least 2mm for a pack of 4 cells. Now these 0.5mm go in some direction, one cell pushes the other a little bit further.
In your installations: like this one I see 4 cells connected by a solid copper bar.
Where does the movement go here? My theory is that there must be a lot of strain on the rods where the solid bar is screwed on. So after a few (hundred) movements, the rods might become lose or might push something inside the cell.
Sorry for my ignorance, but I just received my cells 3 days ago and I wonder how this all works.

(that's my build). My personal experience is that the space between terminals moves very little compared to the middle or bottom of the cell. After experimenting with flexible "bus bars" (wires) and measuring the changes in distance, the movement was so small that I decided to stick with rigid bus bars. I have not seen any problems since I deployed this arrangement 7 months ago (although I do think that, scientifically speaking, more time and more points of data are needed here).
 

Cdkipp

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well I did a test and carefully measure the expension of an EVE brand new cell from 50% to 100% SOC...this was NOT in a fixture, just free standing.

The answer is that I measured an expansion of .762mm so that is much less than what I thought it would be however it is certainly more than 0.5mm... so an 8cell fixture would need at least 0.24" of room.
I wonder if the 0.5 expansion is when the cell is compressed with the 300kgf???
Wow, that is a lot.
 

HRTKD

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I'm playing Devil's Advocate so much on this topic that I think I might be starting to grow horns...

If these cells need room for expansion and don't have it due to a fixed compression frame, wouldn't the vents be popping more than a series of wildcat wells that had just struck a high pressure crude oil pocket?
 
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