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

Do you think it’s in the best interest of a Chinese manufacturer to have his product last as long as possible? Well if you do I have a fortune cookie factory I want to sell you so that all your dreams can come true.
That may be true of some Chinese companies. But I am quite certain battery manufacturers like EVE, CATL, Lishen and the other big ones including Samsung and LG stick by whatever they document in their spec sheets. There have been people post on this forum who have good functioning cells after 10 plus years in service.

I have a pair of Valence batteries and the cells were manufactured in China. They are connected in parallel and still produce 95% capacity even though they are around 10 years old. That is a dream come true and I did not need a fortune cookie to make it happen...:cool:
 
As far as I can recall that document was supplied to Amy Wan by another forum member as a favor to her. It's a basic guide and compression is tricky unless using springs. It's good to keep in mind too much compression is worse than no compression.

EVE has made recommendations for compression and there is an abundant of information on this forum regarding that. I don't know of any other manufacturer that has made compression recommendations with regards to aluminum cased cells. :unsure:

I think I may have been the one that sent it to Amy -- its been so long ago .... i remember when the compression thing came up and i spent a few hours on the phone talking to the EVE designers in China - and quickly realized that each and everyone of them - as you move up the food chain - had their own individual thoughts on compression -- BUT - (and if I remember correctly) the senior SENIOR design engineer, Mr. LiFePO4 himself stated that at 72F with compression, that they saw a noticeable difference in longevity. NOW of course - again - not Black and White -- BUT I do remember that EVE stated to compress their cells when it was in the 45-55 SOC range and I think that someone actually found the newtons or foot/lbs to do it to ...

All I know of of the 1000's of cells we have out here now scattered across NM and Texas - we compress each of them - drop them in a carrier box - hook them up -- and never look back ...

BUT there is a document out there - I will see if i can find it -- its on many of the manufacturers websites -- pretty sure its all been translated to English by now ... but tells exactly what to do and how much to do it ...
 
I’m of the belief that the corners of a prismatic cell normally Keep their shape and any bulging comes from the large flat sides, the weakest point, which would probably be the center of the cell. By using a full spacer pad, any expansion will have A place of resistance. I chose not to use a solid substrate because during expansion it may cause excessive resistance pressure (I believe usually from the center of the cell) But from everything I’ve read any pressure greater than 17 psi and any part of the cell may cause internal problems.
The correct soft “goldilocks silicone” spacer should meet all compression requirements, and be relatively easy to incorporate in a cell pack. I stated earlier…..to obtain 8psi resistance force, starting approximately 40-50% SOC. I intend to compress them 25% of their thickness, thereby their resistance to expansion of @1mm (according to the liquid silicone foam pad manufacture) will be well within the range of 17 psi resistance.
I came to many of the same conclusions as you with regard to the strength of the corners but ended up at a different solution.
I have read all of the specifications on the 270A-304A cells and in none of them do I find the word "compression" What they actually say is "fixture".

I am a Structural Engineer and part of my daily work is to read and interpret specs so that the products are correctly used in my projects. the word "fixture" in a spec has a specific meaning and it is not synonymous with "compression". Fixture is to "fix" or hold in place when subjected to an outside force. Compression on the other hand is to actively apply a pressure to an object. The way that I read the spec is that they want each cell held in place with a "fixture" that is strong enough to not move when subjected to a 300kgf (660-lbs) Given that the cells are about 7" x 8", that works out to 11.8-psi which is less than the 17-psi you mention as a max.

In my build, I am using 3d printed corner spacers that will support all four corners but hold the flat sides 2mm apart. This will then be held together with 1/4" threaded rods with Nyloc nuts to pull plywood end plates so that they are all in snug contact. My plan is to prevent any differential movement between individual cells so that there is as little induced stress as possible in the terminals which are the weakest link. I will then further reduce the remaining stress (thermal and vibration) by the use of flexible multiplate buss bars.
 

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One of the trusted suppliers actually asked EVE about that and it was confirmed that the fixture they used was designed to apply a constant force on the cell, no matter what the SoC was.

Also, I know we should read datasheets using the correct definition for each word but that only works if the datasheet was written in good english, which is usually not the case with Chinese manufacturers (mainly due to how those languages have a very different structure). By "fixture" they really mean "apparatus" here.
 
In my build, I am using 3d printed corner spacers that will support all four corners but hold the flat sides 2mm apart. This will then be held together with 1/4" threaded rods with Nyloc nuts to pull plywood end plates so that they are all in snug contact.

I like your corner pieces. I may take that idea and modify them slightly for my setup. I've already printed the top pieces and added a bit of extra "safety" to them, but need something for the bottom.

Battery Terminal Protector v9.pngIMG_0291.jpgIMG_0292.jpg
 
Here are the drawings I used for the printing. I do not have the stl files.
 

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The way that I read the spec is that they want each cell held in place with a "fixture" that is strong enough to not move when subjected to a 300kgf (660-lbs)
An interesting interpretation. I wonder what would cause a 300kgf load (and subsequent motion) on a cell under test in a laboratory environment?
 
An interesting interpretation. I wonder what would cause a 300kgf load (and subsequent motion) on a cell under test in a laboratory environment?
I would see that coming from the normal expansion of the cell as it nears full charge. The specs say that they should increase in thickness by about .5mm.
 
I would see that coming from the normal expansion of the cell as it nears full charge. The specs say that they should increase in thickness by about .5mm.
Mine are in a spring compression fixture and that's about the amount of expansion I see. Actually slightly less, but in that ballpark.
 
I would see that coming from the normal expansion of the cell as it nears full charge. The specs say that they should increase in thickness by about .5mm.
Yes, they can increase by 0.5mm (0.4mm for my 230 Ah cells), but that is specified under 300+/-20 kgf. If you don't constrain the side walls, you aren't providing that force. Holding by only the corners is not meeting the specification.
 
Mine are in a spring compression fixture and that's about the amount of expansion I see. Actually slightly less, but in that ballpark.
If you are holding the cells in place with springs, then they will move outward due to swelling. If you are using a typical flat buss bar, that movement will create a tention force between each coupled pair of terminals and they are the weakest link. That does not sound too healthy to me.
 
If you are holding the cells in place with springs, then they will move outward due to swelling
I agree for the most part. Many of the "spring" Afficianatos actually calculate the spring force to match or exceed cell expansion criteria to reduce that risk.
 
I agree for the most part. Many of the "spring" Afficianatos actually calculate the spring force to match or exceed cell expansion criteria to reduce that risk.
It doesn't really matter what "spring force" it is rated for because that would be in units of kg/mm which will always by design, allow for movement. That is what springs do. That movement will create tension in the buss bar which will then stress the terminals. I cannot see that as a good thing.
 
One of the trusted suppliers actually asked EVE about that and it was confirmed that the fixture they used was designed to apply a constant force on the cell, no matter what the SoC was.

Also, I know we should read datasheets using the correct definition for each word but that only works if the datasheet was written in good english, which is usually not the case with Chinese manufacturers (mainly due to how those languages have a very different structure). By "fixture" they really mean "apparatus" here.
I know there was a photo posted somewhere of the hydraulic fixture they use for testing. It does apply the same force no matter the SOC. and this came from another source.

I don't know what they mean by fixture. I think the best information we have from EVE came from the conversation ghostwriter had with them.
 
It doesn't really matter what "spring force" it is rated for because that would be in units of kg/mm which will always by design, allow for movement. That is what springs do. That movement will create tension in the buss bar which will then stress the terminals. I cannot see that as a good thing.

You're totally right but the solution to that is easy: flexible busbars.
 
that works out to 11.8-psi which is less than the 17-psi you mention as a max.
Yes, but IIRC, the 11.8psi you arrived at is what at least 2 companies (EVE and A123 I believe) state as a target (12psi), and what a few people had already mostly deduced independently as best we could from the spec sheets of EVE and possibly others, as well as a video on the topic and A123 documentation, prior to hearing from the EVE engineers.

I don't pretend to understand all of this, in fact the more this conversation goes on, the less I feel sure about (and I'm quite mindful of my lack of technical understanding in this area), but it does seem that a handful of independent sources arrive at a rough target of ~12psi, my understanding was 17psi was the max not the target.

I tried to consolidate some of those other earlier sources are summarized way back in post #195 when we were just starting to dig into this topic, and the following few pages are where the EVE info was originally posted if you would like more context. Probably a lot has come to light since then, but that is where/when this topic really go rolling and where a lot of info was consolidated.
 
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It doesn't really matter what "spring force" it is rated for because that would be in units of kg/mm which will always by design, allow for movement. That is what springs do. That movement will create tension in the buss bar which will then stress the terminals. I cannot see that as a good thing.
I am not an advocate of spring fixtures. The spring advocates go through complex calculations to find a spring rate that gives them the pressure per square inch which manufacturer recommends and a spring rate that increases such that there is little to no movement.
I prefer the simplicity of thread rod because it does not move.
 
If you are holding the cells in place with springs, then they will move outward due to swelling. If you are using a typical flat buss bar, that movement will create a tention force between each coupled pair of terminals and they are the weakest link. That does not sound too healthy to me.
Here are my busbars. Connection surfaces were meticulously prepped and the terminal connections torqued to 75 inch-pounds.

Results- Minimal heating at 200 Amps continuous and plenty of compliance for expansion & contraction.

What is your opinion of the "health" of this setup?
 

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Would I expect 280ah cells to position squarely 4 cells deep or would I expect them to be bulging at all ?
I store my cells at about 90 to 95% charge. Do I need to discharge them to 50% for them to nicely and squarely 'touch each other' with any signs of a bulge ? This is on the sides that have the largest area.
 
Would I expect 280ah cells to position squarely 4 cells deep or would I expect them to be bulging at all ?
The manufacturer apparently expects them to bulge and that is why they recommend compression. You would be safe making the same assumptions as the manufacturer and expect that they will bulge. I stored mine at 80% for six months and there was slight bulging of some but they compressed when I reconfigured them.
 
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