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

Gazoo

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Some amount of pressure is good for the life of the cells.
I think your post sums it up nicely. But as I said in the other thread, there is no way to put pressure on the pouch encased in the aluminum housing unless one wants to crush their cells. I will reiterate, the idea is to mount the cells in a fixture that will keep the the cells from expanding. No pressure is needed except to keep the fixture in place flat against the cells. When the aluminum housing begins to expand it will apply pressure against the fixture and the fixture will stop it from expanding. That's my take on what EVE told me. That's what I am going to go with unless EVE has some other explanation to give to ghostwriter.
Do any of them tell you what state of charge the cells should be in when you apply the 12psi?
I tightened mine until my lock washers were flat. That is exactly 12psi
The SOC would be a good question for EVE. I am planning to mount mine at a low SOC...probably empty...10 volts or so.

I have six 5/16 threaded rods and .5 inch plywood. I am going to torque mine down until the lock washers are flat and stop. I don't have a torque wrench. I am building a 8S square pack. Two rods will be on each side with 2 in the middle.
 

dRdoS7

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Hi,

300kgf = 661lbf = 2942N = 12psi spread across the broadside of an EVE cell.

300kg pressing the broadside of a cell?

Anybody like to test that by parking a wheel of a 1200kg car on one of their cells?

Maybe someone with a unusable cell would like volunteer?

Please take a video.

dRdoS7
 

Dzl

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That's the big kicker as I see it. Given temperature changes and various SOC, the pressure on the cells is not going to be constant.

That is why I came up with the idea of putting springs on the ends of the threaded rod that were manufactured for the desired pressure .... I seemed to be the only one who thought that was a good idea, and I haven't pursed purchasing the springs, although I did a little searching and found out that they can be bought fairly inexpensively. There would probably still be a little pressure change with temperature, but nowhere near as much as without them.
I definitely felt this idea had promise when you (and I believe Airtime also) brought it up, the finer points of implementation were/are over my head though.

I believe Dacian (Electrodacus) used a similar approach, I used to have a picture but can't find it now) If memory serves he used pouch cells sandwiched between aluminum plate (on closer look it seems to be some sort of composite, maybe foam board) compressed with threaded rod and springs

edit: found it:
P1220395.JPG
 
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ArthurEld

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I have six 5/16 threaded rods and .5 inch plywood. I am going to torque mine down until the lock washers are flat and stop. I don't have a torque wrench. I am building a 8S square pack. Two rods will be on each side with 2 in the middle.
I have an inch pound torque wrench. 12 inch pounds isn't much. I assume that value would be incorrect if any screws were more than 1 inch apart.
 

Dzl

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Do any of them tell you what state of charge the cells should be in when you apply the 12psi?

This is the most important outstanding question I think.

I think your post sums it up nicely. But as I said in the other thread, there is no way to put pressure on the pouch encased in the aluminum housing unless one wants to crush their cells. I will reiterate, the idea is to mount the cells in a fixture that will keep the the cells from expanding. No pressure is needed except to keep the fixture in place flat against the cells.
This is pressure though (or at least I think it is). Maybe not at low SOC, but if the internals of your cell want to expand, and the cell walls would normally bulge out a little on the broadside, and your fixture prevents this expansion from happening, you are applying pressure the way I see it, and not just to the exterior, you do not need to crush the cell structure.

But this brings us back to the question, at what SOC should pressure be measured and at what point should fixture be applied. My guess is that pressure is important at high SOC but I cant say for sure.

Out of the million and a half links I posted the ones most relevant to your comment are: This, this, and this.
 
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Bob B

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I definitely felt this idea had promise when you brought it up, the finer points of implementation were/are over my head though.

I believe Dacian (Electrodacus) used a similar approach, I used to have a picture but can't find it now) If memory serves he used pouch cells sandwiched between aluminum plate (on closer look it seems to be some sort of composite, maybe foam board) compressed with threaded rod and springs

edit: found it:
View attachment 27081
HMMMM .... That's really interesting. It is different than I visualized. I was visualizing the opposite spring action with the spring attached to one end of the threaded rod attached to one of the end plates.

Does anyone have a good enough rapport with Dacain to ask him about his approach to this..... I like it better than what I was visualizing.
 

Dzl

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In any case, I don't think any of the new info I dug up changes or contradicts any of our thoughts on how to implement fixture. And I don't think it really helps answer the "how" question, but I don't think it helps answer the "why" question, which may help with the how question in a roundabout manner.

If there is any takeaway relevant to implementation, I would say it reinforces our current approach.
 

Dzl

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Does anyone have a good enough rapport with Dacain to ask him about his approach to this..... I like it better than what I was visualizing.
This was the text that accompanied the picture:
Dacian said:
Allen, Unfortunately none of them include proper compression. The Bright Star have those plastic end caps but there will be spaces between cells so those offers no compression force at all.
I will say get the largest capacity cells that will fit (need to consider the connection height also) and then just set them in a single row or two rows depending on your space and add two thick aluminium plates on the ends and use long screws and compression springs to secure and compress them. The connections between cells should be flexible as you will have a lot of vibration in a vehicle.
Below are a few photos of my battery
I will provide the link to the post too but for some reason I can't post links from his forum so it won't work. But just in case it does.. here is the link:
https://groups.google.com/forum/m/?...n/electrodacus/pouch/electrodacus/bKIRlxsSLvk
 

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Dzl

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You and I are on the same wavelength today...
So ... now where do we get those springs.
...Page 14, apparently

But, the specific springs depend on the specific cells and number of springs I believe (this is where it starts to get over my head)
 

Gazoo

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But this brings us back to the question, at what SOC should pressure be measured and at what point should fixture be applied. My guess is that pressure is important at high SOC but I cant say for sure.
That is what I would think too. To me it doesn't make sense to clamp the cells at a high SOC. They will have expanded and I read that once the cell expands it will not deflate if there is a gas buildup within the cell. Another monkey wrench thrown into this discussion. It's not only the pouch causing expansion.

As far as the other links, my post is assuming a perfectly flat cell. Two of my cells arrived "out of shape" like what Aussiesim explains here. I really don't know what happened with these cells. The rest of my cells expanded slightly while I was parallel charging. I did not have them mounted in a fixture. By arranging the cells I was able to make a square pack. The plywood will mount flat at each end. I hope to start draining the pack tomorrow. After it is drained I will be able to tell if any of the cells changed their shape.

In any case, I don't think any of the new info I dug up changes or contradicts any of our thoughts on how to implement fixture. And I don't think it really helps answer the "how" question, but I don't think it helps answer the "why" question, which may help with the how question in a roundabout manner.
I agree and well put. If we could talk to the tech at EVE then we could get much more information. Honestly, recently the more I read through the threads the more weird things I see happening with these cells. I will be happy to get 270 amps from my capacity test.
 

Supervstech

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That is what I would think too. To me it doesn't make sense to clamp the cells at a high SOC. They will have expanded and I read that once the cell expands it will not deflate if there is a gas buildup within the cell. Another monkey wrench thrown into this discussion. It's not only the pouch causing expansion.

As far as the other links, my post is assuming a perfectly flat cell. Two of my cells arrived "out of shape" like what Aussiesim explains here. I really don't know what happened with these cells. The rest of my cells expanded slightly while I was parallel charging. I did not have them mounted in a fixture. By arranging the cells I was able to make a square pack. The plywood will mount flat at each end. I hope to start draining the pack tomorrow. After it is drained I will be able to tell if any of the cells changed their shape.


I agree and well put. If we could talk to the tech at EVE then we could get much more information. Honestly, recently the more I read through the threads the more weird things I see happening with these cells. I will be happy to get 270 amps from my capacity test.
AmpHours...
 

ghostwriter66

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In reference to the 300Kgf (ie 12PSI) I have called them and talked to the EVE folks. My Chinese is pretty much ghetto Chinese (being from LA) so it took me a while to get past the Help Desk ppl becuase they didn't think i understood what I was trying to ask -- I finally was able to get sent back to their engineering design team ... now please understand that these guys have a tendency to not want to look foolish especially to an American so often times they just blurt out the wrong answers just to say something -- so we are passed that hurdle and now am waiting for one of the senior (real) engineers to call me. It may be this afternoon (his time) or early morning Tuesday (my time) ...

So one of the EE that was there that did talk to me that DID seem to know what he was talking about did say that YES they did see a dramatic increase in longevity by putting the cells under pressure -- BUT that 12 PSI was the sweet spot ... and that one of the issues is that the 12PSI could change rapidly on temperature of the battery and SOC. That the median on where you set the 12 PSI depended on how you were going to use them and what environment you were using them in. Of course they do all their testing at 72F/22C degree AND that the 12 PSI was maintained for testing using monitored hydraulic clamps as they went through their charge and discharge ... IOW -- their clamp always exerted a perfect 300kgf or 12psi regardless of temp, or SOC... for those that don't understand SOC concerns - the battery figuratively breaths -- when it charges its lungs expands - when it discharges it lets its breath out (if that makes sense) ....

so i explained to them that we were DIY sort of ppl and just trying to figure out the best way of doing all of this since most of us did not have a 10,000 USD software controlled hydraulic pressure clamp ...

so once the senior guy calls me I will let you know what he said .. but so for - the 12PSI seems to be the sweet spot ... one of the guys did say that if a person is only going (for example) to do a 25% to 85% charge - then they should calculate when the 55% is hit and then THATS when to make the 12PSI adjustment so that 12PSI at 55% SOC is the centre line and everything else will be +/- off the centre ... that actually makes sense ...

And he did say that the difference between NO pressure and 12 PSI in lifetime cycles was noticeable (but did not state a number) ... but it sounded like they were saying literally 1.5X ... ALMOST .... HOWEVER he did say that its a upside down U curve where anything OVER 12 PSI the longevity starts going down evenly ... so 12 is perfect ... 13 is same as 11 ... 14 as 10 etc .. BUT that honestly ANYTHING between 6 and 17 would be virtually the same and a range you want to shoot for.... Apparently at 6 it is like 1.5X and anything over 17 it starts getting crushy (ie thin aluminum) ...

sorry for the rambling .. will wait for the senior guy to call ... I have night shift so that means NETFLIX for 7 more hours so i will let you know what they say ...

IF THERE IS ANY SPECIFIC QUESTION WE WANT TO KNOW LET ME KNOW AND I WILL ASK ... THX
 

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I think I hit on a treasure trove of wisdom and info!

It doesn't answer all questions, but it gets us closer.
http://electrodacus.com/solarforum.html?place=msg/electrodacus/n7vodfh1j84/_v3paOjeBAAJ

In case the length won't work, some relevant excerpts (all from Dacian):
Dacian said:
The cells will change volume slightly based on state of charge so compression is helpful for prismatic type cells. A spring will ensure a constant pressure but even a fixed compression should be better than none.
GBS cells are sold as set of 4 cells with compression plates and steel straps (not sure how effective that is but that is what they offer).
Springs are the easiest DIY solution in some EV packs they use some sort of pads I think made form polyurethane.
It is important for the pressure to be uniform so end plates need to be thick else they will bend and pressure will not be uniformly distributed on the cell surface.
I happen to have proper spec for the A123 System cells that I use here
On page 32 you will find life cycle vs pressure level and there is a fairly large range 4psi up to 18psi you get about the same great results and that is just 0.3 to 1.3kg/cm²
At page 14 here www.daytonlamina.com you can find my springs (not quite) they are 14mm OD and 7mm ID but only 20mm long there is just a 25mm as the shortest and that should get about 6kg/mm of compression but shorter travel I'm guessing mines are at 30 to 35kg each so x8 = 280kg
But my cell's dimensions are 21cm * 16cm = 336cm² so 280kg / 336cm² = 0.83kg /cm² maybe a bit less so around the middle of that ideal range.
All cells need compression unless they are cylindrical cells. Compression will improve cycle life by 2 to 3x so is worth doing.
Not sure about the exact compression needed for those cells but there is a fairly large range that is good
 
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Dzl

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This is all great info @ghostwriter66 and dovetails almost perfectly with a lot of what I unearthed today! Finally we are getting some clarity :)

Thanks for reporting back your findings

HOWEVER he did say that its a upside down U curve where anything OVER 12 PSI the longevity starts going down evenly ... so 12 is perfect ... 13 is same as 11 ... 14 as 10 etc ..
That matches the same trend shown in the video and graph I posted earlier:
Screenshot_20201108_185254.png

BUT that honestly ANYTHING between 6 and 17 would be virtually the same and a range you want to shoot for.... Apparently at 6 it is like 1.5X and anything over 17 it starts getting crushy (ie thin aluminum) ...
This corresponds with what I just read elsewhere (in relation to A123 pouch cells):
"there is a fairly large range 4psi up to 18psi you get about the same great results"
We now have three datapoints to go off of:

SourceMin RecommendedOptimalMax Recommended
EVE6 PSI12 PSI17 PSI
A123 (from Dacian)4 PSI??18 PSI
Data From Video4 PSI12 PSI18 PSI
 
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Gazoo

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IF THERE IS ANY SPECIFIC QUESTION WE WANT TO KNOW LET ME KNOW AND I WILL ASK ... THX
I would like for you to ask him if mounting the cells in a fixture strong enough to prevent expansion would be better than nothing...and if he says yes what SOC to mount them in. I am thinking that 12 PSI should be maintained through the high and low SOC. In that case springs would be required. I am not going to go in that direction. So please ask him what would be the best for someone using plywood and threaded rods.

I would also like you to ask him why some of us have received cells with expansion on the side of the cell that has the positive terminal as explained here. What could cause that to happen?

Lastly please refer to this post and ask him if gas build up is a problem with these cells and under what conditions.

I know these are not exactly specific questions, but if you don't mind asking it would be helpful.

I really appreciate it and the info. you have conveyed so far. Thanks.
 

Luthj

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I think the easiest method is a durable high density closed cell foam. We can easily calculate the compression required for 12psi. Should be cheap and reliable long term.
 

Luthj

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As a follow up to the foam idea, here is some EPDM foam sheets. Looks like medium firmness is 13 psi for 25% compression. A 3/8" sheet compressed 1/8" should provide ~12PSI. The main issue is compression set. I don't know how much the foam will relax over time. EPDM is pretty good in this aspect, but I don't know the precise range. It may require a follow up after a couple month to retighten. You could always overshoot to 50% compression at the start.

 
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