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

Dzl

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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.

Holy crap, so 300 kgf is equivalent to laying on your back with a 300kgf weight on your chest?

Is there a 'per unit area' aspect to this? like 300kg/m^2 or /cm^2? I'm struggling to understand exactly what this means in practice
 

madmax

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There may have been more details in the full document. I can't speculate exactly on pack configuration.
 

Dzl

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There may have been more details in the full document. I can't speculate exactly on pack configuration.

There are only two references to fixture I could find in the full document, the one I posted earlier, and this:
Screenshot_20200530_175100.png

I just used a text search for the terms "fixture" "300" "force" "compression" and "pressure", so its possible there are other relevant sections that I overlooked.
 

Dzl

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What's interesting looking at the two graphs, is that the relationship between cycles and remaining capacity is relatively linear without fixture, but with fixture, after an initially steep drop-off, the curve starts flatten and the loss of remaining capacity per cycle seems to decrease
 

Airtime

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It would have to be kgf/sqcm

660kg over 100cm2 is only 6.6kg
No, units are kgf not kgf/cm2. Yes if you applied 300kg (660lbs) to a 100cm2 plate then the pressure would be 3kgf/cm2 (6.6lb/cm2).

It still means you‘d have to apply a force of 660lbs to the cell. For example you could sandwich the cell between stiff flat plates with four 165lb compression springs, one at each corner.

But again, 2500 cycles is already pretty high, not sure that’s worth the trouble.
 

Dzl

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But again, 2500 cycles is already pretty high, not sure that’s worth the trouble.

I suppose its all relative and depends on your priorities and design model/use-case. >2500 cycles is quite a lot, but >3500 is a lot more (7 years vs 10 years of daily cycling--maybe much longer if you restrict bandwidth, maybe much shorter if ambient temps are above ~30*C).

Regarding whether its worth the trouble, I don't think designing for compression would be any more trouble than designing for airflow/spacing (though designing for precisely 300kgf might be difficult/overkill)

Would be nice to get some clarity from EVE, as well as some clarity on whether this is a factor with other cell manufacturers or cell sizes.
 
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NEWYORKHILLBILLY

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whats odd is i have older version of the specification may 25 2018 and unter 5 cycle life it say 3500 cycle with no break down for fixture.
 

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Dzl

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whats odd is i have older version of the specification may 25 2018 and unter 5 cycle life it say 3500 cycle with no break down for fixture.

Interesting, I wonder if this is due to a difference in cells, a difference in measurement, a different assumption on fixture or another factor, or just sloppiness/inaccuracy/unreliability
 

NEWYORKHILLBILLY

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Interesting, I wonder if this is due to a difference in cells, a difference in measurement, a different assumption on fixture or another factor, or just sloppiness/inaccuracy/unreliability
I just went over my document comparing to the one you posted and it word for word except 2 things. the mention of fixture and the graph showing that info. The other item mine list the discharge current at 1c and your is .5c
 

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Dzl

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Looks like it was the most recent change:

Screenshot_20200530_190312.png

This gives me a little more confidence in the credibility of the data, the fact that EVE felt it was important enough to revise and reissue their datasheets, gives it a little more weight in my eyes.
 

NEWYORKHILLBILLY

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Looks like it was the most recent change:

View attachment 14304

This gives me a little more confidence in the credibility of the data, the fact that EVE felt it was important enough to revise and reissue their datasheets, gives it a little more weight in my eyes.
now it makes since. I wonder if this is current or there has been other updates . I will print this one . I got my from the seller of the cells i hope the cells are not as old as the specifications.
 

zorlig

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Yeah need confirmation, and also the correct way to do it. I hadn't thought of springs before reading your guys posts, I assumed more like really long bolts or wire set to a fixed length.

I suspect the reason is to keep it from bulging, so it might be reasonable to fit them together at low charge and only have real pressure at high charge to prevent any movement.
 

mapguy525

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Looks like it was the most recent change:

View attachment 14304

This gives me a little more confidence in the credibility of the data, the fact that EVE felt it was important enough to revise and reissue their datasheets, gives it a little more weight in my eyes.
When reviewing the specification updates - significant items change in Revision D and E. Sometime these documents are difficult to read -as related information is not clearly identified without the reader making some correlative assumptions between document sections.
The expansion /contraction characteristic is first identified in Revision D. Heat and use patterns influence whether the clamping/fixture is needed. Regardless, some fixture is required to prevent cell post damage in "non-stationary" applications.
 

Steve_S

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In any Mobile Application, it is critical to secure the cells and everything attached thereto. That not only includes the cells bundled up but the BMS Harness, the Leads running from cells to BMS, the BMS and everything to prevent vibration from loosening up anything. One loose connection can cause a short,, heat and subsequently a fire if bad enough.

Everyone falls over this but it is quite simple....
Cells heat up while charging even at .2C they warm up some. All warming will increase the mass and cause some "swelling" as it were.
High Temperatures exacerbate that to some extent but not much until close to 95F and above.
As cells discharge, they make little to no heat, as this occurs as well they will shrink slightly due to the chemical changes within.
The Documentation states the shinkage / expansion is limited to roughly 2% under normal use conditions (not heavy discharge or charge).

Aluminium Bodied Cells are intended to be "packaged" into casings of some sort by design, which also relies on the casing to provide said compression / containment of the cells. The casing also is to act as a "Protective Envelope" for the cells themselves for external damage potentials.

Cells like those from Calb, Winston SinoPoly which have the hard plastic casings have their basic protection provided by the "packaging" which also puts a certain amount of compression on the internals by design BUT they are still recommended to be installed within a casing of some sort with support for the cells and to provide that safety margin as well. We have ALL seen the videos & photo's of Puffed Up LFP Cells (due to overcharging) including the Aluminium Blue-ees to the Calb & Winstons, so teh expansion due to overcharge is consistent regardless of the casing the cells actually have.

Bottom Line: Follow the Manufacturers Specs & Documents and everything else is on you. Some people always seem to think they know more than the Scientists or Engineers who designed the material/equipment, they can take whatever risks they choose because it is their money & lives they are risking. Smart Money is on those who follow the guidelines and Best Practices (who some will argue against) for the longest lived, better functioning system while squeezing the maximum out of the investment dollars.

It's funny how dividing such a simple thing can be, because of opinions.
Also funny is that many opinions originate from people who have never RTFM'd anything who always wind up with extra pieces from a kit they assembled.
 

Ampster

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Regardless, some fixture is required to prevent cell post damage in "non-stationary" applications.
Even in a stationary application my building inspector will surely require some form of seismic constraint. So i can accomplish both objectives if I give it some thought during assembly.
 

mapguy525

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I

Even in a stationary application my building inspector will surely require some form of seismic constraint. So i can accomplish both objectives if I give it some thought during assembly.
yes the official with jurisdiction is worth considering. Got to pick and choose which details are worth discussion:cool:. Combustible construction might be an issue.
 

Airtime

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Yeah need confirmation, and also the correct way to do it. I hadn't thought of springs before reading your guys posts, I assumed more like really long bolts or wire set to a fixed length.

I suspect the reason is to keep it from bulging, so it might be reasonable to fit them together at low charge and only have real pressure at high charge to prevent any movement.
Agreed it is about preventing bulging with charging. I'm not clear if the longevity issue is related to the cells themselves or to repeated flexing of the terminals due to the bulging. My plan is to use 1/4" 6061-T6 aluminum plate with threaded rod and a Lucite top, similar to what many have done including mainesail at marinehowto.com. Tighten lightly at low SOC, then expansion with charging will create its own pressure due to the rigid structure. Of course that is a variable and unknown amount of pressure, but it seems like a tried and proven solution.

As for the 300kgf force, I hope we can get some more information from EVE about that. If it really is critiical I will use some compression springs like these:
https://www.leespring.com/compression-springs-hefty?search=LHL625D

These are compression springs that apply 380lbs force per inch of travel. These ones are 1.5" extended and 1.02" full compressed, so you could get up to about 190lbs of compression per spring. One at each corner of a stiff plate could provide up to 760lbs to the battery bank. I did buy some LHL 625D 03 springs just in case, they are only $4 apiece. But the protruding springs interfere with my desired installation, so not sure if it's worth doing or just stick with a more rigid setup that everyone else has used. I'll decide after (if) I get any more info from Eve on their "fixture" and any recommendation on applying the 300kgf force they mention in their specs. For now, still waiting on my cells...
 

Airtime

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Bottom Line: Follow the Manufacturers Specs & Documents and everything else is on you. Some people always seem to think they know more than the Scientists or Engineers who designed the material/equipment, they can take whatever risks they choose because it is their money & lives they are risking. Smart Money is on those who follow the guidelines and Best Practices (who some will argue against) for the longest lived, better functioning system while squeezing the maximum out of the investment dollars.

It's funny how dividing such a simple thing can be, because of opinions.
Also funny is that many opinions originate from people who have never RTFM'd anything who always wind up with extra pieces from a kit they assembled.
Not sure who you're talking to here but it seems like a nice civil discussion to me. If you have any manufacturer information from EVE on recommendations for compression could you post it?

From EVE, there is just a vague mention of a fixture and 300kgf force applied. Lacking any further information, I plan to follow the example of marinehowto.com. If I learn more from EVE that it is vital to have exactly 300kgf force applied, I'll use compression springs. But I've never seen anyone do that yet, and I'm not sure it's worth it over just having rigid plates.

1590948580061.png
 

Airtime

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Regarding whether its worth the trouble, I don't think designing for compression would be any more trouble than designing for airflow/spacing (though designing for precisely 300kgf might be difficult/overkill)

Would be nice to get some clarity from EVE, as well as some clarity on whether this is a factor with other cell manufacturers or cell sizes.
Completely agree
 
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