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

Dzl

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How about some small hollow copper tubing.. every inch or so, and pour some sort of epoxy/urethane to create a diy 'venting' compression spacer.

I'll be running these in my garage that can get hot in the Texas summers. I wonder if clamping them, yet providing some air-flow will make more of a difference than somebody running these in A/C space.
Remember if the ambient temperature is as hot or hotter than the cells themselves airflow, heatsinks, etc, will not be effective, and could actually be counterproductive.
 

BiduleOhm

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Here is the corrugated stuff with plastic core. Its important to note, that for convection to work, you need much larger channels. Its a viscosity and thermal gradient thing. Those channels are more than 10 times their diameter in length, and convection would be minimal.


I was talking about a full aluminium one. This one is basically coroplast with a glued aluminium sheet on each face. But thanks for the research ;)


The face of the cell is razor thin where as the small sides of the cells, as I understand it, are fairly hefty. I would be interested to know the thickness of the aluminum all the way around of these cells. When I mount my plywood I will torque down until all lock washers are flat and leave it at that. All I want to do is alleviate stress on the terminals.

AFAIK the thickness is constant. However the dimension is what make the difference here. It's like if you take a piece of 1x2 of 1' length and try to bend it by hand: you'll not do much. However if you take a piece of 10 or 15' it'll bend under its own weight if you pick it by the middle or by each end.


Yeah, that worries me as well.

Springs would remove any concerns as you can easily know the force applied by measuring how much you compress them ;)
 

BiduleOhm

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I was talking in a general way, not necessarily for you to do it.

This is a totally optional thing, you're not obligated to do it if you don't want to ;)
 

Colonel.lp

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I was talking in a general way, not necessarily for you to do it.

This is a totally optional thing, you're not obligated to do it if you don't want to ;)
I have to say I'm quite taken with the spring idea, its a very simple and elegant solution. And having an ElectroDacus and seeing it used by Dacian is great, in my few dealings with him on the forum, the guys is incredibly knowledgeable.
 

ghostwriter66

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How about some small hollow copper tubing.. every inch or so, and pour some sort of epoxy/urethane to create a diy 'venting' compression spacer.

I'll be running these in my garage that can get hot in the Texas summers. I wonder if clamping them, yet providing some air-flow will make more of a difference than somebody running these in A/C space. It also has me wondering if I need to try to feed a small air-duct into a battery box.

Don't think the wife would like that.

Absolutely no need to do that I would think unless you are at 1C or above ..... SOOO from where I sit -- if you are more concerned about heat the life-cycles then I would NOT clamp them but instead do the totally opposite and put spacers in between the batteries ... #1 killer of LFP is heat ... so some of us in West Texas where we see 120F days and 90F nights in the summer (Summer is Mar-Oct it seems) I am NOT trying to go from 2500 cycles to 3500 cycles BUT trying to get to 1000 cycles without burning up my cells ...
 

ghostwriter66

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These batteries are already costing me a bundle. One more thing here, one more thing there.
I seriously should have just gotten larger AGM batteries to be honest.

Honestly - for a decade it seems - 99% of the ppl just got the batteries in -- taped them together -- hooked up some cables - and were done ... and honestly - 99% of the batteries I have I do the same thing ...and for the next decade 99.99% of people will just wrap-n-slap and be fine ... hell I barely wrap them anymore ... BUT please Don't let the good idea fairy start whispering crazy things in your ear about using AGMs instead of LFP .. LOL ...

BUT YES I try not to follow some of these things these guys are doing here because they are totally awesome - but can get a little expensive ... sort of like BMS's ...you can get a bareboned $40 one that keeps the highs from being too high and the lows from being toooo low and thats what 99% of the ppl need ... OR you can get the $500 one that tells you the same thing your mother does that just because you are working in an oil field that thats no excuse for you not to have any makeup on for the last month ... OK .. month and a half ... crap -- 6 months ....
 

SherylinRM

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Honestly - for a decade it seems - 99% of the ppl just got the batteries in -- taped them together -- hooked up some cables - and were done ... and honestly - 99% of the batteries I have I do the same thing ...and for the next decade 99.99% of people will just wrap-n-slap and be fine ... hell I barely wrap them anymore ... BUT please Don't let the good idea fairy start whispering crazy things in your ear about using AGMs instead of LFP .. LOL ...

BUT YES I try not to follow some of these things these guys are doing here because they are totally awesome - but can get a little expensive ... sort of like BMS's ...you can get a bareboned $40 one that keeps the highs from being too high and the lows from being toooo low and thats what 99% of the ppl need ... OR you can get the $500 one that tells you the same thing your mother does that just because you are working in an oil field that thats no excuse for you not to have any makeup on for the last month ... OK .. month and a half ... crap -- 6 months ....
My batteries cost me about 10% of my annual income. I got them because they will last for a decade. And they are much more powerful than what I have.
But all the extras have made it so that I am losing weight not eating properly. Of course losing weight is a good thing for me but even so.

I haven't worn makeup for years myself. I am old and I was never pretty and just gave up and saved a lot of money since LOL. :)

Someone sent me a BMS but it stopped working and I have no clue why dang it.
Oh well. It was free. So I can't complain. I just feel bad for the person that sent it wasting all that money on postage. :(
 

Gazoo

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AFAIK the thickness is constant. However the dimension is what make the difference here. It's like if you take a piece of 1x2 of 1' length and try to bend it by hand: you'll not do much. However if you take a piece of 10 or 15' it'll bend under its own weight if you pick it by the middle or by each end.
That's interesting. I thought I saw some where the sides were thicker then the faces. But what you said makes sense. It would be totally awesome if someone could dissect one of these. It would also be interesting to know the thickness of the aluminum at the bottom of the terminal. Some have been concerned about bottoming out with a screw and puncturing it. Does anyone know if that's ever happened?
 

zorlig

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I think reading this that I'll strap them and make sure I'm putting a lot of body weight on them when I tighten them. Three or four straps.

Then I'll have to do the math to see how much force it takes to move the band out and see how much pressure is actually being applied.

I'm guessing one could also take a strap and use a stick to twist it and create more pressure. Again, not sure exactly what the math would show there. That would let someone tighten it further later without much trouble (just add another half twist).

The straps say they will take 300 pounds without breaking so it should be viable.
 

Bob B

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Well .... since we are tossing ideas around .... lets get a little more crazy for those worried about what the springs do over time.

Lets add an air bladder ... and springs. Someone touched on that idea earlier ....Since the ultimate goal is to keep the compression at 12 psi .... pretty easy to measure that with a tire gauge instead of going to a more complex pressure gauge.
These are a wide variety of air bladders available with some of them being pretty close to the size of the cells.
Something like this .... https://www.amazon.com/Calculated-Industries-1194-Inflatable-Contractor-Grade/dp/B073XL88HP/ref=sr_1_6?dchild=1&keywords=Inflatable+Air+Bladder&qid=1605127291&sr=8-6&th=1

I know ... totally crazy bazaar idea .... but it sure would be easy to check the pressure with a tire gauge .... and put nitrogen in it if needed. But .... the way I'm thinking about it, the springs would still control the pressure. The bladder would even out the pressure by conforming to the battery and make an easy way to truly know what psi is being exerted. With a solid object on the side of the battery the pressure is NOT going to be even.
You could even scrap the springs and just use nitrogen in a bladder.
I have nitrogen in my car tires now and went an entire year without the pressures (as read by my TPS system) getting far enough out of range to worry about. (The temperature around here varies from well below zero to up around 100 F.)
 

ArthurEld

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If you torque to 12 inch pounds at 3.3V resting like they send them.
It is probably 17 inch pounds when they are charged
And 6 inch pounds when they are discharged.
That's easy and I'm lazy
 

Bob B

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If you torque to 12 inch pounds at 3.3V resting like they send them.
It is probably 17 inch pounds when they are charged
And 6 inch pounds when they are discharged.
That's easy and I'm lazy
Yeah, but 17 lbs is worse than no compression .... and since it us a U shaped curve with 12 in the middle ... anything close to 17 is not very good either.
 

Colonel.lp

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If you torque to 12 inch pounds at 3.3V resting like they send them.
It is probably 17 inch pounds when they are charged
And 6 inch pounds when they are discharged.
That's easy and I'm lazy
This metric and imperial mixing is driving me mad. 🤣 And I'm a carpenter so work in both.

If the surface providing the pressure is not fixed, i.e. able to move (springs or bladder) then from my previous calculation with springs should translate to a bladder. Clamped at 50% charge, 270kgf to 330kgf, on an eve cell that translates 11psi to 13.5psi

Look what you made me do, mixing units now. 🙈

I'm not sure how a fixed surface effects the pressure, in my head I want to assume it's the same, but my physics has 30 years of rust on it.


How did you get 17psi?
 

ArthurEld

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See post 233
You are correct. I read it there. But I don't know what the torque it. I just assume it is about that.
12 psi is hard to measure and there are a lot of other variables. I find it difficult to believe this is an exact science.
She also said too loose is better than too tight.
 

JoeHam

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You are correct. I read it there. But I don't know what the torque it. I just assume it is about that.
12 psi is hard to measure and there are a lot of other variables. I find it difficult to believe this is an exact science.
She also said too loose is better than too tight.

And most importantly > 18 PSI is worse than no compression at all!

Also there are multiple posts converting psi to other units.

Please note that I can convert no compression at all in PSI to any other measurement unit without difficulty 😎
 

Dzl

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Yeah, but 17 lbs is worse than no compression... and since it us a U shaped curve with 12 in the middle ... anything close to 17 is not very good either.
I think this is a slight but very meaningful misunderstanding of what was actually said.

From the EVE 'jr engineer':
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

Frome the EVE 'sr engineer':
Any compression is better than no compression. BUT NO compression is better than compressing it above 18 PSI.
Anywhere between 6-17 are good numbers - but those numbers will change on SOC and temp.
As long as your high and low is between 17-6 you are fine but a constant 12 is what you are looking for.

The chart (related to the A123 cells) basically tells the same story visually:
screenshot_20201108_185254-png.27072

But its important to note these are pouch cells, so there are no cell walls to crush.


Point being 17 is not equal to 0 on the U curve, it is equal-ish to ~6 in terms of cycle life, which is substantially higher than 0 in terms of cycle life. The reason 18+ is said to be worse than 0 is because it is the upper limit due to the mechanical strength of the cell, not because it is the mirror image of 0 on the U curve. "Anything close to 17" is just as good as anything close to 6, so long as you don't surpass 17, which due to the consequences you should try very hard not to do and stay away from :).
 
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