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

BiduleOhm

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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?

Pretty sure the expansion is because of the material migration and not because of some internal gaseous pressure. But I can be wrong, I'm not specialized enough on that subject to say for sure.
 

conquistador

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(that's my build).
Let me first say that your whole setup looks impressive.
I'm just at the beginning and have crimped a "flexible" connection with cable and lugs today.There I realized that the lugs turn when I move the batteries a bit. (they were not screwed tightly)
Now I feel the need to build a mOhm meter first, as I don't trust the lugs and crimping, and soldering lugs to cable seems to be considered a sin LOL.
Was the resistance the reason why you moved away from "flexible" ?
 

100 Proof

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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
Just as an fyi, you might want to talk with your spring vendor about the effects of full compression of the springs. Some springs need to be de-rated if they are ever compressed beyond a certain percentage, often 70%. Having said that, we are not exactly building furniture with a spec that has a +/- 50% tolerance.
 

cinergi

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Let me first say that your whole setup looks impressive.
I'm just at the beginning and have crimped a "flexible" connection with cable and lugs today.There I realized that the lugs turn when I move the batteries a bit. (they were not screwed tightly)
Now I feel the need to build a mOhm meter first, as I don't trust the lugs and crimping, and soldering lugs to cable seems to be considered a sin LOL.
Was the resistance the reason why you moved away from "flexible" ?

Thanks! I moved to bus bars due to relatively high resistance (I believe skin effect caused by the AC waveform induced on the battery pack by the inverters) which was confusing the BMS due to wild voltage fluctuations at the per-cell level. Indeed I was also concerned about the rotational force on the terminals as the batteries expanded & contracted, causing the cables to exert different rotational forces on the terminals ... and whether that would cause a problem in the terminal or the connection loosening up. But the main concern was the resistance. I don't think I would have made the change just on the terminal forces concern alone.
 

cinergi

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Pretty sure the expansion is because of the material migration and not because of some internal gaseous pressure. But I can be wrong, I'm not specialized enough on that subject to say for sure.

From what I remember reading, this is correct.
 

Bluedog225

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I’ve read a lot of this thread but not all. Sorry.

What about a weighted lever arm? That is, an angled arm with a weight on it that exerts pressure on a side plate. This could provide a reasonably constant pressure on one side of the cells without regard to expansion or contraction.

Basic force vector calculations and a really clever person could stack staggered batteries in a way that each bank provided the mass to compress the side of the bank below it.
 

noenegdod

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I’ve read a lot of this thread but not all. Sorry.

What about a weighted lever arm? That is, an angled arm with a weight on it that exerts pressure on a side plate. This could provide a reasonably constant pressure on one side of the cells without regard to expansion or contraction.

Basic force vector calculations and a really clever person could stack staggered batteries in a way that each bank provided the mass to compress the side of the bank below it.
If you have the space for it, it would be a really good solution. Obviously not for a mobile application.
 

TWNomadin

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Has anyone seen the need for compression when using the cells between 3.5v-2.7v at a .35c discharge/recharge rate? I want to build a box to hold my 8s battery but not really wanting to worry over meeting the 12psi, just keep them contained.
 

Frank in Thailand

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Has anyone seen the need for compression when using the cells between 3.5v-2.7v at a .35c discharge/recharge rate? I want to build a box to hold my 8s battery but not really wanting to worry over meeting the 12psi, just keep them contained.
Don't over complicate things.

Having them stiff in a box is good enough.

Just a light compression is enough when you start with new cells.

If you already received them, you will notice they are slightly hollow (I don't know the English term)
Look a bit like this:. )(

They expand at the center what is now bend inwards.
Simply stacking them snugg in a box, the edges tight together is enough.
No matter how many PSI, the edges of the aluminium battery casing take all the force, not yet the lifepo4 sheets.
If you put enough force, crush.. lol..
That's different.

In time ( many cycles) the sheets will slightly delaminate.
As result the cells no longer look like this )(. But more like this | |

If the cells aren't kept in a tight space, they can expand further to ()

Abuse, failure or other mishaps will make then look like balloon / pillow

So at start making a tight fit that is strong enough to compensate for the slight swelling during charge, is enough.

I used the word "slight" alot

Before the swelling is "so bad" it will push the cells apart, you are a long from home..
(Unless mishaps)

If you want to prepare for this possible movement, flexible busbars are the way to go.

Professional build (and laser welded) busbars have a bit "omega" shape to allow the tenths of millimeter extension and retraction.

Clamping it in a box without any springs or other things works just fine.
Snugg fit with new cells.
And when your box can withstand over 12psi force...
Your good to go :)

Compression slightly bloated cells..
That is not a good idea and might result in fire.
Or better "spontaneous" discharge of a cell, that heat will affect the adjoining cells and the cascade continued...

Just keep it simple.
Even without real compression , S4 schrink wrap, or S8 duckttape..
Or ...
Many things work.

Having them standing free, will make them slightly bloated in. Several years of usage.

Clamping probably real life result 15 instead of 12.5 year usage.
(For solar)

In 12.5 years...
You probably don't need the extra 2.5 to get replacement.
Either way, they don't last forever.

If you want 100 years or longer (not for mobile application) Edison batteries are the way to go.
And they aren't that inefficient...
At 85% no way near lifepo4, but similar to lead acid.

You just need a big room 😜
 

Ampster

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Has anyone seen the need for compression when using the cells between 3.5v-2.7v at a
I use my cells from 3.0 to 3.45 and compress them. I based my decision on the manufacturers recommendation. Mine are EVE LF280 cells. Some older style prismatics and most cylindrical cells do not need compression.
 

TWNomadin

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Messages
59
Don't over complicate things.

Having them stiff in a box is good enough.

Just a light compression is enough when you start with new cells.

If you already received them, you will notice they are slightly hollow (I don't know the English term)
Look a bit like this:. )(

They expand at the center what is now bend inwards.
Simply stacking them snugg in a box, the edges tight together is enough.
No matter how many PSI, the edges of the aluminium battery casing take all the force, not yet the lifepo4 sheets.
If you put enough force, crush.. lol..
That's different.

In time ( many cycles) the sheets will slightly delaminate.
As result the cells no longer look like this )(. But more like this | |

If the cells aren't kept in a tight space, they can expand further to ()

Abuse, failure or other mishaps will make then look like balloon / pillow

So at start making a tight fit that is strong enough to compensate for the slight swelling during charge, is enough.

I used the word "slight" alot

Before the swelling is "so bad" it will push the cells apart, you are a long from home..
(Unless mishaps)

If you want to prepare for this possible movement, flexible busbars are the way to go.

Professional build (and laser welded) busbars have a bit "omega" shape to allow the tenths of millimeter extension and retraction.

Clamping it in a box without any springs or other things works just fine.
Snugg fit with new cells.
And when your box can withstand over 12psi force...
Your good to go :)

Compression slightly bloated cells..
That is not a good idea and might result in fire.
Or better "spontaneous" discharge of a cell, that heat will affect the adjoining cells and the cascade continued...

Just keep it simple.
Even without real compression , S4 schrink wrap, or S8 duckttape..
Or ...
Many things work.

Having them standing free, will make them slightly bloated in. Several years of usage.

Clamping probably real life result 15 instead of 12.5 year usage.
(For solar)

In 12.5 years...
You probably don't need the extra 2.5 to get replacement.
Either way, they don't last forever.

If you want 100 years or longer (not for mobile application) Edison batteries are the way to go.
And they aren't that inefficient...
At 85% no way near lifepo4, but similar to lead acid.

You just need a big room 😜
Thanks for the great explanation and a better understanding on what is being done without going overboard. I appreciate that. (y)
 

TWNomadin

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I use my cells from 3.0 to 3.45 and compress them. I based my decision on the manufacturers recommendation. Mine are EVE LF280 cells. Some older style prismatics and most cylindrical cells do not need compression.
With yours, did you do the typical compression with threaded rod and boards on each side?
 

HRTKD

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With yours, did you do the typical compression with threaded rod and boards on each side?

My cells are used like Ampster's are. I use the typical threaded rod and boards on each end. Better safe than sorry. Mine are used in an RV trailer, so the compression fixture is also a handy way to secure the battery to the floor of the compartment too keep it from moving.
 

TWNomadin

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Joined
Mar 18, 2021
Messages
59
Yes. Two rows are about 70 inches.
My cells are used like Ampster's are. I use the typical threaded rod and boards on each end. Better safe than sorry. Mine are used in an RV trailer, so the compression fixture is also a handy way to secure the battery to the floor of the compartment too keep it from moving.
Thanks fellas. Appreciate the feed back.
 

KYSolar

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Jul 17, 2021
Messages
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I have read through this thread (and a few others on the "clamping" issue) and this way of distributing the load on the cell faces has me the most puzzled. It was mentioned by noenegdod but there doesn't seem to have been any discussion about it.
My understanding is that if you have one EVE LF280K cell with a surface area to be compressed at 12psi that would be :
173.7mm X 204.6mm = 35,539.02 or 55 square inches......X 12psi = 660 pounds of force on that surface.
If you were to use 4 bolts for the clamping then you would divide 660 pounds by 4 and apply 165 pounds at each bolt, therefore applying a total of 660 pounds on that cell face. I think everyone agrees on this.
If you were to use 2 bolts for the clamping then you would divide 660 pounds by 2 and apply 330 pounds at each bolt, therefore applying a total of 660 pounds on that cell face.
If you were to use 6 bolts for the clamping then you would divide 660 pounds by 6 and apply 110 pounds at each bolt, therefore applying a total of 660 pounds on that cell face.
If you had two cells side by side and used one plate to cover both cell walls and 4 bolts to do the clamping you would need (660 X 2) or 1320 pounds of clamping force or; 1320 divided by 4 equals 330 pounds at each bolt. This is assuming there is no deflection in the plate.
If you assume there might be deflection in the plate you might consider putting two more bolts at the midway point to counteract that deflection bringing your total to 6 bolts. That would be 1320 pounds total divided by 6 equals 220 pounds at each bolt.
I don't understand how varying the pressure at different places on the clamp will create an even pressure on the cell walls.
I would be very happy if someone could explain this to me. Thank you.
By the way, I love this forum, how everyone works to be helpful and considerate and all the good information that is passed around. I certainly wouldn't be where I am without it.
 

Frank in Thailand

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Some start confusion to make..

You seem to assume the surface is FLAT.
Probably you did not receive your cells yet, or didn't look at them in this way.

When you receive they are )(
During charge the expansion starts at the center and 0 on the outer edges.

You probably have a 5x5 cm surface that takes the "first hit".
2 cells expanding, at the center on a 5x5 cm surface.

When they "hit" touching eachother), the expansion force is gradually expanding over larger area.
"Never" the full cell surface, about 15mm from the edges the 90 degree angle of the aluminium sheet will keep it in nice shape.

So what's it all about??

Without clamping the "bulging" at the center have little to none force to prevent delamination of the sheets.
You don't want this.

The 12psi ??
In blocks of 8 cells, Eve uses 12PSI for their laser welded aluminium box to compress the cells together.
Each cell with a thin separator sheet (I think plastic)
Not 8 X 12psi..

The outer edges of the cell first will take all the force.
The cells are still )( shaped.
After many cycles...
They will try to bulge, but can't.
Metal box prevent this from happening.

How much force is there between each cell, and if it is equal on all sides?
People a lot smarter then me can try to calculate.
With the variable that they don't know how much the expansion and the "urge" to "bulging" is.

What we do know.
Snug fit, some clamping is enough.
They won't expand.
And if you, after a few years, are dumb enough to unclamp them, take then out the snug fit.. (probably need to destroy that box) it will never have the same size again.

Sure.. you can clamp it together.
And it will work for a while.
My personal experience in this, is self discharged cell, aka short, aka fire.. and that one cell took down $2500,- of lifepo4 batteries..

Better don't.
Don't try to fix a winning team.

For me, a bit of bad luck with 152Ah cells who had the same housing as 120Ah..
Somehow.. that 32 AH extra let the cells expand quickly (days/weeks) ..
Not really somehow... Engineering mistake..
Anyway.. I tried to get them more flat again, not on purpose but by clamping, the delamination seemed to reduce, and by hand I could tighten the nuts from the 6 bolts.

After a few months...
Spontaneous fire...

You can not uncook an egg, or delaminate cells.

You can prevent it, and all it needs is a little compression at the start when you build your battery pack.

The 12psi is an other word for snug fit.
Prevent expansion.
How much PSI is generated by the cells...
That can be a lot!!

After the fire I disasambled the battery pack.
Yes, many hot way to hot and look like balloon.
The clamping prevented this from expanding.

I removed (or tired to) the 6 X 1/4 inch threaded rods I used for the clamping.
With 2 left, the one 1/4 inch rod snapped in 2 when I tried to untighten the nut.

People smarter then me can calculate how much PSI was on those 2 rods before it will snap.

I keep it simple : too damn much!!

In a normal situation, it should never be this high.
I was genuinely surprised that the vent didn't rupture!

More simple..
The cell wants to expand.
When you prevent this, it can't expand.
But will generate force on the material you used to prevent it.

When you can keep your battery pack upside down without any cell sliding out.. it's a strong enough (snug) fit :)

Any more force is useless.
The outer edges of the cells take that force and has nothing to do (yet) with expansion.
 

noenegdod

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Messages
878
If you had two cells side by side and used one plate to cover both cell walls and 4 bolts to do the clamping you would need (660 X 2) or 1320 pounds of clamping force or; 1320 divided by 4 equals 330 pounds at each bolt. This is assuming there is no deflection in the plate.

The plate deflects, so you must put bolts in between cells.

If you believe the plate does not deflect then you would not proceed to your next arrangement, Correct?

If you assume there might be deflection in the plate you might consider putting two more bolts at the midway point to counteract that deflection bringing your total to 6 bolts. That would be 1320 pounds total divided by 6 equals 220 pounds at each bolt.

You have gone to 6 bolts because you are believing there is some deflection to the plate. If you took two single rows of cells each with 4 bolts from your arrangement above where each bolt had 165 lbs on it and put them side by side, how many springs would be between the two rows of cells? How much total force would be being applied to that middle row? Remember, you have gone to 6 bolts to mitigate deflection in the plate. That middle row of springs is acting on half of 2 sets of cells. The outside bolts are acting on half of one set of cells. Again, remember why you have stuck a row of springs between the cells and not just on the outside edges.

I don't understand how varying the pressure at different places on the clamp will create an even pressure on the cell walls.
I would be very happy if someone could explain this to me. Thank you.
By the way, I love this forum, how everyone works to be helpful and considerate and all the good information that is passed around. I certainly wouldn't be where I am without it.
 
Last edited:

KYSolar

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Messages
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The plate deflects, so you must put bolts in between cells.

If you believe the plate does not deflect then you would not proceed to your next arrangement, Correct?



You have gone to 6 bolts because you are believing there is some deflection to the plate. If you took two single rows of cells each with 4 bolts from your arrangement above where each bolt had 165 lbs on it and put them side by side, how many springs would be between the two rows of cells? How much total force would be being applied to that middle row? Remember, you have gone to 6 bolts to mitigate deflection in the plate. That middle row of springs is acting on half of 2 sets of cells. The outside bolts are acting on half of one set of cells. Again, remember why you have stuck a row of springs between the cells and not just on the outside edges.
I suspect I am not very clear in describing my lack of understanding.
I think if you have two rows of cells side by side and a plate covering both of them and each row needs 660 pounds of force then the plate
covering both cell rows would need 1320 pounds of force. I think we agree on that?
I think no matter how many bolts/springs are used their combined force has to equal 1320 pounds of force.
 

KYSolar

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Only part of my message was posted! What a nuisance.

In this particular case of two cells side by side and a force of 1320 pounds or 12 pounds per square inch being brought
to bear on the plate (and thereby the cells) and there was 6 bolt/springs distributing that force; what would be the force
at each of the bolt/springs? That is two bolt/springs on either end and two in the middle.

In my particular case there are four cells side by side.
 
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