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

[Kajitis]

So what would the pro and cons be for using springs vs static space (with pressure)?
Using springs;
+ Keep the recommended pressure at all times, and thereby prolong battery life.
- Require cables inbetween cells.

Static space (with pressure)
+ No extra force on cell connection points.
+ Can use solid burbars
- Pressure will vary.

 

[ArthurEld]

Home Depot is where I found Blue PEX pipe. They had red and white too. They are straight pieces.
I'm using 3/8 threaded rod so I would have to use 1/2" ID plastic hose.

 

[Deleted member 9967]

Ok so this was my take on all of this.

I got the spec sheet from EVE for my cells.
The thickness measurement per cell when depleted and when full is given there.
Then I made a box with the exact measurement of depleted cells which is 4 times 71. [Four cells per box].
Then I put the cells into the box and snugged it up.
Now when they expand to 72mm each, they have no where to go.
Problem solved.
The cells provide all the compression needed.

So no springs, no torquing, no special bolts or nuts etc etc.
Just measure properly and let the cells do the work for you.

I know that many here will find this WAY to easy and simple for you.
But for the rest of us it will work.

 

[Frank in Thailand]

My 2 cents:

We all know the recommendation:
300kgf compression force.

It supposed to give even 1000 extra cycles, for what those numbers are worth anything.

I know from my own experience that it highly dependent on the cell.

I have 48* 152Ah, in March my Idea was bigger is better..
First indent was the 120Ah cells.
These where a fraction more expensive and same casing size......

- that matter a lot.
You can not keep on piling sheets into a casing without getting in the danger zone..

They needed to be compressed, if not they will bloat / delaminate.

My 280Ah came a few months after the 152's, and together they have made up 736Ah battery.

It never was overcharged, never undercharged, kept between 15 and 85%.

After 150 days I'm ready to make my new Powerwall installation...

150 days ago most of the 152Ah where still flat.
I ordered 3 replacement as I knew 3 where starting to bloat a little.

View attachment 27506

All the 152Ah are bloated / delaminated.
And all about the same.
They have 1.25mm (in total 2.5) bloating.

The 280??
View attachment 27507

0.0 mm, no bloating at all.

I'm in day 4 of building the new Powerwall.

When finished I'll post the progress.

Then this thread popped up again..
I could not let it pass to show what not compressing can have for result.
I have no idea how much capacity I lost due the delaminating.
Perhaps I'll test some day one to know for sure.
I guess 10% or less.


Should you compress???
Absolutely.
Even if your cells are not "overfilled" like mine, it still won't hurt to compress them

And allowing expansion??
That would be stupid.
The cells are make of sheets LiFePO4.
Once they get space between them, it doesn't revert.
It's not a balloon...
You can't "de-bloat" or re-compress cells.

There is air inside what we all know is really good comprassable.
If the sheets need to expand due to temperature difference, it can do within the housing.
Sure, you should not smash the cells.
Too much of everything is bad.

Allowing space between the cells for expansion...

Look at my lovely 152Ah...
That is what will happen.
Without over charging, without undercharged, without too high C rates.
On average C0.1..max C0.2

After reading backwards in this thread, I now understand the thing about expansion a little better.

My 280 eve cells look like "vacuum".
Not 100% flat, but bend inwards a little.
Perhaps 0.3mm..
They are at 3.338 volts.

That's my new set.

The "old" are flat, totally.
Used for +150 days without compression.

For me, I just clamped them now between plywood.




Spring washers aren't even flat.
Just firm enough to prevent delaminating, or more delaminating then I already have.

I guess that's mostly to it.
Compression, yes, it doesn't have to be a lot, "firm" is tight enough.

I'm holding the cells at max 90%, low as far as needed.
The few times I hit the 5% isn't to be a problem at all.

With +50 kWh LiFePO4 and 5 to 15 kWh usage at night, I have enough spare for the rainy days.
14kw solar (42*330w) give enough to slowly eat the battery on those days.
Rainy season just ended here.
Cool season now with night temperature below 20!!
( Normal +35 day time, + 30 at night)

That really makes huge difference in energy usage for refrigerator and air-conditioning at night.

Why 50 kWh?
When there is sun.. I have loads of power left over.
Off grid is also not feeding back..
Crypto mining is a perfect fit for excess energy, 650-1000 watt 24/7 depending on the calculation.

It makes me about 150 - 300 USD a month

Except for the rainy season..
Then no mining.

With 15* 1/4" nuts..
It's pretty difficult to know the torque.
Pipe wrench and screwdriver in the center works fine for me.
I'm not the strongest guy out there, "tight" is good enough.

Math is not my strongest point on this part of calculation.

As you can see I have 4 rows with 4 cells (the 280Ah) and 4 rows with 6 cells (the 152's)

Each cell have 3 * 1/4 inch threaded rod of total 65 cm length.

(Thailand is chaos with inch and mm used where ever when ever it suits, or what people have on hand..
In the stores it's not uncommon to have mixed environment where inch and MM are mixed in the same shelf..
They look the same size

So I ended up having enough of both now.

Do you guys now a good way of calculate how much torque it should be?

It's easy enough to get the feeling of light torque.
Many household tricks to find on Google.
You are bound to be a few Nm off, but with the margin of 6-17 there is some room for errors

 

[Frank in Thailand]

Ok so this was my take on all of this.

I got the spec sheet from EVE for my cells.
The thickness measurement per cell when depleted and when full is given there.
Then I made a box with the exact measurement of depleted cells which is 4 times 71. [Four cells per box].
Then I put the cells into the box and snugged it up.
Now when they expand to 72mm each, they have no where to go.
Problem solved.
The cells provide all the compression needed.

So no springs, no torquing, no special bolts or nuts etc etc.
Just measure properly and let the cells do the work for you.

I know that many here will find this WAY to easy and simple for you.
But for the rest of us it will work.

That's about what I'm doing, except that I don't have to have depleted cells before I can fit them in a box..

I just give them tight as they are now at 85%.

Usually I stay above 50%, so tight is good enough

 

[vtx1029]

Ok so this was my take on all of this.

I got the spec sheet from EVE for my cells.
The thickness measurement per cell when depleted and when full is given there.
Then I made a box with the exact measurement of depleted cells which is 4 times 71. [Four cells per box].
Then I put the cells into the box and snugged it up.
Now when they expand to 72mm each, they have no where to go.
Problem solved.
The cells provide all the compression needed.

So no springs, no torquing, no special bolts or nuts etc etc.
Just measure properly and let the cells do the work for you.

I know that many here will find this WAY to easy and simple for you.
But for the rest of us it will work.

My worry with this is could you over compress because that seems to be worse than no compression at all. Second will your box be strong enough to hold up to that unknown force?

 

[Frank in Thailand]

My worry with this is could you over compress because that seems to be worse than no compression at all. Second will your box be strong enough to hold up to that unknown force?

That's actually a good question, if the box is strong enough, would that mm extra per cell give too much force at "full"?

Making it stronger than the expansion should not be too difficult.
We read about springs and stuff, and not even the strongest ones.
15mm or 20mm plywood glued and screwed box should be able to withstand a lot more.

10mm probably would move a little with the expansion force.

(One of the reason I choose 10mm)

One thing I also like to know if the expansion from 71 to 72 mm goes gradually or little bit at start and a lot more at the end??

I still have hard time wrapping my head around it.
The aluminium sides are 72mm
They never get 71.
Aluminium wall have a hard time expanding...
In the center...
Yes.
That is probably what I see.
Like vacuum, dented inwards a little.

If the outside walls are 72, but the center of the cell is 71, compression will be on the outside walls, and not onto the center..

Foam sheets and stuff would even out the forces..
But it should be in a pillow shape, as it should be thicker in the center where the most expansion force is.

....

That's really difficult to accomplish!
I just press the 72mm sides together, and that is it.

My 152Ah...
Now looking like pillows...
They probably would be the best shape to fit with my 280Ah...
Only almost impossible to make good parallel sets have 152-280-152-280-152 stacked...

(I have one set build from the 280's, and one set for the 152's both own BMS controller)
560 and 456Ah

 

[Deleted member 9967]

The whole point is to prevent the cells from expanding and contracting repeatedly over the years in order to extend their life.
So how much they expand or don't is not the point.
Just hold them in place and they will stop expanding. Simple.

 

[ArthurEld]

I think the restraining is to keep the original general shape. But not to smash them into shape.
The jellyroll needs to expand into the available rectangular shape and not be allowed to bulge in the middle

 

[Gazoo]

Mine have gaps between the cells that get wider going from the top to the bottom when charged. Not as bad when discharged except the two cells I received undulated. Those two don't appear to change any. But the cell bottoms are flat on my cart and tops appear to be flat. Its a really weird shape.

 

[Ampster]

Ampster, can you provide more photos? Maybe a wider shot and include the top? I am looking for ideas. (Thanks)

I will tomorrow. I have been busy on a brief bath remodel.

 

[Frank in Thailand]

I think the restraining is to keep the original general shape. But not to smash them into shape.
The jellyroll needs to expand into the available rectangular shape and not be allowed to bulge in the middle

I missed the part about "jellyroll"

One thing many seem to forget is that the cells are 72mm at the edges, but 71 in the center.
Shaped like this )(

All the springs and other solutions need to place pressure at the center, not the edges.
The center goes from )( to [] the 72 edges stay 72.

One could stack the cells, but need something like mention before , closed air "balloon" or some form of gel like silicone.
It should be firm/ rigid enough to give the 300kgf , and flexible enough to spread out over the whole surface.

)(*)( Where the * is the gel/silicone that will get flattened during the expansion of the cells going to from 71 to 72mm at the center.

Or..
If no compression on the center at start, but prevent expansion beyond the 72mm aka bloating/ delaminating.

If you want to use springs, you need 2 springs per cell, pressing at the center ~)(~
Having more cells stacked...
~)()(~. The 2 cell sides on the outside do get the compression force.
The joint between 2 cells getts no compression!!
That will have a gap of 1mm when empty and 0mm when fully charged.

If the cell wants to expand beyond the 72mm, yes, it does stop them, depending on strength of the springs.

A firm ball of some kind, once between the cells, eclipse shape, would be the best solution.
It get flattened, going from 1mm thick to minimal during the expansion.

I don't know what material can stretch out over the whole surface and still be rigid enough to give the compression force with empty cells.

Elastic, really flexible, rigid, and stay elastic during many, many cycles.

Just compression on the sides will do nothing for the extraction at the center who will reach the same 72 mm that the sides already are.

Stopping from going beyond the 72mm..
Yes, springs or whatever..
Just keep it at 72mm

The 71mm at the center, that is a whole different ballpark.
What can compress +/-5000 times without losing integrity?
Syrofoam won't stay good for 5000 times.

I really don't know what is capable of sustaining +10 - 15 years, while being compressed for over 5000 times.
I'm counting every day as a cycle, being used at night, charged at day.

While it probably will spend the most time being flattened, as the cells are mostly full...
It should stay elastic enough to contract itself into the ellipse shape after 100+ days when the cells do get empty enough by accident...
And go from 0.00x mm to ellipse shape of 1mm center distance, providing the 300kgf at that center spreaded out over enough area to not make a dent in the cells..

It wont make any difference on how I will install my cells.
Or am installing for the last 4 days.

I don't have that material, so I can't place it between my cells.

They cen expand to the 72, and beyond this... They meet a nice strong plywood sheets, or an other cell who is having more or less the same SOC, the same level of expansion.

Keeping the the pressure at the center so it does have pressure @71mm...
Tell me when you found it

Compression force on both sides, at the center of the cells.. (not just the sides)
Not doable for me.

 

[Frank in Thailand]

So what would the pro and cons be for using springs vs static space (with pressure)?
Using springs;
+ Keep the recommended pressure at all times, and thereby prolong battery life.
- Require cables inbetween cells.

Static space (with pressure)
+ No extra force on cell connection points.
+ Can use solid burbars
- Pressure will vary.

I disagree.

The cells stay at 72 mm at the edges.
They aren't miracle aluminium that can stretch.

It's the center that is dented inwards )( outside size stay 72, no matter the SOC.

Rigid bus-bar can be used with or without spring solution.
72mm stays 72.

Only the center goes from 71 at 0% SOC to 72 at 100% SOC.

Compression of the cells like I do will prevent delaminating/bloating but won't give 1000 extra cycles.



If you want the 1000 extra, you need to have gel pads or something that are 5mm at the center and 4 at the edges.
That will give enough mass to expand the gel pad from 5 to 4mm at 100% SOC
Perhaps a pad of 2 at the sides and 3 at the center would work also.

The cells do NOT go like from [ ] at 0% SOC to ( ) at 100%
The cells go from ) ( @0% to [ ] @ 100%

Huge difference for all the solutions that are being posted.

It's not easy to capture on a picture.

Here is the new, never cycled 280Ah. Cell:


To make that a little more clear I used my drawing skills....


Still hard to notice..

You can feel it clearly.

Less then 0.5mm difference is hard to photograph.
Being at 3.338v.. it's a lot less.

The cell that have done about 180 cycles is little different.

Again hard to see in real life, some light difference in blue colour, easy to feel, for me impossible to capture good on camera, who probably automatically correct the slight difference..


This to show why spring and stuff have no influence on the total length of the battery.

They are 72, stay (or should stay) 72mm

And not like my unlucky 152Ah..
Who are supposed to stay 52mm and are now 54 mm

All the solutions that won't give the pressure at the center have no effect what so ever for the 1000 extra cycles.

Those who do keep th terminal distance the same, depending on how tick your layer is.

Simple foam really won't do it.

I can't be the only one who left something pressed down on foam for a few months leaving an imprint in the foam that stays there for always.

You normally never will go to 71mm, 0% SOC.
Probably stay as close to +/- 90% as possible.
That's almost the 72mm

After months on 72, going to 71..
Your foam won't expand anymore
It for sure won't give you the needed 300 kgf for 10 years!!!

Interesting..

But please do look at your cells carefully and see that there is a square, about 5 cm smaller then the cell size that is dented inwards.

The same square I see bull out on my 152Ah.

I haven't been careful laying them on concrete floor. (During building processes, at use they are on their feet)

It does show nicely where the bloating (or expantion / contraction) is.



Not at the outer edges!!
Center square.

That is what's gets from 71 to 72, the outer edges stay 72 mm.

For all solutions...
That needs to be the starting point to be able to work at all.

Not compressing cells against the other cell, but compression force on the LiFePO4 sheets in the cell.
And they are at the center, not outer edge.

 

[ArthurEld]

I missed the part about "jellyroll"

One thing many seem to forget is that the cells are 72mm at the edges, but 71 in the center.
Shaped like this )(

All the springs and other solutions need to place pressure at the center, not the edges.
The center goes from )( to [] the 72 edges stay 72.

One could stack the cells, but need something like mention before , closed air "balloon" or some form of gel like silicone.
It should be firm/ rigid enough to give the 300kgf , and flexible enough to spread out over the whole surface.

)(*)( Where the * is the gel/silicone that will get flattened during the expansion of the cells going to from 71 to 72mm at the center.

Or..
If no compression on the center at start, but prevent expansion beyond the 72mm aka bloating/ delaminating.

If you want to use springs, you need 2 springs per cell, pressing at the center ~)(~
Having more cells stacked...
~)()(~. The 2 cell sides on the outside do get the compression force.
The joint between 2 cells getts no compression!!
That will have a gap of 1mm when empty and 0mm when fully charged.

If the cell wants to expand beyond the 72mm, yes, it does stop them, depending on strength of the springs.

A firm ball of some kind, once between the cells, eclipse shape, would be the best solution.
It get flattened, going from 1mm thick to minimal during the expansion.

I don't know what material can stretch out over the whole surface and still be rigid enough to give the compression force with empty cells.

Elastic, really flexible, rigid, and stay elastic during many, many cycles.

Just compression on the sides will do nothing for the extraction at the center who will reach the same 72 mm that the sides already are.

Stopping from going beyond the 72mm..
Yes, springs or whatever..
Just keep it at 72mm

The 71mm at the center, that is a whole different ballpark.
What can compress +/-5000 times without losing integrity?
Syrofoam won't stay good for 5000 times.

I really don't know what is capable of sustaining +10 - 15 years, while being compressed for over 5000 times.
I'm counting every day as a cycle, being used at night, charged at day.

While it probably will spend the most time being flattened, as the cells are mostly full...
It should stay elastic enough to contract itself into the ellipse shape after 100+ days when the cells do get empty enough by accident...
And go from 0.00x mm to ellipse shape of 1mm center distance, providing the 300kgf at that center spreaded out over enough area to not make a dent in the cells..

It wont make any difference on how I will install my cells.
Or am installing for the last 4 days.

I don't have that material, so I can't place it between my cells.

They cen expand to the 72, and beyond this... They meet a nice strong plywood sheets, or an other cell who is having more or less the same SOC, the same level of expansion.

Keeping the the pressure at the center so it does have pressure @71mm...
Tell me when you found it

Compression force on both sides, at the center of the cells.. (not just the sides)
Not doable for me.

I just use 10 inch pounds when they are 3.3V from China. I'll measure them to see what thickness I restrain them at.

 

[ArthurEld]

I lined up 24 cells because that is the most that will fit in a 6' threaded rod.
I torqued them to 10 inch pounds then measured the length and divided by 24.
They are 71.9 mm apart.

 

[Pyrofx]

Good load people. This ain't rocket science. Clamp them snug . The edges will meet.
Done.
If it were any more than that , the whole world would have white papers on them . There are probably a few million out there in service.

Now if your so bored you want to make Devinci look like a slacker , by all means have at it.

 

[Steve_S]

22 Pages. 436 posts, 9000+ views, the Mulberry Bush has been surrounded, the grounds around it trampled to dust.
Is there 200 ways to say the Same Thing ? Appears there are more.
Lost in details and minutia and then regurgitating it... what do we end up knowing or learning ?

One thing, new members do not read from the start, just chime in and restart the Whole Adventure again.

You know that Mulberry Bush ? Kepp trampling the circle around it, it will eventually become a Moat and fill with water while drowning the tramplers with too much circular information (that only results in confusion).

THE IMPORTANT BITS:
Cells should be packed / bound snuggly @ 12-15 PSI.
Cells should be Electrically Isolated within the casing / housing used.
- If a metal box is used, a non-conductive lining is a MUST.
- Cells with exposed aluminum (tears in cell wrapping) should have such taped over with electrical tape to prevent contact.
- ! Some Cell brands have a charged casing (negative) (I have not experienced these myself but some folks report such)
- Putting a "pull string/strap" around your bundled cells before installing into a casing, makes it easier to pull them out IF you have to separate the cells for any reason.
Cells will Expand slightly with charging and Contract when discharging.
Cells are best "compressed" when at 50% State of charge with the Hopes of doing so at the average between the expansion & contraction potential of the cells.
Over compression can harm cells by reducing their effective cycling. If cells get crushed due to overzealousness, they are scrap.

PRO-TIP: Try to bundle cells in "sets" of 4 rather than a large bundle of 8 or 16 cells. Not only due to weight handling of 4 cells is easier but if you ever need to separate the battery pack, you do not have to "free all the cells" (they will expand as they relax from being compressed). If you ever have to take apart the pack to replace a cell, it's easier to extract the smaller bundle to work with it. Think of future maintenance requirements... hopefully you never need it.

People are overly preoccupied about battery temps & heating / expansion.
It is all relative people. IF you are going to push 1C Charge Rate at a 100AH battery it will heat up obviously, if you drain it at 1C rate of course it will heat up for that too. ESS systems don't use 3C or 5C capable cells, typically 1C is the average. WHO HERE IS PUSHING 100A @ a 100AH Battery ? MOST do .5C "at best".
Reality check, I have 910AH of LFP (2x175AH & 2x280AH batts) and my SCC only pushes 79A max at that Beastly Bank! NO WARMTH !
Seriously, How much Charge / Discharge are you dealing with ? will it even "warm" the batteries ?

THE BIG EXCEPTION for Load Warming is of course 12V systems because they have to work much harder and use more amps due to the low voltage. 1000W@12V=83A and pulling 1kw on 12V is very easy to do and a 12V system can easily exceed 100A demand (tripping many a BMS).

Sometimes, one can get lost in the minutia of details and only end up confused with a migraine headache.

 

[Solarfun4jim]

I used 3mm insulation material between each face. 8cells @72mm plus 9 layers insulation should = 576 + 27=603mm
I tightened the end clamps till the total length = 594mm, which means i have compressed the insulation layers by 1mm each. The pack feels tight and rigid. the cells are not in much compression, since the outside edges of the casings are strong enough not to deform (versus the insulation compressibility). Now, when the cells are full, the centres of the cells may expand a little into the now remaining 2mm insulation(ie 1mm per each cell), but the more they expand, the more resistance they will meet as the insulation compresses. Each cell can only expand up to 1mm now at which point the insulation would be compressed to zero...that cant happen, so restricts the cell expansion on each face to less than 1mm. Even after many cycles if the insulation stays compressed, it wont matter that the cell shrinks back at low cell charge, so long as when it is full, that extent is restricted. I do not believe the cells need to be in compression all the time, only when they want to expand past the dimension limits, otherwise all these cells sold with concave side would already be useless.
Just my theory....tell you in 10 years how it went....

 

[ArthurEld]

Good load people. This ain't rocket science. Clamp them snug . The edges will meet.
Done.
If it were any more than that , the whole world would have white papers on them . There are probably a few million out there in service.

Now if your so bored you want to make Devinci look like a slacker , by all means have at it.

I agree. Snug is what they are saying.
I have a torque wrench and 10 inch pounds is snug.

While we are picking everything to pieces, lol
If I come back and re torque, the nuts tighten more. I think I could come back forever and still get them to turn a little with 10 inch pounds of torque. I'll check the torque when they are at full capacity.

 

[ArthurEld]

My cells are on a piece of redwood fence I bought for 99 cents. It's rough as hell.
If I had them on Formica or rollers my torque would reach the cells in the center better.