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

I asked a vendor I’m in contact with about this issue of whether or not to clamp cells today. They answered :

“If discharging at 1C or more then yes, it would be better to compress them. Because high current charge/discharge will cause the cell inflating. Otherwise, it is ok to make them without compression. Because if amps is large, much heat will generated, and the cells will inflate a bit.”

And they supplied the attached photo to illustrate a typical clamping arrangement. Note, this wasn’t specifically in connection with Eve 280Ah cells, just general info.

View attachment 27192
I might add that when I clamped mine that I measured the space between the boards at each rod and equalized them to within a 1/16th of an inch [or less].
This way there was absolutely no unevenness in the compression. Looks like they did this also in the picture above. :)

Sounds like good advice. :)
 
My take on it is that if you can take a simple action that will pretty radically increase the life of your pack .... go for it. Installing springs on the threaded rods is pretty simple to accomplish. When doing compression without the springs, it looks to me like the biggest risk would be that there would be conditions that cause excessive compression .... the EVE engineer said that pressure over 17 psi would be worse than no pressure.

I suspect it won't be long before springs are identified and verified to work as expected for different cells and different number of rods and the cookbook for doing this is established along with sources.

Airtime already has some springs identified that can be ordered from an online source. I know there are a lot of ElectroDacus fans on here and Dacian has his packs set up this way.

The only thing that concerns me about compression is that the pack will have to be set up without spacing between the cells to accomplish this ... and heat is a big factor in reducing life cycle also ... so, where is that balance between ventilation and compression? If the pack is in a temperature controlled environment, it seems pretty pretty evident that compression would take the priority. In an RV application ..... there might be trade offs.
 
I asked a vendor I’m in contact with about this issue of whether or not to clamp cells today. They answered :

“If discharging at 1C or more then yes, it would be better to compress them. Because high current charge/discharge will cause the cell inflating. Otherwise, it is ok to make them without compression. Because if amps is large, much heat will generated, and the cells will inflate a bit.”

And they supplied the attached photo to illustrate a typical clamping arrangement. Note, this wasn’t specifically in connection with Eve 280Ah cells, just general info.

View attachment 27192
I like the step for Plexi Glass. ?
 
My take on it is that if you can take a simple action that will pretty radically increase the life of your pack .... go for it. Installing springs on the threaded rods is pretty simple to accomplish. When doing compression without the springs, it looks to me like the biggest risk would be that there would be conditions that cause excessive compression .... the EVE engineer said that pressure over 17 psi would be worse than no pressure.

I suspect it won't be long before springs are identified and verified to work as expected for different cells and different number of rods and the cookbook for doing this is established along with sources.

Airtime already has some springs identified that can be ordered from an online source. I know there are a lot of ElectroDacus fans on here and Dacian has his packs set up this way.

The only thing that concerns me about compression is that the pack will have to be set up without spacing between the cells to accomplish this ... and heat is a big factor in reducing life cycle also ... so, where is that balance between ventilation and compression? If the pack is in a temperature controlled environment, it seems pretty pretty evident that compression would take the priority. In an RV application ..... there might be trade offs.
My plan is 10mm aluminium at the end and 4mm aluminium in between, bottom and sides are 25mm bigger in each direction, so will act like a heat sink. Overkill? Very likely! But it keeps me out of trouble.
 
The only thing that concerns me about compression is that the pack will have to be set up without spacing between the cells to accomplish this ... and heat is a big factor in reducing life cycle also ... so, where is that balance between ventilation and compression? If the pack is in a temperature controlled environment, it seems pretty pretty evident that compression would take the priority. In an RV application ..... there might be trade offs.

For solar installations it's not usually a problem as we only use very low C rates. Even a tight pack will only rise a few °C at most when used.

But if you really want, then, as @Colonel.lp said, you can put an aluminium sheet of a few mm between each cell, bigger than the cells.

Ideally something like coroplast but in aluminium instead of plastic would be awesome, but I never found any when I searched for another project.

Going really extreme you can put waterblocks, but unless you power an EV I don't really see the need for that ?
 
“If discharging at 1C or more then yes, it would be better to compress them. Because high current charge/discharge will cause the cell inflating.
I can say without a doubt 6 of my EVE cells expanded slightly while I was parallel top balancing them and I had the charger set at 12 amps. The bottoms did stay flat in the table and there were gaps between the cells when I started except between two of them and those cells were received with undulating sides. Those two cells did not appear to expand.
 
Yeah that vendor don't really know what he's talking about as the main factor in swelling isn't heat but chemical reactions (increasing electrode size and producing gases).
 
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My take at looking at the chart I'm going to try and shoot to be within the 6-12psi range and not worry about getting it exact. The one thing I haven't seen in this thread is anyone accounting for cell expansion and contraction. One needs to take this into account when selecting springs as to not coil bind your spring and exceed that 17psi mark.
Going off of 53.89sqin my target pressure would be 6psi=323lbs to 12psi=646lbs
From the spec sheet it looks like the expansion at 40% SOC is =/- 0.5mm per cell so a total range of 4 mm for a 4s pack
So for simplistic sake I would like a spring(s) that reach that 6-12 psi with .2 inches for cell expansion, not exceed that 17psi at coil bind.
The next thing I looked for was the shortest spring possible. It looks like this spring would work well with 4 rods.
Installing the attached spring at 0.4" compressed would give you around 90lbs per spring or 6.6psi at the cell and still give you over 0.2" of expansion and still not exceed our 17 psi.

 
This is inspiring me to incorporate a battery pressure sensor into the kit I'm building.
 
Hmm,
Well I can certainly see why you would expect the cells would be 2020 cells based on that exchange. Basen did not say it explicitly, (they said they received the cells in July, and that they are 'brand new') And if they added the red boxes to the image, the date they highlighted roughly translates to "Production Date: 2020.7.10" and the next line down says "Shipping Date 2020.7.11." If they added the red boxes they definitely explicitly gave you reason to believe the cells were produced in 2020.

View attachment 23761

One complicating factor is that that label appears to be the shipping label from the wholesaler or middleman or manufacturer, it is quite possible the cells are being represented to Basen this way. Of course they should be doing there due diligence and have knowledge of the product they are selling and represent it accurately. Realistically, I don't have great faith in resellers knowing the product they sell in great detail, or being willing to do the digging if it doesn't benefit them.
the meatpacking industry does this commonly in the USA. They repackage the product with a new date to make old products look new.
 
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I can say without a doubt 6 of my EVE cells expanded slightly while I was parallel top balancing them and I had the charger set at 12 amps. The bottoms did stay flat in the table and there were gaps between the cells when I started except between two of them and those cells were received with undulating sides. Those two cells did not appear to expand.
Mine swelled too and I used a fixture
 
My take at looking at the chart I'm going to try and shoot to be within the 6-12psi range and not worry about getting it exact. The one thing I haven't seen in this thread is anyone accounting for cell expansion and contraction. One needs to take this into account when selecting springs as to not coil bind your spring and exceed that 17psi mark.
Going off of 53.89sqin my target pressure would be 6psi=323lbs to 12psi=646lbs
From the spec sheet it looks like the expansion at 40% SOC is =/- 0.5mm per cell so a total range of 4 mm for a 4s pack
So for simplistic sake I would like a spring(s) that reach that 6-12 psi with .2 inches for cell expansion, not exceed that 17psi at coil bind.
The next thing I looked for was the shortest spring possible. It looks like this spring would work well with 4 rods.
Installing the attached spring at 0.4" compressed would give you around 90lbs per spring or 6.6psi at the cell and still give you over 0.2" of expansion and still not exceed our 17 psi.

Earlier in the thread I calculated that if you clamp a 4s eve cell to 300kgf at 50% charge the resulting range would be 270kgf at 0% to 330kgf at 100%. Or 595Ib to 727Ib for you Americans.
 
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The only thing that concerns me about compression is that the pack will have to be set up without spacing between the cells to accomplish this ... and heat is a big factor in reducing life cycle also ... so, where is that balance between ventilation and compression?
I view this as a still somewhat open--and very context specific--question. As to 'where the balance is', based on what I have read, the balance is roughly in the ballpark of 0.5C to 1C continuous discharge current. The data I have seen shows that cell temperatures at <0.5C continuous discharge will be within a few degrees of ambient. However it should be noted that this testing was done on 20Ah pouch cells (I swear every study I bring up uses 20Ah pouch cells.. :rolleyes:). If memory serves 0.1C, 0.2C, and 0.5C were all within 3-5 degrees of ambient 1C was maybe ~7-8 degrees above ambient but was increasing fast towards the end of the discharge. Note: these are continuous discharge currents, and the test ends when the battery is fully discharged.
See Here
Screenshot_2020-03-22 A123 cell testing MATLAB Simulink pdf.png


Eric of Nordkyn Design Also observes that:
"The gaps between [cylindrical] cells can present an advantage for cooling when thermal management is necessary due to very high currents, but, in marine applications, the currents are modest and the battery cells never seem to get more than a few degrees above ambient temperature." Mechanically, cylindrical cells are very robust and very resilient to mechanical damage from shocks and vibrations, which is good in electric vehicles.

But why I consider this question still some what open ended.
1. The study only covered discharge, not charge, I don't know if there would be differences here?
2. The study was for a small capacity pouch cell, how similar or different would a large form factor prismatic cell behave?

If the pack is in a temperature controlled environment, it seems pretty pretty evident that compression would take the priority. In an RV application ..... there might be trade offs.
At the same time its worth remembering passive air cooling can only be effective when the ambient temperature is significantly cooler than the thing being cooled (at least that is my understanding, I am neither an engineer nor a physicist, and often exhibit my ignornance when it comes to such subjects ;))

Ideally something like coroplast but in aluminium instead of plastic would be awesome, but I never found any when I searched for another project.
This exists, I came across it last year when searching for some coroplast type material. I just did a quick search and can't find it anymore. Not sure if it would be strong enough though.

Earlier in the thread I calculated that if you clamp a 4s eve cell to 300kgf at 50% charge the resulting range would be 270kgf at 0% to 330kgf at 100%. Or 595Ib to 727Ib for you Americans.
Us American need to get comfy with metric no need to coddle us ;)
 
This exists, I came across it last year when searching for some coroplast type material. I just did a quick search and can't find it anymore. Not sure if it would be strong enough though.

OMG now I need to know where we could find it ?
 
OMG now I need to know where we could find it ?

Are you talking about aluminum honeycomb panels? Care needs to be taken with point loads, or they crush though. Typically you need to epoxy in inserts to carry fasteners, though a backing plate around a bolt/nut can work.


1605048683690.png
 
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Are you talking about aluminum honeycomb panels?


View attachment 27206
It may have been this, (though from a heat shedding POV, I would think vertical ribs/corrugation would be ideal, the honeycomb would trap air pockets, and may not have any advantage over plain solid aluminum, does that make sense? I'm thermally challenged :))
 
Are you talking about aluminum honeycomb panels? Care needs to be taken with point loads, or they crush though. Typically you need to epoxy in inserts to carry fasteners, though a backing plate around a bolt/nut can work.


View attachment 27206
Wow ... That stuff is expensive
 
Are you talking about aluminum honeycomb panels? Care needs to be taken with point loads, or they crush though. Typically you need to epoxy in inserts to carry fasteners, though a backing plate around a bolt/nut can work.


View attachment 27206

Nope, I'm talking about having the channels the other way so air can pass through it.


It may have been this, (though from a heat shedding POV, I would think vertical ribs/corrugation would be ideal, the honeycomb would trap air pockets, and may not have any advantage over plain solid aluminum, does that make sense? I'm thermally challenged :))

No, air is an insulator (and a good one...).


Wow ... That stuff is expensive

Well, not easy make... and not a lot of it sold probably.
 
It may have been this, (though from a heat shedding POV, I would think vertical ribs/corrugation would be ideal, the honeycomb would trap air pockets, and may not have any advantage over plain solid aluminum, does that make sense? I'm thermally challenged :))
It's not a terribly good conductor. Probably better than wood or plastic, much worse than solid aluminum.

There are aluminum composite panels that at first glance look like they have corrugated aluminum cores. However its actually typically a plastic core. Alu/Alu type would be harder to come by.

Personally I think its kinda silly for under 0.5C, as the heat buildup isn't significant.
 
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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.

 
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