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

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 :))

There appear to be lots of options for corrugated alluminum panels, most from mfrs in China and India. Metawell would be an alternate company (German)
 
Here is the corrugated stuff. 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 learned something new! Thank you :)
 
Now if we are talking forced air cooling? A small CPU/computer blower (think graphics car) could move plenty of air through those channels. Now we still have to deal with overall heat transfer, which is limited by the delta T compared to ambient.

As a note these cells have the layers oriented top to bottom. So the thermal transfer might not be symmetric. Such as the conduction is better vertically, as the material is continuous, vs thickness wise, where its broken up by the separator membrane, which is probably not very thermally conductive.

For High C rate applications, I still wonder if an oil bath would do the trick.
 
I love this forum, we start off with clamping cells and we have covered expansion, compression, springs, are now onto the merits laminated aluminium spacers and forced air cooling. It's like the inside of my brain when I'm contemplating projects while falling asleep. ??

... And oil baths. ?
 
Not even sure if this will help but what I have done is put a piece of plywood on each end and put 6 threaded rods on it [3 on each side] then tightened them until I could lift the batteries without them falling out.
I figured that was strong enough and did not need to be any tighter.

It might not be exact science, but it works for me. :)

The only issue i see with that is that you don't know if you hit 12 or 17 or 25 ... anything over 17 is worse than not having anything - in fact it apparently crushes easily with this razor thin aluminum they are using ... but to test you need a torque wrench - and 12 PSI is a pretty hefty torque
 
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

AND he is 100% correct -- but you asked a totally different question to him then what we are taking about ... we are talking about if clamping - and if so how much - will increase the cycle count before hitting the 80% end of life mark ...
 
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 going to suggest Laminators, Inc. also. I was looking at using some of their panels in aluminum door frames and as shelves in an aluminum cabinet.
 
No, springs don't work like that. A 10 N/mm spring will exert 10 N of force when compressed by 1 mm, 20 N for 2 mm, etc...

Of course you are correct. Sorry for the bum steer on the spring rates. Your explanation of what you need to do is excellent.
 
The only issue i see with that is that you don't know if you hit 12 or 17 or 25 ... anything over 17 is worse than not having anything - in fact it apparently crushes easily with this razor thin aluminum they are using ... but to test you need a torque wrench - and 12 PSI is a pretty hefty torque
I agree one should have a way of determining the torque. We haven't noticed any cells being damaged from mounting in a fixture by forum members whatever that fixture may be. I do think most have measured the torque. 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.

My whole take on this is while it is good to get the info from EVE, and I really do appreciate that, attempting to mount cells in a perfect fixture with the correct amount of constant force at varying temps will be challenging. Many of us have received cells that are already slightly deformed and that's another concern to add into this mix. In my case I was able to arrange my 8 cells so I have a relatively square pack.

I look at like this. If one does a full 1C cycle every day with no compression, the cells should last better than 5 years according to the EVE specs which states 2000 cycles. Does anyone do a full 1C cycle every day? And there will most likely be better battery technology in the near future.

I appreciate why some might feel the need to go through the process of attempting a proper compression fixture, and I will be interested in whatever results might be reported 5. 10. or 15 years from now.
 
The only issue i see with that is that you don't know if you hit 12 or 17 or 25 ... anything over 17 is worse than not having anything - in fact it apparently crushes easily with this razor thin aluminum they are using ... but to test you need a torque wrench - and 12 PSI is a pretty hefty torque
Yeah, that worries me as well.
 
I look at like this. If one does a full 1C cycle every day with no compression, the cells should last better than 5 years according to the EVE specs which states 2000 cycles. Does anyone do a full 1C cycle every day? And there will most likely be better battery technology in the near future.

I appreciate why some might feel the need to go through the process of attempting a proper compression fixture, and I will be interested in whatever results might be reported 5. 10. or 15 years from now.

That's where I'm at. I have a compression assembly implemented that I think is reasonable. Not too tight, not loose. I'm calling it good and spending my time on other things. I understand the adventure in taking things to the Nth degree, but I've been doing the techie thing for 40 years. I've lived on the bleeding edge and have the bloodstains to prove it. I've learned that good enough is really quite good and I'm happy where I'm at.
 
The only issue i see with that is that you don't know if you hit 12 or 17 or 25 ... anything over 17 is worse than not having anything - in fact it apparently crushes easily with this razor thin aluminum they are using ... but to test you need a torque wrench - and 12 PSI is a pretty hefty torque
Sadly my main problem is keeping them stable as I ride my mobility scooter. They CAN'T be jumping around as I ride. And many of the sidewalks here are just horrible. The city likes its trees. But the roots lift up the sidewalk making it dangerous to walk on and even worse to ride on.
Ok so I only get 10 years out of them LOL.
I hope I can get new batteries in my 70's LOL :)
 
This is inspiring me to incorporate a battery pressure sensor into the kit I'm building.
This seems like a good idea, given the pressure may change over time if the cells begin to swell a little despite the compression mounting. What kind of sensor were you considering?
I see pressure sensitive thin film resistors available cheaply on Amazon, which might be able to be sandwiched in the compression plate construction, but haven’t found one which goes over 30kg yet.
 
AND he is 100% correct -- but you asked a totally different question to him then what we are taking about ... we are talking about if clamping - and if so how much - will increase the cycle count before hitting the 80% end of life mark ...
I asked ”Do these cells need to be clamped and compressed together to prevent delamination and bloating/swelling?” and then clarified “The reason I asked is I was looking at the data sheet for the Eve 280Ah cell and they actually define a longer cycle life if the cells are clamped.“

So can you tell me why you think I asked ”a totally different question”?
 
Yeah, that worries me as well.
I have been thinking about this. I don't recall if you ever parallel top balanced your cells but as I recall you have never fully charged them. When/if you do either I think it would be a good idea to loosen up the nuts a little. Then retighten as necessary.

I want to eventually put my pack into a case and I plan on having something to support the bottom to lift them in. Or tilt the pack sideways and slide it into the case, then lift the case upright. Another challenge...lol. Perhaps you could mount a piece of wood to the bottom of your cells using brackets? Then you would not have to worry about them sliding out.
 
I have been thinking about this. I don't recall if you ever parallel top balanced your cells but as I recall you have never fully charged them. When/if you do either I think it would be a good idea to loosen up the nuts a little. Then retighten as necessary.

I want to eventually put my pack into a case and I plan on having something to support the bottom to lift them in. Or tilt the pack sideways and slide it into the case, then lift the case upright. Another challenge...lol. Perhaps you could mount a piece of wood to the bottom of your cells using brackets? Then you would not have to worry about them sliding out.
They have wood on 5 sides. A lid is next. :)
I said earlier that i tightened them until I could lift it up as in the degree of tightness I put on the sides.
I suppose I should have taken the extra ten minutes to explain I was going to add more wood to the "BOX" to give it 5 or six sides.
My negligence in not explaining that by BOX I meant a six sided BOX and not a 2 sided box.
Sorry about that. :)
 
They have wood on 5 sides. A lid is next. :)
I said earlier that i tightened them until I could lift it up as in the degree of tightness I put on the sides.
I suppose I should have taken the extra ten minutes to explain I was going to add more wood to the "BOX" to give it 5 or six sides.
My negligence in not explaining that by BOX I meant a six sided BOX and not a 2 sided box.
Sorry about that. :)
Got it. You are good then. :)
 
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 look at like this. If one does a full 1C cycle every day with no compression, the cells should last better than 5 years according to the EVE specs which states 2000 cycles. Does anyone do a full 1C cycle every day? And there will most likely be better battery technology in the near future.

I appreciate why some might feel the need to go through the process of attempting a proper compression fixture, and I will be interested in whatever results might be reported 5. 10. or 15 years from now.
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.
 
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