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

I am bitterly jealous of 3 groups of people here:
1. Y'all with 3D printers
2. Y'all with the skills to program shit to do make it do what you want
3. Y'all with a deep understanding of the fundamentals of electricity
?
Not sure how old you are Dzl, but it is rarely too late to start learning. I have a 3D printer less than one year. The design software I use is Fusion 360, free for home/non business use. Previously my 3D CAD skills were limited to cylinders and cutting holes in existing designs, but after a year of messing around with the program, I can do many things that i couldn't do before. Don't be afraid to dive in.

"Fundamentals of electricity" was literally the name of my first college electrical class, a 6 credit hour class that i took when I realized that in my job a good understanding of electricity would help me. So I went back to school at age 26. I remember worrying that the younger students would be far ahead of me but not so, as life experience helped me more than I would have guessed. Get you a meter and a beginner kit of some sort and get your feet wet. Nothing beats hands on learning and burning up a few things.
 
I've 3d printed end plates for my lishen 273A batteries. I've compressed the cell bij tightening the thumbscrews I've printed by hand at 50% SOC.
The end plates have 20% infill, so they are a little bit flexible.
When I charge to 3.4v you can hear the plates are being compressed.
View attachment 30841
Looking amazing!

If you ever need to redo the terminal contacts, please use headless bolts/ studs. The thread in the terminal will thank you for it.

After a few mouts/ remounts....
There ain't much thread left...

I'm over 50 and have a 3D for 2.5 years now.

I tried a few things,the only one that worked was the test print of a cutie dog. :)
(So it ain't the printer)
After moving to Thailand it hasn't been re-assembled yet. No location enough dust/ water/ cat / child / wife free to safely build.


My 8 year old daughter just had her first hands on experience...
Trying to shove the cables back, that playing cats pulled loose, before my wife could notice and stop her..
IMG_20201221_102338_copy_750x1000.jpg
I don't think those Christmas lights still will work...
Lucky only some sparks inside the plastic housing.
And a crying scared girl.
The last one is good...
Now she now.
Always unplug before you try to fix :)

Europe did have it's benefits for safety.. at, obviously higher price.
 
I am bitterly jealous of 3 groups of people here:
1. Y'all with 3D printers
2. Y'all with the skills to program shit to make it do what you want
3. Y'all with a deep understanding of the fundamentals of electricity
?
yea agreed. 3d printers are beyond me. I use wood and a saw or iron, a welder, a saw, and drills to accomplish it the hard way. had to re-do the wood and rods compression 0nce. I am sure a 3d printer would be quicker and easier. but I repurposed the plywood from an old entertainment center thrown out in the trash. the threaded rods are the expensive part.
 
I am bitterly jealous of 3 groups of people here:
1. Y'all with 3D printers
2. Y'all with the skills to program shit to make it do what you want
3. Y'all with a deep understanding of the fundamentals of electricity
?
So, basically jealous of everyone but me?
 
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I'm trying to recall if I read somewhere in these 24 pages... Doesn't the springs have to divide the pressure by the number of cells clamped together? At this point, I'm wondering if just making it snug at 50% and assume expansion to 100% will provide the remaining pressure?
400Lbs of pressure across 4 cells doesn't seem like it would equally apply across each cell as they would each absorb some of it and squeeze down reducing pressure to the other cells. Has anybody actually measure the pressure on a fixed rigid box enclosure?
 
If the cells are stacked up, the force is not spread/divided among the cells. The force is spread across the surface area.

If the cells were laid out in a 2x2 array, then the force would be spread/divided among the cells. The force is spread across the surface area (more surface in this example).
 
I'm trying to recall if I read somewhere in these 24 pages... Doesn't the springs have to divide the pressure by the number of cells clamped together? At this point, I'm wondering if just making it snug at 50% and assume expansion to 100% will provide the remaining pressure?
400Lbs of pressure across 4 cells doesn't seem like it would equally apply across each cell as they would each absorb some of it and squeeze down reducing pressure to the other cells.
You may have misunderstood (or maybe I am misunderstanding you). Could you be referring to needing to divide the force by the number of springs/threaded rods? Or could you be referring to the need to account for more expansion the more cells you put in a row?

Has anybody actually measure the pressure on a fixed rigid box enclosure?
It would not be static, pressure at 0% SOC vs 50% SOC vs 100% SOC would be different. But I would be very interested to see measurements for this (I haven't seen any yet though). I think the snug rigid enclosure is still a totally acceptable approach.
 
Not sure how accurate they are, but pressure pads are available with up to 22lbs force measurements. I may order it and try it.

What im asking is, if 4 cells were stacked and clamped at say 12psi across the surface of the top cell, would every cell in the stack experience that same 12psi?
Actually, I think they would, because any 'give'/compression of each cell would still need to be overcome to reach 12psi. Sorry, been a long time since I took physics. :)

Or, we could drill a hole 33ft deep, fill it with water and drop the batteries down. 14.7psi pressure and stable temps year round.
 
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I've 3d printed end plates for my lishen 273A batteries. I've compressed the cell bij tightening the thumbscrews I've printed by hand at 50% SOC.
The end plates have 20% infill, so they are a little bit flexible.
When I charge to 3.4v you can hear the plates are being compressed.
View attachment 30841

Battery Porn ... :oops: :cool::oops:
 
Not sure how accurate they are, but pressure pads are available with up to 22lbs force measurements. I may order it and try it.

What im asking is, if 4 cells were stacked and clamped at say 12psi across the surface of the top cell, would every cell in the stack experience that same 12psi?
Actually, I think they would, because any 'give'/compression of each cell would still need to be overcome to reach 12psi. Sorry, been a long time since I took physics. :)

Or, we could drill a hole 33ft deep, fill it with water and drop the batteries down. 14.7psi pressure and stable temps year round.
Yes, the same force would be on all cells. My cells might be in the ocean (still waiting to find out) but I have two 3/8" AL plates drilled for 3/8" rod and have some die springs that will deliver 137lb force (each) when compressed. That is my plan for and eight series stack.
 
So, in the specs for the LF280N cells, the drawing shows the metal aluminium case is already the fixture (and holds the internal cells with 300kgf). EVE also told this to one of my viewers apparently... the slight swelling we see here and there is normal but does not need any further compression.
1608993424192.png
I have seen battery packs from EVs which uses these type of cells and none of the cells are actually compressed even given the high discharge rates in a vehicle. They are usually installed in a 'module box' which prevents them from moving around but there is no compression. In fact, they have fairly large gaps in between to allow for air cooling.

This guy here took a cell apart (yes, he's brave!) and it seems the two cells inside the aluminium case need the actual compression, but not the aluminium case itself. The case seems to be fairly sturdy when he pulls out the cells at the end of part 1
Part 1:
Part 2:

Keen to hear your thoughts and thanks for this great thread!
 
So, in the specs for the LF280N cells, the drawing shows the metal aluminium case is already the fixture (and holds the internal cells with 300kgf). EVE also told this to one of my viewers apparently... the slight swelling we see here and there is normal but does not need any further compression.
I don't know how far back you read through this thread but EVE was asked by one of the members about compression. It's in this post:

(1) EVE-280 cells should these be clamped tight or spaced for expansion? | Page 12 | DIY Solar Power Forum (diysolarforum.com)

I asked EVE directly before she did and they basically told me mounting the cells in such a way to keep them from expanding would extend cycle life.

What started all of this in the first place is it is noted in the EVE spec sheet compressing the cells will extend the cycle life to 3500 cycles. That could be what the drawing you mentioned is referring to. Another reason to do this is to help prevent stress on the terminals using busbars. If using braided busbars or short flexible cables then compressing doesn't matter and one should expect 2000 cycles.

Yeah, I watched your video and as is the case with some of the videos I have watched, viewers need to inform themselves more about whatever the topic of the video is. In the case of EVE cells, they are not a simple plug and play solution. Parallel top balancing is necessary because the cells are not capacity matched. They are voltage and IR matched and that's it.

In addition we have found the threads strip easily. This could be due to some of the holes being poorly tapped. It's now being suggested to torque around 4.5nm and use a thread bonder like Loctite. I stripped a thread and personally will not torque more than 4nm. The 8nm torque the spec sheet refers is wrong and some of us believe it's the amount of torque that can be safely applied without damaging the cell terminal.
 
It was not directed at you, but offered for the benefit of other readers. I did not agree that a supplier in China should know what they are selling. Yes that is a normal expectation in the USA. but not in dealing with Chinese merchants.
I can't change your expectations or the expectations of the original poster and I don't need to either. If the shoe fits, wear it. My responses were intended as general comments. The quote I picked was for the purpose of illustrating the concept and not intended as a personal attack.
I was involved in a number of process automation project in Mexico back in the 80's and 90's and learned to fear one phrase more than any other: "No problem". It took a while, but eventually I learned that when I heard those two words, I was probably in for a tough time.

I think in cultural context that phrase is the equivalent of an Angelo saying "whatever". I took it to mean, that what I asked for was reasonable and would be provided in a reasonable timeframe. But based on what happened, the people saying it to me were actually saying, "no problem for me because it isn't going to happen."

Different cultures, different ways of communicating. And agreeableness is not the same thing as agreement. Some cultures have some difficulty in saying "no" in direct terms. They still say it, but it is couched in polite terms that someone from a different culture could interpret as OK and Yes. I know I did.
 
Some cultures have some difficulty in saying "no" in direct terms. They still say it, but it is couched in polite terms that someone from a different culture could interpret as OK and Yes. I know I did.
Yes I have noticed that about certain cultures. My Chinese wife says "No problem" a lot and I am careful when I hear that. She also has the ability to say NO when she means it. LOL
 
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This is fun, I independently came up with the 12 PSI number based on the clamping force divided by the surface area of the large side of a cell: 661 lb / (8" x 7") = 11.81 PSI

Is anybody looking at using Belleville Disc Spring Washers? They provide a very high spring rate for their size.


I just bought some of these 5/16" Belleville Spring washers for my rig. I am building an 8S, battery and plan on using the U configuration. This means I will have 4 cells in compression twice. I will be using 1/2" Baltic Birch plywood for the compression plates with three pieces of 1"x1" uni-strut and 6 pieces of 5/16" threaded rods per set of 4 cells to apply clamping force evenly to the plywood.

These are the washers I purchased: https://www.mutualscrew.com/product/m8-516-belleville-washers-carbon-steel-219124.cfm

I think I will put together small test fixture and determine what configuration of Belleville spring washers is required to develop 300 KGF. I design load cell instrumentation so coming up with a load cell and instrumentation to measure this is pretty easy (just look in my desk drawer). I am not an ME, but that is not very much force when spread over 4 or 6 threaded fasteners. I may end up backing off to 4 threaded rods per set of cells.
 
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This is fun, I independently came up with the 12 PSI number based on the clamping force divided by the surface area of the large side of a cell: 661 lb / (8" x 7") = 11.81 PSI

Is anybody looking at using Belleville Disc Spring Washers? They provide a very high spring rate for their size.


I just bought some of these 5/16" Belleville Spring washers for my rig. I am building an 8S, battery and plan on using the U configuration. This means I will have 4 cells in compression twice. I will be using 1/2" Baltic Birch plywood for the compression plates with three pieces of 1"x1" uni-strut and 6 pieces of 5/16" threaded rods per set of 4 cells to apply clamping force evenly to the plywood.

These are the washers I purchased: https://www.mutualscrew.com/product/m8-516-belleville-washers-carbon-steel-219124.cfm

I think I will put together small test fixture and determine what configuration of Belleville spring washers is required to develop 300 KGF. I design load cell instrumentation so coming up with a load cell and instrumentation to measure this is pretty easy (just look in my desk drawer). I am not an ME, but that is not very much force when spread over 4 or 6 threaded fasteners. I may end up backing off to 4 threaded rods per set of cells.
I thought about Belleville right away. But I ended up with die spring. The main reason is the distance of compression is easier to measure, a larger span.
 
So, in the specs for the LF280N cells, the drawing shows the metal aluminium case is already the fixture (and holds the internal cells with 300kgf). EVE also told this to one of my viewers apparently... the slight swelling we see here and there is normal but does not need any further compression.

I have seen battery packs from EVs which uses these type of cells and none of the cells are actually compressed even given the high discharge rates in a vehicle. They are usually installed in a 'module box' which prevents them from moving around but there is no compression. In fact, they have fairly large gaps in between to allow for air cooling.

This guy here took a cell apart (yes, he's brave!) and it seems the two cells inside the aluminium case need the actual compression, but not the aluminium case itself. The case seems to be fairly sturdy when he pulls out the cells at the end of part 1
Part 1:
Part 2:

Keen to hear your thoughts and thanks for this great thread!
Interesting info, thanks for adding to the discussion.

I will point out 4 points worth pondering in relation to your post:

1. I think you need to followup with that viewer if you want to believe (or at least if you want others to believe) what they are saying. There are details (who told them, in reference to what cell, and when) that would help establish the credibility and context of that comment.

2. My understanding (not an EV guy) is that EV's have different priorities than energy storage systems. Solar the main concern is cycle life, EV's have to consider high c rates and thermal management in a way that solar ESS does not. Engineers may make the calculated tradeoff to sacrifice cycle life or cost for better cooling.

3. Form factor matters. A large prismatic cell, a small prismatic cell, or a cylindrical cell, are to a degree different beasts. Cell construction probably matters too. I can think of two small aluminum prismatics designed to have air gaps (CALB CAM 72Ah, Frey <100Ah) but I have never seen a large form factor prismatics designed this way. From the little bit I understand large form factor prismatic cells sacrifice strength for energy density. And the broad side of the cell is the weak point. I won't pretend to be an expert here.

3. One of our forum members spoke with two separate engineers at EVE, that was covered above so I won't go into detail, but they were pretty clear on fixture being recommended. The 12PSI seems somewhat universal, and based on other info from other sources (A123, etc) it seems this number is derived from the ideal pressure for the internals of the cell. Or at least that is how I have interpreted the info we have.

Cliff notes of the evolution of our understanding and discussion can be found here and here

edit: also I stumbled upon the video of that cell being deconstructed a few months back and found it super interesting
 
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.
My company makes these. You probably don't want to pay what we charge for them.


I can see it now, add motorized tensioners plus a control system to dynamically adjust tension in real time.

I can totally see spending $10K to extend the life of a $1K battery pack.
 
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