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How to achieve up to spec battery compression?

If I take the plunge, I will need enough for at least 6- 16s packs (current packs) or plan on enough for the current and future packs.
Have to consider options I guess.
Speaking of compression, rather than springs, I wonder why no-one ever considers using compressed air... rubber bladder pouch at the end of each row connected to a small air tank and pump, set to any pressure you like...maybe just too much to bother with.
 
If I take the plunge, I will need enough for at least 6- 16s packs (current packs) or plan on enough for the current and future packs.
Have to consider options I guess.
Speaking of compression, rather than springs, I wonder why no-one ever considers using compressed air... rubber bladder pouch at the end of each row connected to a small air tank and pump, set to any pressure you like...maybe just too much to bother with.
I don't think the -50 would be a good fit for a battery pad operation. Namely because Rogers doesn't provide the CFD curve for additional compression beyond 25% like they do for the -40.

So with the -40, you can compress 25% to get say 6.5 psi. Over the lifetime of the cell, as it expands, the pad compression could reach 50% and you are still within psi limits.

With the -50, we don't know what it's going to do as the cells age but you could end up in an overpressure situation, with the firmer material that seems quite likely as there's less "give"


Screenshot_20240707_074518_Samsung Notes.jpg

Screenshot_20240707_073026_Samsung Notes.jpg
 
What about the fire rating of this PORON foam? Can it survive 250C without melting? If not you may want to have a fr4 sheet as a separator in addition to the foam.

I looked and it seems getting this PORON foam locally will be a challenge for me, but I have lots of spare 3mm thick neoprene. Does anyone know how to measure stress strain curve? (Assuming a well equipped machine shop).

I'd think something like this might work. Get a scale that does up to 400g. Cut a 5x5mm square of the foam. Squeeze it between a scale and a flat piece of metal and put a dial indicator on it. Keep applying force on top and measure displacement. Put it on graph paper and read...

12 psi is approximately 8g per square mm. So 5*5mm square should need about 200g to compress. If the neoprene does that... Bingo. No poron required.
 
It it my (current) understanding the Poron foam is a polyurethane based product, while Neoprene is a polychloroprene. There are other foams made from latex, polyester, and vinyl (etc) - each has it's own properties and trade-offs. The main issue is to find a relatively "flat" stress-strain curve so the pressure is nearly the same as the batter cells expand slightly, and to deal with compression-set, which is the long term break-down of the foam over thousands of stress reversals leading to loss of the initial stress-strain response.
 
I wouldn't think foam good to 250c is needed. If your battery gets that hot it is likely venting and ruined?
 
True,
Back to a compressed gas in a bladder (ie an Air-wedge) to provide constant pressure, instead of air use CO2/fire suppressent to fill the bladder LOL.
 
Does anyone know how to measure stress strain curve? (Assuming a well equipped machine shop).

Metal plate, weights, depth gauge.

I think a stack of several sheets of compliant material would increase displacement, reduce measurement error.

Stack of exercise weights might do it. Don't want too tall, to the point it feels like tipping.
Weights on barbell shaft could work, top end supported against tipping.
 
Metal plate, weights, depth gauge.

I think a stack of several sheets of compliant material would increase displacement, reduce measurement error.

Stack of exercise weights might do it. Don't want too tall, to the point it feels like tipping.
Weights on barbell shaft could work, top end supported against tipping.

I think the cells in upright position with a stack of weights hanging from the end of an arm by a shelf. A lever and gear to apply pressure horizontally.

A Rube Goldberg machine at its best

I have been thinking, a screw with a pulley wheel on it and weights hanging in the air, then a plate with a center mount ball/socket. Even pressure all around and gravity would have to fail to break it.... for that we would need to call MC Escher
 
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So it should not really sustain fire (as I understand it) but it is very likely above 121C/250F it looses its properties so it may for example become runny and squeeze out. Sobif I was building with it (and I very well might) I would add the fr4 sheet just in case.

Why? To avoid case to case short if a cells "runs away". This will prevent adjacent cells from being damaged.
 
Let me move back to the basics.
Can someone confirm that my understanding of the compressions is correct?

If I take 280Ah prismatic cell that has the area of 305mm² (204x173mm) and compress it with 300kgf as per data sheet resulting pressure is 84kPa or 12.2psi
If I take a 50Ah prismatic cell that has the area of 243cm² and compress it with the same force resulting pressure is 122kPa or 17.7psi

The manufacturer recommends same force for both cells even though the resulting pressure is different, correct?
The 50Ah cells are high discharge 3C so they need more pressure?

One more thing, the 300kgf or 660 pounds is nothing more than 660 pounds weight sitting on top of the cell enclosed in rigid plates.

Is my understanding correct or am I missing something?
 
Likely the only misunderstanding is thinking that the English language manuals contained a manufacturer recommendation of different pressure for different cell.

More likely they copy/pasted information without calculating what it should be for a different size cell.

The "ask me anything" thread mentions compliant material between each cell, such that pressure remains within range for a certain amount of expansion, and cells (which have busbars between them) don't have to move.)

Could be that discharging isn't where the issue would occur, and charging is what requires pressure to constrain, but I'm not sure. Maybe it prevents bubbles from forming, keeps gasses in solution. (model being a soda pop can.) Again not sure.
 
Likely the only misunderstanding is thinking that the English language manuals contained a manufacturer recommendation of different pressure for different cell.

More likely they copy/pasted information without calculating what it should be for a different size cell.

The "ask me anything" thread mentions compliant material between each cell, such that pressure remains within range for a certain amount of expansion, and cells (which have busbars between them) don't have to move.)

Could be that discharging isn't where the issue would occur, and charging is what requires pressure to constrain, but I'm not sure. Maybe it prevents bubbles from forming, keeps gasses in solution. (model being a soda pop can.) Again not sure.

Maybe it's copy/paste error, but I doubt it.
The 300kgf initial compression is stated on EVE product specification for LFK50K and LF280K.
Both documents have EVE logo and are in English and Chinese. (Both are available online)

Other thing that confuses me is info on envision prismatic cell product specification.
Safety characteristics section contains data from various tests like overcharging, short call circuit and crush test.
"Squeeze level: Until the cell voltage reaches 0V or the deformation reaches 30% or the extrusion force reaches 13±0.78KN"

"extrusion" seems odd English to me but apart from this the 0.78KN force equals 79kgf.

And yet the preload compression is recommended to be 300kgf

The force doesn't mean much without knowing an area it affects.

Any thoughts, anyone?
 
The force doesn't mean much without knowing an area it affects.

Any thoughts, anyone?
The "squeeze" test is likely a standardized apparatus and the squeezing isn't spread over the entire side of a cell, just a standard sized probe/small plate or similar applying pressure to the side of a tested cell. When they say "until 30% deformation or 13kN of force - I suspect they mean in either case the load or deformation of the probe relative to the side of the cell.
 

He do it this way .
And it looks like a good explain about it.
No way to get 600 lbs. of compression with that plastic cutting board material. Need 3/4 plywood, or steel plate I'm going to compress with 1/4" steel and fiberglass insulator between. I don't want any wood near my batteries.
 
No way to get 600 lbs. of compression with that plastic cutting board material. Need 3/4 plywood, or steel plate I'm going to compress with 1/4" steel and fiberglass insulator between. I don't want any wood near my batteries.
I wouldn't be so quik to dismiss it. There are steel angles bracing it from the back. The plastic is really just a force spreader.

Also, what kind of plastic is it? If it is hdpe I believe at this thickness it could easily support 600lbs/300kg.
 
I wouldn't be so quik to dismiss it. There are steel angles bracing it from the back. The plastic is really just a force spreader.

Also, what kind of plastic is it? If it is hdpe I believe at this thickness it could easily support 600lbs/300kg.
I went 7/8” marine grade plywood, been working fine in an off road environment for almost 3 years.

FCF93968-D832-4AE5-8FC3-C2D7C64930AF.jpeg6A1B31B7-0FE2-4BAC-BB1C-78BE1D287CA0.jpeg
 
No way to get 600 lbs. of compression with that plastic cutting board material. Need 3/4 plywood, or steel plate I'm going to compress with 1/4" steel and fiberglass insulator between. I don't want any wood near my batteries.

Not all plastic is created equal. Some recipes of glass fiber reinforced nylon have the same tensile strength as aluminum. Depending on which exact plastic, it could easily handle the force.

Why no wood near your batteries?
 
Not all plastic is created equal. Some recipes of glass fiber reinforced nylon have the same tensile strength as aluminum. Depending on which exact plastic, it could easily handle the force.

Why no wood near your batteries
Wood is fuel for a fire my battery bank will be enclosed in a 11 gauge steel box less fuel in the box the better. I don't trust fuses or circuit breakers after reading this thread below there was another one where a garage burnt down. Electronics fail, and things get hot only way to contain it is put it inside a box that is capable of containing it. The less fuel in it the better plus the box is on large casters I will keep a battery cable cutter hanging on the wall worse case cut the cables and roll it out in the driveway. The battery bank will have class T fuses disconnect switch and 2/0 wire likely never have a problem who knows with DIY batteries better to be safe then sorry way I look at it.

https://diysolarforum.com/threads/house-burned-down.83098/
 
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Wood is fuel for a fire my battery bank will be enclosed in a 10 gauge steel box less fuel in the box the better. I don't trust fuses or circuit breakers after reading this thread below there was another one where a garage burnt down. Electronics fail, and things get hot only way to contain it is put it inside a box that is capable of containing it. The less fuel in it the better plus the box is on large casters I will keep a battery cable cutter hanging on the wall worse case cut the cables and roll it out in the driveway. The battery bank will have class T fuses disconnect switch and 2/0 wire likely never have a problem who knows with DIY batteries better to be safe then sorry way I look at it.

https://diysolarforum.com/threads/house-burned-down.83098/
Lol.

No not really ever see container burning ?
This container is burning on a farm that use solar panels.
Here in the Netherlands


Translate

Batteries caught fire in a barn of a farm in Zuidland on Voorne-Putten. The fire started on Krommedijk on Monday morning around 5:45 am. Energy from solar panels is stored in the batteries. Flames came out of the roof of the barn and a lot of smoke was released.

The batteries are divided between two containers opposite each other in the shed.

The smoke is moving towards the polder area near Hekelingen. The fire brigade may spend several days extinguishing the fire. This is because a battery fire is difficult to extinguish, a spokesperson says.
 

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Lol.

No not really ever see container burning ?
This container is burning on a farm that use solar panels.
Here in the Netherlands

Lithium battery fire started it? 11G steel is heavy 18x36 sheet is 40 lbs. I wanted to use 1/4" plate steel for the top but it would have weighed 120 lbs alone. I'm thinking about lining the inside with fireboard. I was looking for a wood burning stove but used ones take lot of work to clean them out.
 
Wood is fuel for a fire my battery bank will be enclosed in a 11 gauge steel box less fuel in the box the better. I don't trust fuses or circuit breakers after reading this thread below there was another one where a garage burnt down. Electronics fail, and things get hot only way to contain it is put it inside a box that is capable of containing it. The less fuel in it the better plus the box is on large casters I will keep a battery cable cutter hanging on the wall worse case cut the cables and roll it out in the driveway. The battery bank will have class T fuses disconnect switch and 2/0 wire likely never have a problem who knows with DIY batteries better to be safe then sorry way I look at it.

https://diysolarforum.com/threads/house-burned-down.83098/

Plastic is fuel too. Shrug.
 
Exactly why I won't be using plastic I will be using 1/4" steel with a thin sheet of fiberglass to insulate the battery from the steel.
Grid scale battery farms also have vents. I saw some pictures of containers with a row of them on each side. I think the idea is if runaway is detected they start powerful fans and there is enough airflow the electrolyte vapour never reaches the concentration to support combustion.

Although my favourite is "clean gas" fire extinguishers. Years ago I visited many a datacenter where little bottles of oxygen and masks were located alongside the walls "in case oxygen depletion fire system activates". This is not what I'm talking about.

Now, there is a gas that extinguishes flames at only 9% concentration and it is (relatively) safe to breathe in. (Safe as in, you don't die instantly. Who knows what long term consequences it might have). It is called hfc-277ea.

Too bad it's impossible to buy it here in my part of Europe. There are some websites of companies that advertise small automatic dispensers of this gas, but they are all out of stock.
 
Now, there is a gas that extinguishes flames at only 9% concentration and it is (relatively) safe to breathe in. (Safe as in, you don't die instantly. Who knows what long term consequences it might have). It is called hfc-277ea.

Too bad it's impossible to buy it here in my part of Europe. There are some websites of companies that advertise small automatic dispensers of this gas, but they are all out of stock.

Possible alternative Ansul CleanGuard



1,1,1,2,2,4,5,5,5-Nonafluoro-4-(trifluoromethyl)-3-pentanone


Where Halotron LC-50 is lower than effective concentration, CleanGuard LC-50 is much higher than effective concentration.
 

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