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The secret to compression

If you want a rigid plate instead of a flexible bladder, just put a plate between the cell and the bladder(s) to distribute the force. i.e.

bladder -> plate -> 3.2V cells -> plate -> bladder

I personally wouldn't want a flexible rubber/poly-something/etc bladder against a sharp corner of a metal cell anyway, but to each their own.
 
I know a TON has been written on this topic, and admittedly I am a rookie. However, one concern I read was about the concern of cells passing current between each other with contact. This would explain the various foams mentioned.

I did a trial of cutting a one gallon freezer bag which has two layers and placed it between cells. The advantage of this over the 1/16 foam I have is that it allows a little more spacing for the bus bars. The foam made a tight contact point and would stress the terminals if there was any swelling.

I respect the views on rods, boxes and springs mentioned here. Having theraband on hand, I found this reference table helpful:

 
I know a TON has been written on this topic, and admittedly I am a rookie. However, one concern I read was about the concern of cells passing current between each other with contact. This would explain the various foams mentioned.

I did a trial of cutting a one gallon freezer bag which has two layers and placed it between cells. The advantage of this over the 1/16 foam I have is that it allows a little more spacing for the bus bars. The foam made a tight contact point and would stress the terminals if there was any swelling.

I respect the views on rods, boxes and springs mentioned here. Having theraband on hand, I found this reference table helpful:

I used those thin cutting board mats. Stuff is less than a 32nd thick.

Theraband is only rated in elongation though. There's no data there on compression.

I'm sure I missed more context in the discussion though.
 

Also known as Poron:

Foam compresses 25% at 11psi.

If you buy 1/4" foam, then plan for 3/16" between your cells when you design your busbars and your box, and you have 11psi compression with no springs and no hassle.

Worked great for me.

I designed my box to be slightly longer than the uncompressed length, and added a compression plate to push the cells and foam together to achieve the compression I wanted.


editing to add my later post here:




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My battery:
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Now thems are buss bars!
 
They have samples of the material available. I ordered some and I'm going to leave it stuck under something heavy for a while and see how it holds up. I'll report back.
Samples never showed.
 
People, I hear a lot of talk about how things feel or look good and probably might work . None of this is real or has direction, guessing and looks good isn’t an answer. I have been an engineer for over 40 years and much of the guesses people make in this forum literally scare me to death. Take measurements collect data , talk to your suppliers, and dont guess. I have taken measurements on thermal expansion on 280 AH cells and there is a difference between cells and a larger difference between suppliers. Battery suppliers don’t have a clue as to the amount of stress that the terminals can take nor the ductility of the cases, hence how can you calculate IF or WHAT stresses are being generated. Your suppliers may help with that, but in previous discussions I have had with them they don’t have a clue nor thought it was an issue. You need to go to the battery manufacturers if you want that data and cannot do the work yourself. And polymers only work for compression for a short period of time, compression comes with closed cell foam compressing air in the film. When you supply constant compression and a thermal cycle, the material takes a set, and no longer has a compression . Data and measurement people is the way for success.
 
People, I hear a lot of talk about how things feel or look good and probably might work . None of this is real or has direction, guessing and looks good isn’t an answer. I have been an engineer for over 40 years and much of the guesses people make in this forum literally scare me to death. Take measurements collect data , talk to your suppliers, and dont guess. I have taken measurements on thermal expansion on 280 AH cells and there is a difference between cells and a larger difference between suppliers. Battery suppliers don’t have a clue as to the amount of stress that the terminals can take nor the ductility of the cases, hence how can you calculate IF or WHAT stresses are being generated. Your suppliers may help with that, but in previous discussions I have had with them they don’t have a clue nor thought it was an issue. You need to go to the battery manufacturers if you want that data and cannot do the work yourself. And polymers only work for compression for a short period of time, compression comes with closed cell foam compressing air in the film. When you supply constant compression and a thermal cycle, the material takes a set, and no longer has a compression . Data and measurement people is the way for success.
The one I linked to from McMaster is Poron foam which is specifically made for resistance against setting (also why it is pretty darn expensive). Here is specs for one manufacturer of Poron foam (extra soft version): https://rogerscorp.com/-/media/proj...pad-applications-poron-4790-92-extra-soft.pdf
 
I spent quite some time reading 10 pages of this thread. Really a lot of good info, buried in between lots of conjecture :D

The only contribution I can add is that if you look at OTS/retail batteries, they use the foam. I have to assume that they would not put it in and increase the price of their product, unless it was necessary.

For an example, look at this video of a Gyll 5kw battery review:

At around 11m30s he has the cover off, and pans over the entire assembly. You can clearly see the foam running down the left side of the case. There does not appear to be anything in between each individual battery/cell. I do not see foam on the right side of the case, either.

Anyone know of a better supplier in Canada for Poron foam aside from Grainger?
 
Anyone know of a better supplier in Canada for Poron foam aside from Grainger?

I ordered from McMaster-Carr, but they aren't in Canada.

 
The one I linked to from McMaster is Poron foam which is specifically made for resistance against setting (also why it is pretty darn expensive). Here is specs for one manufacturer of Poron foam (extra soft version): https://rogerscorp.com/-/media/proj...pad-applications-poron-4790-92-extra-soft.pdf

I spent quite some time reading 10 pages of this thread. Really a lot of good info, buried in between lots of conjecture :D

The only contribution I can add is that if you look at OTS/retail batteries, they use the foam. I have to assume that they would not put it in and increase the price of their product, unless it was necessary.

For an example, look at this video of a Gyll 5kw battery review:

At around 11m30s he has the cover off, and pans over the entire assembly. You can clearly see the foam running down the left side of the case. There does not appear to be anything in between each individual battery/cell. I do not see foam on the right side of the case, either.

Anyone know of a better supplier in Canada for Poron foam aside from Grainger?
Look on Ebay, I bought mine there at a bargain, left over drop. Just about the right size too.
 
What's also interesting (to me) is that if you look at the manufacturer's website, Poron EVExtend is a specific foam sheet that only comes in 1-3 mm thicknesses. I can't help but wonder if what McMaster-Carr & Grainger are selling is even the same foam product, since they sell them in 1/4", 3/8" or 1/2" thicknesses, none of which are close to 1-3mm that EVExtend is. Like yes they are Poron foam, but that doesn't mean they have the same properties as the EVExtend product...right?
 
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What's also interesting (to me) is that if you look at the manufacturer's website, Poron EVExtend is a specific foam sheet that only comes in 1-3 mm thicknesses. I can't help but wonder if what McMaster-Carr & Grainger are selling is even the same foam product, since they sell them in 1/4", 3/8" or 1/2" thicknesses, none of which are close to 1-3mm that EVExtend is. Like yes they are Poron foam, but that doesn't mean they have the same properties as the EVExtend product...right?
If you check the SDS for the poron McMaster is selling you'll see it is made by Rogers Corporation. Not sure the exact one,
 
If you check the SDS for the poron McMaster is selling you'll see it is made by Rogers Corporation. Not sure the exact one,
Yes, it is Poron foam made by Rogers, but they make many different types of Poron foam sheets with different properties.

The EVExtend product has a quite different density than the thicker sheets that people are buying from McMaster, according to the Rogers spec sheet? Food for thought.

Source: https://rogerscorp.com/-/media/proj...lyurethanes-product-availability-brochure.pdf
 
I actually reached out to Rogers Corporation directly and was referred to a local converter (via this page -> https://rogerscorp.com/Elastomeric-Material-Solutions/Preferred-Converters )

The guy I talked to, knows a *ton* about building battery packs and says they have lots of different foams for different uses and requirements. He asked me a bunch of information about the cells, what pressure the manufacture recommended, the size of the cells, and how much the cells are expected to expand under normal charging (appears to be about 0.5mm from 30% -> 100% on EVE 280ah cells). I am not sure as yet what the costs will be to acquire the right product, but after talking to the guy it feels like it might be kind of expensive.

I will update the thread with any further information I gather!
 
I preparing to build up a 2p8s 280ah pack. Cells will be arranged as four side by side in four groups. I have 1/4 aluminum for clamp plates and thinking about using bicycle spokes to apply the tension. Some sort of foam sheet are required to help equalize and insulate the face to face loads.
One concern are the connection straps between cells. They are stiff and stress the battery terminals. The best would be flexible cables but that is costly. An alternative would be fabricating some flat copper straps with a Z in the center to allow for small length changes.
 
I preparing to build up a 2p8s 280ah pack. Cells will be arranged as four side by side in four groups. I have 1/4 aluminum for clamp plates and thinking about using bicycle spokes to apply the tension. Some sort of foam sheet are required to help equalize and insulate the face to face loads.
One concern are the connection straps between cells. They are stiff and stress the battery terminals. The best would be flexible cables but that is costly. An alternative would be fabricating some flat copper straps with a Z in the center to allow for small length changes.
Just get the JWeberTech busbars that have a flexible middle section to handle this exact scenario. They've been mentioned many times on the forum and LithiumSolar reviews them on his youtube channel.
 
FYI, I ended up using the poron, threaded 1/4" rods, and plywood for my assemblies.


Check back in five years to see if that was the right choice... ;)
 
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