Another Cell Compression Thread, this time about foam

[Ron-ski]

@justgary Those cables are cable tied down the side, and the plate actually also locks the lugs off, there is no gap underneath.

The plates are the original busbars cut in half (actually a bit shorter than half) and an M5 hole tapped for the balance leads.

I also spy a bit of fluff under the edge of that nut.

One thing you do have to watch with this style terminal is the bolt holes (they are heli-coiled as well) go straight through, so if not careful you can screw the stud into the top of the cell, I used some 2mm plastic under the terminal to stop the stud, which I thread locked in.

 

[Honuz]

@Honuz I put two layers of heat shrink on the 6mm studding, the G10 also sticks out past the cells, so this will also keep the studding away from the cells. My battery is in a pull out drawer/rack, in my garage, so very easy to check periodically.

I used 10mm aluminium plate end plates, I tightened the outside tubes first, putting a straight edge across the plates revealed they were bowed, measuring confirmed this, tightening the 6mm studding pulled it straight again. Adding a cross tube like you have would have alleviated the problem, but I do wonder if the top and bottom would still be bowed, and I don't have enough space to do that.

I'll post some pictures later.

I know i do not want any metal part near my cells, seen some tape been destroyed and contact been made, in automotive situation i got to admit.
Now, 1cm of aluminum .. seems plenty sturdy and rigid to me, i'm surprised it has been bent by tightening the 4 outside tubes... be carrefull not putting too much pressure on them ...

 

[Ron-ski]

i'm surprised it has been bent by tightening the 4 outside tubes... be carrefull not putting too much pressure on them ...

I'm surprised it bent as well but alluminium if fairly flexible, presuming my calculations are correct, it should be OK, I followed @justgary example.

 

[justgary]

I'm surprised it bent as well but alluminium if fairly flexible, presuming my calculations are correct, it should be OK, I followed @justgary example.

That looks great to me. I still think that 40% is good for two layers of 1/4" Poron in an 8 cell stack.

My end caps are held on with 18 #4 screws, so maybe it distributes the force a little better. I'm only using 1/4" (6mm) aluminum for the end caps, and they aren't bent. Notice also that I have to clamp the caps together to get the screw holes to align for assembly.

 

[Checkthisout]

You guys are getting a little carried away on your boxes don't you think??

 

[SilverbackMP]

You guys are getting a little carried away on your boxes don't you think??

That's my thinking too. Of course, I'm running off of old assed golf cart batteries, a 3500 watt 25 year old Outback 12 volt inverter, and need to leave the country in a month or two (I'm about three months past the length I was going to stay and am approaching a year where I would need to reapply for a long-term visa in the country that I currently live in). Trying to get this thing together so my mom has better power and I can keep my shop from freezing/melting while I'm gone. I don't have Digital Mermaid/Ray Builds Cool Stuff time to mess with it.

Had a hell of time getting my shop built, the powershed revamped, and getting the electrician out here. Due to a bad back (thanks Army!), I can only DIY so much. My shop won't have it's mezzanine completed, interior, cistern, or all of it's stuff added by the time I leave (which was not the plan).

 

[SolaroSsaurius]

Is retention or compression only necessary along 1 axis or does it also need to happen on the sides?

Please read your's cells datasheet.
Most probably if needed, it's described there.
For EVE 280k it's described as 3 rods each side, 10mm alu or wood (?), compressing on the larger side - IIRC

 

[Checkthisout]

Please read your's cells datasheet.
Most probably if needed, it's described there.
For EVE 280k it's described as 3 rods each side, 10mm alu or wood (?), compressing on the larger side - IIRC

Will do. I don't have them yet. I assume they are all the same though.

Just making small talk.

 

[Ron-ski]

My end caps are held on with 18 #4 screws, so maybe it distributes the force a little better. I'm only using 1/4" (6mm) aluminum for the end caps, and they aren't bent. Notice also that I have to clamp the caps together to get the screw holes to align for assembly.

Your plate only spans one row of eight, whereas mine spans two rows, my plate is 386mm wide. I tightened the outer bolts first which pulled the edges in, then tightened the middle 6mm studs, I intentionally did it this way as I was curious as to whether the plate would flex. Now I've tightened the 6mm studs its straight.

You guys are getting a little carried away on your boxes don't you think??

You should see the rack

 

[timkarla]

Your battery pack above looks fabulous.

I actually managed to find this foam in the UK, but what did you use between the cells?

Hi, Could you post a source of Poron in the UK, having trouble locating it outside of massive quantities.

 

[Ron-ski]

Hi, Could you post a source of Poron in the UK, having trouble locating it outside of massive quantities.

Unfortunately the source I found was just importing it from America, and it was cheaper to do that myself - I ordered from McCaster, but shipping still made it expensive.

I emailed quite a few suppliers, and none replied or could help.

 

[stacks]

im not understanding why people are fixated in using the foam. eve specifies that the cell should be compressed by a rigid material at a specific force at a specified state of charge.... on top of that, no battery pack manufacturer (even ones that offer generous waranty periods) are using foam between the cells. the only time foam is even offered in the industry (between the cells) is when a diy box is made to fit multiple sized cells, so they include the EVA foam to take up extra space if the end user puts the smaller sized cells in the box. i.e. a box that can fit 304ah and 280ah, they include the foam as a cost effective way to take up space when 280ah are used, but no foam is used and its a rigid compression if the 304's are used.

it seems as if someone read EVE's data sheet, took the initial compression force number and incorrectly assumed that the pack should never reach higher compression than that.
battery manufacturers are pretty smart people with tons of research and development, and if the cells needed a way to keep the pressure consistent as cells were charged/expanded, they would have stated such information.
but they didnt. they published certain clamping parameters with the clear understanding that the pressure would increase as the pack is charged.
it almost seems as if they needed to put a simple statement under those parameters that says "we are pretty knowledgeable about these batteries. we understand that the pressure will increase. compress cells as we instructed." lol

then again, im not a genius, so maybe they didnt account for the exact phenomenon that happens every time they charge and the fact that they are ALWAYS assembled in a pack of more than 1 cell. lol

 

[Ron-ski]

@stacks Your clearly not a genius, this thread was started over three and a half years ago (not many DIY boxes if any back then), even when I was designing my batteries two years ago good information was lacking, probably still is. IIRC EVE had a test rig diagram for one cell not multiple cells, there was no information for 8 cells, or 16 cells in row. I also thought the only difference between 280 and 304ah cells was the latter was a little taller.

You should go and read all the compression related threads, you might get a better understanding of the situation at the time, of course now in August 2024 people have a better understanding.

If the cell manufacturers cared, they would give examples of popular configurations, but they didn't and probably still don't.

 

[stacks]

@stacks Your clearly not a genius, this thread was started over three and a half years ago (not many DIY boxes if any back then)

i agree that the thread was started over 3 years ago, yet your post from just over a year ago is still talking about using foam.

IIRC EVE had a test rig diagram for one cell not multiple cells, there was no information for 8 cells, or 16 cells in row.

If the cell manufacturers cared, they would give examples of popular configurations, but they didn't and probably still don't.

again, i repeat:

battery manufacturers are pretty smart people with tons of research and development, and if the cells needed a way to keep the pressure consistent as cells were charged/expanded, they would have stated such information.
but they didnt. they published certain clamping parameters with the clear understanding that the pressure would increase as the pack is charged.
it almost seems as if they needed to put a simple statement under those parameters that says "we are pretty knowledgeable about these batteries. we understand that the pressure will increase. compress cells as we instructed." lol

 

[Zwy]

I'm building another large battery bank and using Poron in between the cells.

As mentioned, there is plenty of reading material over the last 3.5 years regarding cell compression. I researched for some time before posting this thread which was my first post on this forum after lurking for some time anonymously. Go back to the very first post of this thread and read the links in that post.

 

[stacks]

i did, and i just went back and made sure i remembered correctly.

This is how the EV manufacturers are handling cell compression with prismatic cells. https://www.tapesolutions.saint-gob...icles/foams-are-driving-ev-battery-innovation As you can read here, compression is important and how it is done is equally important.

One more article on this subject from the same manufacturer, although it is primarily direct toward pouch type packs but I feel it equally applies to prismatic cells also. https://www.tapesolutions.saint-gob...ssembly-robust-efficient-batteries-norseal-pf

you said that one of the articles is directed towards pouch cells, when both of the articles are only about pouch and li-ion cells. nothing about prismatic.
you actually state that you "feel" that it also applies to prismatic.
so i took from it that you gathered articles from different battery types and chemistries and then applied their findings and practices to a completely different chemistry and design?

 

[Bob B]

It's funny how every once in a while someone shows up who thinks they know SO much more than everyone who has come before.

Some of the other threads include posts by a forum member who has talked directly to EVE engineers about compression ..... There ARE maximum pressures that shouldn't be exceeded. The EVE engineers said no compression was better than too much compression.
Forum members have measured the amount of movement due to expansion in the cells at various SOC and under various pressures ..... This brought about the conversations about flexible bus bars due to the strain on the connection points due to expansion. There have been serious discussion about methods for top balancing and whether holding the voltage too high during balancing can reduce cell life. There are and continue to be conversations about torque specs and various types of products designed to improve cell to bus bar connections and longevity. There have been extensive conversations about the evolution of the recommendations in the Spec sheets.

I think it was YouTuber Andy who fostered the idea that in a stationary application snug was good enough since calendar aging would be much more of a factor than compression ..... Heat, charging too cold or over charging are probably the primary dangers to reducing cell life.

Mobile applications require much more attention to compression and connections.
YouTuber Ray from Texas who used to also frequent this forum has some VERY novel ideas about ways to improve a DIY pack. He has specific ways to burnish the contact points and drills and taps a separate connection point for the balance leads. He was mostly putting together stationary packs but in his recent videos is building a 48V pack for a mobile application.

Hours and hours of reading is available to those interested in what others have discovered.

 

[stacks]

It's funny how every once in a while someone shows up who thinks they know SO much more than everyone who has come before.

i never said anything about me knowing a single thing, and especially not more than anyone else. on the contrary, i said EVE were intelligent people that understood how the cells would be used when they prescribed the clamping conditions.

Some of the other threads include posts by a forum member who has talked directly to EVE engineers about compression

very nice, i would love to see the conversation

There ARE maximum pressures that shouldn't be exceeded.

i agree, and its true with anything that has a specific clamping pressure... but that has nothing to do with clamping a pack under EVEs specified pressures.

The EVE engineers said no compression was better than too much compression.

again, i dont disagree. but that is NOT the same statement as "no compression is better than the specified compression in the data sheet that EVE released".
if the engineer wouldve said that, then it would be a different story.

I think it was YouTuber Andy who fostered the idea that in a stationary application snug was good enough since calendar aging would be much more of a factor than compression ..... Heat, charging too cold or over charging are probably the primary dangers to reducing cell life.

idk whether he came up with that concept or not, but he did say that.
also, backing over a cell with a car could also shorten its calandar life, but that is not what is being discussed. we are not discussing all of the other ways cells could face advanced degradation. we are talking about eve's specified clamping conditions and how people are assuming that the prescribed method was somehow open to interpretation.

Mobile applications require much more attention to compression and connections.
YouTuber Ray from Texas who used to also frequent this forum has some VERY novel ideas about ways to improve a DIY pack. He has specific ways to burnish the contact points and drills and taps a separate connection point for the balance leads. He was mostly putting together stationary packs but in his recent videos is building a 48V pack for a mobile application.

not to take anything away from any innovation he may or may not have came up with for mobile applications, but we arent talking about niche/specific scenarios that require additional measures from keeping a pack from shaking apart. we are talking about optimal clamping instructions in a static condition. everything you have to specialize for a specific use case or mitigate role specific problems, is just that, specific for that problem and use. it is not to be confused with actual best practice.

 

[Bob B]

i never said anything about me knowing a single thing, and especially not more than anyone else. on the contrary, i said EVE were intelligent people that understood how the cells would be used when they prescribed the clamping conditions.


very nice, i would love to see the conversation


i agree, and its true with anything that has a specific clamping pressure... but that has nothing to do with clamping a pack under EVEs specified pressures.


again, i dont disagree. but that is NOT the same statement as "no compression is better than the specified compression in the data sheet that EVE released".
if the engineer wouldve said that, then it would be a different story.


idk whether he came up with that concept or not, but he did say that.
also, backing over a cell with a car could also shorten its calandar life, but that is not what is being discussed. we are not discussing all of the other ways cells could face advanced degradation. we are talking about eve's specified clamping conditions and how people are assuming that the prescribed method was somehow open to interpretation.



not to take anything away from any innovation he may or may not have came up with for mobile applications, but we arent talking about niche/specific scenarios that require additional measures from keeping a pack from shaking apart. we are talking about optimal clamping instructions in a static condition. everything you have to specialize for a specific use case or mitigate role specific problems, is just that, specific for that problem and use. it is not to be confused with actual best practice.

I just provided a synopsis of what is available to be found on this forum .... and some on YouTube.

I'm not going to do the search engine work for you .... all the things I mentioned along with detail are available to be found on various threads.

 

[stacks]

I just provided a synopsis of what is available to be found on this forum .... and some on YouTube.

I'm not going to do the search engine work for you .... all the things I mentioned along with detail are available to be found on various threads.

i understand, and i agree. that is what you did... and i never asked you to search anything for me.
but you made a pretty weird statement which i assume is towards me:

It's funny how every once in a while someone shows up who thinks they know SO much more than everyone who has come before.

..but then you didn't even address the actual thing i was discussing, proper cell compression which is outlined by eve. you just mention other issues, and youtube channels that have videos addressing those other issues.
just overall offtopic.

 

[Bob B]

i understand, and i agree. that is what you did... and i never asked you to search anything for me.
but you made a pretty weird statement which i assume is towards me:

You were the one who came on the thread with a condescending attitude .... I just responded in kind.

..but then you didn't even address the actual thing i was discussing, proper cell compression which is outlined by eve. you just mention other issues, and youtube channels that have videos addressing those other issues.
just overall offtopic.

It's all in the threads to be discovered .... There are even video's of the hydraulic mechanism EVE uses for compression.

 

[Zwy]

i did, and i just went back and made sure i remembered correctly.

you said that one of the articles is directed towards pouch cells, when both of the articles are only about pouch and li-ion cells. nothing about prismatic.
you actually state that you "feel" that it also applies to prismatic.
so i took from it that you gathered articles from different battery types and chemistries and then applied their findings and practices to a completely different chemistry and design?

You can take the methods and theory and use it or you can leave it. Just make an educated decision and determine what you think is best for you.

For every 10 people using one compression method, there will be 10 advocating for a different compression method. Some of this is pioneering, the long term data has yet to be collected and time will provide the answers.

 

[stacks]

You were the one who came on the thread with a condescending attitude .... I just responded in kind

thats fair, i did come in hot with a layer of sarcasm.

 

[Ron-ski]

proper cell compression which is outlined by eve

Please show us all this, what is EVE's proper cell compression for a 16S pack in two rows of 8 cells, please post a link or the document.

PS. My first battery was built January 2023, but its design was finalised many months before, for my second battery I just copied the first. I spent many months trying to decide the best way to build the battery, in the end I had to settle on one of the many ways, and which worked best for me.

Had I been building my system now, I would use DIY battery boxes.

Andy was very anti compression, seems even he has changed his attitude, although he still runs his original system without compression.

 

[justgary]

I agree that the EVE datasheet now suggests rigid clamping. The previous version did not say that. I built my boxes when the concept was constant pressure, so I used Poron foam.

Those of you who think that a sheet of foam between each cell is a good thing should go back and look at my test results. One 1/4" sheet for every four cells is the sweet spot. Stacking foam is just like stacking springs. Know what happens before you do it, because the answer isn't what you think it will be.