Pack / Cell compression Optimized By Using Springs.

Dzl

Perpetual Newbie & Unofficial Forum Librarian
Staff member
Moderator
Joined
Dec 10, 2019
Messages
5,089
I just wanted to be one of the cool guys. LOL
Guess it's kind of the polite way to post off topic with minimal disruption.
That was my thinking but in retrospect I'm not sure it helped. It was my attempt to retroactively not drag the thread off topic but also not delete posts with useful info.

I have some bad news for you though.. If coolness is what you seeek, following my lead is the opposite of what you should be doing 😄
 

Luthj

Photon Sorcerer
Joined
Jul 1, 2020
Messages
956
I wonder if there is a limit to how many recursive quoted spoilers once can have before the forum code crashes?
 

Capt Bill

Sailing Options
Joined
Mar 18, 2020
Messages
726
Location
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
Possibly, but the suppliers should still make it clear what they are selling. And why are so many receiving cells that are not flat on the sides? Like shown in this thread. From reading the forum since I joined, people were not having these problems.
Thanks for thread link Gazoo. I am reading "another interpretation" that kind of make sense to me: (from... sorry I did not copy name, think page three of other thread link: ... poster/ and moderator saying ... " I think that the purpose of saying it is 300kgf [or 602 pounds] is not to APPLY that amount so much as that the compression force should be able to RESIST that amount of force. By being able to resist that amount of force it will stop the cells from expanding. I think this is a reasonable plausible interpretation."

My Thoughts : ... I will be looking forward to what further clarity might come from the questioning the suppliers.
 

fafrd

Photon Sorcerer
Joined
Aug 11, 2020
Messages
2,584
Thanks for thread link Gazoo. I am reading "another interpretation" that kind of make sense to me: (from... sorry I did not copy name, think page three of other thread link: ... poster/ and moderator saying ... " I think that the purpose of saying it is 300kgf [or 602 pounds] is not to APPLY that amount so much as that the compression force should be able to RESIST that amount of force. By being able to resist that amount of force it will stop the cells from expanding. I think this is a reasonable plausible interpretation."

My Thoughts : ... I will be looking forward to what further clarity might come from the questioning the suppliers.
Problem with this interpretation is that I thought an engineer from EVE was quite clear in a response to ghostwriter that you ideally want not less than 6psi and not more than 17psi of pressure on the cell through the entire charge/discharge range (even providing a graph if I’m not mistaken).

Of course, EVE’s data and analysis seems to be focused on single cells, so in terms of translating EVE’s inputs to what they should mean for 4S or 8S packs, we’re heading into largely uncharted territory...
 

Capt Bill

Sailing Options
Joined
Mar 18, 2020
Messages
726
Location
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
Problem with this interpretation is that I thought an engineer from EVE was quite clear in a response to ghostwriter that you ideally want not less than 6psi and not more than 17psi of pressure on the cell through the entire charge/discharge range (even providing a graph if I’m not mistaken).
... been studying by forum search on battery compression, ... and did not yet see that (EVE engineer response to ghostwriter); while also wondering about the 600 lb figure I read in some compression threads as compared to 6 psi (lbs per square inch) and getting a different figure when I go 6 lbs x 7" x 9" for an Eve 280Ah LiFePO4 = 6 lbs x 63 sq inches = 378 lbs I also copied this from another thread;
posted by Steve_S: "COMPRESSION: Compress / bind cells at 50% SOC @ 25C/77F ambient / static temp.
The generally accepted compression is 12psi or 300kgpf. (it is not much, think "very tight, hand tight"
They can & do expand & contract up to 2mm during cycles if under heavy load & charge.

and another piece of Steve_S info I came across has me wanting to look at EVE spec sheet to get clearer about lbs for pressure vs/or a torque wrench inch lb spec ? ... on thread entitled / Compressing Prismatic Cells?
Steve_S wrote: WOW, 500Kg force ? That will make a pancake ! ... Good God, Inch Pounds not Foot Pounds ! Never crush the cells, basically, not more than a really good Hand Squeeze amount of pressure.
Compressing the cells prevents bloating & delamination internally (kiss explanation) and does extend the lifecycles accordingly. Almost all manufacturers recommend a certain amount of "binding", "compression" or "fixing", all of which means that the cells should be bound, slightly compressed to maintain their form factor and prevented from moving freely. Also this reduces any stresses on the terminals which are not as "tough" as most people think they are. "

... Still Studying for more clarity over here as I get ready to make my case for updating my 24v 280 Ah LiFePO4 battery bank into a 560 Ah battery bank :+)
 
Last edited:

fafrd

Photon Sorcerer
Joined
Aug 11, 2020
Messages
2,584
A bit of expansion data for those who may be interested. I set up an 8S pack of EVE 280Ah cells for top-balance when they were ~1/3 full.

As the pack charged to 100%, the dual common busbars kept the top spaced as it was at the beginning while the bottom expanded with increasing charge and ‘accordioned’ out. There was no fixture or pressure on the cells though pushing outward obviously meant overcoming the friction at the bottom.

The pack is now at 100% so I took some measurements:

Top Left (along - terminals) 23-1/16”
Bottom Left 23-5/16” (so 1/4” expansion)
Top Right (along + terminals) 22-7/8”
Bottom Right 23-1/8” (so 1/4” expansion)

So in terms of the ‘range’ that a fixture needs to accommodate, this data suggests that 1/4” for 8 cells or ~0.8mm/cell is sufficient.

Since the cells did not start out at 0% SOC but closer to 35%, it’s possible/likely that cells will shrink below my starting dimension when empty.

I’m doing a full-battery capacity test soon and will remeasure at 0% SOC to get some idea how much shrink range is also needed.

(Note that the nominal dimension per cell is 71.5mm or 572mm / 22-1/2” for 8 cells.)
 

Gone

Solar Enthusiast
Joined
Sep 29, 2020
Messages
99
Already leaning this way, but that data pretty much convinces me to use flexible cables, rather than busbars, thanks.
 

HaldorEE

Photon Sorcerer
Joined
Apr 20, 2020
Messages
1,632
I have been top balancing my cells this weekend and decided to put together a compression fixture.

This is not what I will be using since my plan is to compress the cells in stacks of 4, but I figured I might as well.

This is using the Belleville disc spring washers I have been researching.

I will be interested to see how much the springs compress at full charge. I am currently near 50% SOC so I set the spring preload at 75 KG per threaded rod.
 

fafrd

Photon Sorcerer
Joined
Aug 11, 2020
Messages
2,584
I have been top balancing my cells this weekend and decided to put together a compression fixture.

This is not what I will be using since my plan is to compress the cells in stacks of 4, but I figured I might as well.

This is using the Belleville disc spring washers I have been researching.

I will be interested to see how much the springs compress at full charge. I am currently near 50% SOC so I set the spring preload at 75 KG per threaded rod.
Will be looking forward to seeing what you learn...
 

HaldorEE

Photon Sorcerer
Joined
Apr 20, 2020
Messages
1,632
Pics of the compression fixture.

I made the end plates from some 1/2", 9 ply Birch plywood from Home Depot. This is the experimental version, once I am convinced I have everything figured out I will rebuild it using 1/2" Baltic Birch plywood I have. The end plates are 12" high, because I didn't both to cut them to final size (the end plates were cut from a 12" x 24" piece of plywood).

PXL_20210124_030757306[1].jpg

There will be a bottom to the compression fixture, but the packs are going to be mounted on the rubber vibration isolators. Mounted to the bottom reinforcing tubes.

PXL_20210124_030745963[1].jpg

This pic shows the Belleville spring washers. I will cut the threaded rods to the correct length when I build the individual 4 cell packs.

PXL_20210124_030732864[1].jpg


This is what I have in mind for the final packs. I am using 1"x1" square tubing instead of Unistrut. The bus bars are braided copper straps. Each pack of 4 cells are individual so I can more easily remove them from my van. I live in Phoenix AZ and want to be able to move the cells to the air conditioned house when I am not using the van as an RV in the summer. The cable joining the two packs in series is a longer piece of 1/0 AWG wire. I wanted to give this piece of cable as much flexibility as possible, hence the reason why it is the longest.

BatteryPack.jpg
 

HaldorEE

Photon Sorcerer
Joined
Apr 20, 2020
Messages
1,632
The threaded rods are 5/16" diameter. I am using 3/8" ID polypropylene hose to cover the threaded rod. I original bought some 5/16" ID PVC tubing, but it was too much like work trying to stuff the threaded rods through that. The polypropylene hose is a lot harder and tougher than the PVC hose anyways. I cut the polypropylene hose to the right length for 4 cell packs and just doubled them up on the threaded rods for the top balance fixture.
 

Capt Bill

Sailing Options
Joined
Mar 18, 2020
Messages
726
Location
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
Pics of the compression fixture.

I made the end plates from some 1/2", 9 ply Birch plywood from Home Depot. This is the experimental version, once I am convinced I have everything figured out I will rebuild it using 1/2" Baltic Birch plywood I have. The end plates are 12" high, because I didn't both to cut them to final size (the end plates were cut from a 12" x 24" piece of plywood).

View attachment 34379

There will be a bottom to the compression fixture, but the packs are going to be mounted on the rubber vibration isolators. Mounted to the bottom reinforcing tubes.

View attachment 34380

This pic shows the Belleville spring washers. I will cut the threaded rods to the correct length when I build the individual 4 cell packs.

View attachment 34381


This is what I have in mind for the final packs. I am using 1"x1" square tubing instead of Unistrut. The bus bars are braided copper straps. Each pack of 4 cells are individual so I can more easily remove them from my van. I live in Phoenix AZ and want to be able to move the cells to the air conditioned house when I am not using the van as an RV in the summer. The cable joining the two packs in series is a longer piece of 1/0 AWG wire. I wanted to give this piece of cable as much flexibility as possible, hence the reason why it is the longest.

View attachment 34382
Looks Great! Might want to take initial measurement of battery packs, and see that change any after cycling the battery cells through some larger amp draws though their SOC form low to full a few times. My Question (think other may have too): Do the sides of those batteries with some space showing between them from slight curves in side surface ever get pliable enough to straighten out a little and make for flatter battery sides? If that happens, that pack length dimension will change. Food for Thoughts on Experimenting; as in measuring, and sharing info. for our forum's knowledge base.
 

Capt Bill

Sailing Options
Joined
Mar 18, 2020
Messages
726
Location
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
Pics of the compression fixture.

I made the end plates from some 1/2", 9 ply Birch plywood from Home Depot. This is the experimental version, once I am convinced I have everything figured out I will rebuild it using 1/2" Baltic Birch plywood I have. The end plates are 12" high, because I didn't both to cut them to final size (the end plates were cut from a 12" x 24" piece of plywood).

View attachment 34379

There will be a bottom to the compression fixture, but the packs are going to be mounted on the rubber vibration isolators. Mounted to the bottom reinforcing tubes.

View attachment 34380

This pic shows the Belleville spring washers. I will cut the threaded rods to the correct length when I build the individual 4 cell packs.

View attachment 34381


This is what I have in mind for the final packs. I am using 1"x1" square tubing instead of Unistrut. The bus bars are braided copper straps. Each pack of 4 cells are individual so I can more easily remove them from my van. I live in Phoenix AZ and want to be able to move the cells to the air conditioned house when I am not using the van as an RV in the summer. The cable joining the two packs in series is a longer piece of 1/0 AWG wire. I wanted to give this piece of cable as much flexibility as possible, hence the reason why it is the longest.

View attachment 34382
2nd comment: Wow to that roundish elongated dent that shows in one picture, on outer battery edge. Is that a user accident, or the way your battery arrived? ... I would test the heck out of a battery like that, and would want a replacement if it arrived that way (if was one of mine)/ plus know there would certainly be contrasted opinions here) :+)
 

HaldorEE

Photon Sorcerer
Joined
Apr 20, 2020
Messages
1,632
2nd comment: Wow to that roundish elongated dent that shows in one picture, on outer battery edge. Is that a user accident, or the way your battery arrived? ... I would test the heck out of a battery like that, and would want a replacement if it arrived that way (if was one of mine)/ plus know there would certainly be contrasted opinions here) :+)
Reflection, not a dent.
 

Electro Dan-O

Current Situation
Joined
Nov 15, 2020
Messages
40
Location
Middle TN
Just about to wrap this project up! I wound up buying some .75"OD x 1" OL 135lb. springs. Thanks for the help guys. I think this will work!(y)


xmbjZuR.jpg
 

cinergi

1.21 Jigawatts
Joined
Aug 9, 2020
Messages
1,294
Just about to wrap this project up! I wound up buying some .75"OD x 1" OL 135lb. springs. Thanks for the help guys. I think this will work!(y)


xmbjZuR.jpg

This looks beautiful! Do you mind sharing info about the physical construction (where those parts came from, etc)?
It appears the end plates are secured at the bottom so I'm wondering how the end plates are supposed to move with the breathing cells?
 

Electro Dan-O

Current Situation
Joined
Nov 15, 2020
Messages
40
Location
Middle TN
This looks beautiful! Do you mind sharing info about the physical construction (where those parts came from, etc)?
It appears the end plates are secured at the bottom so I'm wondering how the end plates are supposed to move with the breathing cells?
Absolutely! Check out post 27,51 and 54 in this thread to start. The springs came from WB Jones(part number 283). Compressing these .187" should net ~106lbs each. The end plate bracket screws on one side, slide in elongated(baseplate) holes and are held loosely with flat washers/lock nuts. Let me know if you need any more specifics. BTW, these are 105ah cells, so a little smaller that what most are using...
 

cinergi

1.21 Jigawatts
Joined
Aug 9, 2020
Messages
1,294
Absolutely! Check out post 27,51 and 54 in this thread to start. The springs came from WB Jones(part number 283). Compressing these .187" should net ~106lbs each. The end plate bracket screws on one side, slide in elongated(baseplate) holes and are held loosely with flat washers/lock nuts. Let me know if you need any more specifics. BTW, these are 105ah cells, so a little smaller that what most are using...

Ah, OK I think I'm seeing that you've got plywood there but it must be painted and also a piece of CF on the end.. and a way to cut a rounded edge.

I can't quite figure out the bottom .. I see plexiglass and also 3 black strips (plywood?) ... the bolt comes in from underneath ... I can't see the channel or how the bottom doesn't have a bolt protruding unless you countersank it. Sorry for all the questions lol - this part was the most complex to figure out. Mine (link) will be mounted on rubber vibration feel which I hope allows for 4mm of movement.
 
Top