Compression question for EVE LF280K

[skippsterr]

I know this has been beaten to death, and depends on an opinion as well all have one. I am not sure I understand this, but the comment 300kgf is mentioned and what I am trying to get from this document is what is tested/optimal compression. I want to top balance and put into production the 4 280w batteries.

Would appreciate any feedback, guidance. I want to compress w/ plywood (plastic cutting board like) and put some thin plastic separators. Bit of a noob and haven't done much with much solar, but want that in my shed now

 

[HRTKD]

If you've read all the threads on compression, what is your take away? What questions do you have?

 

[skippsterr]

I was hoping that info was in the PDF I posted from the OEM. Maybe the German standard is ok (goodentight)

 

[HRTKD]

I was hoping that info was in the PDF I posted from the OEM. Maybe the German standard is ok (goodentight)

Gudentite maybe too tight. Especially if you equate ugga dugga's to gudentite's. What you really want to SnugEnough. As I recall, 17 ft/lbs is too much, 12 ft/lbs is just right. But those numbers depend on how many threaded rods you're using as well as the size of threaded rod and the backing plate. Some of the posts in the compression threads have specific numbers for a limited number of situations.

 

[CavemanDS]

I'm a caveman, so take this for what it's worth:

300kgf/m2 is 0.43 PSI.

Assuming you use 4 through-bolts (one on each corner) you would apply enough pressure on each corner (0.11 PSI roughly) to compensate.

Since PSI is a measurement of pressure, it's impossible to convert it directly to total energy/force (ft/lbs). I saw a build that used springs to maintain the appropriate pressure somewhere on this forum and looked to be the best way to maintain the pressure without having the expansion of the battery increase the total PSI within the system.

I'll be building my own system shortly so will be following this thread and will also post what I find.

Edit: Found one of the threads here

 

[Dzl]

I know this has been beaten to death, and depends on an opinion as well all have one. I am not sure I understand this, but the comment 300kgf is mentioned and what I am trying to get from this document is what is tested/optimal compression. I want to top balance and put into production the 4 280w batteries.

Would appreciate any feedback, guidance. I want to compress w/ plywood (plastic cutting board like) and put some thin plastic separators. Bit of a noob and haven't done much with much solar, but want that in my shed now

From what I recall (bit rusty right now) 300kgf is the kilograms force needed to equal roughly ~12psi for this size of cell. From what I've read, manufacturers have settled on roughly 6-17psi as the goldilocks range, with 12psi being the sweet spot, for compression, but anywhere in that range being better than no compression and definitely better than too much compression which would/could damage the cell.

 

[curiouscarbon]

Gudentite maybe too tight. Especially if you equate ugga dugga's to gudentite's. What you really want to SnugEnough. As I recall, 17 ft/lbs is too much, 12 ft/lbs is just right. But those numbers depend on how many threaded rods you're using as well as the size of threaded rod and the backing plate. Some of the posts in the compression threads have specific numbers for a limited number of situations.

*taking notes intensifies*

Système International d’UggaDugga ?

1 hectoUggs should be enough. 1 kiloUgg could cause damage from over compression.


17 pounds per square inch on the face of the cell is the number i heard to definitely not exceed. but how that number was reached, i cannot precisely describe.

 

[HRTKD]

If ugga duggas are in mind when dealing with LiFePO4 cells, you're out of your mind.

I mixed up my units of measure in my above post, using ft/lb instead of PSI. I did use a torque wrench on my compression frame but the best I can recall is that it was a really low torque that made me grateful for the 1/4" digital torque wrench.

 

[Roswell Bob]

For some reason I think the force that you put on the cells may be related to the charge rate. I intend to charge the 280 cells at 70A so maybe I don't need to squeeze so tight.

I intend to put springs on each of the 4 threaded rods I will be using. To run a threaded rod and tighten without a spring may be problem. Any small amount of flow of plywood, plastic or whatever material within the system will cause large changes in the force.

good luck

 

[skippsterr]

you guys are awesome.. thank you so much!

 

[Roswell Bob]

you guys are awesome.. thank you so much!

Yes, we are awesome. This forum is todally awesome.

 

[fafrd]

I know this has been beaten to death, and depends on an opinion as well all have one. I am not sure I understand this, but the comment 300kgf is mentioned and what I am trying to get from this document is what is tested/optimal compression. I want to top balance and put into production the 4 280w batteries.

Would appreciate any feedback, guidance. I want to compress w/ plywood (plastic cutting board like) and put some thin plastic separators. Bit of a noob and haven't done much with much solar, but want that in my shed now

300 kgf = 660 pounds of force.

That force should be presented to the full flat sides of the pack, measuring 200mm x 173.6mm = 35720mm^2 or 53.8”^2 (for EVE’s 280Ah cells).

660 pounds of force distributed over 53.8”^2 = 12.264psi.

The ends should be constructed from something rigid, but anything conductive is not recommended. So wood or plastic are commonly used and metal frowned upon.

How the 12.3psi gets applied is generally by dividing that pressure across some number of springs (4 is most common, 8 also fairly common).

I use 4 rods with 2 calibrated springs each, allowing me to tighten nuts pressing washers to compress the springs to about 82.5 pounds of force being applied by each of the 8 springs…

 

[manly]

Would air pressure work? If the cells were in an airtight box that was pressurized to 12psi, seems that would give even compression to the cells.

The box could have a pressure relief valve in case cell(s) outgassed for whatever reason.

 

[ArthurEld]

An inch pound torq wrench will work. Just set the torque when the cells are fully charged.
If you set it when they aren't fully charged the pressure will increase when you charge them.
In my opinion, the compression is just to keep the cells from bulging too much.
If you use springs it is less important to have them fully charged when setting the torque.
I set my torque to about 10 or 15 inch pounds when the cells are fully charged.

It is important to realize the side pressure on your busbar screws too. I think it's better to tighten the busbars when the cells are fairly well charged too.

 

[toms]

You should contact EVE directly and ask them how they deal with compression of cells in their pre-made packs.

 

[HRTKD]

Would air pressure work? If the cells were in an airtight box that was pressurized to 12psi, seems that would give even compression to the cells.

The box could have a pressure relief valve in case cell(s) outgassed for whatever reason.

There is a vent on top of the cell. Putting the cell under pressure could damage the vent. Speculation on my part.

 

[S Davis]

I just went the easy route and used four 160lb die springs, set at 50% soc, this puts me just under 12psi.

 

[Rogermija]

How do companies like Battleborn provide batteries in which compression is not apparent and yet claim 3K-5K cycles?

 

[HRTKD]

How do companies like Battleborn provide batteries in which compression is not apparent and yet claim 3K-5K cycles?

Not sure about current versions, but Battleborn used to use cylindrical cells. No compression needed for that type.

 

[Rogermija]

Not sure about current versions, but Battleborn used to use cylindrical cells. No compression needed for that type.

Yes BB uses cylinrical. Lion Energy uses prismatic and, again, there does not appear to be a compression mechanism and they claim 3K cycles and offer a lifetime warranty. Just curious on the various packaging schemes I could consider in building my 4s packs.