EVE-280 cells should these be clamped tight or spaced for expansion?

cinergi

1.21 Jigawatts
Joined
Aug 9, 2020
Messages
1,162
Maybe so. However there seems to be a hundred ways people are doing this compression idea. Springs, this pressure at this SOC/voltage etc....
So I’m using 12 inch pounds on a torque wrench to tighten down my threaded rods. Maybe I should have said 12 inch pounds on a torque wrench instead of PSI...
But it’s not perfect, but should achieve compression without over compression. Hence the blood pressure cuff to see how much increase I get at 3.65v.

12 inch pounds on a torque wrench is a VERY wrong interpretation of the 12 PSI of pressure required on the surface of the cells. You need to use the calculation tables and take into account the size of the threaded rod, the pitch, and the number of threaded rods, in order to derive the force that 12 inch pounds of torque on each nut is applying to the cells.
 

Shawn Hayes

Learning Everyday
Joined
Jan 11, 2021
Messages
127
Location
South Carolina
12 inch pounds on a torque wrench is a VERY wrong interpretation of the 12 PSI of pressure required on the surface of the cells. You need to use the calculation tables and take into account the size of the threaded rod, the pitch, and the number of threaded rods, in order to derive the force that 12 inch pounds of torque on each nut is applying to the cells.
I have not seen these tables, can you share a link? I would say I’m not looking for an exact 12 PSI, but enough compression without over compression. So, thinking 12 inch pounds would be good without over compression with the rubber matting in between each cell giving me some support both during expansion & contraction.
However I would like to see these tables you mentioned if you can share a link? This site has to many threads and opinions on this topic. I’m sure I’ve missed many....
 

Short_Shot

Photon Sorcerer
Joined
Jul 13, 2021
Messages
1,811
I have not seen these tables, can you share a link? I would say I’m not looking for an exact 12 PSI, but enough compression without over compression. So, thinking 12 inch pounds would be good without over compression with the rubber matting in between each cell giving me some support both during expansion & contraction.
However I would like to see these tables you mentioned if you can share a link? This site has to many threads and opinions on this topic. I’m sure I’ve missed many....
As I stated earlier. 12 inch pounds absolutely does not translate to 12 psi. That's not at all how that works.

The amount of force the nut is applying is a somewhat complex formula.


www.engineeringtoolbox.com/amp/bolt-torque-load-calculator-d_2065.html
 

Short_Shot

Photon Sorcerer
Joined
Jul 13, 2021
Messages
1,811
And keep in mind psi needs to be multiplied by the cell area. So you don't enter 12 for the load in pound force. It's whatever the surface area is in square inches * 12 psi.

The one thing I can't remember if you need to then divide that by the number of fasteners or they all get the full torque.

And as tired as I am I'm not even sure I have the right calculator in that link.
 

Shawn Hayes

Learning Everyday
Joined
Jan 11, 2021
Messages
127
Location
South Carolina

glub

New Member
Joined
Jul 27, 2021
Messages
13
Can I mount EVE 280Ah on the side like the red marking?
 

Attachments

  • lifepo4.png
    lifepo4.png
    561.7 KB · Views: 16

thaddeusk

New Member
Joined
Jun 7, 2021
Messages
1
I just want to chime in here... I just recently built a 24v bank out of 80ah eve cells for a solar storage project. 15p8s. I used 1" boards on the ends of each parallel string with heavy duty 6" screws into 2x2's along the top and bottom to clamp them. I attempted to clamp them to the point that the assembled parallel string could be moved without cell movement. if I calculate 12psf for these cells it's something like 350 lbs of force on the face of the cells. I don't think I reached that amount of force before I noticed the cells shifting on their own during the tightening because the faces were compressing enough that the edges/corners were wanting to slide past each other. I stopped compressing at that point. I have fear that I've damaged the cells by overcompressing them but cant really find any info so far on what that looks like or what the effects might be other than 'possible punctures in the separating membrane and internal shorts'. but, so far they seem to be fine. I guess we'll have to wait either until they fail prematurely, or we have 20-something years of using them to report on the ultimate outcome.
 

Simi 60

Solar Enthusiast
Joined
Jul 10, 2021
Messages
107
Interesting read but a bit above my pay grade doing the proper calculations even if using the links above.

Anyone got any further input as to what the "actual" torque wrench setting would be to get to the 12ft/lb in the eve280 specs?

I have started at 5 ft lbs (lowest click on torque wrench) over 6 X M10 threaded rod and that holds the batteries in place when lifting without a base.
Seems pretty tight for cranking on something as delicate as a battery cell.

17mm marine ply with plastic cutting board between cells
Garden hose over threaded rod.
This is one of three 24v batts.
 

Attachments

  • IMG_20211108_123553_547.jpg
    IMG_20211108_123553_547.jpg
    1.1 MB · Views: 22
Last edited:

S Davis

Solar Enthusiast
Joined
Sep 25, 2021
Messages
46
36A98D14-1FA9-4FBD-8B87-8BF6C83647DF.jpegI decided on using four 160# die springs, I set them at 11.6psi at 50%soc. Based on the expected expansion they should be in the sweet spot. I was worried just clamping with no room for expansion that the pressure could build over the max recommended.
 

Bob B

Photon Sorcerer
Joined
Sep 21, 2019
Messages
3,366
View attachment 71722I decided on using four 160# die springs, I set them at 11.6psi at 50%soc. Based on the expected expansion they should be in the sweet spot. I was worried just clamping with no room for expansion that the pressure could build over the max recommended.
Do you have a link to the springs?
 

kuranaga

Solar Enthusiast
Joined
Sep 24, 2021
Messages
137
I suppose the 300kg compression is the total force onto the cell surface. other units do not make lot of sense
 

Diysolar123

Solar Addict
Joined
Feb 28, 2021
Messages
645
Anyone got any further input as to what the "actual" torque wrench setting would be to get to the 12ft/lb in the eve280 specs?
here is the tricky park with that question when looking at the EVE fixture spec and how I am reading what they are TRYING to tell us...


From the EVE 280Ah spec version E page 4/11 we get ONLY the following:
1636393240265.png

Notice it mentions a fixed FORCE; it does not say 300kgf at 30% and <some other>kgf at 100%; it just says a 300kgf is applied.

We can derive the PSI (whichis a force over an area) by looking at the same spec and getting the area of the cells so that is how we get to PSI.

1636393365618.png

so now we have a FIXED force per square inch.

the next issue is the spec clearly states the THICKNESS of the cell WILL change (ref page 4 of spec):
1636393598807.png

so the challenge is how to maintain a FIXED force across a battery in a fixture that WILL expand.
Worst case expansion of a NORMAL battery is:
(71.5mm - 1mm) = 70.5mm at 30%SOC
(72mm+1mm) = 73mm at 100% SOC
====UPDATE===
others have pointed out below that what the spec sheet really means is that the expansion due to charging is only 0.5mm (that is 20thou of an inch); the rest of the +/-1 is manufacturing tolerances. This could be, however, measuring my cell actually expand more than 0.5mm and they are grade A eve cells so not sure what to make of it..could still be a variance which means over a series fixture of many cells it should "average out"...
============


so the battery WILL change its width by 2.5mm PER CELL and that is normal!

A 24v-8cell battery pack in a series fixture will increase its overall length by (8 * 2.5mm) = 20mm or 0.78in when charged from 30% to 100%

this is why you need to be careful on using a RIGID fixture if you are trying to follow the spec; if the cell fixture is rigid the pressure will get quite high as it is normal for the cells to expand when charged, you must actually let them expand.

basically you need to design a system that provides 300kgf at 30% capacity AND a 300kgf force at 100% capacity.
This is why engineered linear compression springs are important as they provide a true spring constant(lbs/inch of travel) so you can actually calculate what will happen to your battery pack as the series cell expands.

I use engineered foam spacers every other cell (so each cell has at least 1 foam side to push against) AND springs so that cells can still expand while the springs are continuing to provide a known force (but not to much force hehe)

another option is if your cells spend most of their time charged, well, make sure to apply the 300kgf when at 100% and for the time when cells are disharged let the pressure drop a bit ;-)
 
Last edited:

100 Proof

"Please Lord, don't let me do something stupid."
Joined
Feb 14, 2021
Messages
95
keep in mind the spec is literaly +/- 1mm at 30%SOC and again +/-1mm at 100%SOC... so your measurement is in that range ;-)
I only mention it because purchasing and/or preloading springs to handle expansion of ~20mm vs ~4mm (in the case of 8 cells lined up) could be critical.
 

BiduleOhm

Electronics Sorcerer
Joined
Jan 30, 2020
Messages
1,777
Location
France
keep in mind the spec is literaly +/- 1mm at 30%SOC and again +/-1mm at 100%SOC... so your measurement is in that range ;-)

I think you misunderstood that part (but really nice post otherwise BTW ;)), the +/- 1 mm is just a manufacturing tolerance, the expansion will be around 0.5 mm between 30 and 100 % no matter what.

The typical cell will be 71.5 mm @ 30 % and 72 mm @ 100 % but for example you can have a cell that is 70.8 mm @ 30 % then it'll be 71.3 mm @ 100 %.

I guess the datasheet should have been clearer and said 71.5 mm +/- 1 mm @ 30 % and +0.5 mm @ 100%. But I think we're quite lucky with what we have, I've seen datasheets much worse than that...
 

Simi 60

Solar Enthusiast
Joined
Jul 10, 2021
Messages
107
Damn interwebs and it's rabbit holes
Woke up this morning, read comments, searched some more, got even more confused
Went down and backed off nuts, did up until finger tight and gave them a couple of turns more.
Not enough for my torque wrench to register.
 
Top