Pack / Cell compression Optimized By Using Springs.

Bob B

Photon Sorcerer
Joined
Sep 21, 2019
Messages
3,342
I am opening this thread to split it off from the general cell compression thread. That way those looking for info don't have to sort thru a thread that has many paths for pack compression.

If you are new to this idea, it stemmed from an EVE cell specification that indicated a significant increase in cell cycle life could be gained by keeping the cells under pressure.
Through the course of the discussion, it has been determined that the optimal pressure would be 12 PSI .... and any pressure above 17 psi would be counter productive.
@vtx1029 has gone to the trouble of putting together a spreadsheet to calculate variables depending on springs used and pack sidewall area. He will send it to you if you message him.

If you haven't seen the other thread, it can be found here. https://diysolarforum.com/threads/e...ed-tight-or-spaced-for-expansion.7892/page-23
 
Last edited:

Dzl

Perpetual Newbie & Unofficial Forum Librarian
Staff member
Moderator
Joined
Dec 10, 2019
Messages
4,772
Good idea starting a new thread on this specific topic, that one is getting pretty lengthy and hard to wade through. For anyone who has not been following that thread, some highlights to give context to what is being discussed are posts: #4, #24, #195, #215, #216, #217, #233, #248, #340 (there is a lot of specific and useful information contained in that thread, specifically pages 1-3ish and 10-14ish, but its a lot to wade through)
 
Last edited:

Bob B

Photon Sorcerer
Joined
Sep 21, 2019
Messages
3,342
In general, to determine the spring capacity needed. .... I am using Sq In since the 12 psi number is what we have to work with .... but the same principle will work if converted to metric.

1. Determine the area of the side of the cell.
So, for a cell that is 7" x 8", the area will be 56 Sq Inches.
2. Multiply the area by 12 since we want 12 psi. (56 x 12 = 672 total lbs of force needed)
3. Divide the total force needed by the number of springs being used. (672 / 4 = 168 lbs per spring if 4 springs are being used.)

There are pictures of a pack done by Dacian (Electrodaucus Guy) on that other thread ... maybe it can later be added here along with pics from others who have done this.
 

Bob B

Photon Sorcerer
Joined
Sep 21, 2019
Messages
3,342
Oh, and just to be clear up front .... I you are not interested in this idea .... or think it it a bad idea .... or think it is a waste of time or resources ... There are other threads where you can post that sentiment.
This thread is for those who are interested in or think it is a good idea .... or are already pursuing the idea.

This way, we don't have to police unproductive comments later on.

Thanks for indulging this somewhat rude post.
 

Sillyputty

Solar Addict
Joined
Jul 21, 2020
Messages
178
It looks like this info provided by @vtx1029 may be helpful in other areas as well.

I have a "spring" related issue I'm trying to solve. This is regarding vibration-proofing and isolating as much as possible a 280ah battery that will be in a camp trailer that travels some very bumpy roads.

Basically it involves a relatively rigid container to house the cells and keep them compressed, which (I think) will be further isolated from the trailers floor (or tongue) by relatively short compression springs beneath it, and perhaps some counter-acting extension springs above and/or laterally. If anyone has experience with this idea (good or bad) I'd like to hear it.

Very interesting stuff! Thanks to all the contributors.
 
Last edited:

BiduleOhm

Electronics Sorcerer
Joined
Jan 30, 2020
Messages
1,777
Location
France
Basically it involves a relatively rigid container to house the cells and keep them compressed, which (I think) will be further isolated from the trailers floor (or tongue) by relatively short compression springs beneath it, and perhaps some counter-acting extension springs above and/or laterally. If anyone has experience with this idea (good or bad) I'd like to hear it.

It's a good idea. You want a rigid pack on compliant mounts to attenuate the vibrations and shocks. Some additional info here ;)
 

Sverige

A Brit in Sweden
Joined
Oct 8, 2020
Messages
338
I know it was the Eve 280Ah cells which sparked this discussion about compression at 12psi, but how likely is it that this also applies to other manufacturer’s cells? I mean are we safe to assume that this method is safe / worthwhile for prismatic cells whereever they come from?
 

Sverige

A Brit in Sweden
Joined
Oct 8, 2020
Messages
338
I found some springs in my garage, which might be suitable for this purpose. What would be the most effective way to test their strength and figure out what compression I need to apply to get to my 12psi (once I’ve done the sums to figure out what force is needed per spring)?
 

Luthj

Photon Sorcerer
Joined
Jul 1, 2020
Messages
945
I found some springs in my garage, which might be suitable for this purpose. What would be the most effective way to test their strength and figure out what compression I need to apply to get to my 12psi (once I’ve done the sums to figure out what force is needed per spring)?

Get a force gauge, such as a luggage scale. Then measure the springs coefficient. Its found by taking force divided by distance. So 50lb at 2" compression yields a K of 25lb/in.

1605889344419.png
 

vtx1029

Solar Enthusiast
Joined
Mar 30, 2020
Messages
130
I found some springs in my garage, which might be suitable for this purpose. What would be the most effective way to test their strength and figure out what compression I need to apply to get to my 12psi (once I’ve done the sums to figure out what force is needed per spring)?
If you know of any automotive machine shops in your area its not uncommon for them to have spring testers that would work well for this.
 

Sverige

A Brit in Sweden
Joined
Oct 8, 2020
Messages
338
Get a force gauge, such as a luggage scale. Then measure the springs coefficient. Its found by taking force divided by distance. So 50lb at 2" compression yields a K of 25lb/in.

View attachment 28097
Thanks - i have one of those but it will only work in extension rather than compression. Is the K for a spring the same in both directions?
 

Luthj

Photon Sorcerer
Joined
Jul 1, 2020
Messages
945
Thanks - i have one of those but it will only work in extension rather than compression. Is the K for a spring the same in both directions?
Just run a bolt/rope though the spring with a washer on the other side. That way you can test compression with a pull gauge.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,391
For a compression spring with relatively square ends and short/squat aspect ratio like valve springs ...

Use four springs to support the corners of a square of plywood.
Measure height off floor.
Stack exercise weights, car batteries, or something else heavy and measure new height.
Increase weight and measure again.

Probably you'll find a linear displacement vs. force.

Could also make a platform above a bathroom scale, or support a bathroom scale off the floor with springs.

Any way you do it, best to keep force centered in platform and not tilting. Otherwise each spring gets different displacement, and assuming all linear you might then solve for spring constant K.
 

Electro Dan-O

Current Situation
Joined
Nov 15, 2020
Messages
35
Location
Middle TN
Interesting stuff! I just got some new EVE cells that need to be put together for my boat project. I'm a decently crafty guy in the shop and feel like I could whip something up. I understand that these aluminum case cells can short out if not properly insulated from each other. That being said, I really liked the idea of using a thin layer of closed cell foam for insulation, but I wonder how that and also other materials would effect the constant pressure thing. Also, I was wondering if(instead of measuring spring height) it would be possible to figure out the bolt torque value on the "fixture" to pull up the spring pressure with a torque wrench. Just a thought. Might be getting into the "splitting hairs department" here...:)
 

Dhasper

Solar Addict
Joined
Jul 29, 2020
Messages
757
I have an RV also. Does anyone have an opinion on whether 4 spings or 5 with one in the center or a 6 arrangement would be better? I found this site which lists springs and their rating. Any engineers out there that could get someone in the ballpark on rating for each spring? Also would need some type of hardware to compress the spring and hold it in position. https://www.digikey.com/en/products/filter/springs-compression-tapered/1002 These also look interesting.. https://www.mcmaster.com/shock-absorbers/high-load-fastener-mount-compression-springs/
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,391
Stiff end plates and threaded rods through the springs would seem like an easy way to go.

Just look at the "rate" parameter on Digikey: pounds per inch of compression.
 

Dhasper

Solar Addict
Joined
Jul 29, 2020
Messages
757
Stiff end plates and threaded rods through the springs would seem like an easy way to go.

Just look at the "rate" parameter on Digikey: pounds per inch of compression.
I was actually thinking of something for the under the base upon which the batteries rested to provide a buffer from the bumps. Maybe dense foam would be the best bet.
 

Dzl

Perpetual Newbie & Unofficial Forum Librarian
Staff member
Moderator
Joined
Dec 10, 2019
Messages
4,772
I was actually thinking of something for the under the base upon which the batteries rested to provide a buffer from the bumps. Maybe dense foam would be the best bet.
I would think something like that would be a good idea, particularly for conditions like washboard I would imagine.
 
Top