Clamping Pressure

Tdevery

Solar Enthusiast
A lot of discussion on clamping cells with threaded rod on four corners.
Has anyone figured out how much to tighten each nut with a Torque wrench to achive the required PSI?
 

Johncfii

Solar Addict
There have been some proposals of methods of such calculation, but none that have seemed definitive that I recall.

The general approach that most are using does not rely on a torque wrench to tighten a set of rigid-set long rods. I think this is because it is so hard to estimate the net applied force per square inch, and because pressure will change significantly as cells expand or contract.

I think that most who are actually trying to apply a relatively constant pressure (and many forum users end up deciding not to bother with it at all) are relying upon calibrated “die” springs that have a known spring constant, and calculating the number of turns of each nut that compress the springs by an amount that will yield desired force on each rod, converted to pounds of pressure per square in of cell cell surface area.

This entire matter is deeply discussed in this thread below. On the page that will open, I show you my solution, if interested..

 

Tdevery

Solar Enthusiast
Thanks for your reply. I spent about 2 hours reading the compression discussion.
Finally ordered a few die springs, picked up threaded rod, ordered Al plates.
Just waiting for the cells.
 

Northernchateau

Solar Enthusiast
A lot of discussion on clamping cells with threaded rod on four corners.
Has anyone figured out how much to tighten each nut with a Torque wrench to achive the required PSI?
Let me spit ball for a min.
I have a degree mechanical engineering.
If you give me the length, width of the battery and psi your looking for I can calculate the load you need to apply.
From there I need the diameter of the threaded rod and pitch of the screw you will be using to calculate the torque required.
That's easy and just math.
The hard part is going to be how you apply it. The surface finish on both the screw and nut as well as the type of lubrication used can change things big time. The calculated torque is just that, a number but who knows how accurate.

So whats your option, well still calculate the load require, then purchase springs that can apply that load, built it, set the spring gap and you will have as best a DYI set-up as person can do.
 

lexio

feel the balance 3.65
hi can you calculate this one will be appreciated yes am a carpenter
lishen 280 ah is 71.45mm wide
 

Northernchateau

Solar Enthusiast
hi can you calculate this one will be appreciated yes am a carpenter
Length (inches) x Width (inches) x PSI = Load in pounds
Load in pounds / 4 = Load required by each spring.
[Free length of spring - Compressed length of spring ] * spring rate = Load
 

G8trwood

Solar Enthusiast
Pitch rate and diameter of bars oh my!

Add in recommendations from different manufacturers. Some cells (for EV for example) advertise they won’t expand at full charge. Some of the calb and others have internal stiffeners for rigidity. Secure but not smushed?
 

Diysolar123

Solar Addict
you can purchase engineered springs that literaly are design with a linear pressure profile; you know the psi force by just measureing the length of the spring vs free length. These are NOT ebay springs...engineered heavy duty compression springs are designed to have predictable compression rates.
 

ohthetrees

Solar Enthusiast
I read lots of this thread, but not all, so forgive me if I'm retreading old ground. I just bought springs (9-1010-26 5/8 X 2-1/2 RED DANLY DIE SPRING) from suprdie.com for cheap! According to their data sheet (https://www.daytonlamina.com/pdf/DS117_DieMax_XL_Springs.pdf) these have a length of 2.5" and at solid compression (1.07" deflection) provide 177lb of pressure. Each 1/10" is worth 16.5lb of pressure.

I have two rows of EVE 280ah cells, and 7 springs/rods. My plan for "calibration" is to assemble my pack at a low SOC, compress the springs about half way (should provide around 6 psi). Then I'll charge them to 100% SOC, and adjust the springs nearly to "solid", then back off 1/10". This should theoretically provide 10.5 PSI. So from then on, my pack, assuming they don't swell bigger over the years, should max at 10.5 PSI, and min at something above 6 psi (not sure yet, but will be able to calculate by measuring length of springs).
Battery_Box_2021-Sep-02_05-59-25AM-000_CustomizedView22735957254_jpg.jpg
 

nate_syd

Solar Enthusiast
Depends on your spring...

How about you grab a kitchen scale, put the scale on a piece of wood & put the spring on the scale. Then use a clamp to slowly compress the spring & read the scale at each length of compression.

Or just push on it...
You have a 40mm spring, get 3 pieces of wood - 10mm, 20mm, 30mm. Put them next to the spring so you know the compression distance & it stops when you hit the wood (do it by feel).

:)
 

Simi 60

New Member
Do any of the pre made batteries use springs?
If not, why do you feel you need them

Serious question.
 

Northernchateau

Solar Enthusiast
Do any of the pre made batteries use springs?
If not, why do you feel you need them

Serious question.
The theory behind compressing the cells is that it keeps the battery material in contact with the terminal post.
The result should be increase cycle life.
The use of springs keeps a uniform and per-determined load on the face of the cell.
I am a DIY guy so I will do whatever to improve and increase the life of my very costly LifePo4 batteries.
Now as far as pre-made batteries, I never looked into them as they tend to be more then if I did it myself plus I am not sure they are worried about selling anyone a battery pack that can increase the life cycles and last longer.
 

Bob B

Photon Sorcerer
Thought you might be interested to see how my actual build turned out compared to my 3-D model posted up thread.
View attachment 66314
Would you consider posting the details of your build and springs over here?

 
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