Has anyone used gravity to compress the cells?

[cajocars]

One way it stacking the cells vertically with ~ 300 kg of weight on top to ensure a constant pressure no matter what the expansion of the cells is
Obviously the bottom cell will get a higher load than the top one


In my drawing one side of the battery pack (right) is constrained and the other one on the left is made of a lever that reacts to the force on the ground, basically the weight of the batteries and any additional weights you want to add to the enclosure.

 

[RV10flyer]

So far my 1 inch cargo straps work fine.

 

[cajocars]

Another way would be to use 4 750N gas struts; they provide a constant force; if only "reverse" gas strut existed...

 

[newbostonconst]

Another way would be to use 4 750N gas struts; they provide a constant force; if only "reverse" gas strut existed...
View attachment 122764

They do make reverse ones...

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[newbostonconst]

One way it stacking the cells vertically with ~ 300 kg of weight on top to ensure a constant pressure no matter what the expansion of the cells is
Obviously the bottom cell will get a higher load than the top one


In my drawing one side of the battery pack (right) is constrained and the other one on the left is made of a lever that reacts to the force on the ground, basically the weight of the batteries and any additional weights you want to add to the enclosure.


View attachment 122720

You could also stack them vertical...the lowest one would get most force but I bet the first one in your setup gets the most force anyway.

 

[cajocars]

You could also stack them vertical...the lowest one would get most force but I bet the first one in your setup gets the most force anyway.

No, the force would be equal across all of them

 

[newbostonconst]

No, the force would be equal across all of them

Equal is a relative term.....may the force be with you...

 

[cajocars]

Equal is a relative term.....may the force be with you...

It’s simple physics my young padawan

 

[SeaGal]

Has anyone used gravity to compress the cells?

I suspect that, unless you're on the international space station ?️, everyone is using gravity to compress their cells, whether they like it or not ?‍?

 

[cajocars]

I suspect that, unless you're on the international space station ?️, everyone is using gravity to compress their cells, whether they like it or not ?‍?

There is some confusion in your answer. Most people are using axially loaded threaded bars, so no: no gravity on playing a role there; it would work the same way on the ISS

The point is that they require constant force; any spring loaded device has a stiffness so the force increases a lot with expansion of the cells (there is about 1mm difference between fully charged and fully discharged)
While the force exerted by a weight is constant

 

[SeaGal]

Was jesting - you can't remove the effect of gravity from your cells completely on planet earth!

 

[newbostonconst]

Was jesting - you can't remove the effect of gravity from your cells completely on planet earth!

And then you got atmospheric pressure...that seems like the most even force of them all....

Put them in a hyperbaric chamber...

 

[cajocars]

So what you’re all saying is ‘don’t bother compressing them’, right?

 

[SeaGal]

No, they need to be compressed.

 

[newbostonconst]

No, they need to be compressed.

It all depends on how hard you are going to run them and if you have a safe plan to never over charge them....IMHO

 

[SolaroSsaurius]

No, they need to be compressed.

What I understand is that compression is needed, but not a constant degree of compression along the SOC.
In the EVE datasheet only 6 rods are used to compress a cell to 300kgf at 30-40% of charge, there are no springs involved, hence I believe pressure will raise quite a bit during charge.
To how much?
I have no clue

 

[cajocars]

What I understand is that compression is needed, but not a constant degree of compression along the SOC.
In the EVE datasheet only 6 rods are used to compress a cell to 300kgf at 30-40% of charge, there are no springs involved, hence I believe pressure will raise quite a bit during charge.
To how much?
I have no clue

By quite a lot; if each cell expands by 0.5mm and you have 8 in a row, that’s 4mm
A steel M6 rod 576mm long (8x EVE 280Ah) has a stiffness of 10000N/mm
So if the cells expand 4mm in total you have 40000N per each rod; if the rods are 4, it’s 160000N or 16000kgf, which is 53 times the initial 300 kgf

 

[SeaGal]

It all depends on how hard you are going to run them and if you have a safe plan to never over charge them....IMHO

I should have qualified, it is recommented that they are supported in such a manner to prevent excess swelling and de-lamination if you want to maximise their longevity.

 

[Ampster]

In one configuration I stacked the cells on their sides. I had a cell leak a little electrolyte but it is still functioning in a new horizontal configuration.

 

[newbostonconst]

In one configuration I stacked the cells on their sides. I had a cell leak a little electrolyte but it is still functioning in a new horizontal configuration.

Funny, I did the exact same....my leaky cell is still fine but is now vertical....My 2 expanded ones are fine also.