Compress or not, flexible busbar or not

[Cheap 4-life]

In the video shown here

Can you share the video?

 

[Cheap 4-life]

Surely they define the preload conditions somewhere in the document.

Preload is an engineering term. It applies to beams, bearings, springs, and lots of other things.

They are referring to a fixed/rigid fixture as far as I can tell.. preload imo meaning pre high SOC, like as the cells try to expand there is load and previous to that load there is low SOC which is the preload stage which is when the 300kgf should be set..
If I could figure out how to share the data sheet I would. It was a pdf on an email.. I click copy and come back to paste it here and it doesn’t work..

 

[Skypower]

Can you share the video?

I could snag the text statement from the site of eelbattery.myshopify.com but it wouldn’t let me paste the whole block here. I didn’t even look at the vid to be honest. Not trying to advertise here, just pass on some info.

 

[Cheap 4-life]

Very similar to what I purchased. These are also medium duty. 10mm gives a little extra room for 3/8 all thread. i got them 80mm (slightly over 3”) due to all the expansion my 19 cells in a row will have. However I really want to keep the expansion of each cell below .5mm, so no more than 8mm for my 19cell pack.

Just got the 20mmx10mmx80mm springs in the mail
I set up a jig of sorts and had the wife and I stand on two of the springs. Combined we weigh 330lbs. I know,,,perfect weight for half of the 660lbs these cells require.. the two springs compressed 1.25” with our 330lbs on them. The springs are 3.15” so there’s still plenty of room (if the 19 cells need to expand a little) before the spring is fully compressed. The spring is fully compressed when it’s tightened/shortened 1.85”. That leaves .60” for the 19 cells to expand if I tighten the springs 1.25” to start with at 40% SOC.
Now just waiting on the cells to arrive

 

[fafrd]

That’s seems rather fast to degrade to 80%.. that’s only 1825 cycles if it’s fully cycled everyday..

Look at table 7: https://mdpi-res.com/d_attachment/e...ploy/energies-14-01732.pdf?version=1616229789

Close to 24 years of calendar aging before cells degrade to 80% of rating as long as they were stored at 25C (77F) but that degraded to only 53.5 months / less than 4.5 years if those same cells were stored at 40C (104F).

So yes, assuming we are all using our cells at temps under 80F, calendar aging should not be nearly as much of a concern as cycle degradation…

 

[Cheap 4-life]

Look at table 7: https://mdpi-res.com/d_attachment/e...ploy/energies-14-01732.pdf?version=1616229789

Close to 24 years of calendar aging before cells degrade to 80% of rating as long as they were stored at 25C (77F) but that degraded to only 53.5 months / less than 4.5 years if those same cells were stored at 40C (104F).

So yes, assuming we are all using our cells at temps under 80F, calendar aging should not be nearly as much of a concern as cycle degradation…

Although that study was of cylindrical cells, but I’d assume prismatic cells would be similar but degrading faster from calendar aging

 

[justgary]

There’s an amazing amount of good info out there, but every year it’s getting harder to find the cream out of the mounds of mostly crap background. It use to be so easy to do a search. Now it’s buried in incorrect results.

It seems like you are suggesting that the newest EVE datasheet is crap. I can't download the paper you linked where I am right now. What was the date on it?

 

[Skypower]

It seems like you are suggesting that the newest EVE datasheet is crap. I can't download the paper you linked where I am right now. What was the date on it?

That paper is old, February 7, 2014. Probably some of the earliest aluminum bodied prismatic cells.
Not implying that the EVE data sheet being crap. Just searching things in general.
Ever just wanted to get a torque spec on your car? Junk comes at you before the answer lol. I didn’t even know there’s a torque spec on the little blue pill ?

 

[Skypower]

Look at table 7: https://mdpi-res.com/d_attachment/e...ploy/energies-14-01732.pdf?version=1616229789

Close to 24 years of calendar aging before cells degrade to 80% of rating as long as they were stored at 25C (77F) but that degraded to only 53.5 months / less than 4.5 years if those same cells were stored at 40C (104F).

So yes, assuming we are all using our cells at temps under 80F, calendar aging should not be nearly as much of a concern as cycle degradation…

 

[Skypower]

That’s an interesting paper too.

 

[justgary]

That paper is old, February 7, 2014. Probably some of the earliest aluminum bodied prismatic cells.
Not implying that the EVE data sheet being crap. Just searching things in general.
Ever just wanted to get a torque spec on your car? Junk comes at you before the answer lol. I didn’t even know there’s a torque spec on the little blue pill ?

It's just that a huge portion of this thread discussed the new specifications from EVE. Showing that an upper pressure was considered bad eight years ago may not help. The whole question is whether an upper bound exists any more.

 

[Cheap 4-life]

It's just that a huge portion of this thread discussed the new specifications from EVE. Showing that an upper pressure was considered bad eight years ago may not help. The whole question is whether an upper bound exists any more.

My read is that the new data sheet is how they tested a cell. Yes it can be done that way but it’s still not necessarily the best way. A high upper pressure from a completely rigid fixture is still imo not optimal for the cells.. My understanding is that starting our cells at 300kgf with springs or Poron foam is better than having them in a completely rigid fixture. Better as long as the cells are not allowed to expand to much. To much being anything over .5mm each.. I don’t see how the new data sheet changes that.. the springs or foam should also leave extra room to not compress the cells to much at high SOC. Rigid can’t do that. Also as the cells age they expand more (or whatever) causing more compression (or whatever) within the rig.. Springs or foam can accommodate that where as rigid cannot.
I do think an upper pressure amount is still of concern. For best life for the cells the higher pressures shown in the new data sheet and the high pressures that the tested cell experienced should be avoided..

 

[Skypower]

My take is that CATL and it’s distributors currently highly recommend correct fixturing/compression whereas EVE not so much. Is that the read you guys have?

 

[Cheap 4-life]

I think the cells are so similar that they should be treated the same. Fixture/compression of some sort should be done. Only argument was calendar aging would happen before cycles..

 

[Skypower]

I think the cells are so similar that they should be treated the same. Fixture/compression of some sort should be done. Only argument was calendar aging would happen before cycles..

I thinking that temperature is going to be the biggest issue in regards to calendar aging. If someone’s battery capacity is insufficient and they are being charged hard and heat is being accumulated within a server style battery enclosure, it’ll probably be a factor in the future. During the last heat wave mine got pushed hard for a few days but they reside under a bench top with an air gap. Luckily I was able to have a small fan on a timer to blow cool early morning air across the top which made a huge difference within hours to cool the mass down for a repeat heat and load.

 

[SolaroSsaurius]

This is my mock up of planned compression / drawing, will have 18 x springs in total ( 3S6P).
So far has cost £10.77 for the springshttps://www.ebay.co.uk/itm/Compress...a-e7d6-46cc-9b0e-f90b5ac460ca&redirect=mobile + couple of £ for the 12mm OD plastic pipe(sleeve on inside of spring to allow threaded bar to slide, plus on threaded bar along it's lenght to ensure isolation against cells) - all other bits are sourced from work for free? - hence why 8mm threaded bar - 6mm would be ok but none at work ?.
Spring rates chart is as tested under various compressed lengths, also compressed spring for a week to check for long term deformation and seems good.
So as far costs go- negligible, just a bit of time in man cave.View attachment 113409
View attachment 113410
Note - this is my take on a solution for compliance with requirment, you make your own minds up how you wish to build.

Thanks for sharing!

I was thinking...
If cells expand 0.5 mm at full charge, then springs will be above 500kgf considering 8 cells per row (4mm expansion).
Or I getting it totally wrong?

 

[SolaroSsaurius]

EVE has shown you how you can get 6000 cycles to 80% of initial capacity by building a rigid structure.

Just trying to understand / learn as much as possible to build my enclosure...

Are you referring to the test with a fixed structure with a single cell?

If so... I was thinking that expansion of a single cell will result in less pressure then multiple cells like in a battery.
Considering the previously stated 0.5mm per cell expansion, in a quite typical 8 cells per a row, 4mm expansion total would be a lot of pressure, no?

 

[justgary]

Here we go again!

 

[Cheap 4-life]

Here we go again!

9min into this video

He basically says more cells is more force..
For example, if I added more weight to the rig I used to do my testing of my springs, then the spring would get shorter because there was more weight on the spring. Therefore at the ends of the springs there is more force/pressure being applied.. Now if those same springs are used on my 19cell pack, then as the 19 cells expand (up to .5mm each) the spring would get shorter. Then the same as I just explained happened on my test rig would happen,, more force/pressure would be applied to the cells because at the ends of the springs there’s more force/pressure being applied do to the expansion of 19cells and how much shorter they made the spring get. Now the kicker,, IF THOSE SAME SPRINGS were used for 1 cell (not 19) the spring would NOT get nowhere near as short as it does with 19 cells. Now if it’s understood the shorter the spring gets the more pressure/force that’s applied, then there’s no way it can’t be agreed that there should more pressure/force in the 19 cell rig than the 1 cell rig..
Yes I understand to use different size springs to make sure the pressures/forces are the same in a 19 cell or 1 cell pack.. but that doesn’t change that more cells are causing more pressure/more force (due to the additional expansion length) in a fixed fixture that can’t change its springs because it doesn’t have any..

 

[1234enough]

Here’s the link to the papers,( chart is on pg32) lots of info;

https://electrodacus.com/battery/A123_AMP20_battery_Design_guide.pdf

Pretty crazy huh? Yeah, the right side where the blue line ends is probably where things got gooey. There’s not much difference between 10 and 12 psi, so I went with 10.

Good read that one, i know it's not Eve, so some might say irrelevant.

I'm in same ballpark as you at around 10psi / 500kgf/ 82% of Eve 300kgf per cell to start with, the springs I'm using for compression of double row of LF280K then allow 6mm of linear movement which takes kgf up to 660 / 13psi / 110% of 300kgf per cell. Before anyone says - figures rounded up / down, so not spot on, but near enough for me.

In the paper - page65 specifications psi 8 - 14psi, which equates to 200 - 350 kgf per cell. Which is all but bang on what I've designed from Eves specifications.

Interesting to read on thermal dissipation with thermally conductive cell separators, don't feel this is required for my set up as not planning on high C charge /discharge rates, but if required ideas already in my head.