I asked for force....
Compress or not, flexible busbar or not
- Thread starter Cheap 4-life
- Start date
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
Imo we should not go by a data sheet that only shows how they tested a cell and then make all kinds of implications that are not stated on that data sheet. My research is from what I read on this forum and so far that’s no more than 17psi is the latest best life for our cells..
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
Well then was this statement by Ellcon123 also false?
“You are mixing units. A 16 cell has to expand 4 times more than a 4 cell under the same pressure. Math. The spring is not rated in psi. It is rated in force/distance. Psi is force/area.
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
B, the cells would start off having whatever pressure (psi) the plates are applying to each cell. Each cell and each plate is only influenced by itself because the plates cannot be influenced by the other cells/plates, unless your saying the interior plates can move with the expansion of the other cells then the force each cell has in it is slightly more than it would have if it was in its own plates like A. Slightly more force from the other cells can slightly increase the pressure within the rig if everything in the rig can influence everything in the rig..
C, would be the same as B if the plates in B can move with the expansion of the cells..
Bonus; the range of force idk, but the plates would experience slightly more force than A because of the linear movement/force/expansion of 4 cells instead of 1. No it wouldn’t be 4 times the force but still more force applied to those plates than one cell would.
Or it could be looked at like the plates have to apply more force or resistance in C than A simply because the walls do not have springs to allow for expansion. If there’s was the exact same springs used on C and A then with C the springs would allow the walls to move out more than the same springs would with A simply because the springs would be applying the same psi in both rigs but the expansion distance of 4 cells is greater, and would take more force (slightly more not 4 times more) from the springs to be contained..
I know your answers would be that it’s all the same but I disagree
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Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
I know your just answering the question, but 20psi is to high going by what we were actually told and not going by how a cell was tested in a data sheet.. so that means a rigid structure is too rigid.
“Force extremes remain the same” that's what im having issue with.
For example. If there’s 2 inch springs used on a 1 cell structure and the same 2 inch springs used on a 16 cell structure and those springs were both tightened down 25% of their length at 30% SOC on both structures (all end plates on both structures now applying the same psi). The 16 cell structures springs would be compressed more at 100% SOC than the 1 cells springs at 100% SOC. That tells me that those 16 cells expanded more than the one cell, which then tells me that the 16 cells applied more force to the endplates/springs than one cell did. If it was the same amount of force with 16 cells as one cell then the spring in both structures would compress the exact same amount.. I agree it’s not 16 times more spring compression but still more spring compression than one cell,,... now if the structure was rigid for 16 cell and the 1 cell, then there would simply be more force against the endplates with 16 cells (slightly more not 16 times more) which would increase the pressure more so than the endplates/cell would experience in the 1 cell rigid structure..
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
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42OhmsPA
What's in a title?
336-560 lb-f or 6-10 psi?
This is all a bit out of my scope of expertise but I love keeping the brain healthy.
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
@cinergi comment
“You're falling into the trap of combining distance and force. They're unrelated. A sufficiently long spring would exert the same force for a 4-cell pack as a 16-cell pack regardless of their SoC. It's a cheap way to apply a relatively fixed amount of force against an object that changes dimensions.”
My comment
Sufficiently long spring” what do you mean by this. If the correct springs are used and they apply let’s say 160lbs at 50% compression and 4 are used.. Then couldn’t that same spring be used for a 4 cell and 16 cell pack? If it’s exerting the same lbs to both packs when it’s at 50% of its length then regardless of how many cells are in that pack, the length of the spring should not matter, IF the amount of cells in the pack doesn’t change the force
BUT i think the length of the spring does matter,,, and i think the reason your saying “sufficiently long spring” is because the 16cell pack needs more/longer spring/room to expand therefore compressing that spring further than 50% or further than a 4 cell pack, which is caused by none other than more force against the spring in a 16 cell pack.. yes it’s more distance the 16 cell pack needs to expand but if the spring is applying the same amount of 160lbs pressure to a 16cell and 4 cell pack, and IF there’s supposedly no more force with more cells, then how can the 16cells squeeze the spring more than a 4 cell pack?
Justgary... how am I wrong
Only way I could be wrong is if the spring compresses by the same length for both packs at 100% SOC. And since 16 cells expand more than 4 cells, I can’t see how that’s possible. And again I’ll say the spring didn’t compress 4 times more, just slightly more with 16cells vs 4 cells
BUT if strong enough springs are used (or rigid/fixed rig) that basically completely stops expansion then idk, I mean since expansion is stopped, did it take more force to stop expansion of 16 cells vs 4 cells. Going by what I said above about the springs that were applying the same lbs to both packs and the spring compressing more with 16 cells, I’d think it took more force or more resistance from the walls of a rigid structure to stop the expansion of 16 cells vs 4 cells.. which would increase the psi in the rigid rig more so than if springs were used.
Also I’m thinking if the expansion is stopped with the force of springs or rigid then the expansion never happened so there isn’t all that extra expansion mass force moving springs,, so maybe in a rigid/fixed structure or with strong enough springs that basically completely stop expansion, that then there maybe ISNT MORE FORCE WITH MORE CELLS.. that’s if there’s enough pressure/lbs applied that all but completely stops expansion so that additional cells are not adding slightly more force to the rig...
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I've only seen the rev B datasheet and nowhere does it mention psi. It also doesn't state the test rig is for optimal life. It's just a test setup for repeatability of results. Looks to me that the biggest issue, outside of over/under voltage, is temperature. Better of worrying about temperature and voltage if you want long life.
Mobile application you would need to fix, by whatever method you see fit, but suspect your batts will suffer more from temperature related issues.
Mobile application you would need to fix, by whatever method you see fit, but suspect your batts will suffer more from temperature related issues.
Spring rate of the spring determines the length required. The threaded rods are "springs" along with everything else so I'll leave out the springs and keep it simple. Just trying to get to 20 pages. I don't think it's a stretch but the pressure is on!!!
I see what you did there ?
Technically, one plate has 672 to 1120 pounds, and the other plate has -672 to -1120 pounds. The sum of the forces have to equal zero if nothing is moving.
I said in B they are rigid plates just like in A. Take four A and cram them together, and none of the plates can move.
In B and C, the cells start at the same compression as in A.
Pressure is force over a unit area. If you know the force and the area it is applied over, you know the pressure.
Oh, boy! I think you are catching on!
It's a joke.
Whoops! Sorry I missed that.
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
My point is that there only is possibly not more expansion/force with more cells if expansion is all but completely stopped from even starting by the compression.
As I said if the same exact springs are used for a 16cell and 4 cell pack, then the spring on the 16 cell pack will be compressed more than the springs on the 4 cell pack.. to me that means there’s more force in the 16 cell pack because the extra cells compressed the spring more than the 4 cell pack.. that’s if the springs WERE NOT strong enough to completely stop all compression from happening/starting..
is this correct?, or are you still saying that even if the springs are not strong enough to completely stop expansion and expansion does happen in the pack, that there’s still no more force with 16 cells vs 4 cells? As I said that wouldn’t make sense for you to say because the pack with more cells compressed the spring further due to the extra expansion force...
More thoughts on compression.
I've seen EVE's videos on youtube where they put pressure on a stack of batteries and then laserweld it into a fixture, and it seems like a common method on this forum, minus the welding.
But I can't square this with the battery spec. sheet. I'll use 1kgf = 10N for ease of conversion. Numbers for LF105 since that's what I intend to use for my UPS battery:
So we can see that they should have 300-500kgf of compression, shouldn't peak over 700kgf and at 900kgf it will cause damages, while 1500kgf will cause leakage.
If we then look at the expansion force the cells themselves generate:
At Beginning Of Life they'll generate less expansion force than the recommended compression, but at End Of Life they can generate 3000kgf. This obviously exceeds the force that'll crush the other cells. With multiple cells stacked in a static fixture this sounds like a countdown to cascading failure.
If I instead use 6x 32 mm/16mm hole/inner diameter ISO-10243 medium load springs that are 102mm long I get 32 N/mm/spring. Compressing these 15.625 mm give 15.625 mm * 6 springs * 32 N/mm = 3000 N ≃ 300kgf. If a cell nearing end of life decides to start bloating, it can violently bloat 10mm and I'd still only put 25.625 mm * 6 springs * 32 N/mm = 4920 N ≃ 492 kgf on the other cells, i.e. still remaining within the recommended compression force parameters.
Ignoring having to use flexible cell interconnections and other considerations that are besides the point, why wouldn't this be the preferred solution?
I've seen EVE's videos on youtube where they put pressure on a stack of batteries and then laserweld it into a fixture, and it seems like a common method on this forum, minus the welding.
But I can't square this with the battery spec. sheet. I'll use 1kgf = 10N for ease of conversion. Numbers for LF105 since that's what I intend to use for my UPS battery:
So we can see that they should have 300-500kgf of compression, shouldn't peak over 700kgf and at 900kgf it will cause damages, while 1500kgf will cause leakage.
If we then look at the expansion force the cells themselves generate:
At Beginning Of Life they'll generate less expansion force than the recommended compression, but at End Of Life they can generate 3000kgf. This obviously exceeds the force that'll crush the other cells. With multiple cells stacked in a static fixture this sounds like a countdown to cascading failure.
If I instead use 6x 32 mm/16mm hole/inner diameter ISO-10243 medium load springs that are 102mm long I get 32 N/mm/spring. Compressing these 15.625 mm give 15.625 mm * 6 springs * 32 N/mm = 3000 N ≃ 300kgf. If a cell nearing end of life decides to start bloating, it can violently bloat 10mm and I'd still only put 25.625 mm * 6 springs * 32 N/mm = 4920 N ≃ 492 kgf on the other cells, i.e. still remaining within the recommended compression force parameters.
Ignoring having to use flexible cell interconnections and other considerations that are besides the point, why wouldn't this be the preferred solution?
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