Compress or not, flexible busbar or not

[Cheap 4-life]

Yes, but without cells the springs are not putting pressure on anything, nor does the pressure go up more with more cells vs fewer cells in the fixture without cells in it

 

[justgary]

This is relevant somehow?

 

[Cheap 4-life]

I’m thinking it’s relevant as saying force doesn’t exist without springs and force is all due to springs.. without the cells (more or less of them) the springs are not applying pressure to anything..

 

[justgary]

If you push on a spring you get force. If you let a cell expand you get no force.

 

[Cheap 4-life]

If you push on a spring you get force. If you let a cell expand you get no force.

Yes if you push on the spring with something which is mimicking the cells for our discussion.. no force on the cells unless mimic springs or walls with something.. either way the same

 

[fafrd]

Yes if you push on the spring with something which is mimicking the cells for our discussion.. no force on the cells unless mimic springs or walls with something.. either way the same

This has got to be the most inane thread I have ever witnessed on this Forum.

Apologies to any poor newbies that have wandered into this morass this deep, but I’m out…

 

[justgary]

This has got to be the most inane thread I have ever witnessed on this Forum.

Apologies to any poor newbies that have wandered into this morass this deep, but I’m out…

I need your help to get to 1,000 posts in this thread!

 

[justgary]

either way the same

I guess the walls of a house keep the roof from falling to the ground, and the roof keeps the walls from floating into space.

Either way the same... except that one of the two doesn't happen.

 

[Cheap 4-life]

No, this is not correct. You do not understand what pressure is and how it is different from weight or force.

This has got to be the most inane thread I have ever witnessed on this Forum.

Apologies to any poor newbies that have wandered into this morass this deep, but I’m out…

My comment,,
so when more cells shrink/compress that same spring more than one cell would compress that same spring, the mor3 cells would be under more pressure like more weight on the spring.
Your response,,
No, this is not correct, and that I do not understand...
I’m sorry sir but you are the one incorrect.. what is insane is continuing to say that this is wrong,, and anyone else that says more cells can not create more expansion length force in a spring fixture.. I’ve been saying that it can and told I was incorrect for many pages.. yes different springs can be used that apply different pressures at different deflections when there’s different amount of cells in a pack.. that doesn’t mean that more cells would not move/compress a spring more than less cells due to their additional expansion length force.. I understand that your cells barely expanded so you think otherwise, but others have had much more expansion with cells in a spring fixture.. I don’t know if some have the cells compressed more than others or what, but it’s irrelevant. If each cell is allowed to expand in a fixture .5mm each (as they are said to in the data sheets) then they would compress the same spring more with more cells vs fewer cells and that couldn’t happen unless the additional cells were adding more force than fewer cells. Thats the only thing that could compress the springs more..

 

[Cheap 4-life]

If you push on a spring you get force. If you let a cell expand you get no force.

It’s doesn’t matter if a spring is applying force if it’s not applying it to any cells ... nor does it matter if cells are expanding when not being compressed by a spring because then there’s no expansion force..

Anyways I’m going to stop discussing more cells can create more expansion length force than fewer cells in a spring fixture.. for some reason that’s not popular..
I think a lot of people are/were thinking a 16 cell pack will only expand .5mm in a spring fixture same as a one cell pack would expand only .5mm.. that’s not so, maybe thats clarified thru this post, maybe not.. I don’t care at this point.
I have learned that if expansion is completely stopped in a rigid fixture then the pressures in the pack would raise by the same amount and be the same amount thru the entire SOC regardless of how many more or less cells are in the pack..
And I’m sure others reading this have also learned that.. for example Cinergi (much earlier in this thread) said that there would be to much pressure force (or whatever he said) if a rigid fixture was used for 16 cells.. maybe now he (and others) thinks otherwise after reading this thread..

 

[filippomasoni]

This is a very interesting and controversial topic. I didn't read the entire thread but I think I agree with most stuff and something I wasn't thinking about but definitely makes sense is this:

And I’m sure others reading this have also learned that.. for example Cinergi (much earlier in this thread) said that there would be to much pressure force (or whatever he said) if a rigid fixture was used for 16 cells.. maybe now he (and others) thinks otherwise after reading this thread..

So my 8S pack will definitely have a 4x2 configuration instead of an 8x1.

I think everyone is here to learn and share experiences and knowledge to apply to their own setup, and that's exactly what I'm here for. So I'll go ahead with my own question.

My 8S 24V 280ah with JK BMS battery will be used in a mobile environment, a truck camper which will experience light offroad and hence a lot of vibration. What's the best setup for this? My goal is to have the smallest and lightest pack possible.
I was planning on using the classic rigid busbars that came with the cells and also a copper busbar to connect the BMS, t-class fuse, and battery switch, mainly because I already have the copper bar but also so I can get short and efficient connections without adding too many points of contacts. My thinking was to mount everything on the battery enclosure made of plywood, have it lightly compressed with simple threaded rods as a whole rigid package, and then mount that to the camper with rubber dampening. But after reading this I'm concerned about vibrations loosening all of the bolts over time. Not sure if lock nuts have been mentioned here, is that a bad idea? EDIT: It is, never mind, better to stick with serrated nuts.

 

[justgary]

So my 8S pack will definitely have a 4x2 configuration instead of an 8x1.

I think this is a good choice simply for management. Eight cells in one pack is very heavy, and you might require two people to lift it.

My thinking was to mount everything on the battery enclosure made of plywood

Why not 8mm aluminum? That is the recommended material, and it is non-flammable.

have it lightly compressed with simple threaded rods as a whole rigid package

Why lightly compressed? The specification is 300kgf at 30%-40% SOC. Light compression will allow your rigid busbars to move more than the specified compression will.

I think the best way we have seen so far in this thread is to use springs to compress the pack to the proper force, then use threaded rods in separate holes. Snug up the nuts on the threaded rods, then release the springs and remove them. You will greatly appreciate having extra holes in the end plates to use with ropes as lifting handles. I left extra holes off of my design, and now I regret it.

then mount that to the camper with rubber dampening.

A great idea. I think it would be worth a bit of your time to study the mounts you plan to buy so that you get the dampening you expect. I don't really know what cutoff frequency would be appropriate for these cells, but if you could get the whole pack under 10 Hz while allowing a few centimeters of motion, that would probably be fantastic.

 

[S Davis]

This is a very interesting and controversial topic. I didn't read the entire thread but I think I agree with most stuff and something I wasn't thinking about but definitely makes sense is this:

So my 8S pack will definitely have a 4x2 configuration instead of an 8x1.

I think everyone is here to learn and share experiences and knowledge to apply to their own setup, and that's exactly what I'm here for. So I'll go ahead with my own question.

My 8S 24V 280ah with JK BMS battery will be used in a mobile environment, a truck camper which will experience light offroad and hence a lot of vibration. What's the best setup for this? My goal is to have the smallest and lightest pack possible.
I was planning on using the classic rigid busbars that came with the cells and also a copper busbar to connect the BMS, t-class fuse, and battery switch, mainly because I already have the copper bar but also so I can get short and efficient connections without adding too many points of contacts. My thinking was to mount everything on the battery enclosure made of plywood, have it lightly compressed with simple threaded rods as a whole rigid package, and then mount that to the camper with rubber dampening. But after reading this I'm concerned about vibrations loosening all of the bolts over time. Not sure if lock nuts have been mentioned here, is that a bad idea? EDIT: It is, never mind, better to stick with serrated nuts.

That is basically what I did, my cells are set at 640psi and mounted on vibration dampers. I go off road quite a bit for work and they have been holding up for about a year and a half. If you are heating you have air space under the cells for air circulation as well.

 

[SolaroSsaurius]

That is basically what I did, my cells are set at 640psi and mounted on vibration dampers. I go off road quite a bit for work and they have been holding up for about a year and a half. If you are heating you have air space under the cells for air circulation as well.

View attachment 115661

Thanks for the photos.
Are you sure you are using 640 *psi* ?

 

[justgary]

mounted on vibration dampers.

Do you happen to have a source or part number for your dampers?

 

[filippomasoni]

@S Davis awesome setup, you've shown me a couple of those photos on another thread, and I got the idea of the dampers from you. I'm also interested in knowing where to source those.

My system is 24V and I have a single BMS so I was thinking of packaging everything together, in 2 rows of 4 cells, also to optimize space. The entire pack will probably be more than 50kg so I'm not planning on carrying it but actually assembling it in place.

 

[S Davis]

Thanks for the photos.
Are you sure you are using 640 *psi* ?

I am using four 160lb die springs.

 

[S Davis]

@S Davis awesome setup, you've shown me a couple of those photos on another thread, and I got the idea of the dampers from you. I'm also interested in knowing where to source those.

My system is 24V and I have a single BMS so I was thinking of packaging everything together, in 2 rows of 4 cells, also to optimize space. The entire pack will probably be more than 50kg so I'm not planning on carrying it but actually assembling it in place.

I will look for where I got the dampers, if I was doing a 24 volt system I think I would still build my packs the same with four cells and just mount them next to each other and connect them with the Eri Flex buss bar. I can move four cells, eight no way.

 

[Cheap 4-life]

I am using four 160lb die springs.

I could be very wrong, but doesn’t 160lbs max deflection at .63” mean that the spring when fully compressed .63” will apply a max of 160lbs and that then there’s no room left for expansion because the spring is bottomed out? Meaning that you will only get 160lbs if the spring is fully compressed.63”?

 

[S Davis]

I could be very wrong, but doesn’t 160lbs max deflection at .63” mean that the spring when fully compressed .63” will apply a max of 160lbs and that then there’s no room left for expansion because the spring is bottomed out? Meaning that you will only get 160lbs if the spring is fully compressed.63”?

The springs are not fully compressed, only half.