How much compression can an 18650 cell take

[Wrecker Magoo]

Title says it all..

If you were building a compression battery housing and were effectively clamping the cells in there, how much force could they take?

I don't need to know exactly but a little will damage them?? or you could start to actually make them a couple mm shorter and they'd be ok??

will they squeeze in much? or will they explode goo out their sides if you compress them just a little too much??

just curious

 

[999zip999]

? A round compressed cell needs compression ? What ? ? Buy them spot welded in series. A spring ?

 

[Hillhater]

With a handle like yours, I'm sure you will be able to tell us the answer very quickly. :lol:
No one would recommend that you physically deform the cell at all if you expect it to perform normally.
how much force can a cell withstand without deformation is a much more relavent question :wink:
PS.... It will vary depending on the cell type / make, if you load it on the "button", or if it is a flat top cell. ?

 

[999zip999]

Compress what termanion, pos. - neg. Or something else.

 

[Ypedal]

I would this this would be very cell specific, the positive end is usually softer and would deform first with excess force, you would need to build a jig/device to apply measurable pressure to your cell of choice and test it to destruction, then dial it back enough to maintain proper electrical contact without causing deformation .

 

[eas]

I would have thought that cell manufacturers would publish some mechanical engineering specs on their cells, but in a little digging around, I haven't been able to find any.

 

[Wrecker Magoo]

awesome.. thanks for all the replies.

looks like too many variables and HillHater was right the more relevant question would be
how much force can a cell withstand without deformation??

I guess I will just have to find out the way I know best.

Destroying $#!+ :lol:

What does everyone think will be the type of case we will end up using in the future?
compression
magnet
or something else.

I love the magnet idea, it just didn't look like it was going to work out.. but I see xspeed seems to be getting somewhere with that now too..
exciting times

 

[Ypedal]

Magnets are heavy = Fail

 

[\/ampa]

Another question to consider is how much vibration they can withstand while compressed?

 

[e-beach]

My answer would be to apply no more pressure then the manufacture of a pre-made pack uses, which is extremely little, or none at all.

As an example, when I open up computer battery packs the cells are not compressed at all. The tabs are spot welded to the cells keeping them together and the cells are cradled in some sort of plastic holder with a thick rubber-cement like glue to keep them from moving around. Sometimes they have a double stick foam in there as well. I don't see any cell compression at all.

If you want to compress something, build your battery pack with some sort of foam around the cells and compress the foam.

 

[\/ampa]

My answer would be to apply no more pressure then the manufacture of a pre-made pack uses, which is extremely little, or none at all.

As an example, when I open up computer battery packs the cells are not compressed at all. The tabs are spot welded to the cells keeping them together and the cells are cradled in some sort of plastic holder with a thick rubber-cement like glue to keep them from moving around. Sometimes they have a double stick foam in there as well. I don't see any cell compression at all.

If you want to compress something, build your battery pack with some sort of foam around the cells and compress the foam.

The foam only makes the compression force even out over the full contact area but the compression force is still the same on the cells with or without.

 

[Wrecker Magoo]

Magnets are heavy = Fail

Hmmm interesting. I hadn't thought of that.

I guess it may depend on perspective.. If I added 2 pounds to a cromotor build that already weighed 88 pounds, I might not care..
actually even just writing that seems weird.. 88 -> 90 pounds just by adding magnets does kinda seem like alot. I mean you didn't even really add anything to your bike?.?

Yeah i see your point

 

[e-beach]

The foam only makes the compression force even out over the full contact area but the compression force is still the same on the cells with or without.

If the compression is "evening out the force" applied, then it is less force per square centimeter the more the force spreads out...... which equals less pressure per contacted area. The widest and most even compression possible is probably the best for the use of foam.
If done properly the "full contact area" of the cells receives almost no compression while remaining firm enough to keep from rattling around.

But...As stated, the factory made batteries I have disassemble have almost no pressure on the cells. They do sometimes use foam to keep the cells from rattling around, along with a rubber cement like substance, and the cells are tab welded which really is the thing that keeps the cells together.

 

[marty]

http://endless-sphere.com/forums/viewtopic.php?f=14&t=51271&p=758973&hilit=zero+inner+tube+battery#p758973

2009-2010-2011 ZERO MOTORCYCLES BATTERY ASSEMBLY METHOD:

One great and ingenious method that already was in use by zero motorcycle is to use copper braided strap with rubber ring to hold them on the top of neg and po of the cells! Then you can add a heatshrink to add pressure and avoid rubber to move.

Easy, cheap and easy to repair your pack.

for the rubber they used some bicycle tire rubber tube sliced to form some ring ! the advantage is that these rubber do not dry very fast and they are not too affected by moisture or temperature so they sustain pressure between the copper braided strap and cell tab very well!

Here is couples of pictures i took when i had to do some maintnance on a ZERO battery for a friend of mine. This battery was made to take 300A burst and i s a12P config meaning about 25A per cell tab and only holded by a rubber tensil pressure!
Please note that these are 26700 cells and each cylinder is in fact 2s1p ( 7.4V):

Doc

 

[Wrecker Magoo]

Wow. great reply Marty.

I'll have to read up on that some more.

Thanks