Could I make cylindrical-cell pack with rubber bands?

auraslip

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Take a strip of copper or whatever metal. Heat shrink it. Dimple it according to how you want you pack set up. Cut the heat shrink away from your dimples.

Place 18650 cells between the strips and use rubber bands to secure the cells. The strips hold the parallel cell groups in shape and form an easy conductor to put the groups in series.

You don't even have to test the cells before you put them in a pack. If a parallel group is sagging, it should only take a few minutes to disassemble the pack and find the bad cell.

Seems a lot easier to build and maintain then welding (unless you already know how to weld battery packs lol)

edit: title spelling corrected by spinningmagnets
 

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Rubber bands rot fast, and stretch permanently after some time especially past a certain tension.

You'd be much better off using something you can adust the tension of, like pallet straps, etc., if you want to use something unconventional.

There are a few threads around on non-weld options, but take some reading around to find them. One of the more detailed (IIRC) is by Leamcorp.
 
I have seen (I am pretty sure it was somewhere here but I haven't been able to find it again) where someone was making parallel groups of 18650's using braided copper and pieces of bicycle inner tube. Often wondered how well it held up. It was always my gut feeling that you get a couple years out of cutting fairly wide strips from a quality rubber inner tube. Wish I had the money to be a guinea pig.
 
Speaking of 18650s. I've been out of the loop here for quite some time. Working as a school bus driver full time and renovating my home doesn't leave time for much. What is current price per cell for good quality 18650s? I'm pricing out a new pack.
 
auraslip said:
define fast

10 years is about the max i would need, so lets say 15 years. I have bike tubes that are 15 years and still have elasticity in them.
IF you're making the rubber bands out of wide enough strips of thick enough bike tubes, then they'd probably be ok for a while, but how long I don't know. You'd basically have to do it and see what happens.

I used to use tubes and sections of tubes to secure things on my bikes, but here in AZ the sun rots them pretty quick (months). If they are not exposed to direct sun then they last a couple years or more, but generally most of the tubes I used for the purpose were already several years old (at least) before I got tired enough of fixing patches on them that I used them for the tiedowns.

The problems I saw were usually slow tearing along the "seams" where ridges from mold lines were on the original tubes, or from where I had cut them (I usually used scissors--perhaps if I had used a single long cut from a very sharp razor blade it would have been better than scissors, leaving less weak points).

The narrower a section I used, the shorter they lasted. Less than an inch and sometimes they'd actually tear thru while I was putting them on, depending on how far I had to stretch them and what surface I was moving them over (and probably their age).



If you're using regular rubber bands, like from an office supply store, or the even better ones you get off bunches of celery, brocolli, onions, etc at the grocery store, well, those probably won't last months, and I wouldn't begin to expect years from them. For me, those things rot out within weeks to months depending on how thin they are and what I put them on, and what quality they were to start with.

I usually use them for holding bunches of unused cable ties together, or bundling up cords, wallwarts, etc., for storage; most of the time when I come back to use any of whatever they're on, i have to replace the ones on the other items that I'm not using yet. :/



I don't know how long bike tubes would last in your application, but certainly longer than regular rubber bands.


Personally, I'd still use pallet straps instead, just because I can adjust their tension and they tend to keep it. They can be had for free whenever shipments on pallets are received at various places, and many of them are reusable if they use the plastic or metal "spring" clips instead of being metal straps clamped together or plastic straps melted together. They just get shorter each time you cut the strap, but the springs are removable and can be put on other straps that had once been melted together instead, if you need longer ones.

YOu can alos buy the stuff in rolls, with the springs, though I've never looked into it so I don't know cost.


I use pallet straps to secure stuff to the bike fairly often, to move cargo around. I also have used them to hold heavy ammocan packs to the bike, and the trike, with no slippage and no mvoing around, even on bumpy roads, once I tension them enough (which is hard to do by hand for me, but someone stronger could do it easily enough, and there are also tools for the job or you could jury-rig one).
 
Making a rubber band battery or a press together battery is one thing, but what demands will you put on it. 300 watt or a 1,000 watt. So what you going to use it for ?
 
As crazy as the idea sounds Zero Motorcycles did just this commercially on their NiMh battery packs. Thick copper braid was used as the bus, held with slices of rubber tube and all secured with heat shrink. There are a few photos here: https://evmc2.wordpress.com/2013/12/04/inside-the-2010-zero-x-battery-pack-molicel/
 
Hmm...well, those arent' NiMH AFAICS, but Molicel LiMn2O4 types (you generally wouldnt' want to parallel NiMH).

I expect the shrinkwrap on the cell groups is doing at least some of the compression on those cells to push them together. None of the images shows clearly what's inside the shrinkwrap, though.

I see what is probably the busbar under it (approximately horizontal in the images showing the cell-ends part of the pack), and what might be the elastomer bands vertically around each series cell stack tube and the busbar.

In one pic showing the side of the shrinkwrap that's open, I can see a thin black "line" that is probably the elastomer band.



As long as the elastomer band is also held by the shrinkwrap, I expect there's no real issue with how well the elastomer holds up over time, as long as it does not shrink in thickness (because that would reduce pressure on the busbar/cell connection).

Without the shrinkwrap (or something) tightly compacting the whole assembly, I expect that vibration and bumps would stretch the elastomer more than with it. No way to know till it's tested, though. Several layers of elastomer bands in different directions would probably accomplish the same thing, though.


It's certainly worth a try to build it and see what happens, if you already have all the stuff to do it. :)
 
Not the one I was looking for but definitely on topic

Building a 18650 cell case without soldering

http://endless-sphere.com/forums/viewtopic.php?t=51271
 
And this post:
http://endless-sphere.com/forums/viewtopic.php?t=51271#p758973
within that thread has the internal pics of the Zero pack showing the "busbar" and elastomer bands. :)

file.php
 
Hi Amberwolf,

Good point about the battery chemistry, my memory failed me on that one. The pictures I linked weren't the best but I couldn't remember where I'd seen the more detailed ones like you just posted.

It still seems slightly mad to me, but I guess they tested it and found (perhaps to their surprise) that the technique worked well.
 
Seems like it could work well in theory, but the problem will be the quality of the bands.

So what about other sources of elastomer, such as the rubber tubing used in wrist rocket sling shots, flat braided bungee cord, smaller diameter bungee, etc. Then you will have some kind of knot taking up space, but it could be worth some experimenting.
 
IMO (new) inner tune would be close to ideal. High-quality synthetic rubber with excellent long-term resistance to degradation or taking a set (permanent deformation). It's also cheap, and widely available in a range of sizes.
 
Have you considered using nylon brackets?


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auraslip said:
I wonder if I can email zero and ask them what bicycle tubes they use. They look cut too cleanly to be simply cut up tubes. Maybe special order part made just for them?
Maybe he used something like a paper cutter to cut it, it'd make perfect edges !

cortador-de-papel-dellocut-plus---dello_1752102_92595.jpg
 
That picture is the exact direction I was going with my thought experiments on my 18650 build.. and separate note... but damn, that guys thumbmnail is jacked up..
 
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