A No Solder/Weld 18650 Build

S

snath

100 W
Joined
Jan 4, 2010
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126
Location
Colorado, USA
I wanted a pack that would enable me to remove individual cells. To accomplish this, I built a case of 3/16" PVC sheet for the covers, 1/4" sheet for the sides, and 1/4" dia rod. for a series of spacers for the interior. I used a height gage to lay out a grid for (ultimately) 122 screws that position the cells and hold the case together. I made a die to create a series of dimples on copper strip for bus bars. And, I used a "compression blanket" of high density urethane foam to ensure constant pressure on the bus bar/cell/ bus bar sandwich.

A few pictures to show how this all works:
Bus Bars.jpg
Fly Press.jpg
Die Parts.jpg
Punching Holes.jpg
Spacers Installed.jpgSpacers.jpgBus Bars Installed.jpgFilling it up.jpgView attachment 2View attachment 1
 
Wow, nice craftsmanship to solve a problem, that really wasn't one to begin with.

Can you measure the resistance of the connections you made?
How does it fare with vibrations, I would imagine that it requires quite a bit of pressure to keep the resistance of the connections low enough.
 
Didn't set out to solve a problem; mostly, was just using materials and technology at hand (i.e. no spot welder). I do have several high wattage soldering irons, but I just don't like the idea of heating up the ends of the cells. I do, however, like the idea of being able to monitor/replace individual cells if necessary.
As far as vibration goes, the cells are locked into place from side to side by the spacer bars and, of course, from end to end by the covers and compression blanket.
I've been curious about resistance myself. I'll set up a dummy connection and see what I can determine. I was trying to, sort of, duplicate the forces exerted by the typical "spring loaded" battery holder by using the urethane blanket (1/16" compressed to 1/32").
 
I'm working on a similar method myself, although my method is much simpler than yours. One variable you might want to consider is the material that you're using as your 'compression blanket'. Most types of foam/rubber have a 'memory', and after being compressed for a certain amount of time, will take that shape, and the compression will loosen, especially if you have a 'fixed' compression point. This is something that I haven't yet found a solution to, after looking at many different types of materials.
Also, some cell manufacturers warn against compression mounting the cells, not that this would stop me from doing it if I felt I could get away with it, but they do extensive testing on these cells, and I certainly don't ignore their warnings.
 
I selected this material based on the supplier's comments: "Also known as Poron urethane, this high-performance foam has the quickest recovery from compression even after extended use. It is ideal for sealing applications when compressed".

In my trials of different type materials, this one seemed to work best. Natural rubber was good too but didn't have as much compression strength as I desired.
 
i did look into this. my plan was to use a stainless steel bolt at the end which handles the current, BUT the threads extend beyond the case and a spring goes on .after a nut/washer.
a piece of wood, the pack end cap, forms the pressure sandwich, loading the springs.
cancelled all this because i live at the beach, and high humidity and salt air corrode everything. But, prevent air contacting the cells and it could work a long time. Use dielectric grease at every touch connection, and coat the copper strips with solder. copper corrodes way too fast uncoated.
Nice job!
 
very cool !... 8)

I'm wondering if over time, the soft copper will retain the dimple depth or if they will recede and lower pressure on the cells.. a backing plate of plastic to support the copper and keep the dimple profile, then the memory foam on top of that would be an idea..
 
Great ! What cell are you using and what amp. draw will you be using ? Copper does form a flim on it over time and with weather and can be a problem. I'm not to worried about losing compession on the cells. Keep us updated.
 
Brilliant work! It's possible some issues may arise over time, but since I am familiar with your past work, I am confident that you will figure out how to fix anything that makes itself known. When you say "compression blanket", does that add any springiness to the connections to the two ends? (heat expansion, cold contraction, vibration, etc)
 
Looks a lot better to me than some no weld schemes we have seen here.

But I also think the foam will not maintain the pressure you want for years.

I wonder, what about some kind of inflatable device for applying the pressure. Then you can not only adjust the pressure, but be sure it stays the same too. Gotta be durable of course, better than stuff a bike tube in there.
 
Someone above asked about connections resistance. I took a AA (no extra 18650s :oops:), chucked it up in the lathe and pressed a dimple and piece of foam against the end of the cell with the end of a boring bar until it made contact and then advanced it 1/32" (to emulate the compression in the pack). I checked resistance of the contact/connection and it read 0 ohms with my two decimal place ohm meter.

Ypedal, I believe, asked about the dimples crushing so I rigged up the test shown below on my shop press:

With the following results:
40 psi no change
60 psi .002 reduction in height
75 psi .010 reduction in height
85 psi .012 reduction in height
250 psi .025 reduction in height

Here's a picture of the results:
Crush Test Results.jpg

The copper stock is .010 thick

Dogman, I've quite a bit of faith in the foam but we'll just have to wait and see. I did subject it to several weeks of compression and it held up well.

Spinning Magnets, the case/spacer/blanket setup is designed to compress 1/32" inch when all the screws are tightened. That should accommodate any expansion/contraction.

Some one asked what type cells I'm using. They are Panasonic NCR18650PD.
 

Attachments

  • Crush Test.jpg
    Crush Test.jpg
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Open cell foam (like a common kitchen sponge) will compress over time and lose its elasticity, but closed-cell foam (like the insoles of the Doc Martin boots) are reported to retain their sponginess for many years.
 
Dogman, inflatable devices would not work, since inflation pressure will change with temperature. spinningmagnets, I've tested some closed cell foams, and they will retain an indent after pressure is applied for a certain amount of time. It's very hard to find any kind of foam that will not have some kind of memory. Natural rubber is a possibility but it's fairly heavy, so that is one mark against it, and it also does not have a very large range of rebound ability like foam does. I'd probably want at least 1/4 inch thick material on each side of the pack.

This is a very well made pack snath, so kudos to you for that, however, it's not very easily replicated due to the fact that you used some machinery that most of us won't have. It may not have been your purpose to make it easily duplicated, I know, but KISS is always a plus.
 
snath said:
...

With the following results:
40 psi no change
60 psi .002 reduction in height
75 psi .010 reduction in height
85 psi .012 reduction in height
250 psi .025 reduction in height
Click to expand...

Love the data.
 
Natural Path, don't let the flypress, height gauges and all that stuff scare you off.
If you have a drill press, a digital caliper, and an Exacto miter box and saw, you can make this. Heck, I cut my sides and end plates on my circular saw turned upside down in the vice (using a straight edge clamped to the shoe set with my calipers). You might have to get creative in drilling the ends of the spacer bars (maybe a little drilled fixture made out of a piece of wood to stand the bars up on end under the drill press).
The point is, creativity is what makes this stuff so much fun. I didn't have a spot welder but I made a battery that's equal to, or, in some respects, better. :D
 
I totally hear ya snath. I spent 35 years designing and building power electronics as a job, and many times I had to 'fly by the seat of my pants' so to speak. To this day, even though I only have hand tools now(no electric tools) and I live in an apartment, I still find ways to build the things that I want. Like you say, it does take a bit of creativity, and it is fun. I've always enjoyed building things, it's just that now I do it in a much simpler way, mostly because I don't have a choice :wink:
 
Hey, if the foam works it works.

I was just throwing out something to try if you find the foam becomes a problem. Air bags lift huge barges, so I know you can get the pressure with air. As pointed out, air would change density with a big enough temp change, just like your car tires do. You would have to add checking the psi of the air bag to the bike maintenance list to keep it dialed into the psi you wanted. It just sounded simpler than other ways to do it other than the foam. You don't want heavy metal springs or something too complicated.

Could be, replacing the foam annually or whatever will be easier still. Even if you have to change the foam fairly often, it's an easy thing, and not so costly.
 
Advantages to springs:
1. will likely last forever, look at how long valve springs last on cars!
2. available in any tension-custom springs available
3. can be long enough to maintain tension on pack even on severe bumps
4. adjust instantly, foam can take seconds to rebound as it ages.
Just don't try to conduct electricity thru them!
 
ebay member "supowerbattery111" has been getting noticed as a maker of re-building packs for cordless tools that have used-up packs. He will do spot-welding of the parallel groups, and he has a wide selection of cells available, high-current, high-capacity, low-price, etc

A 6P group of 2000-mAh 20R high current cells would mean a pack of 12S would have a capacity of 12-Ah, and cell_man reports they easily deliver 40A without stress. A 6P group of high-capacity Panasonic 29E cells have a lower C-rate per cell (than the 20R), but because of the higher capacity they still deliver high amps at 6P=17-Ah

Here's their new website: http://www.batterysupports.com/liion-battery-c-4_5.html?page=2&sort=20a

If such a case as this had the ability to accept strip-welded parallel groups that just dropped in (as opposed to loose individual cells being the only option) then I think the bus connections would be less of a concern, since several springs touching the 5-cell group would mean there is always at least one or two with a secure connection? I'm not saying that a clamshell case like this should only accept single cells, or groups of strip-welded cells...I just think that it should be reasonably easy to make a minor adjustment so that a case could be made and/or sold, and the builder/buyer has the choice. Here is a pic of what I mean:

file.php
 
If the foam has low 'set' properties (and I expect it does), this will be an extremely rugged and robust low-interconnect resistance pack.

The copper to nickel plating surface could use a little dab of an appropriate dielectric grease in the stack to minimizing surface oxide formations and galvanic effects that can be greatly accelerated by moisture that the grease can keep displaced.

Very nice job!! Awesome cell choice too, this is one of the best designed packs I've ever seen outside EV industry.
 
Nice work! Throw a temp probe on each string. If any cell or cell contact develops a problem the busbar temp will show it (difference). I like the foam as it solves two problems in one (compression and insulation). Poron is open cell but does have excellent compression set resistance. For this app it is perfect. If this was a twenty-year pack I would look a silicone foam. When poron is not fully compressed it absorbs moisture and over time turns into dust. Your pack looks pretty well sealed though. Reminds me of a NTS Works pack.
 
liveforphysics said:
If the foam has low 'set' properties (and I expect it does), this will be an extremely rugged and robust low-interconnect resistance pack.

The copper to nickel plating surface could use a little dab of an appropriate dielectric grease in the stack to minimizing surface oxide formations and galvanic effects that can be greatly accelerated by moisture that the grease can keep displaced.

Very nice job!! Awesome cell choice too, this is one of the best designed packs I've ever seen outside EV industry.
Click to expand...

WOW!!

Thank you for the nice words and the advice to use the dielectric grease.
 
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