Fusing 18650 cells without soldering

Every build I've ever seen with fused cells has been done via soldering small gauge wire from the positive cap to a buss bar. Is there a viable way to fuse individual cells without having to solder?

Tesla used ultrasonic friction-welding. The wire is rubbed back and forth an extremely tiny distance, but its done thousands of times a second. Of course they used an expensive proprietary purpose-designed machine, but....there might be some way for someone to re-purpose some type of cheap ultrasonic gadget to do something similar?

A more realistic method might be to spot-weld the wire onto the can, maybe lay the wire across the can tip, and hit it in two spots?

edit: If you want to try that, I'd recommend using the plastic cell holders, because when cells are hot-glued together with all the connections being nickel strips (not recommended BTW), then the nickel strips become part of the support structure, holding all the cells together, and sometimes the spot-welds crack due to vibration. If the plastic holders bear all the support loads for dropping and vibrations, that takes the load off of the nickel strips.

Personally, I think that is a major benefit of the Tesla wire, with heat expansion, cold contraction, hitting road-bumps, and vibration...the short length of Tesla fuse-wire that connects each cell to the bus can flex a little...millions of times ...

Soldered fuse-wire, from jdevo2004
https://endless-sphere.com/forums/viewtopic.php?f=14&t=65718


Friction-welded fuse-wire from Tesla, purchased from a car wreck (I'm fairly sure that bus is thick copper that is plated)
https://endless-sphere.com/forums/viewtopic.php?f=14&t=79950


Fuses cut into the positive side of laser-cut bus plates, intended to be spot-welded [two fuses per each cell positive end]
http://insideevs.com/18650-lithium-ion-battery-cell-fuse-test-video/


a similar style as above [left half, no fuses, right side: four tiny fuses on each positive end]
https://endless-sphere.com/forums/viewtopic.php?f=14&t=55870

spinningmagnets said:

A more realistic method might be to spot-weld the wire onto the can, maybe lay the wire across the can tip, and hit it in two spots?

Click to expand...

I hadn't even considered something that simple. I just assumed the wire would get obliterated by the welder, even at a 50ms pulse. I'll give it a try and see how it goes.

What type of wire ?

999zip999 said:

What type of wire ?

Click to expand...

I've seen several types used, but the one I'm going to try is 28 gauge galvanized steel craft wire. I saw a YT video of a guy who tested it and it severed at 10-12 amps every time, but was fine under normal loads.

In some power tool packs I've seen them just use thinner nickel material for a fuse, which is welded directly to the cell.. You could also use a PTC fuse, but these have kind of high resistance. I've used these in the past when rebuilding a radio battery pack.

Damien Rene is now using a very thin pure nickel strip as the parallel connection between all the cells in that P-module. He has a video out where he purposefully shorts a particular cell, and the strip instantly glows for a second and then pops open. You could try the same thing by using a dremel to "narrow" a spot-welded section of the nickel-strip between each cell to a prescribed width.

In this method, the thin and narrow nickel-strip parallel connections only keep the P-cells charged and balanced, so the paralleled cell-to-cell current is tiny, even when charging (3A? 5A? max). His series connections between P-modules carry the full current of the pack, so they are beefy (30A, etc). If you prefer to use resistor wire that is a precise diameter and quality (like Tesla) you could solder a short section of wire between each P-cell, with an 8mm X 8mm square of 0.20mm nickel strip spot-welded over each cell end (assuming 18650's are used). Its more time and trouble (maybe?) but the wires' fuse-blow burn-time and current-volume would be consistent that way.

Damien states the parallel strips are nickel-plated steel, and the cross-section is 1.6mm X 0.1mm

https://www.youtube.com/watch?v=c7PGLFgkdf4

[youtube]c7PGLFgkdf4[/youtube]

I used just Nickel plated steel tab. Not fully solderles solution but still.
Bursts ~12A


Whole pack: http://i.imgur.com/ulea1jX.jpg

What is the thickness and width of the 12A nickel-plated steel strips?

edit: ebay: tinned copper fuse wire

0.1mm thickness, 1.2-1.5 mm wide.
Copper bar is 0.2x7mm. Pack is 30A rated.

http://electricguru.in/page_view.php?id=29

It looks like, (according to this chart) that tinned copper fuse wire at 30-ga is 0.0125-inch diameter, 8A continuous, and blows at 13A...does that sound right?

8A / 13A

Next higher on ebay is 28-ga at

12A / 18A...

Then 26-ga is

14A / 28A...

I tried some Copper wire from the stuff used for the phone lines in homes. There's a number of single strand Copper wires in there that measure 0.018 inch in diameter (26AWG). I was able to repeatedly weld those on 18650 cells using my JP Welder at 12MS. One probe firmly on the wire and the other on the can. My welder is modified a little and is using a 60Ah 3S battery made of tool pack 18650 cells.

Very good idea for non spot-welders as me!

Would it be possible to use a bunch of similar enamel wire as phase, just through the axle, in the same shrink wrap? Maybe even sensor wires wrapped on grounded tin foil...

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