Solder-blobbing 14500 and 18650 cells with Bi50Sn18Pb32 (Rose's Metal)

Gaaaah! Get a hotter one. It’s a one-time investment, so make it good. I got an AEIOU variable-temp iron, and crank it up to maximum when doing that kind of thing.

Hit it fast, hit it hard, get in and get out. You’ll never have to linger for 20min cooking everything else in creation just to make one little solder-blob.

I had a 30W iron long ago, tried to solder with Sn63Pb37 onto Ni-MH AA cells unsuccessfully: cold joints and damaged cells.

Also, while Lightbringer's X + Y tip is fair please note that, in this case, heating up the cell takes away most of the heat and, in any case, you should at least pre-moisten the iron's tip in some amount of solder in order to maximize contact surface and thus heat transfer.

Cheers :-)

The big hanging solder-blob is moisture enough. :smiley:

Thanks for the answers, to both :slight_smile: I guess I will try first in some old batteries (from a powerbank) and see how the solder iron behaves! I didn’t want to buy another one, budget is becoming short for some things on the hobby :smiley:

I’ll experiment! Thanks again :slight_smile:

Well, just tried it and it was not the most perfect surgery, but so far the cell is working :smiley:
Further work will be needed, namely to combine the flux and the soldering time over the battery! I’ll learn!
Again, thanks to the answers!

Huh, it looks like in a local shop it costs about $7 for 100g pack.

I also used different brass buttons to add to the top

I found those on Aliexpress which might a nice option for soldering

Definately cheaper than the brass buttons from Fasttech or Kaidomain

Even gold plated ones

After reading this thread i bought some 1 lb ingots (~$15) from rotometals. i was hoping i might form it into wire such as we use for solder, but it is much too brittle and not suitable for wire. It melts at 208F and does not contract or expand between liquid and solid phases.

It melts and drips off a soldering iron quite easily, and it is easy and fun to make the “blobs”. i used a hacksaw to cut an ingot in half to give to a friend, but in hindsight it would have been easier to ‘cut’ with a hot iron. He is using a few ounces to heat up and pour into his antique rifle chambers, then press it back out with a wooden dowel. From this he can measure the diameter and wear in the bore and see the erosion of the rifling edges to determine if the barrel is okay or not.

If i hold the iron high and let it fall the drops splatter into thinner and flatter pieces than the “blobs”. These might be easy to mail by taping them to an index card, then put it in an envelope with regular postage.

That’s how you get cold joints.

x and y have to be at least as hot as the melting point of the solder to fuse both materials together.

Otherwise the solder will just flow into the surface imperfections which is more like glueing the solder to the cell.
Mechanical force can tear the solder off and the electric resistance is much higher.

And how is that technique defective?

A wet/molten solder-blob hanging off the iron is already at temp, and you’re not relying on pressing a solid to a solid with small contact area, but letting the liquid flow all over the surface and provide lots more contact area.

The other surface (eg, button-top) heats up more quickly, and unless it gets up to temperature, the solder simply won’t wet to it.

So if you have a ball of solder just stuck to it, of course it’ll be a lousy connection.

But what I’m specifically referring to is having a HOT iron with equally HOT blob of solder, quickly heating up the other surface, wetting to it, and then finally cooling down.

What Y is, is the heat necessary to initially heat up the solid solder to its melting point, actually melt the solder (LHF) and further bring it up to temp, enough to wet and stick to the button-top.

It’s the exact opposite of someone saying, “hot water freezes faster”. No, hot water has to drop in temp, to the FP of water, and then freeze. Ice-cold water already has that head-start.

You don’t press a solid against a solid the tip is always a bit wet.
The tip is used to heat up the object not the solder. After heating up the object you melt the solder directly on the object.
That’s the only way to guarantee that the object is hot enough.
To speed that process up you can bring the solder wire and tip together as soon as the solder starts to melt and melt on the object and tip simultaneously. This will than melt bigger amounts faster.

Solder will wet to an object that is not hot enough, otherwise cold joints due to cold irons weren’t possible but that’s a well observed phenomenon.

Also your flux is burning up while you are forming that blob on the iron.

I use a dremel with a “polishing” bit to rough up the surface, like this one:
It makes for perfect adhesion of the solder and it takes way less time to heat the batteries. The solder literally just flows right into the roughed up surface made by the tool… takes more prep but ensures a good bond too!

Polishing the surface uncovers unoxidized metal Philaphlous, allowing the solder and in this case the steel to fuse together.

As you can see in my video I use an aggressive flux which just straight does the job:

Unfortunately, I believe this stuff is discontinued, though of course there are other flux manufacturers.

Cheers fellows

Yeah, I just scuff the surface with 1000grit. Never ever ever had any problems soldering to it. No cold joints, no problems whatsoever.

I use this blue organic flux (was given a half-pint from a gallon-jug where I worked), and just wetting the surface does the job. Scuff, wet, apply molten blob. Flux sizzles away while the blob form-fits to the surface, once it wets and spreads out, keep holding it a few more seconds, then pull away the iron. It cools and is a perfectly-stuck blob.

Anyone tried this:

I confirmed it has a melting point of about 150 C — so much lower than typical solder.

The ad specifies a 144 - 163 °C solidus - liquidus “mushy” state range. Non eutectic alloy.

Never heard of it. In that temperature range I would probably try Sn42Bi58, which is also eutectic.

P.S.: Some cheap links for steel flux here and there.

On the one with 2 bottles, do both have the same thing in them (with one just being larger)? The listing is not clear at all to me.

Yeah it's also not very clear to me bcm00re. Made another search and found this among others: