Hot enough to melt metal, but cool enough to rub it on your genitals.
How does it do that?
I like it hot when I rub it on my genitals.
It’s just a low-mass soldering tip. The electrical connection is actually completed by pressing the tip to the work, and the low-mass tip heats up and cools down very rapidly–compare the rate at which aluminum foil cools off after being taken out of a 400-degree oven, compared to a much heavier aluminum cake pan. It’s fine for small jobs, like electronics repairs but for larger jobs, it’s not so good.
This is quite correct; the aluminium foil was cool to touch within seconds, but the cake pan burned my genitals quite badly.
I just got one of these at Costco (damn Costco and their evil, tempting, blister packages!), and I noticed that the TV advertising is very careful not to disclose the mechanism by which it operates - to the point that one wonders if they’re hiding something.
So, as mentioned above: it’s a mini ‘arc welder’, on a very small scale. The tip is a little tiny fork-like thing, and pressing it to the solder causes the current from the 4 x AA batteries to pass through the solder, melting it. The tip only gets hot via heat “back-transferred” from the solder, so as advertised, it almost immediately gets cool enough to touch when you remove it from the work.
That said, I tried it on a couple of little projects and so far, not impressed - the solder kept sticking to the tip, rather than to the work, and I couldn’t get it to behave and join the wires. I don’t think it’s my soldering technique because I can do this fine with a conventional soldering iron.
Note to Self: Don’t ever have dinner at Mangetout’s place. Especially avoid any dish which requires any sort of temperature monitoring.
No, it’s OK to eat at his house. Just, if he bakes a cake? Don’t ask to lick the beaters.
Well as a Cold Heat soldering [del]sucker[/del] owner, I’d say that the factual answer to “How does the Cold Head soldering iron work?” is “Not very well”.
I have one. Bought it at Costco because it was cheap, I was curious and it included a nifty-looking wire stripper*.
It’s a resistance soldering tool. Instead of using electricity to heat up an element that melts the solder, it uses the two electrodes that make up the tip to send a low voltage but high amperage current through the thing(s) being soldered. The natural resistance of the things being soldered is what heats them up.
That’s the theory, anyway. In practice, you wind up poking the thing’s giant tip around trying to get good contact, and when you finally do get good contact you discover that the batteries are dead. Or it arcs and suddenly you have a nice carbon film on the metal and it won’t make a connection anymore.
Since it’s directly electrifying the things being soldered, you can’t use it on anything that might have an IC or other electrically sensitive components. Also, it doesn’t work on anything particuarly large, but the tip is so huge that it’s not very well suited for small things either.
Really, it’s a huge pain in the ass. Don’t waste your money like I did. The ghost of my lost $14 will haunt me forever.
Note: Resistance soldering does have its place, but the tools to do it properly are much more expensive than this toy.
*With its cheap sheet metal and brittle plastic construction, it broke after three uses.
OK, this article says it works fine, as advertised - not just the cooling down thing, but that it solders well too.
I, and a couple of other posters have found that it works very poorly.
What’s the deal?
OK, I think the customer reviews on Amazon tell you all you need to know.
As it should have. God punishes sexual deviance. Never use an implement. Why do you think you were Intelligently Designed with hands? 
I found this bit of one to be amusing:
Heh.
I also have one, and I’m regretting spending the money. The only place it might be useful is very light soldering repair jobs on easily-accessible electronics and jewelry. Any serious project will be far easier with a plug-in soldering iron.
The tip of the cold-heat is as others have described; two tiny prongs that heat up when a conductor (i.e. solder) touches both. This means you can forget about any project where you can’t hold the cold-heat iron very steady and square; any shake or angle will break the contact and accomplish nothing.
I’ve actually had pretty good luck with it, but only in very narrow circumstances. Soldering thin wires together works well, but much else is not good. Luckily most of the soldering I need to do in ackward places, it works well for.
A horrible idea on so many levels. In order to make a good solder joint, the two items being joined should be heated to a solder-melting temperature, else you won’t get good wetting of the joint and it may fail (the classic “dry joint”). I like a nice hot iron (400 - 450 degrees C), a bit that’s not too narrow, and fine gauge solder. It shouldn’t take more than a second to make a good solder joint anyway, so it’s easy enough to keep the heat fairly localised.
Time to share my embarrasing solder story.
This summer I was working at a summer camp, in charge of maintenance. I had just spent almost $4K on new on-demand water heaters to replace the old ones which were rusted out POSs.
The first one I installed, I spent about 12 hours trying to solder the new copper inlet/outlet lines.
No. Matter. What. each time I soldered it all together and went to pressure-test it, all the joints would leak. Badly.
About 4am, I came to the realization that for some bizzare reason, the hardware store had bundled the plumbing solder (which I had bought) with some tinning solder (which I had been using).
20 minutes and much self-criticism later, the project was complete.
I installed one of these in my girlfriend’s house. Since we had to reroute most of the plumbing and the crawlspace was only about three feet high, I used PEX piping and compression joints, not wanting to do (nor having the room for) a lot of welding.
Later on, I removed her old kitchen sink and tried capping the lines. Surprise surprise, metal compression fittings don’t work well on copper pipes. Rather sheepishly, I tried again the following day (the store had closed) with plastic fittings. No problem.