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When I first learned to solder, I did so using a cheap iron, not realizing how atrocious such things are. It wasn't until several years later that I purchased a temperature-controlled soldering station. These use thermal feedback to keep the tip at a set temperature, and I soon learned that good solder joints are easy to make when you have good equipment. I've had that very same Weller WTCPN soldering station for almost four decades now, having forsaken non-temperature-controlled irons completely. This stance on soldering irons did, however, put me in a quandary recently when I started to explore the options for cordless soldering irons. Cordless irons are essential for those times when you need to solder something and there's no power outlet available. Yet I could not find a cordless iron for sale that had temperature control. So I figured I'd build myself one. My fondness for my faithful Weller soldering station dictated the first design criterion—it had to provide the same quality temperature control—and also suggested a strategy to attain that goal: Weller's Magnastat system. Let me explain. Weller long ago devised a clever way to provide temperature feedback and control without using any electronics. It's based on the physics of ferromagnetic materials, which lose their magnetism when heated above a certain temperature, known as the Curie point. Weller's Magnastat system uses three magnetic components near the tip: two inside a normally open switch, the other built into the tip itself. The components inside the switch (one movable) have a very high Curie point, whereas the one in the tip has a Curie point equal to the desired soldering temperature.