How to build a simple soldering iron

Build a low voltage soldering iron with a copper rod, some nichrome wire and thermal insulator.

Although soldering irons are quite cheap, widely available and come in various shapes and sizes, here's the DIY way. This article will describe some simple to build soldering irons that can provide 15 - 30 W and are powered at low voltage (5 - 12 V, depending on heater wire you use). This means you can power it with any power supply that meets these requirements (a computer PSU will be a good choice). The project is simple: a heating resistor wounded over a copper tip is used to heat it. The main difficulty here is to find a thermoresistant insulator that can be rolled over the copper tip. I used some material found between power transistors and heatsinks.

There are two variants described. The difference between them is made by the method used to attach the copper rod to the handle.

DIY Soldering iron (variant 1)

Take the copper tip (1) (a piece of 7...10 cm of 3...4.5 mm diameter copper rod) and roll the insulator over it on about 4 cm. Attach one end of the heater nichrome wire (about 0.3...0.5 mm diameter) near the sharp end (3) and start winding it over the insulation to make the heater resistor (4). Turns should be close but must not touch each other. It takes a little experiment to get the best wire length (number of turns), so you should power it and see how it behaves. Hold tip from the other end with a pair of pliers and apply some DC voltage. You can safely start with 5V from an ATX computer PSU. It has enough current and in case of shortcircuit it switches off automatically. The tip connects to one end of the nichrome wire. This will also be the ground of the device. The other end of the nichrome wire must go to supply voltage (VCC).

It is very important to use current limited or short circuit protected power supplies. The insulator between nichrome wire and copper tip may break at high temperatures and cause short circuit.

The wire must not get incandescent. If so, try with a lower voltage. A good match is when the wire is slightly visible in the darkness. In no more than a minute, the tip should be able to melt solder. Otherwise, if you touch solder to the nichrome wire and it melts, but it doesn't melt on the tip, it means you used an insulator that is too thick or has thermal insulation properties, which is not good. If the wire resistor doesn't seem to get hot enough, try with a higher voltage.

If you managed to build it, now you must attach this heater to a handle. The first variant involves placing the tip with heater inside a metal pipe after inserting some ceramic spacers (2) at the extremities. You'll have to attach the metal pipe to a washer (7) that will be fixed with some screws (9) and spacers (8) to the handle (10). The spacers are recommended to improve handle thermal insulation so it doesn't get hot during usage.

DIY Soldering iron (variant 2)

The second variant is a bit easier to build. Instead of inserting the tip with heater into a pipe, the opposite end of the tip is fixed onto a metal sheet (6) that is bent into an 'L' shape to ease handle (8) attaching. This metal sheet also serves as a heatsink.

Here is a building detail of washer (7) from variant 1 and the metal sheet piece (6) from variant 2:

Metal pieces detail

The following photo shows an attempt to build the tip with heater. The copper rod diameter is only 2.5 mm. In my tests, that worked good at 6...7 volts AC, straight from a transformer.

Soldering iron tip with nichrome wire heater

The opposite end of the tip can be thermally attached to a temperature sensor (possibly a thermocouple) in order to build a temperature controlled soldering station. More about that in a future post.