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Power Control for a Soldering Iron

Its a simple matter to use a light dimmer to control the power delivered to a soldering iron. The objective of the control is to prevent the iron from getting too hot and burning the tip. A soldering iron with a burned and pitted tip is next to useless.

The controller consists of an inexpensive light dimmer wired in series with a receptical. The idea is to plug the controller into the wall and then plug the soldering iron into the receptical.

I prefer the light dimmers with knobs as opposed to the sliding type. Most dimmers switch the circuit off if you turn the power (brightness) all the way down, or the knob may be push-on, push-off. Therefore, the controller will give you the convenience of an ON-Off switch to use with your soldering iron.

I built my controller on a wooden base, ... because I’m a woodworker. Dry wood in an excellent insulator so it is completely safe. No effort was expended to make mine pretty, but you can add pretty to yours if you are so inclined. Further, you can mount the dimmer and receptical any way you wish, using store-bought switch boxes if you prefer to go that route.


A piece of 1/4” plywood 5.5” square serves as the foundation. To this I used medium CA glue to attach the four pieces that form the “box.”  The 1.5” of the foundation that sticks out from the box allows the unit to be clamped to the edge of a worktable. The box and its connection to the foundation was reinforced with dabs of epoxy, especially in the corners.

Don’t forget to drill an appropriate hole for the line cord to enter the box. Anchor the line cord inside the box; I simply tied a knot in mine.

The dimmer and receptical are attached to the box using #6 wood screws, 1/2” long.

The wiring is very simple; go by the wiring diagram. There is a slight difference in wiring between my photos and the wiring diagram.  See if you can figure what it is.

I did not use a third-wire ground for my unit. Read the following section and then decide if you want to include a ground.

The Ground Wire

Generally speaking, small, inexpensive soldering irons do not have a third-wire, dedicated ground (a three-prong plug). Therefore, when you wire your power controller, you can simply ignore any ground wires or terminals that may be on the dimmer and the receptical.

However, if you wish to include the ground, you will need, first of all, a line cord with a three-prong plug and the third-wire ground. Then simply connect the ground (green) wire to the green wires or terminals on the dimmer and receptical.

If you don’t go with the ground wire, you can select a line cord having a polarized plug. This is one where one prong is wider than the other so that it can be plugged into a receptical only one way.

The wider prong is the neutral. If your cord has black and white conductors, the white will be the neutral and will be connected to the wider prong. Otherwise, the cord will be smooth on one side and ribbed on the other. Look at the plug and note which side of the cord, smooth or ribbed, goes to the wider terminal. This will be the neutral.

In wiring the circuit, connect the dimmer in series with the “hot wire.” This will be the black wire if the conductors are color coded. Or it will be the one that is not the neutral if you are dealing with a polarized plug.

If your line cord has neither a third wire or a polarized plug, then all of this is a moot point. You can just forget the grounds, especially if your soldering iron does not have a polarized plug. I think the risk is minimal in this case, but if you are a purist, buy a line cord with the third wire and hook up the grounds. This may not be a bad idea because at some point you may wish to use your power controller with something other than just the soldering iron.

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