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So I have a really cheap soldering iron and a dimmer switch meant to be wall-mounted. The soldering iron has a standard, ungrounded cord. The dimmer switch has four wires: a green (for ground), a black and a red, and another red that's "only for use in 3-way switches". How can I wire this into the soldering iron to allow for variable soldering iron intensities?

I tried cutting the soldering iron cord, binding neutral back to neutral and binding the positive to the dimmer's red, through the dimmer, and back through the dimemr's black to the other side of the positive. This did not work. I also tried it with the red to red, and the black to the other red, and neither worked.

Is it possible to insert a wall-mounted dimmer into a standard appliance cord such as a soldering iron?

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    \$\begingroup\$ "Variable soldering iron intensities" != temperature-controlled soldering iron. What you'll get from this is an adjustable-wattage iron, not one with adjustable temperature. You can buy variable-wattage irons at electronics stores, but they're not much better than the bargain barrel, uncontrolled models. You need to just pony up for the temperature-controlled iron. \$\endgroup\$ Commented Mar 9, 2011 at 18:30
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    \$\begingroup\$ Well, just for the sake of curiosity, can anybody still answer the original question, which is how to wire a dimmer into an appliance? \$\endgroup\$
    – Nate
    Commented Mar 9, 2011 at 23:33
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    \$\begingroup\$ To amplify AngryEE's point, a variable-wattage control might be useful if you could turn it up by just the right amount as you were soldering a component, and down by just the right amount when you were done, but in practice managing to perform the proper adjustments at the proper times would be rather difficult; it's much more effective to simply use a temperature-controlled iron which will adjust the power automatically. \$\endgroup\$
    – supercat
    Commented Mar 10, 2011 at 7:38
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    \$\begingroup\$ @Kortuk: In theory, yes, if you knew exactly how much to adjust the iron. In practice, not really. The problem is that the temperature of the iron is very greatly dependent upon the rate it which it is losing heat, and that in turn will depend upon many other factors having to do with the item being soldered. Actually, there's another problem not yet mentioned: thermal mass. \$\endgroup\$
    – supercat
    Commented Mar 10, 2011 at 16:06
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    \$\begingroup\$ @Kortuk: Irons without temperature controls are usually built with a rather large thermal mass, to minimize the amount by which their temperature will go up and down in normal use. One can try to regulate the temperature of this thermal mass, but during use the tip will be cooler than the mass. By contrast, temperature-controlled irons have much lower thermal mass and can warm up and cool down much more quickly (10 seconds versus 10 minutes). There's just no comparison between working with a good iron versus a $5 thing. \$\endgroup\$
    – supercat
    Commented Mar 10, 2011 at 16:12

4 Answers 4

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The problem is likely the 3-wayness of your dimmer switch. It sounds like you are connecting power and the iron to the runners travelers, instead of through the output pole terminal.

           ___[traveler]____
hot _____./                 \.____  switched wire
           ___[traveler]____      |
                                  |
                                  O [light socket (on)]
                                  |
                               neutral

           ___[traveler]____
hot _____.                  \.____  switched wire
          \___[traveler]____      |
                                  |
                                  O [light socket (off)]
                                  |
                               neutral

Make sure you don't have your's set up like this:

               ___ pwr
wirecap _____./       
               ___ iron

Also make sure you have clicked over the dimmer to the correct traveler or wire the two travelers together (the switch will always be on then).

of the There are some electronic dimmers that detect the other switch's position and go to full brightness, which would probably not work correctly if only partly wired.

You could look at a simpler dimmer switch or cord like this http://goo.gl/Mnwbe, though as other's mentioned in the comments, it's probably only $20-30 more to get a new variable wattage iron.

Whatever you do, please be careful.

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  • \$\begingroup\$ What do you mean that I'm connecting power and iron to runners? Can you explain the iron and the runners a little better to me? Is there a way to make a three-way dimmer work on a household appliance? \$\endgroup\$
    – Nate
    Commented Mar 15, 2011 at 17:38
  • \$\begingroup\$ Sorry I used the wrong term for the travelers (I mistakenly called them runners), they are just the two (or more) wires that connect the hot wires when the switches are in matching positions. I edited my answer to show how they work, and what to avoid when using them as single switches. \$\endgroup\$
    – Nilloc
    Commented Mar 18, 2011 at 18:46
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Yes, you can. I did it with a iron solder sucker. It does reduce the voltage to the iron, however that alone does not control the temperature. The temperature will continue to rise to some maximum. That value will be a lower temperature than with a higher voltage. So yes it does work, only not like a temperature controlled iron.

I mounted the dimmer in a project box, and added an outlet receptacle in the rear to accommodate the iron.

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Ofcourse you can. Dimmering the solder iron won't alloy you to set temperature directly, but with some little practice you'll be able to obtain great results with a cheap iron. Pofessional soldering sets allow you to set temperature in degrees but who says which temperature to use ? The same practice that will tell you how to adjust not degrees but dimmer scale. Another thing the professional set can do is to control temperature by a sensor and feedback loop. This is a nice feature that a dimmered iron won't have but again, with some practice you'll be able to overtake this.

Note the dimmer's point where your iron still can melt the soldering alloy. Keep the soldering iron on this position or a little lower when idle, or to solder smallest pieces, increase it according your experience as you need more power to solder bigger pieces. If the alloy can't stay on your iron's top, you're using too much power.

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  • \$\begingroup\$ +1, this will be o.k. as a better-than-nothing approach, and you mention the limitations. Also, I hope that "... but who says which temperature to use?" is a rhetorical question. If so, it is a valid rhetorical question because I've seen many fancy temperature-regulated soldering stations that had their knob set to tea-time (rightmost position a.k.a 5 o'clock; guitarists know this as "British setting" for their amps... xkcd.com/670) \$\endgroup\$
    – zebonaut
    Commented Jul 22, 2012 at 10:29
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The principle is power to the iron changes the temperature. The dimmer reduces the power by cutting off part of the mains sinewave. By setting different levels on the rotation of the dimmer you should then be able to measure the temperature, at each level, with a cheap oven temp probe to determine what amount of rotation represent what temperature. The thermal mass of the iron will help in reducing the tip temperature variation, but with small joints it should not be noticable. The main advantage would be that when you have finished soldering but have more to do later you can turn down the dimmer to minimum to keep the tip warm and allow it to speed up quickly. This prevents the tip corrosion when leaving the iron at a high temperature.

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  • \$\begingroup\$ Supply Earth to Lamp and Dimmer earth Supply Neutral to Lamp Neutral. (If the dimmer has a Neutral connection then connect to it also) Supply Live in to dimmer "In" terminal and out from the dimmer "Out" terminal to light. The dinner in and out may not be marked as such and either terminal can either in or out. Good luck. \$\endgroup\$
    – Dave
    Commented Jun 13, 2021 at 12:57

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