Introduction: $10ish DIY Variable Temp Soldering Iron Controller

Picture of $10ish DIY Variable Temp Soldering Iron Controller

This instructable will show you how to make your Radioshack "firestarter" soldering iron into a variable temperature version using around $10 in parts. This idea came to me after i started lifting traces on a circuit board because I was using a 30w soldering iron to solder on a chip. Plus, I am cheap and variable temp soldering irons cost a lot more than $10. Caution: this instructable deals with household AC current. If you don't feel comfortable wiring things up or plugging things in, this is not for you. Also, this is my first instructable so I'm sorry if it sucks.

Step 1: Parts You Will Need

Picture of Parts You Will Need

Flat Head Screwdriver
Wire Stripper
Tin Snips or a dremel

Grounded wire pigtail (mine came from a florescent light, you could just cut the end off an old computer cord. Just make sure it has clearly defined wires. (i.e hot, neutral, ground.)
Romex Connector
4" x 4" Handy Box
4" x 4" Handy Box Outlet / Switch Cover + included screws
600w rotary light dimmer + included screws and wire nuts (mine is made by Leviton and was the most inexpensive model at home depot.)
Lamp with incandescent bulb for testing.

Step 2: Assembly

Picture of Assembly

1. Take the lock nut off of the Romex connector and slide it onto the wire with the screw down clamp side towards the plug.
2. Pop out one of the holes in the handy box. I chose the top center one because it seemed like it would give me the most room to put the rest of the components in there.
3. Put the Romex connector through the hole you punched out and thread on the lock nut. Tighten it down as much as possible with your fingers. DO NOT TIGHTEN THE WIRE CLAMP YET!
4. Separate and peel apart the wires. A knife might be helpful here depending on your cord.
5. Use the wire stripper to strip about half an inch of insulation off each wire.
6. Break off the "ears" off the outlet. These are the things that stick up by the outlet screws.
7. Use a pair of tin snips (what I used) or a dremel tool to cut the excess aluminum off the lamp dimmer. Since the handy box cover has indents where the screws are, we need to modify the dimmer a bit. I cut just above the plastic screw holes on the top and bottom of the dimmer and it fit perfectly.
8. Wire up the components. Isolate the black (hot) wire of your pigtail (mine was conveniently marked with black insulation under the white) and attach it to one of the black wires on the dimmer with the included wire nut. Next, take the other black wire and attach it to the brass screw side of the outlet (if you look really close on the back of the outlet you'll see that it says "hot" on the brass side.) Now, isolate the white (neutral) wire of your pigtail and attach it to the silver screw side of the outlet. Finally, wrap the ground wire from the pigtail and the ground wire from the dimmer together and attach them to the ground terminal on the outlet. That's it! If you got confused your dimmer comes with a wiring diagram. Just substitute the light bulb for an outlet and you're good to go.
9. Screw the dimmer and outlet onto the handy box cover with hardware included with the cover.
10. Make sure all wires and components fit easily into the handy box and screw handy box cover to the box.
11. Make sure there there is a little bit of slack on the pigtail inside the box then tighten the screws down snug. Not so snug that you short out the wires, just snug enough to hold the pigtail securely.
12. Finally, you are ready to test! Go find a lamp with an incandescent bulb (you still have one, right?) and make sure the lamp dims when you turn the knob and goes on and off when you push. I recommend getting a marker to put a + and a - at the appropriate places on the dimmer so you don't have to guess when you plug your soldering iron into it.
13. Have a beer, you're done! (unless it didn't work, in which case you should go back and figure out what happened.)

Step 3: Conclusion

You could probably use this for a variable speed controller for a dremel tool as well, although I haven't tested it. Just make sure you don't exceed the 600w rating of your dimmer. Thinking about it now, it would be really nice to have one of those outlet / pilot light outlets so you could see if the controller is on or off. Hope you enjoyed my instructable!


GaryD96 made it! (author)2016-09-25

Here is a little project I did. I scanned the internet for various wattage soldering irons, the less expensive types and looked at their wattage/power rating and temperature. Then I plotted temperature vs. wattage/power. And found temp vs. power to be Temp = 10*power + 300 (in degrees farenheit), or Temp = 10*V^2/R + 300 where R is the resistance of the soldering iron as measured with an ohmmeter. You can also infer the resistance for a soldering iron by the following formula power = v^2/R where v = 110 v and power is the power rating listed on the iron (this is approximate). Anyhow after all that I made out the following chart which can be overlayed onto a dimmer cover plate. I have not tested this but you get the point, these are estimates. Additionally, these irons aren't temperature controlled, I know you have to take into account thermal mass, heating and cooling rates, the mass of the thing you are soldering etc. This is more or a less an estimate of the initial temperature at the tip after the soldering iron has been fully heated and before any solder is melted. There is plenty of room for criticism about the above idea and template, which is not very accurate and certainly not temperature controlled. But I think if you use this to set a maximum temperature, it could be helpful, and is probably more useful to estimate a maximum temperature and then solder an item that has a much lower thermal mass than the iron. Which is a very common situation. Bottom line is, I'll use it to cut my 60 watt or 30 watt iron down to 15 watts, which is safe to solder most common electronic components. See faceplate below:

GaryD96 made it! (author)2016-09-20

Ok I made it, and I did a little experimenting. Bottom line is power is V^2/R where power is power dissipated by iron, voltage is the voltage applied, and R is the resistance of the soldering iron. So I measured the resistance of 3 "30 watt" soldering irons hot and cold and found this:

Soldering iron 1, 490 ohms cold, 550 hot, iron 2 500 ohms cold 510 ohms hot, iron 3, 650 ohms cold, 550 hot. Anyhow when averaged, that's 550 cold and 540 hot, and I'll just say 545 ohm average altogether. So bottom line is a "30 watt" soldering iron has about 545 ohms resistance, and doesn't change a lot with heating.

That leads to the following chart:

P=V^2/R ("30 watt" soldering iron)

22 watts for 110 volts

15 watts for 90 volts

10 watts for 75 volts

5 watts for 50 volts

1 watt for 25 volts

So although I didn't measure the temperature, this chart should allow yout to label your dial for a 30 watt soldering iron and I attached a picture. Just measure the voltage as you turn the dial an mark those voltages as shown.

A 60 watt iron would make more sense actually. In order to make a chart for a 60 watt iron, all that you need to do is measure the resistance of the 60 watt iron cold and hot, make sure they are similar and use those numbers to estimate the resistance.

I don't own a 60 watt iron, so if someone does, would you please measure the resistance with and ohm meter cold, then hot. Then I could label this a little better for a 60 watt iron.

Great idea, thanks! Here are the pics:

mbjg0788 (author)2016-07-01

I understand that you can control the watts with the dimmer switch but how does the iron get more wattage? If you plug an iron into a normal socket doesn't it get a full dose of the electricity from the socket?

Digleer007 (author)mbjg07882016-08-09

My thoughts exactly

ErnestZ1 (author)mbjg07882016-08-04

The iron won't use any more wattage than it is rated for. With that being said what you are actually doing in this circuit is adding resistance, which in any circuit when one variable changes there is either a rise or fall of another of the 3 ( Voltage, Resistance, or Amperage). The voltage of this will remain at 110-125 VAC, while the amps will change resulting in a rise or fall of wattage. Hope this helps you understand a bit more about what you are actually doing by using this with whatever you have plugged into it. If not do some research on the relationship between Voltage, Resistance, and Amperage. Happy building.

ErnestZ1 (author)2016-08-04

Great instructable, works very well.

framistat (author)2016-05-15

Almost made this... rumaging for a wall dimmer switch I thought I had, I found an old one of these:

Done! :-P

Roselakesawmill (author)2016-01-31

Most of you can barely write and you are going to mess with electricity?
Yes the dimmer will work, for the unskilled just remember that black wires go on the brass screw ( B on B)
Will not matter if you use top or bottom screw or any combination as they are tied together. Do not use two wire lamp cord as your power cord, use three wire and attach the ground to the metalic box and the ground screw on the duplex recepticle, plug a cheap nightlight in one plug to let you know the power is on, don't use a led as they don' like dimmers, always unplug the unit when not in use. You can buy dimmers with a built in led but it shows light when off and goes out when switch is on so it could be confusing and lead to an accident. Ad in burn your house down.

Wow--check out your last sentence and then read and consider your first sentence. Perhaps you should stick with low voltage, low amp. DC projects while brushing-up on your remedial English.

Hey--I'm pullin' your chain--no harm intended--couldn't resist the temptation. PAX!!

IanM114 made it! (author)2016-01-10

wood version; don't worry, its has a plastic boxing inside and insolation

HVACRguy (author)2011-04-01

ALSO you could use an amp meter to see how many amps the iron is using then multiply amps by volts and that will give you watts! you can then mark on your dimmer control box where 15 watts is 20 watts 25 watts 30 watts 35 watts and 40 watts are!!! hope this helps

tinkernick21 (author)HVACRguy2015-09-25

Would you mind elaborating on this? I would love to this and have tried to get a reading from mine while plugged into the outlet only to switch the breaker in my house (bad idea). Thanks.

johnyradio (author)HVACRguy2014-01-13

i've read that current draw might be proportional to tip-temperature, and will therefor vary as temp varies. Anyone know if this is correct?

yashrobo (author)johnyradio2014-12-01

Bro i think you are correct as I to reas about it and a practical on it

Just test the amperage after the soldering iron has fully heated.

JacobF9 (author)2015-09-22

Awesome idea, man! Thanks so much for sharing. Going to totally do this tomorrow! :)

chago1 made it! (author)2015-04-10

I made it with an enclosure from Home Depot. I also added a switch that will let me turn on and off the soldering iron without having to move the dimmer. Thanks for the idea.

tinkernick21 (author)chago12015-04-14

Did you have to wire any differently to add the switch?

chago1 (author)tinkernick212015-05-11

I don't remember. I believe that the black wire connected to the brass will be conected to a silver one and that is were you will connect it.

jhall82 (author)2015-04-30

20$ mutimeter at Harbor Freight has a Celsius temperature readout, and a temperature probe. just check temperature, use online celcius ferenhight conversion calculator. adjust dimmer..wait for temperature to settle, recheck. when correct temperature is reached mark the dimmer selection spot.

tinkernick21 made it! (author)2015-04-19

Thank you for uploading this very helpful project! Really like the idea of using a multimeter to mark the wattage and that's my next step.

Ember Autumn RoseL (author)2015-04-09

I test if its water proof for you..

atlantica (author)2012-01-12

Can I use this to plug a 1500 watt heater into, thereby controlling the temperature?

titaniumw41 (author)atlantica2012-01-12

No! Don't do it! It the dimmer is rated for 600 watts max, and some of the aluminum for cooling has to be cut off to fit it in the box. It would be a good idea to stay under the 600 watt rating.

Do they sell higher wattage rated dimmers we could use instead?

Then make sure you ground out the circuit by place all four of you fingers on the metal enclosure... What other fingers??? You dont need those....

After doing a little research I found the Harbor Freight has a Router Speed Control. Basically used the same was as this dimmer. The Router Speed Controller is $19.99 online.

The controller is 120 v x 15 amps. Wattage = Voltages x I (current). So, the Router Speed Controller is rated as 1800 watts.

I found some companies to have 2000 watt dimmers. Did not see one on Home Depots website. Maybe a lighting store would have one. Also, homedepot has a 20 amp Plug/Receptacle. You could probably use that in Titaniumw41's plans with the 2000 watt dimmer to control the heater temperature.

Alpha2904 made it! (author)2015-03-21

Love it. The switch that I had I picked up allows you to save a favorite setting by simply pushing on the knob. Works great on my hot glue gun as well.

prototyping_science (author)2014-12-07

What a great idea! Saved me a bundle, I wanted to share my attempt- it's slightly less homemade but great for me because I worry about working with high current wiring! (made using standard 8$ 40w iron and Ikea DIMMA switch

sdtacoma (author)2009-11-22

Great INS. Very easy project to complete.

Quick question... Does it matter which silver screw is used for the white wire? You specify the "hot" side for the black wire, is there a certain side for the white wire? I just picked one and it works but I just want to make sure.

SIRJAMES09 (author)sdtacoma2011-12-25

not saying it WILL short out, it just makes it easier for the electricity to produce a short.

yashrobo (author)SIRJAMES092014-12-01

This one's?

yashrobo (author)SIRJAMES092014-12-01

This one's?

yashrobo (author)SIRJAMES092014-12-01

This one's?

sdtacoma (author)sdtacoma2009-11-22

Another question...

Does anybody know where in this circuit I could put an LED to show me when the unit is on/off? I would like the LED to be either on or off and not to dim with the dimmer.


scoobbrandon (author)sdtacoma2009-11-22

 you would need a relay

yashrobo (author)scoobbrandon2014-12-01

No if the dimmer switch is having capity of 200volts then i don't think that relay is as such required

yashrobo (author)sdtacoma2014-12-01

Dude firstly you have a prepare a circuit which is a kind of heat sensor then only you can know it is getting on or off

SIRJAMES09 (author)sdtacoma2011-12-25

another thing you can do is have a single junction box attached to the double junction box. & then inside that smaller box, have a switch that has a light already in would come on when there is power running thru it & off when there is not.

For those who may not know the terminology, a junction box is that galvanized steel box shaped thing in the pic. what is in the pic is a double junction box....a single junction box is half that wide.

MROHM (author)sdtacoma2011-07-04

Yes I Do!!! But It's Far Too dangerous especially at a Beginner's Level!!! Led's draw 10 to 20Ma and shouldn't load down the Dimmer!!! I have used a Led as a Ac Voltage Indicator but feel this project should be geared to our Advanced Electronic Builders!!! Sorry,,That's just how I feel about This.

mightywombat (author)sdtacoma2009-11-25

Look for a dimmer switch that lights up when it's on.

SIRJAMES09 (author)sdtacoma2011-12-25

I'm not an electrician, but this much I DO know to be true.

On outlets like the one pictured, you will see 4 screws on the back....

it does NOT matter which screw you use, as long as the screws are both the same....

what I mean is this: if you hold the outlet like shown in the pic you will have 2 top screws(1 on each side) & 2 bottom screws(again, 1 on each side).

It does not matter if you use the top screws or the bottom screws, as long as BOTH are on the top, or BOTH are on the bottom.
If you have 1 on top & 1 on bottom it makes it easier to short out BOTH the outlet AND whatever is plugged into that outlet.

When looking at the outlets... If you remember that "White Is Bright, Black Is Gold and Ground Stands Alone" then you'll never go wrong. MOST times you want to be controling the Phase (Hot(Gold Screw, Black Wire)) as most things are made that way. Neutral is used to return the unused power back to the source (ie: Power plant). You Can control the Neutral but I wouldn't do this for anything that is servicing electronics. This is also why you will always find the Fuse or Breakers on the Phase (Hot).

TY Sir....
I never thought of it that way before...TY

;) I hope it helps!

I SHOULD mention that this lil poem only works for outlets in North America...I'm not too sure about other countries that use 110-120 VCA.

....and I want to thank Everyone for all the Great Instructables!

if it works in North America, chances are, it will NOT work across the pond....
Europe, Asia, near east, far east & middle east, etc.

what I have been told thru the years is that they have a different set up for electricity over seas than us Americans have.

Now weather that is true or not, I do not know...that is only what I have been told.

andrew.l.arth (author)2014-08-08

i really have no idea what im doing but you might be able to help.Im working on a model train layout, what i want is for a kid to press a button the train goes for 2 min then stops. the child does this 4 more times. after the train stops for the 5th time it activates a cool down clock for 10 min. it would have to work with electricity from an out lit. Any ideas?

yashrobo (author)andrew.l.arth2014-12-01

You can use a timer circuit and add photodiode and ir led to stop train

njurg (author)andrew.l.arth2014-10-11

use a arduino with a relay shield(or without shield, but with a relay) and make sure you switch the hot wire, not the neutral.

also make sure your relay can handle the volts and amps.

yashrobo (author)2014-12-01

Yo can't we put a fan control variable resistantce instead of light one

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