Introduction: Adjustable Power Outlet

Picture of Adjustable Power Outlet

There are a lot of electrical devices that only have two settings: ON and OFF. For a many of these, it would be helpful if you could adjust the output with an external circuit. 

So in this project, I am going to show you how to make an adjustable power outlet. This circuit acts as an external dimmer and can be used to adjust the power on a variety of appliances such as Lamps, heaters, soldering irons, and hot glue guns. 

Safety Note:
The circuit used in this project is designed for simple resistive loads such as heating elements and lights. It is not suitable for inductive loads such as motors or fans. These generally require a different kind of control circuit. Also it should not be used with devices that use AC power adapters or devices that have their own built-in control circuits. These may not function properly when connected to a dimmer. 

Step 1: Materials

Picture of Materials

Here are the materials and tools that you will need for this project:

3 Prong Power Cord
Insulated Plastic Housing
Light Dimmer Circuit
15A Outlet
Insulated Twist-On Connectors
Black and White Large Gauge Wire (optional)

Wire Strippers
Screw Driver
Knife or Rotary Cutting Tool

Step 2: Background: How a Dimmer Circuit Works

Picture of Background: How a Dimmer Circuit Works

The AC electricity from an outlet is basically a sine wave. Most modern dimming circuits work by chopping off part of the sine wave. Above is a simple schematic of this kind of dimmer circuit. These circuits use a semiconductor called a TRIAC. A TRIAC conducts electricity only after the voltage at the gate pin has reached a certain threshold. It is often combined with a DIAC to increase this threshold voltage. The DIAC/TRIAC is connected to a resistor and a capacitor. The resistor sets how quickly the capacitor reaches the threshold voltage. By adjusting the resistor, you determine how much of the sine wave gets chopped off.

At the first part of each cycle, the TRIAC is off. The capacitor begins to charge through the variable resistor. When the voltage of the capacitor is high enough the DIAC/TRIAC is activated and it conducts electricity to the lamp. This process happens at the first of both the positive and negative parts of the sine wave.

Step 3: Purchase or Built a Dimmer Circuit

Picture of Purchase or Built a Dimmer Circuit

You can purchase a lamp dimmer at most hardware stores for a few dollars. There are a variety of types available. The most common type is a dimmer light switch. This is typically mounted to a wall in place of a standard light switch.

The type that I am using in this project is a "500 Watt Torchier Lamp Dimmer." It is normally used to retrofit a regular lamp to add the dimming feature.

If you would rather build a dimming circuit from scratch, you can find a number of designs online. Here is one example:

White and Black Wire
Power Switch
500Kohm Variable Resistor
10Kohm resistor
33ohm Resistor
0.047 µF Capacitor

Step 4: Cut Holes in the Plastic Housing for Each Component

Picture of Cut Holes in the Plastic Housing for Each Component

Open up your plastic housing and decide on the best locations for the dimmer circuit and the outlet. On mine, I decided to mount the outlet to the top surface and dimmer circuit to the front side. This left a convenient place to put the power cord on the left end.

First, you need to mark an outline of the front faces of the outlet. You can do this by holding the outlet upside down on top of the housing and tracing it. You could also use an outlet cover plate to mark the appropriate outlines. Then using a sharp knife or a rotary cutting tool, cut out the two outlines. Then drill a hole between them for the mounting screw. After cutting these holes, mount the outlet in place and secure it with the screw.

Once the outlet is in place, you need to mount the dimmer. Hold it up to the side of the housing and mark where the knob will be located. At this point, drill a hole in the side of the housing that is just bigger than the threads on the dimmer. Then insert the knob of the dimmer and secure it in place with the washer and nut. 

On the left side, I drilled a hole that was just bigger than the power cord. Then I inserted the power cord through the hole. 

Step 5: Connect the Dimmer to the Power Cord and Outlet

Picture of Connect the Dimmer to the Power Cord and Outlet

Before you connect anything, it is important to first identify all the wires. The dimmer and the outlet need to be connected in a certain configuration. The color coding system for electrical wires varies from country to country. In the United States, white wires are "neutral", black wires are "hot" and green/bare wires are "ground." 

If the wires are not color coded, then it may still be possible to identify them from the prongs on the plug or the texture of the insulation. "Neutral" wires are typically connected to the wide prong on the plug and have ridges on the side of the insulation. "Hot" wires are typically connected to the narrow prong on the plug and have insulation with a sooth side. 

After identifying the wires, you are ready to connect all the components. Insert the power cord through the hole in the side of the housing. If you want to make the power cord a little more secure, you can apply glue or a zip tie around it at the wall of the housing. This will help to prevent it from being pulled out and breaking the connections. 

Connect the "ground" wire (green or bare wire) from the power cord to the nut on the end of the outlet. Then connect the white wire to the slot on the outlet that is labeled for white wires. Connect the black wire from the power cord to the black input wire on the dimmer. Then connect the black output wire from the dimmer to the slot on the outlet that is labeled for black wires.

If the wires need to be solid in order to be inserted into the outlet, then you may need to add a few small pieces of solid core wires. Connect the solid core wire to the outlet. Then connect them to the corresponding wires with insulated twist-on connectors. After making all the connections, close up the housing. Your adjustable power outlet is complete.

Step 6: Use Your Adjustable Power Outlet

Picture of Use Your Adjustable Power Outlet

There are a lot of potential applications for an adjustable power outlet.

The simplest application is as an external dimmer for lamps. This can let you adjust the brightness of any incandescent light (and some LED lights). This can make interesting effects with novelty lamps such as lava lamps. 
This outlet can adjust the output of any appliance that uses a simple resistive heating element. Examples of this include: soldering irons, hot glue guns, hot wire foam cutters, crock pots, counter top grills and some coffee pots. 

As noted in step one, this outlet is not designed to work with inductive loads such as motors or devices that use AC power adapters or devices that have their own built-in control circuits. 


rommac100 (author)2015-09-04

I think there is an error where you said 33ohm capacitor.

Thank you very much for catching that. It should be 33 ohm resistor. I have updated the text.

nydogwhisperer (author)2015-07-05

Can a dryer be put into a regular outlet or is there a way to convert one for a dryer?

Anything with a motor should not be controlled with a dimmer circuit. You need a special motor controller circuit.

Yardster (author)2014-02-27

I'm interested in finding a way to reuse a broken iron as a hotplate for cold smoking meat. The issue is that my husband thinks a dimmer switch isn't appropriate for use with the iron. the iron is reduced to the sole plate with, presumably, an electrical heating coil running through it, and electrical connectors. When intact, it draws 1100 amps, but normal dimmers are rated for less. What are my options? Are there any recommendations for a variable power switch for this use …that cost less than a used iron (my alternative cost).

Most iron have their own built in temperature control that you set with the dial. Is that part broke?

Yes, it's missing the temperature controller. That was how it was broken in the first place. I've stripped it down to the sole plate and terminals. It might be cheaper to just go out and buy a used iron at a thrift store if I can't figure out a way to control the power to this one. I thought this would be a cool way to upcycle junk.

Well, you have two options. You can either find a controller that can handle 1100 watts or you can reduce the wattage of the iron.

One controller that you might be able to find is a 1100 watt microwave. The power settings will let you adjust the output at various duty cycles.

To reduce the wattage of the iron, you could wire it in series with another circuit. This will increase its effective resistance and lower the wattage. For instance, putting two irons in series will double the resistance and cut the wattage in half.

Thanks for your help. I'll report back.

My purpose is to make a hotplate for bringing wood chips to the smoking point, I should find out what the combustion temperature would be. I just thought that the highest setting on my iron can burn my cottons, so it seemed a good bet. Perhaps a second iron in series would be possible, they're easy to find in thrift stores. One drawback with an intact iron is all the plastic housing and the fact that the controller is on the iron and would be difficult to reach while in a (meat) smoker.

ALKN (author)2014-01-10

You stole this from make magazine

JeremyA (author)ALKN2014-01-25

Maybe an apology is in order ALKN?

Actually. I work for Make. I am the one that made the project and the video for them. They encourage me to promote our work my submitting it to other websites such as Instructables.

LesB (author)2014-01-06

This is the type of fan I used:
Shaded pole AC fan. Maybe in theory it wouldn't work, but in this real world instance...

Well, what part of "it worked" do you not understand.

nerd7473 (author)2014-01-01

could you add another hot and run it to a switch and make it adjustable at 240v?

Treknology (author)nerd74732014-01-05

Apart from "No", all the answers on this thread alarm me. If you have 220/240VAC in your home, use the appropriate components to make your dimmer for that voltage. If you think you are going to "create" a 220V outlet by linking two 110V outlets you should not be working with mains electricity.

nerd7473 (author)Treknology2014-01-06

yeah I'm not going to try it though

tonemeister69 (author)nerd74732014-01-03

In order to make a 220v outlet out of (2) 110 outlets, you would have to take the hot wire from 2 separate 110 circuits, which usually aren't ran to the same side of the house. I found this out when I was trying to make a 110 to 220 extension cord so I could use my 220v welder all around the house. I hope this is helpful. :-)

nerd7473 (author)tonemeister692014-01-05

it was but I most likely wont ever do this... not enough time or money LOL

nerd7473 (author)tonemeister692014-01-03

ok thanks for the info

harvsch (author)nerd74732014-01-02


nerd7473 (author)harvsch2014-01-02


I am not sure. But that would probably require a different kind of dimmer.

Stan1y (author)2014-01-01

to make a multi strand wire solid to fit the outlet connections I just twist and tin them

stancomm (author)Stan1y2014-01-02

Oooohhh... not good!
While it may seem to be a good method, solder is very soft and will flow under pressure.
What that means is that the connection will feel solid at first but will loosen over time. The same applies to tinning stranded wire and then using a crimp connector on it.

MikB (author)stancomm2014-01-04

Oh yes, I am fed up of finding wires that have been twisted and tinned, "to make them more solid", then squished up in a screw-down connector.

You end up with a flattened cup of solder under the now-loose screw. Arcing, sparking, heat and fire. It's a very bad, very long-standing practice that needs stamping out.

If that don't get you, tinning flexible wires almost always makes them more likely to break as the solder and flux ends up wicking up into the sleeving and making them stiff. Wiggle Wiggle Snap.

pcooper2 (author)MikB2014-01-04

I haven't found what you say to be true. Whether multistrand wires are tinned or left bare, they should be strain-relieved with a cable clamp some distance from the screw termination. If a solid wire is compressed in a screw terminal, it is best to use wavy washers or some other type of spring under the screw head to maintain contact pressure, even if the screw should loosen or the wire should cold-flow.

MikB (author)pcooper22014-01-05

You may not have found it to be true, but then you may be lucky, or may be not looking hard enough :) It is a physical fact. A tinned end ends up flowing into a new shape to try and avoid the pressure. It then ends up not making contact.

Agree on the wavy washers, sprung contact, strain relief etc. but how many choc-block connectors or mains sockets/switches have them? How is it even possible to retro fit them? When the connector is designed to be used with solid static wire, or crimped ferrule ends you wouldn't expect such features.

As Stan1y says "How ever tinned ends or tinned with a crimp does seem to be standard practice here in the UK when an appliance comes with a plug that isn't of the moulded on type and they tend to need replacing after about 2 years as they start to run hot".

Replacing them after 2 years because they run hot means that someone has screwed up. This is the result of the "well I've always done it that way" or "it's alright for me" attitude that leads to "twist and tin" becoming a thing. It shouldn't be a thing.

Tinned and crimp is also bizarre. If you were competent at crimping, the whole point is an airtight metal to metal contact, between the wire and the crimp connector. No tinning. No soldering it as well "to make sure".

If I get a pre-made lead for mains with tinned ends, I cut the things off and do it again. Invariably Mr Twist And Tin has also provided me with 3 equal lengths of wire for the plug, and has clearly never fitted a plug before!

Stan1y (author)MikB2014-01-05

I should have been more careful with my punctuation. It is the moulded on type of plug I have found tends to start running hot after a couple of years and require replacing. Next time this happens I will disect it, because of this disussion I suspect I will find a cable has been arcing in a poory crimped conection to one of the pins. I also suspect that they won't have any form of cord grip other than the moulding which looking at the one in front of me now is not fused to the outer insulation of the flex.
All replacement plugs I have come across have a cord grip, some times this is of a wedge in 'v' arangment and those I avoid. They all also seem to be of the chocolate block type fixing now. Somewhere I do have a very early 3pin(rectangular pinned) plug with a stud turned on the ends of the pins which serves to secure the pin to the ceramic/ bakerlite body of the plug with a round nut and captive crinkle washers on a nut to sercure the flex.
Flex!!! That is what was bugging me. Plugs are not normally fitted to solid cored cable nor are multi socket blocks they are almost always on a flex I have never ever ecountered any one before who goes to the trouble of soldering a section of solid core to the end of a flex to make the connection

Stan1y (author)stancomm2014-01-04

Oh right, never had that happen but in hind sight I realise I never actually get round to the tinning bit I normaly just twist the end and double it up which means I just crush the copper. How ever tinned ends or tinned with a crimp does seem to be standard practice here in the UK when an appliance comes with a plug that isn't of the moulded on type and they tend to need replacing after about 2 years as they start to run hot

dirty_valentine (author)2014-01-02

Nice project. I built one of these ages ago. I used a standard 2 outlet wide metal wall box with a standard outlet and wall dimmer. I was Also able to find a standard metal face plate with outlets on one side and single switch on the other. This covered the outlets and dimmer switch beautifully. The whole thing was easy to wire and the metal box was grounded for safety. Standard metal box wire clamps provided strain relief for the power cord. So easy and cheep to make everyone should make one.

Yep, I got the same idea from hack a day for controlling the temp of a crockpot. Works like a charm and I've already got tons of outlets due to a flea market buy years ago.

asfi235 (author)dirty_valentine2014-01-03

Looks like someone's posted an Instructable describing this exactly:

Though I have to admit that, when it comes to gear that gets used and handled a lot, I prefer enclosures which don't have knockouts....and a Hammond 1441-6 box fits that bill exactly. (Though I will cheerfully admit that having a set of Greenlee hole punches biases me hugely in favour of DIY holes-in-steel.)

dirty_valentine (author)asfi2352014-01-03

Yep, that is just like the one I built. I have not had any issues with the knockouts, but it just gets used lightly around the lab.

cecilomar (author)2014-01-03

Awesome instructable!

I've been thinking about making one of this for ages. I haven't because I'm not sure if I can use a lighting dimmer for what I want, to regulate the electricity that goes to a power tool. They sell the lighting dimmers according to the Watts that it can handle. I'm not sure if the Amps matter too so I have never ventured to make my own. But I confess that I haven't actually done any research... Hahaha,,,

For a power tool with a motor, you would probably need to use a motor speed controller like the kind used on ceiling fans.

asfi235 (author)2014-01-03

I would very strongly recommend adding a 4 ampere fuse, upstream of the dimmer circuit. It will save your dimmer if you (through accident or forgetfulness) do something like plug a big 1000W load into your box. (Though if the dimmer already has its own on-board fuse, you're already covered....)

Also, it looks like the dimmer's mounted pretty close to the outlet. If the nut that's holding it in place comes loose, you'll have a full-sensory failure alert: you'll see it, you'll hear it, and (oh boy) you'll smell it too. A piece of thick cardstock and some electrical tape will be your BFF here.

Lastly, a vote in favour of a better strain relief -- these are the type that are often used in small appliances but it's a pain getting the hole exactly right:

So for handmade stuff I use ones that look like these. Any half-decent hardware store will have them in the electrical aisle:

privatier (author)2014-01-03

You can recycle the dimmer from a torchiere floor lamp; look for an abandoned lamp in your neighborhood.

ahorn8 (author)2014-01-03

I cobbled together a dimmer and outlet in one of those blue boxes. its all ungrounded probably dangerous. I like your design.

ludionis (author)2014-01-02

I like this, I made a similar instructible using a spare wall dimmer switch for my small crock pot, called how to hack a crock pot :-) Yours is much more finished looking though ;-)

EET1982 (author)2014-01-02

Hi. Great project. Thank you for sharing! May I ask where you got that particular dimmer circuit from?

Ace Hardware
500 Watt Torchier Lamp Dimmer
This isn't necessarily better that other models. I just used this one because I already had it.

Cool thanks. I know there are probably better models for the dimmer, but yours just seemed to fit so perfect that I'd rather have that model. Others that I have looked at have been pretty bulky. Thanks again for the instructable! Cheers!

You really ought to remove the coffee maker picture from this project because you used a 500W dimmer while most coffee makers exceed 500W.

applesaucemodifier (author)2014-01-01

I made one of these long ago for use with rope lights. I used a light switch dimmer side by side with an outlet and set it in a plastic outlet box, however I prefer your execution.
This reminds me of this little rig I made years ago for my workshop. After one too many times of abandoning soldering irons in the middle of projects I decided to make an "anti-burn-the-house-down" switch, that turned the iron off even if I forgot to.

I did a similar thing with a count-down timer for battery chargers. Helped avoid the problem of dumb chargers being left attached to batteries and ruining them before their time.

lhharris (author)2014-01-02

Nice project but just to reinforce the warning about plugging in none inductive loads. Be careful with potentially plugging in your laptop or phone charger or anything with a switching power supply. I see two plugs and one might just slip up and think 'oh there's a spare plug socket'. Switching supplies draw more current as the input voltage drops and while most today can handle a noisy (chopped) input some may very well smoke if the average input voltage is too low.

oppie (author)2014-01-02

I use something like this often on inductive loads - Just needs some mods.
Most important is to put a snubber in parallel with the MT1 and MT2 of the triac. This limits the slew rate of the voltage when the triac turns off. With an inductive load, when the triac turns off, the energy stored in the inductance "flies back" and exceeds the triac's dV/dT rating. This tends to make the control unstable and even can cause an imbalance of the positive and negative half-cycles. In resistive loads this isn't important but with inductive loads, this can cause the inductance to saturate (impedance goes to zero and poof). For this reason, it would be good to add a fuse holder and fuse for the capacity of the dimmer. Typical snubber values are 47 ohms and 0.1uF in series and the combo put in parallel with triac. A small series inductor on the input hot lead is also nice to cut down radio interference that comes from the fast risetime at turn-on of the triac. (since you have an earth wire available, look up X and Y suppression capacitors for even better EMI suppression).
Lastly, if you would like a better control of the low voltage range (with schematic as presented, difficult to get less than 50%), add another pole of delay in the adjustment. Add another 10K between the pot and the 10K. At the junction of the two 10K resistors, solder one lead of a second .047uF cap and the other lead to bottom of the first cap as shown in the schematic.
With these tweaks, works very nicely to control the speed of shaded pole motors that are frequently used in blowers.

stancomm (author)2014-01-02

Your description is great, clear and understandable!

I have only one criticism, the way the outlet is mounted.
The electric code (US) long ago said to not use only the center screw to mount an outlet, it is only mechanically appropriate to mount a cover plate. Rather to use the two provided mounting ears. Since you're laying out the mounting holes, drilling them will be simple. Just lay the socket on the plate after the two clearance holes are cut. Then mark the two mounting holes and drill.


ac-dc (author)stancomm2014-01-02

Good point!

Another issue is that the way it's built, but especially if the outlets had side screw terminals too, there should be an insulating panel between the exposed rear of that circuit board and the outlet. Additionally, he really should have used an AC rated electrical box which might already have the mounting holes, not just an ABS project box.

About This Instructable




Bio: My name is Jason Poel Smith I am a Community Manager here at Instructables. In my free time, I am an Inventor, Maker, Hacker, Tinker ... More »
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