Introduction: Build a Microwave Transformer Homemade Stick/Arc Welder

Picture of Build a Microwave Transformer Homemade Stick/Arc Welder

I had no idea making a DIY welder would be so easy to do. And, it's pretty much FREE!

Additionally, the stick welder you get is definitely better than anycheap commercial welder you can buy.
Why is this homemade thing better than something you can buy? Because when you factor in shipping and labor and the little bit of retail markup - the companies that make typical cheap buzz boxes will skimp on copper as much as possible. Whereas you can use enough copper in this to make something really juicy, and still spend less, to nothing, compared to a store-bought arc welder.

So here's what you need to build a welder:
- Two beat up old microwaves
- Some 10 gauge wire
- Wire nuts

People throw out microwaves all the time, if you keep your eyes on the curbs.
Or, you can get microwaves at the local thrift store for $10 each.
Try the warehouse that processes donations - they have to pay to get rid of tons of broken ones.

Stuff you need for welding:
- Welding helmet ($16 and up)
- Welding rods ($6)
- Vice grip or purpose-built electrode holder ($6 for either)
- C clamp for grounding clamp
- Gloves
- Thick nonflammable (leather) clothing that will cover your arms

Disclaimer: High Voltage ELECTRICITY and lots of CURRENT! Heat, electrocution, and DANGER! You could die and you could go blind.

That said, try this at home!

See this for a lot of welding safety tips

Here are the really good how-tos that this project is informed by:
build a 70 amp welder
the tiny tim welder by tim williams
home made welding machine (via afrigadget)

Dan Hartman's how-to is good for reference, too.

And here's the quickest way to make a DC welder with a bunch of 12 volt batteries.

Step 1: Dissect the Microwaves

Picture of Dissect the Microwaves

Invite your non-hardware oriented pals over to help help dissect your donor appliances.
They'll love it. David Grosof donated one of these microwaves under the condition that we take it apart together.

Good safety tip:
You'll find a gigantic capacitor inside the microwave. It looks like a metal can with two tabs on top.
Short it out to make sure it doesn't have any leftover charge on it, before you poke your hands anywhere near. Just put a screwdriver or something metal you aren't connected to, across the two metal terminals shown here.

Step 2: Prepare the Transformers

Picture of Prepare the Transformers

Chop and and knock out the secondary (thin wire) windings.
Don't nick or damage the primary windings in any way.

If you do, you could create shorts where two windings conduct to each other, allowing electricity to bypass certain parts of the coil, making effectively a smaller coil, and creating something different than what you expect at the output. Or, you might chop the connection entirely, ruining the primary. So do your best to keep it intact.

Step 3: Get Some 24 Foot Chunks of Ten-guage Wire

Picture of Get Some 24 Foot Chunks of Ten-guage Wire

We scavenged some heavy wire from an old powerboat the owner was scuttling.
We stripped the outer jacket off and separated the inner conductors to wind new secondaries
on our transformers.

Step 4: Wind the New Transformer Secondaries

Picture of Wind the New Transformer Secondaries

We wound 20 turns of 10-guage wire on each transformer. That's just about how much wire would fit into the available space. It took a little over 20 feet of wire each.

tip: draw tally marks on your table to keep track of the number of windings.

How does a transformer work?
The primary winding is an electromagnet connected to alternating current.
The humming magnetic field of the primary induces a current to flow in the secondary winding. If both windings have the same number of turns, the output voltage is the same as the input.
(minus a smidgin due to eddy currents, resistance, etc.)
If the secondary has more turns than the input, its output voltage is higher. That's the type of transformer you started out with.


Our primary has 100 turns and gets connected to 100 volts AC. We're winding 20 turns on the secondary, so we'll get about 20 volts out.

The available POWER STAYS THE SAME regardless of what the output VOLTAGE is.

If the primary is made take 1000 watts (100 volts * 10 amps) out of the wall, we'll be able to take 1000 watts out of the secondary. With 1/5 of the windings, we can draw 50 amps out of the secondary.

That's the cartoon version with play numbers anyway.
Over here in our shed full of reality we've got two of these beasts in series and plan to short the outputs through a welding rod like Jennifer Beals.

Let's just say we're going to pull a whole lot of amps, which is why we need to wind our secondary with such thick wire.

The copper conductor in ten-guage wire happens to be 1/10" (0.1") in diameter.

Here's a table of conductor diameter, guage, and current rating.

Step 5: Schematic

Picture of Schematic

It's a pretty simple circuit.
In fact there's nothing in it except wire!

We'll take two transformers and wind low-voltage secondary windings on them with thick wire.

We'll put the secondaries in series with our welding rod and workpiece.
We'll plug the primaries into the wall.

I really like the way aaawelder put it: "do not include yourself in this circuit"

Step 6: Wire Your Two Transformers Together

Picture of Wire Your Two Transformers Together

Why do we use two transformers?
Just one of these isn't big enough to make a really juicy welder.
If you happen to find a big enough transformer somewhere, feel free to use that.

Here's how to hook up two transformers.
First we wire both primary windings in parallel to the wall cord.
Then we wire the thick secondaries in series so they both"Push and pull" in the same direction.

Step 7: Test

Picture of Test

Get out yer voltmeter:

Here's the test to make sure the secondaries are both pushing the same direction.
Our two secondaries in series produce 38volts AC with no load. That seems about right.
If they'd phased wrong it could have been fixed by reversing the wiring to any winding.

Where Tim says "out of phase" in the video, he means "in phase". That is, the center tap should be less than the outer two leads, and if things weren't that way, the transformers would be fighting each other, or phased wrong.

Step 8: Weld

Picture of Weld
holy cow, it works!

We wanted to add a series inductor to give the unit more "inertia", but it didn't matter!

Here's Tim welding with some of those.

Built your welder, but not sure how to weld? Check out the instructional videos on youtube - search "how to arc weld". They're very good.

Here's Star striking an arc.
It welds great with these thin 1/16" 6013 rods. Even better with 3/32" 6013 rods.

Step 9: Thick Rod Test

Picture of Thick Rod Test

Those skinny 1/16" electrodes cost about twice as much as thicker ones.
We wanted to see how our welder works with thicker electrodes.
The next size up is 3/32", but we got a box of 1/8" 6011 electrodes.
When we pulled one out of the box we both said "wow, that's thick".

We fired up our welder and I welded this bead across the diamond plate with 1/8" rod.
The arc was pretty short but it burned in well and felt pretty good once I got used to it.
I had to shove it in a bit more than I'm used to to keep the arc going, but sticking wasn't a problem. I welded a long bead and used up more than half the rod without stopping.
That's the long weld in this photo.

Then I set the "torch" in this plastic tub so it wouldn't short out to anything.
I checked the transformers, and they didn't even get warm!
3/32" rods are less likeley than 1/8" to blow a circuitbreaker though. For your first welds get 3/32" 6013 rods.
6011 rods have thinner flux and make it easier to see what the metal of your weld is doing, but tend to spatter a bit more.

The next picture is for reference, from

Udate 4/16/2008:
This is now my favorite welder. I made new leads for it from a pair of jumper cables. I left one alligator clamp on for a ground clamp, and added a $6 electrode holder. I've taught a bunch of people to weld using it.
The next photo is Ita welding for the first time, making an awning frame. That project was welded with this welder by total beginners using 3/32" 6013 rods. As you can see we have every other kind of welder, but the homemade ones are more fun.

Step 10: Welding Stainless Steel

Picture of Welding Stainless Steel

We needed some brackets for Solara's mizzen mast.
So we went to the welding store and bought some 3/32" "Hobart Smootharc+ 316L - 16" stainless welding rods. They're only 12" long because stainless has high electrical resistance and they get really hot.
After much designing and sketching Victor, Kenny, and I cut, drilled, bent and welded these brackets. Very easy. When it cooled the flux went "tik" and fell off the weld. The dark area around the weld is soot from the flux.The welder could have handled much thicker rods due to stainless' high resistance and low thermal conductivity.

Use a fresh grinding wheel on stainless, or one that you only use on stainless.
You'll get rust if you use any abrasives that have been used on non-stainless steel. Same for the wrong wire brush. It will smear rustable iron on the stainless, and due to galvanic effects it'll rust quick if it gets damp.

Hooray! Where did I get the idea you needed TIG for stainless? Stick welds on stainless are just great!

Step 11: Dimmer Control and Welding Thin Wall Tubing

Picture of Dimmer Control and Welding  Thin Wall Tubing

The welder was too hot for thin-walled tubing frames, I kept melting holes even with the 1/16" 6013 rods. So I plugged the welder into a variac dimmer and turned the power down about 30%.
That gave me very fine control over power. Marc Lander and I did some very nice welds as seen here. After a few we got good enough to do the same welds with 3/32" 6013 rods and no dimmer and not burn holes.
More tricks - I used my left hand to feed a piece of mig welding wire into the weld to add more metal in and soak up the heat. Here's Marc doing that. Any wire is fine for this, coathangers are traditional for muffler work. Sand off the paint first if you don't like fumes.
Stopping to eat lunch helped a lot also. Your welds won't be good when you're shaky and tired.

I got my variac for free, don't buy one for this, they cost as much as a welder.
A solid-state dimmer that's rated for inductive loads does the same thing and costs a lot less.

If you're feeling particularly fancy, you can add in your own scr-based switching circuitry to vary the power, like this guy did.

Step 12: Other Welders

Picture of Other Welders
Folks have sent me a few photos and videos of welders they've built off of this instructable. I want you to be able to see them too, so here they are!

Here's a video I got from Paul du Buf, of the Netherlands (nice case, Paul!)


Cheyyne said:
Hey there, here's my welder based on your instructabletion. It outputs 35.5v, because the transformers were a little smaller than yours I think (couldn't wind a single more turn). So far I have managed to lay down gobs of metal on various steel objects in my garage, but I still suckat welding. Luckily I rented a nice welding video from Smartflix that had good reviews, hopefully that'll give me some insight into the process. I did manage to lay down a 1" bead though! The whole thing is going into a tacklebox housing.Props for a great instructable. Thanks for it!

llamafur followed with:
Heres another one, same basic welder, but its housed in a .50 cal ammo can. Looks pretty sweet. Its relay controlled ( two 15 amp HVAC control board relays wired in parallel) , I measured 24 volts ac across the output wires.its also sorta heavy, 30 pounds.


tom1933 (author)2016-08-02

I really like the information. I have started my own project and have the transformers both wound with 20 turns of 10 awg insulated wire. I have 23 vac out one transformer and 22 ac v out the other. Will these voltages be ok?

stoobers (author)tom19332017-11-05

This is good voltage, but osha considers voltage above 40 to be a shock risk so its best to remove some turns & get them under the 40 mark.

Rupesh1998 (author)2016-12-16

what gauge wire is used in primary side?

stoobers (author)Rupesh19982017-11-05

Mine looks like its 12 gauge aluminum, but it could be 15 gauge aluminum.

JaredD23 (author)2016-10-20

Ahsan...sorry that you ran into so much trouble...I wish they were as wasteful over there as they are here (I have 8 transformers that I pulled from microwaves thrown to the but true.

Anyhow you have to limit the current...a 5 pound transformer can only handle about 5 amps for a minute or so before the wire insulating the loops in the coil melts and shorts out... the problem is also that as it gets hotter it becomes easier for the insulation to melt (in the coils of the transformer especially....), so you need more experience then this to make a properly grounded setup before you do this, (and it isn't even safe WITH such a setup....but one way that I have sloppily thrown together a cooler is by putting the transformer inside acontainer and then putting that container into something shallow like a cookie pan or maybe just put mesh in the bottom of a bigger container to allow water to contact the bottom of the container that the transformer is in (metal is good for conduction of heat...but it makes it more dangerous)....then the outside of the transformer will not get much hotter than 100 Celsius (that is the boiling point of water.....assuming you keep it with water in it contacting the whole bottom surface....that will help the overall heat to disipate faster...but at a cost of safety more or less....sorry I cant be of more help....not too much time these days.

bmiller91 (author)JaredD232016-11-25

What about putting transformer in large container filled with mineral oil?

JaredD23 (author)bmiller912016-11-29

good thinking...oil is used as a coolant...but it might be harder to get then water and also the fact that oil has higher viscosity (oil is more has more stickiness than say, 'water', it doesn't transport the heat away as well as something that is 'less viscous' (like water) it will end up cooling it...but won't dump the heat as easily as something that is thin like water...still you could use it if you had it....(more is better (MOST OF THE TIME)....overdesigned things NEVER BREAK....anyone who tells you different is a moron

;) good luck man.

I like the OIL idea, water, unless it's PURE, as in distilled, is a vry good condutor of electricity and a real safety hazard.

You don't need this. You can just add a fan, or reduce the secondary windings & add a 3rd transformer in series.

I DO agree, over design is much better then under. Failures happen much more frequently with 'lightweight' components....

CodyH50 (author)2017-03-05

I have some old transformers in my junk drawer but I don't know the wattage of the microwaves they were originally scavenged from. How do I determine the number of windings present such that I can determine the number of windings necessary for a proper secondary coil suitable for a M.O.T. welder?

stoobers (author)CodyH502017-11-05

You likely can't the non-microwave transformers, as the mot's are sized @ the factory with a high efficiency primary rated for 12 continuous amps inside a chassis enclosure. Putting them in an atc welder with ventalation is a slam dunk. They have a very ideal rating & they are so easy to get out of a junk oven, its sort of suprising.

SantoshG12 (author)2017-08-06

I made it but transformer verry hot outout voltage is 35.5v please solve my problem only hot transformer

stoobers (author)SantoshG122017-11-05

Drop the turn on each transformer secondary, & then add a 3rd transformer in series.

AhsanB7 made it! (author)2016-10-09

I made these transformer with 1 having 25 turns and other having 20 turns but i can only get 17.68 volts max, i had check series and all connections but still unable to get 38 or above volts, can any one help?

SantoshG12 (author)AhsanB72017-08-06

change ac input conection for any one transformer

timmg08 (author)AhsanB72016-12-18

it kinda looks like you kept the secondary coils instead of the primaries. i dont know if this would make problems for you. should give you a lower voltage though and probably cant handle the amperage your putting through it. the coils you need to be using are the ones with thicker wire and less windings. idk if thats the problem but seems plausible.

JaredD23 (author)AhsanB72016-10-15

Where N is the number of turns on transformer “x” or “y”
respectively, you can create two equations and two unknowns and solve for the
number of turns that you made and then check to see if the voltages 120V X Nx…out
of transformer X is what it theoretically should be (or close to it)…if not,
then think about why…

25/Nx (240)+20/Ny (240)=17.68 volts and

Nx(120) + Ny(120) =240 volt

6000/(Nx)+ 4800/(Ny) = 17.68 volt

120(Nx) + 120(Ny) = 240 Volt

Divide the 2 equations gives -à
((120(Nx)^2)/6000) + ((120(Ny)^2)/4800) = (240 Volt/17.68 Volt)

(3(Nx)^2/150) + (3(Ny)^2/120) = 13.575Volt/Volt….-->

Then solve for nx or ny and plug it back into one or the
other equation to get the other then check the voltage in each transformer to
make sure that it is somewhat close to the values you got (it wont be exact
because of impedance and nothing is theoretically perfect (resistence and
losses will make sure of that…., but it should be near the values….

twilliams jr. (author)AhsanB72016-10-11

I wired in series and used 220vac and it works great...before i had it wired 110vac and had them wired in parallel and it worked but kept tripping the breaker but, it worked.

ScottieDigital (author)2015-11-29

This is very nice BUT, this isn't as efficient as an actual stick welder. I have took apart tons of microwaves and a few welders. So I know what's going on with this. Nice how you rigged the wiring to make it work. But EVERY stick welder has a bigger transformer than a microwave roughly 30%. So granted this works great for you especially just using spare parts! But if you wanted something that does every job and have proper circuit protection I'd recommend buying one for only $100 from Harbor Freight. So don't get me wrong I still like this project especially if someone who doesn't have a budget and make something from nothing!

matt4x4 (author)ScottieDigital2016-02-19


But if you wanted something that does every job and have proper circuit
protection I'd recommend buying one for only $100 from Harbor Freight."

$100 or free, and are they comparable in terms of what you can weld? I doubt it. Hooking up multiple transformers in series you can weld thicker metal, the thickest Ive seen for the cheap hobby welders is very thin.

JacobD89 (author)matt4x42017-06-02

I agree. The innovation is using two transformers. With patientience, and some innovation a poor person could make a safe welder, or what I need a cheap spot welder. (A novice should watch at least ten videos. I would also throw on a GFCI recepatcle, and know how to use a DVOM. The price of spot welders is way too high. We are seeing they are basically just a transformer.)

Freekonwheelz1 (author)2016-06-19

In the process of removing my secondaries i bent the primaries on one of my transformers. Should i keep going with it or scrap it and find another junk microwave? They look to be fine and dont look like they will short out but looks can be deceaving. Is there any way to test the primary coils to see if they are junk?

JacobD89 (author)Freekonwheelz12017-06-02

check the resistance with a DVOM. if no shorts--good.

I actually dropped my core and it did slightly damage my primary. but it was still usable. I say keep going and if it doesn't work then use another one

Tomas Meyer (author)2017-03-01

Your breaker is tripping because the plugs that your welder are plugged into are in the same circuit you need to have them 180 degrees from eachother so they a re on diffrent circuits King of random talked about it pretty good honestly and yes this will require lots of extension cords I know I wasn't happy about having cords running through my house either.

Could one use a bridge rectifier to solve the issue?

yaipha (author)2017-02-01

I have this 24vdc batter charger inverter

yaipha (author)2017-01-31

Can i use other transformer instead of MOT beacuse in our place MO are not much often used. But we have to many 12v or 24 batter charger inverter are available. Please give some suggestion

yaipha (author)2017-01-31

Their respected members i have a 24vdc batter charger inverter can done welding work with it without any modification. Plize reply comment

arcano005 (author)2017-01-11

hello, i have done my welder according to the instructable. now i wish to add a dimmer, push breaker and on/off switch. id this schematic good?

RobotsMaking (author)2017-01-07

Why do you need to make a new secondary coil?

John T MacF Mood (author)2017-01-01

Quite nicely done! I may try this before shelling out for one of those off the shelf models. I am only interested in welding layers to make billets for forge welding (another arena) for making blades and doing reproduction work on old style knives (Damascus steel). Once I get some practice, I might want to try other types of welds, but for now this would really do the trick.Good work!

emoravek made it! (author)2016-12-07

Made it, works great but still need to practice because im horrible at welding right now.

AhsanB7 (author)2016-10-09

I made two transformers 1 with 28 turns other with 20 turms then center tap both of them, have check series several times, still i can only get 17.89 volts, can any one help?

JaredD23 (author)AhsanB72016-10-15

In general, if you add the two sources in series then you add the voltage....BUT...also you have to take into account that IF the transformers are different sizes and or different number of turns, or different size wiring, then the impedances of the individuals dont add together like 1volt + 1 volt = 2 volts...but rather 1 + 1 = 1.3 volts (a made up example).

Can you do anything about it....well if you want more voltage, more turns of wire and perhaps smaller wire if needed...or....if you want and can get another transformer of the same size and make them identical in design, then the theoretical voltage should add up like the 1 volt + 1 volt = 2 Volt example another words, to simplify things you should have the same transformers because the impedance will be the same in each respectively.

I am not an electrical engineer (I am a mechanical engineer), but I think that is the information you need. Hope it helps.

AhsanB7 (author)JaredD232016-10-15

thanks brother for your help it is very useful information for me but i already have bought 3 old transformers and waisted almost 30 meters of wire. here we already have 220 voltage so i think i don't to make two sources.

But as i was trying to resolve it I gave both primary coils 220, 220 volts from different sources and centre tap the secondary coils and it actually worked, but soon after 10 seconds secondary coils were smoked, i used insulated 8 gauge stranded copper wire. Then i did same with three transformers together and power was enormous but they could only survive 15 max.

kemikali (author)2016-08-11

in uganda we use 240v instead of 110v power mains, would i still need to connect the transformers in series

JaredD23 (author)kemikali2016-10-15

It depends on the breakers for the circuits...I assume that with a 240 volt mains, it would be be connected to a 50 amp that means that the mains will dump 240 Volts at 50 240*50 Volt Amps....or 1200 Volt 1.2KVa....if the breaker was a 30 amp breaker off your mains then it would be 240 Volts times 30 Amps to equal 720Volt Amps or 0.72KVa.....

That means that with the same voltage ...bigger breaker is 50 amp would be better than 30 comes the safety part...

In order for the TRANSFORMERS to handle MORE AMPS they have to be bigger (the weight of the metal has to be bigger ....that way it doesn't over heat (the metal in the transformer can distribute the heat better if it is more massive...more surface area to get rid of the heat faster and more volume to take up the created electric flux field....

Also the wires need to be bigger to handle more amps....there are rules of thumb, but if you get 10 gauge wire...and just make sure that it doesnt get much hotter than will burn you, then you should be just make sure to turn it off before it gets that hot....(also remember that just because the surface is not hot enough to burn you doesnt mean that the wires in the inside of the transformer (the ones you cant touch) are not getting hot enough to burn you.

The heat burns through the insulation creating a short so dont destroy your transformer by letting it get to hot...

there is much more too it, but hopefully that helps....

more transformers are better than less....and also if your stick wont start an arc, then it is likely too low of a voltage (so add another transformer in series....and if

the welder sounds more like it is cooking bacon in grease, then that means that your amperage is too low for what you are increase it...(one way to increase it would be by using less wraps of thicker wire...

good luck man.

vesousa (author)2016-08-23

hey, do you think 4 (or less, it's just the amount of them that i have) beat up CRT televisions would be any good as to do something as this? Great Instructable :)

stolie32 (author)2016-08-16

How would you lower current to weld thinner material like a bought one. Is there a circuit to reduce it

Yonatan24 (author)2016-08-11

Hi, I've added your project to "The Ultimate Collection of DIY Workshop Tools" Collection

Here is the link If you are interested:

NicholasW46 (author)2016-08-10

Is it possible to use amplifier power cable (8 AWG) with this project?

Also if i put a light switch dimmer on the 240v input would this be able to control the power?

mitchman029 (author)2016-08-05

Just curious, how did the 10 AWG wire work for you? I've got some 8 AWG and some 1 AWG, might test both out

DJchmiel (author)2016-04-28

just a quick question for better understanding when you wrap the 10g wire around for the secondary winding do you strip any insulator from it or leave it on?

AdamT111 (author)DJchmiel2016-07-22

Leave it insulated, transformers work off of the magnetic flux running through the windings; if they are not insulated the path is much shorter, and not wound at all.

Evol777 (author)DJchmiel2016-05-08

I left it on and it works alright

snerual2010 (author)2015-10-03

this is stolen from Grant Thompson, who made a much prettier one

xombie_owo (author)snerual20102016-06-03

to be fair, people have been making these for ages. Also its includes her experiences with the project so it is not the same thing.

twtechnical (author)snerual20102016-05-24

Please send us a link to the stolen one.

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