Build a Microwave Transformer Homemade Stick/Arc Welder

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About: Hi! I'm Star Simpson! I'm a real me! See more at [http://stars.mit.edu stars.mit.edu]. photo by [http://bea.st/ Jeff Lieberman] (http://bea.st) stasterisk - my name is Star, and when I was 13 I ...

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

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

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

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

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.

OUTPUT VOLTAGE = INPUT VOLTAGE * (NUMBER OF SECONDARY TURNS) / (NUMBER OF PRIMARY TURNS)

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.
POWER (WATTS) = AMPS * VOLTS

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

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

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

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

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

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
hobartwelders.com

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

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.

Important:
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

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

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.

2 People Made This Project!

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851 Discussions

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AhsanB7

2 years ago

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?

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MuhammadH345AhsanB7

Reply 13 hours ago

Your one transformer is not working this is why u get your low voltage current.

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JaredD23AhsanB7

Reply 2 years ago

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 above.....so 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.

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AhsanB7JaredD23

Reply 2 years ago

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.

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SamS291

Question 18 days ago

What if I use two power cords in parallel instead of just one? Each one can only handle up to 10 amps, so the two together should be able to get to 20 amps max without having to worry about overworking the cords, right?

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Abhinavr_212

Question 7 months ago

Planning to do the same! Would I be able to connect a 10000w dimmer to control the input power? Will dimmer be damaged due to the inductive load

1 more answer
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MarioL111Abhinavr_212

Answer 2 months ago

I think a 10kW dimmer would be robust enough to handle at least a few kW.

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joesakar

7 months ago

This looks similar to what my father made. He had an adjustment wheel to adjust the spacing of the plates. I’ve attached images.

07594029-5BAF-4264-9AF0-E2CADC3C3DD0.jpeg65EA28B6-8FCB-4B3F-9CAF-BD483DE70179.jpegDD47D704-B7EA-4EB8-AE81-535ABA973CC1.jpeg5494E523-704C-4942-8518-DD3B6E44987D.jpeg
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SantoshG12

1 year ago

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

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stoobersSantoshG12

Reply 1 year ago

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

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JRock1000stoobers

Reply 8 months ago

How would you add a third transformer in series? I'm having trouble figuring that out. I know how to add the secondaries, but which leg of the -120V - 0 - +120V do you connect the third transformer to? I can only figure out how to wire in 2 more to run the primaries AND secondaries in parallel, to double the current...
Thanks! This Instructable is awesome!

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JRock1000JRock1000

Reply 8 months ago

Also, do you leave the shunts in? I've been taking them out and have burnt up and had to rewire the secondaries at least 5 times.

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GifharyS

11 months ago

is there any instruction about making everything from scratch? include DIY the transformer

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tom1933

2 years ago

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?

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stooberstom1933

Reply 1 year ago

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.

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stoobersRupesh1998

Reply 1 year ago

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

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JaredD23

2 years ago

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 garbage....free.....hahasad 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.

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bmiller91JaredD23

Reply 1 year ago

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