Homemade Stick Welder - From Microwave Parts!




Introduction: Homemade Stick Welder - From Microwave Parts!

About: Random Weekend Projects

Did you know you can make an AC arc welder using parts from your microwave?  I just finished mine, so join me in this video as we put its welding capabilities to the test!


Step 1: Watch the Video!

WARNING: I run the system on 240 VAC, which is metered by a power controller I built called the "Scariac".  It's similar to the idea of a Variac (variable auto-controller), with a few more hazards to be aware of.  The Micro-Welder itself does not have an on-off switch, and can pose a fire hazard if plugged directly into a mains power socket.  I made this to be used exclusively with the Scariac.  (Look for how to build that in another project.)  Stick welding, and/or the modification of a Microwave Oven Transformer (M.O.T), can be very dangerous and presents risk of UV radiation, shock hazards, burns, fires, fumes and a multitude of other risks.  This project should not be attempted without adult supervision and adequate training.  Misuse, or careless use, of tools or projects may result in serious injury.  Use of this video content is at your own risk.

Step 2: What Is a MOT Stick Welder?

Quite simply, a MOT stick welder is an AC arc welder made by converting/modifying 2 Microwave Oven Transformers (M.O.T) so they will weld metal using a welding rod (stick).

A MOT (Microwave Oven Transformer) was modified in a previous project into a spot welder, which is a different form of welder, but in this project I wanted to convert it to arc weld.  That requires a different modification which allows an output of about 30 volts A/C and around 120 amps.

This video is the end result of 3 other project videos which will be edited and uploaded over the next couple of months.  Those videos will show how I modified the transformers, and how to control the current, but they aren't available at the moment, hence the "Coming Soon" on the video annotations.

I'm happy to say that the welder in this project does work for me.  It welds 1/16" AC rods very well, and I believe it's very reasonable and sustainable for the amount of welding I plan to do as a simple hobbiest welder.

To see exactly how I built this welder, watch Part 1 and Part 2 below

Disclaimer:  I am not a welder.  This project is my introduction into the world of welding, so if you are experienced in welding and metal working, I'm open to suggestions and critiques, however I do ask that you refrain from being overly critical of my welds.  They are some of my first.  The video/project is mainly to demonstrate what a welder made from microwave oven parts can do.

Step 3: Quick Project History

This project started by finding a couple of microwave ovens for free, like I did here in a previous project video.  2 MOT's were modified so that the output was around 30 VAC and the amperage ranged from 0-120 amps.

I picked up some scrap metal from a welding company down the road, and changed out the blade on my miter saw with a 12" metal cutting wheel.  

I cut one of the metal pieces into smaller bits, so I'd have more pieces I could use to practice welding with.

The MOT stick welder isn't a new idea, but in my experience of trying to duplicate other MOT stick welder projects on the internet, the welder either got so hot that the insulation on the wires melted and shorted it out, and/or it didn't provide enough power to strike and maintain an arc.  I'm under the impression that up until now, they haven't worked for any practical use.

To date, I haven't seen a video or project where anyone actually welded anything useful with one of these "so-called" microwave welders.  The most that's been shown is to lay a bead on a piece of metal.  But this doesn't prove it can weld.  My earlier attempts could also lay a bead, but they didn't have enough heat or penetration to make anything stick.

A welder also needs a way to reliably control the amperage (which I haven't seen other projects do).  I saw one project where dimmer switches were used on the primary coils, however dimmer switches are only able to handle around 600 watts, and these stick welders require upwards of 2,000-3,000 watts.  In my experience, the dimmer switches fail very quickly and within a minute of trying to weld.

I don't claim to be the first, or the best, to make a MOT welder work.  My claim is only that this is a way I've figured out that actually does work with satisfying results.

Step 4: First Welds

I used one of the large pieces of metal as a base-plate, and connected the grounding clip to that. 

Using a (6013) 1/16" cellulose coated rod compatible with AC I tried making my first welds on two of the pieces I cut earlier.

Striking the arc was like striking a match, and I was happy to see the arc was sustainable.  That meant that the voltage and amperage were good.

I regulated the current with a device I call the "Scariac."  It's works as a current controller to vary the amperage to the welder.  You can look for how I made this in another project.

When the slag was knocked off the weld, the only way I really had of testing it was a destructive test - bending it until it broke.

I placed the metal in my bench vice, and bent it all the way over.  I was actually surprised when the weld held strong.  Success!

I tried the same thing with another piece, and did eventually get the metal to rip, but it tore below the weld.  The welds never did break!

Step 5: Second Opinion

I took my unit to a friend who actually is an experienced welder.  I wanted to get a more professional opinion.

He tested it out on some stainless steel, and gave some great feedback.  

His experience was that the weld completely penetrated the metal, and he said it worked as well as the one he had in his shop.  

We tried breaking the weld, and again proved it held fast.  The metal outside the weld tore, but the bead didn't.

Step 6: More Welding for Practice

For extra practice, I welded all the small pieces of metal, and anything else I had lying around.  Some framing nails, and chain got included, and pretty soon I had some metal-art that looked something like a weapon for a zombie apocalypse.  

I also tried making the classic horse-shoe puzzle using 2 horseshoes, some lengths of chain, and a 2" steel ring.  

It worked out pretty well!

The goal is to try and get the ring off, which seems impossible because it's too small.  But I let my wife play around with it, and she proved it can be done.

Step 7: Additional Features

I tried welding with some larger 3/32" rod, but the welder started to overheat fast.  The welds required much more current which made the coils got hot and put them in danger of melting.

I probably wouldn't use this to weld with 3/32" on a regular basis, but to combat the extra heat, I used a fan, salvaged from one of the microwaves, and placed it up to a vent hole in the side of the welder's casing.  This blows air over the coils, and exhausts the air out the other side.

In the even of extreme overheating, the entire top can be removed for maximum cooling.

Step 8: Success!

Well, there it is!  A MOT Stick welder that is proven to work!

If you haven't see the video yet, it's not too late.  Watch it here!

If you'd like to see how it was built, check out Part 1:

And Part 2:

If you like this project perhaps you'll like some of my others. Check them out at www.thekingofrandom.com
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74 Discussions

He did. The scariac changes resistance of the circuit and thereby changes the voltage and current.

Although that high amperage is possible with possible on 220 (in USA) the voltage would drop to 20V or so. I'm not a welder so I'm not qualified to say if 20VAC is high enough to weld with.

4 MOT's across a US 220 line would bring the voltage up to 40 VAC which seems more reasonable to make descent welds with IMO.

Sorry if this has been asked already but I wanted to clarify: what other options are there besides the Scariac? I am willing to buy a Variac (~$85 on eBay), but I have heard that dimmable light switches work too.

1 reply

A light dimmer would work like Cheech and Chong- up in smoke. Unless you found an industrial triac which could handle several hundred amps at say, 200V. Then I might try it.

Your cheapest option is to use the scariac. The physics are sound.

I've been watching a lot of videos on YouTube making sure I do the job right for the MOT but what I'm wondering is I haven't seen anybody saying whether if I hook the primary and secondary coils together they what they show is you wrap the cord around and use that but are they connected at all and can I do this with only one Transformer I have two but was trying to just start on a smaller scale.

2 replies

Eric, it depends on what you have available and what you want to do with it.

If you have 110 VAC, you have no choice. You'll need to hook the primaries in parallel. If you have 220 in USA, eries or parallel won't matter because the current is usually 30-50A. In Europe, wire the secondaries in series.

As for secondaries, that depends on how much volts/amps you want.

Finally you CAN use only 1 transformer, but the best you'll get is around 1/2 KVA. Your best bet is to use 4 MOT's across 220 (in USA). Hook 2 in series. Hook the remaining 2 in series. place both pairs across the 220 (in parallel). Do the same for the secondaries.

Your welder will then comfortably source 2KVA and probably more in short bursts. Watts is the measure of power being used. KVA is a measure of watts available minus conversion losses. So 2000 KVA is roughly the equivalent of 50V at 40A or 20V at 100A.

You do not connect the primary and secondary windings. You basically just need it to function as a simple step down transformer to get the right amperage to strike an arc. If you have any other questions about how the transformers work then just look up the basics of how they work.
And you do you most likely need both of them to get enough juice to actually get a good sustainable arc, but you can always wind one and check if it works with a volt/multi-meter before rewinding the second.

no one seems to be replying in this post anymore, but it won't hurt to ask.

is there a way to wire in the capacitor from the microwave and add a choke to the system and get a smoother weld? I have a sewing machine rheostat that i intend to hook up between plug and transformer in place of the scariac. are these just good ways to burn down your house and stop your heart? I know the capacitor is dangerous. I keep reading wiki pages and instructions, but nothing sticks. I am having a hard time teaching myself how to make do the lectrocities.

2 replies

BTW, as for burning down the house, I'd strenously recommend against the rheostat idea. Unless of course your sewing machine is humongous and uses 2KW!

Honestly, If you don't understand electricity, leave it alone and enjoy watching someone who does. Improperly handled, electricity can and will KILL YOU !!!

Hi, I'll respond but don't know if you'll read it LOL. I'm an EE technician and I can say you're sorta aiming in the right direction.

For the cap and choke to work, you need DC. you'd need either a VERY beefy bridge rectifier on the secondary OR a bank of them. Personally, I'm thinking a bank of them would be a pain to build, but easier to obtain parts.

Under heavy current use, the cap really won't charge much so won't help with filtration. The inductor would have to be fairly large, otherwise it will saturate, get hot, and drop (which it will do to an extent anyway) the voltage.

You got me thinking so I looked up AC vs DC welders. DC seems to have many advantages. Google this and you'll find a neat example:

"Converting an inexpensive AC Welder to DC Service"

As a final thought, MOT usually run around 50% duty cycle. So a tweak to this would be to use 4 of the buggers.

Construct a duplicate of this module and hook your 2nd module across the 220VAC as well. Then hook the output off your 2nd bank of bridges in parallel with the 1st. As 220 VAC outlets are usually at least 30A, you could max this new setup and still not pop the breaker.

Hello All.
I have a question about my Home Made AC welder. I built it using the instructions posted here. The out put is 43 Volts Ac. I see all the posts stated 30 plus volts. Is 43 volts to much and should I get it closer to 30 volts? Another thing is the power cable coming from the ac wall outlet. I used the cable from one of the Microwave ovens. It gets a little warm when trying to weld. Should I use a larger cable? Thanks for any suggestions.

1 reply

The heavier the wire, the lower the resistance. Less resistance means less energy lost as heat in your conductors. Also, shorter lengths heat less (conductors are rated in ohms per foot). If you have long cables, they should be heavy.


19 days ago

can i use another transformer if i don't have microwave transformer?


1 reply

That depends on the transformer and supply voltage.

The core of the transformer has to have a high enough rating, probably around 2KVA for a single and 1KVA if you pair them like this. You'll have to wind it (them) for whatever voltage your country has.

Long story short, expect to get slightly less than what you put in.


watched the vid and really looking forward to build it already.. i got 2 MOTs but they are 230v kind since that is the mains power here...

what kind of change should i do? hook 2 in parallel? maybe use just one?


For the microwave arc welder it keeps setting off the fuse in my house is it to powerful

Great Instructable! You say multiple places online that you center tapped your transformers in the arc welder to power other projects, like an arc furnace. I happen to be building an arc furnace. Could you explain a bit more about how you used the center tap to power the device? I saw that you had a link for a "coming soon" arc furnace video but no actual video. Also, if you have any tips you learned from the project, I would love to hear them!

I've been looking to build a MOT stick welder for some time now and I have to say, yours does look great and most likely the one I'm going to model after.

I'm a bit confused when it comes to the Scariac though. You had mentioned that at short circuit the voltage was 36V but what value was the current at this voltage? Im wondering because I would like to replace the Scariac with a purchasable variable transformer and would need to know what specifications I should be modeling for.

Any recommendations on a variable transformer?


The King,
Big fan of your projects. I'm in the process of building the stick welder and was wondering how many feet of wire it took to do the new secondaries on the transformers? I'm getting ready to buy the wire and don't want to get too much or too little.

Do you know anyone that sells these or would sell one?