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.
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joell115 days ago

Why doesn't the breaker trip frequently? If the welding rod touches the metal then we have a short circuit and with no load a very large current is drawn. Even with the smaller primary current it should well exceed the breaker current.

Bob_12 months ago

I screwed up a little bit, when i took the coils out of the transformer i nicked the primary coil a few times, and managed to make it break in one spot, it was only one wire, and i hammered it back in place so it is in contact with the other end of the broken wire. Will this still work and are there any simple solutions such as adding electrical tape?

stasterisk (author)  Bob_12 months ago
No it will not work, in fact it is dangerous. Throw out that transformer.
TreyC12 months ago

These are simple enough, but one thing I have not been able to come across is a DIYer addressing the current limiting. 10 gauge wire, even at 1000 feet is less than an ohm impedance, which would put your primary at 120Amps - way too much for a household circuit. Secondary windings should use even greater gauge and have even less resistance, that it becomes negligible. So the only room left to bring down the amperage must be the inductance/reactance from the transformer itself and the resistance of the metals you are welding, which is not much either. Unfortunately, I have not studied transformers in depth yet, and do not know what kind of impedance the transformer would have on the circuit. If anyone could help, I would appreciate it. I'm looking to make a 300A welder with a ratio of somewhere between 50:1 and 37.5:1

geocrasher3 months ago

When I built one of these, I used the instructions you linked to at aaawelder.com. Unfortunately, that page is gone. I found it on archive.org and mirrored it on my own site here:


I hope it's useful to you, and please feel free to link to it in your instructable.

n1cod3mus3 years ago
i'm in the UK so if i took one of my transformers with 112 turns on the primary, the UK mains voltage is 230v and about 13amps so...

230v * 20 turns on 2nd = 4600

4600 / 112 turns on primary = 42.67v

13amps * 230v = 2990w (could round it up to 3000w)

is that correct? if so then surely i would only need a single transformer to do the welding? as you guys are using 2 to achieve output voltage of a simlar value

which would mean i would be getting over 100amps right?
i was just reading about how to calculate the amps on this site


looking at number 4 it says that if your reducing 120v to 12v your doing it by a factor of 10 and thus the input amps would be times that factor to give you the ouput.

to work out my amps i would assume i would need to work out the factor for my voltage so

input 230v / out put 41.67 = 5.51

input 13amps * 5.51 = 71.63amps out

am i doing this right? I think this should be the approximate amount of amps i would be putting out from 1 transformer
i know i'm answering my own questions here but i'm hoping that this will help others. and hey its near 2am here in the UK so i'm doing my best work.... more caffine.
ok so looking around the net most home welders produce upwards of 80amps and around 34v and up.

what this means the the US is that with your 50amps (as above) you will need more so doubling up your transformers gives you 100amps and your in the golden zone.

with my higher power and slightly higher amps with one tansformer I would only be able to get 71.63amps so its clear i also need to double up too.

so heres what i got, I have 2 transformers with the following

A) 112 turns on the primary

B) 132 turns on the primary

assuming I will be doing 20 turns on the secondary and the input voltage is 230v with 13amps, i work out its output and my factor for each transformer and then work out its amps

working out A)
230v * 20 turns on 2nd = 4600

4600 / 112 turns on primary = 41.67v output

input 230v / output 41.67v = 5.51 (the factor)

input 13amps * 5.51 (the factor) = 71.63 amps output

working out B)
230v * 20 turns on 2nd = 4600

4600 / 132 turns on primary = 34.8v output

input 230v / output 34.8v = 6.60 (the factor)

input 13amps * 6.60 (the factor) = 85.8 amps output


so once i combine the 2 transformers output

85.8 amps + 71.63 amps = 157.43 amps total output

41.67 volts + 34.8 volts = 76.47 volts total output

now the problem is what wire do i use, i found this site which has a handy table for the amps different wires can handle


so i need wire that can handle up to 85.8 amps for B) and 71.63 amps for A)

looking at the chart i found I would need to use 7 gauge wire in the UK which can handle up to 89amps as you guys in the US are generating around 50amps 10 gauge is fine.

problem with this is that 7 gauge is much thicker so will i get the turns in, well thats where someone on instructables has the answer, you have to work out the area you have to use check this out


this is a series of videos that explain how to prep the transforms and in one of them it shows how to work out the area and how to wind your cable to use the best space and if the wire your planning to use will fit.
just been working this out if i wanted to use 10 gauge wire i would have to have an additional 10 turns so 30 turns and not 20, if anyone wanted to know, again you have to make sure this will fit, if not you will have to increase the turns and thus reducing the amps and you can use thinner wire
the only other way you could get round using 10 gauge with 20 turns is to introduce cooling, otherwise the wire will just melt and fuse together and then your stuffed.

good job i salvaged the fans from those microwaves, of course if you used wire that is enamel coated then i suspect you could fit the 7 guage in, but i'm thinking it will be tricky if its covered in a standard insulation.

i'm rambling i should go to bed, its 2.20am


am using 6mm diameter cable on both of my transformers
i've got 18 turns on both, can you please tell me about how much amps will i have

I have no idea this was over 2 years ago, I ended up just buying an arc welder they are cheap enough. I have since upgraded to a gas mig welder which is epic.

Does anyone want MOT ? I just destroyed my new microwaveoven to take the transformer out and to build a welding machine ,but new i lost my interest in that and want to sell my MoT ,pls help me
OVERLOADED3 years ago
does wiring the sec in series also give you double the voltage ?
No. Wiring in series boosts current. Wiring in parallel boosts voltage.

I know it is an old post, but wiring in series raises voltage, not current. Wiring in parallel raises current.

Also be carefull with your transformers, make sure they are the same gauge thickness and windings, preferably exactly the same transformers. That can bring you trouble both in long term and short term use.

Great project, waiting for my microwave oven to go down so I will give it a go ;)

Sorry, but wiring in series boosts voltage, not current.. Two 6 volt batteries in series gives you 12 volts. In parallel, gives you 6 volts at twice he current.
Sorry, you're right. In series current stays the same, in parallel voltage stays the same. Long night.
correct,no need to be sorry for nature lol. it is what it is.
thx wasint too sure about trans or even why i asked that question so long ago?
sphawes2 years ago
Ive built mine using two transformers wired in series. I was only able to get about fifteen winds in my secondary coil for each of them. Being a new welder, i get the stick stuck to my piece quite often, causing my fuse to blow. Is there a way i could wire it up better so that this wont happen, or is it just a matter of not sucking so much at welding?
DanniM sphawes7 months ago

use a house breaker in place of the fuse. if know ur current then you should be able to find a safe rating.

can you plz tel me if safe totachit with my hands

Hexavalent chromium (a.k.a chrome 6 mentioned below) is carcinogenic. Just a heads up, that you NEED a mask...

does anyone know what the standard output is on one of these transformers?

Its about 1.2kV


hhofkhan1 year ago

between 16 to 24 volts but not more than 24

dan7 years ago
referring to your 'one hand behind the back' electrical safety position - for high voltage work you can't just put either hand behind your back - it must be the LEFT hand behind your back. the reason is that if you are prodding at some high voltage gear with your right hand and get zapped - the primary current flow is the shortest path to ground: through your right arm, down your torso on the right side, down your legs and into the ground. now if you use your left hand instead - then unfortunately your heart is in your left side torso and is now part of the predominant current path. high voltage electrical work is unfortunately not a good career choice for lefties. now, as shown (with either hand behind back) it is usually ok for 120vac work, because if your shoes are dry and have decent rubber soles then 120vac isn't enough to go through that.
Your heart is in the CENTER of your chest and has only a small protrusion to the left. All your talk up about the dangers of putting one hand behind the back vs another are all hoo-nanny.

Back in the dark ages I worked a lot with some very dangerous equipment. We were taught to work with one hand in your pocket or behind your back. The problem was not current thru you shoes (electrical safety shoes were always used), but current from hand to hand with your heart in between. A couple times I had terrible shocks...one bad enough to leave a bad burn on my hand. Good technique meant survival. Always remember things break...a safe place to touch today may really get your attention tomorrow.

tashammer dan7 years ago
The heart being on the left hand side is not always true speaking as one who's heart has been moved over to the middle right due to having a lung out.
There's always one! Lol
Ok but for the majority of people this applies correct?
esumon1 year ago

my microwaven primary side was burned . so i have difficult to make this . any body can tell me . how many turn need for primary( for input 220 (50\Hz)volt supply ) side and which gauge wire ?

Can I have three transformers on lower voltages?
subodh1011 year ago
Can somebody tell me the two transformers specifications if I want to buy those as new ones or if I can find a single one for this kind of diy.
Im also running like 14 gauge wire for the secondary.
So i got the transformers all wound up and ready, when i tested it, it came out to a 30.9v output and im ok with that, but i fogot to unplug it while it was on the multimeter. So over the course of 10-15 minutes the primary coil got hot. one transformer puts out 13v and the other 17v and the the 17v one got hotter but both primarys were pretty hot. should i be worried or is it because i had it on too long.
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