Homemade Arc Welder using Microwave Oven Transformers (MOT)
Homemade Arc Welder- Stick Welder

Since I was a small boy I had a knack of technology and science. When I saw people welding metal and fusing them together using a thin rod and a fierce bright light I was fascinated by it. By the time I was in 8th grade I wanted to build one. Economy was a big barrier and in 10th grade finding the materials was a big challenge. In 12th grade my result and degree was another thing. Even in those times I managed to gather money and things I needed. Finally I managed to pull everything and make a successful welder. This is my guide for all the guys who are trying to make a arc welder or stick welder.

An arc welder also called stick welder. It is a device which uses electrical current supply to create an arc. It uses a consumable electrode to melt and fuse the metals together. This welder is really cool and I highly encourage to make one. This is an engineers and hobbyist’s tool that can create other tools. Always learn skills from superiors before trying to weld. Arc welder uses a transformer to step down high voltage low current supply from wall outlet of house to ow voltage high current.

The low current makes welding safe but suitable enough to create and maintain a arc. On the other hand high amperage helps to create heat and melt the metal, electrode and fuse them. This is a short circuit process. Remember, it is current that kills you and which creates heat. Shorting out very high voltage with very low amps won’t burn anything but they will create dangerous and deadly arc.

Background Knowledge

Please do not try any of these things if you don’t have good knowledge of electricity and what you are doing.

Microwave Oven Transformers (MOT)
Microwave Oven Transformers (MOT)

For welding you will need a good power supply. That is why we need big transformers. Welders found in market have single big transformers, we can use them if you can find of suitable size. Here we are using Microwave Oven Transformers due to many reasons. The big transformers can be of high power. If we use it and lets say get out 40 volts it will have very high amps because (Input Watt=Output Watt) where Watt=Volts X Amps.


Read More: Homemade Spot Welder

So with reduced voltages, the amps will be high which can be dangerous and the weld will also be out of control. One might ask why only Microwave Oven Transformers (MOT).  have tried everything from TV, Inverter transformers there is nothing like MOT. They have big core, less primary winding, big secondary window and great power that is required for us.

Transformer from Oven (Untouched Secondary)
Transformer from Oven (Untouched Secondary)

Preparing the Transformers

We must find at least two MOTs for to salvage. Find any old microwave oven at your disposal. You can find it in your local classified, scrap yard and ask some friends and people. In our country most people don’t use ovens so it is hard to find. Here our traditional food doesn’t require oven so it is rare to have oven in someone’s home. For the sake of science and my knack I salvaged my own working Oven! For another one I searched for more than 2 years and found it in an electrical shop which repaired them. I bought it for Rs 700 or $7.

I chopped the secondary of both MOTs. You can totally break down the transformers by removing their I section from E section using a hacksaw or a grinder. I didn’t have any welding tool or Epoxy glue to stick them back. This I chopped off the secondary using chisel and a hammer. The secondary should be removed without harming the primary. The filament winding and the shunt should be knocked off. The shunts are two metal plates kept at window of transformer to maintain current or to control it. We aren’t gonna need it because we need high amps.

MOT with no Secondary winding
MOT with no Secondary winding

Rewiring and Connections

Now we should put secondary wires in the transformers, as wee need less volts we are going to install thick wires and have less turns. The lesser the turns higher the amps and vice versa. We need appropriate size of wire to fit in so to get suitable current and volts. Too big wire will only give more amps with less volts because we have less winding due to it. Many DIY builders use 12 gauge or 10 gauge copper wire. I am using stranded 14 gauge copper wire. It is also known as 7/22 wire which means 7 stranded wire of 22 gauge. I installed winding in both transformers and got 38 volts out which is about right.

Read More: Arc Welding Requirements

Even if you have 110V, 220v input transformer and same output from wall socket wire the input in parallel so that the MOT can get same voltage. You can do it using single outlet or use two wall outlets that are 180 degrees out of phase. Then install the secondary in series so that output volts will add up. I have 220V transformers and same wall output and my secondary output is 38 volts at 175 amps. The input voltage is 220V (Ideal requirement) and it draws 25 amps.

Finishing and Advice

I also built a casing for it to make it compact and portable. I used some jumper cables to feed the stick holder. You can use any pliers to hold the stick but stick holder makes it easy to weld and I also used some old thick copper wires for ground with a battery clamp. I bought 25 mm jumper wires that cost me $1.5/m but it was good enough to handle good current.

I am having low arc length but I suggest you to decrease the thickness of secondary and fit more turns to get around 50 volts. The amps will be less but 80-100 amp is good for welding 3/32 electrodes. Read these instruction and basic guide before starting to weld.


  1. Which type of transformer can be used stepup or stepdown transformer and which volt transformer I need to buy

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