I'm trying to build a welder from microwave transformers, but I got this weird looking transformers instead.

I recently got two old microwaves from a junk yard and wanted to build an arc welder with its transformers by connecting both in series and getting an output of around 40V all together. But when I open the microwave instead finding the big chunky laminated iron core transformer as shown by many youtube videos, i found a small weird looking transformers instead. ( as shown in the pictures)

I read somewhere stating that the primary coil should at least have 1 turn per volt. However, this transformer only had around 17 turns in the primary. The core was also not laminated and it had a copper wire holding it in place. The primary coil was made of a thick litz wire and the secondary was a very thin wire.

Anyhow, I still continued the project and I experimented with one first. I use the same primary and made my own copper wire for the secondary. I made the secondary by using thick copper wire which I found in some antenna wire and I stacked it up and twisted it and put a heat shrink tube on it. Base on a few tutorials i saw i need an output of 20V from each transformer coming from an input of 240V AC. So with 17 turns in the primary i need around 1.5 turns in the secondary.

When i finished everything and connected it to the power supply, it vibrated for awhile and then blew the 13A fuse in the plug. So i added a light bulb in series hoping to increase the resistance and reduce the current but this time nothing happen and it didn't even vibrate but the bulb did light up. I think its because the primary coil has a resistance around 5 ohm and the bulb have resistance of 100 ohm so the potential differences is very low on the primary coil.

I am not sure why isn't it working. Please help me as i can't find any tutorials on how to make a welder with this form of transformer. There were no other transformer in the microwave so this was definitely the main transformer. Is the problem because it has too little turns in the primary coil or it has too low resistance? I don't know please help me. Thank you!!

Picture of I'm trying to build a welder from microwave transformers, but I got this weird looking transformers instead.
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These are the newer kind, where the supply is made using a switch mode power supply, so the cores are very small. These are NOT suited for your project. YOu need to find a really old microwave.

KhayhenS (author)  steveastrouk2 years ago

Is there any possible way to modify it or take some parts from the microwave to use it for my purpose?

Afraid not. All you need is a good hefty transformer which that system doesn't have.

KhayhenS (author)  mpilchfamily2 years ago

Is there any other projects that i can use it? Because i dont want to put it to waste completely.

Keep the wire. Keep the electronics if you like. If nothing else you can get a DC power adapter to run it and you have a timer/clock there.

KhayhenS (author)  mpilchfamily2 years ago

This runs on DC power? I actually paid for this microwaves so its pretty sad thats its going to waste. I will try to use it as you said and plus i got a few good motors i think. But thanks for the help anyway.

Most circuit boards you find are DC. Just a matter of looking up the data sheets for the chips to see what voltage they run on.

What is the power rating on the microwaves? Obviously what you got is inadiquate for your project so you'll need to find the correct kind of transformer.

KhayhenS (author)  mpilchfamily2 years ago

It says 650W

Find a larger older microwave and it will have the large transformer you need. All of those sub 900W units will not be using a large transformer like you need.

iceng2 years ago

Here is that old style