Print PDF
Favorite
Email
I had the idea to make an arc welder from Tim Anderson's instructable "Build a Microwave Transformer Homemade Stick/Arc Welder". On his instructable he shows how to make a welder out of two microwave transformers.
I began working on it. After many hour of work and $80 spent it was finally finished. However, when I tried welding with it, it would not even arc. After half an hour of failed attempts I accidentally got my welding rod stuck to the metal I was welding. Before I even had a chance to remove it, one of the transformers began melting down.
What did I do wrong? Should I have used larger than 10 gauge wire for the new secondary coil? Should I have wound it more times? Fewer times? Do I have my transformers wired wrong?
If you can answer any of my questions please comment below. It would be greatly appreciated.
I began working on it. After many hour of work and $80 spent it was finally finished. However, when I tried welding with it, it would not even arc. After half an hour of failed attempts I accidentally got my welding rod stuck to the metal I was welding. Before I even had a chance to remove it, one of the transformers began melting down.
What did I do wrong? Should I have used larger than 10 gauge wire for the new secondary coil? Should I have wound it more times? Fewer times? Do I have my transformers wired wrong?
If you can answer any of my questions please comment below. It would be greatly appreciated.
Second, do you have any experience with a stick welder? Difficulty getting a rod started, and rods sticking are the norm when first starting out. Look around for a class or another weldor, to get some time on known working welders. New welder and weldor (welder is the machine, weldor the person) together mean you can't tell where the problem is.
What kind of rod are you using? How has it been stored? Did you try cleaning off the end of the rod, to make sure it would make contact? (you might try a "bounce" start" to see if you can get an arc that way. hold the stinger a little loosely, and tap straight up and down, the idea is to get it to "recoil" so it won't stick - its one way to deal with crud on the tip of the rod, or when a rod burns "into" the flux coating - look at the end, and you will see what amounts to a tube of flux, that will need to get broken off before the rod can make contact. You need to learn regular "match" starting, as its hard to control the bounce start, it often bounces out of arcing distance, but it is a good way to "warm up" a stubborn starting rod)
BINGO!!!! Give the man a prize!
This was my first thought on reading the OP. Not nearly enough space has been devoted to this aspect. It's a shame, because the topic is dear to my heart. I'd build the welder in a heartbeat. I learned how to weld when I was ten years old; but my neighbors would absolutely freak out if I started arc welding on my back porch (the only suitable spot for doing it).
That said, if one isn't sufficiently knowledgeable to understand the basic electricity involved, one shouldn't be fooling with high-current AC. Sorry, kids. DO NOT try this at home without reading a book--even an article--on AC fundamentals. It looks like fun, but you can kill yourself, or burn your house down.
No, I don't have experience using a welder, but I had my dad try it (he's an experienced weldor) and he couldn't get it to work either.
I'm not sure what kind of rod it is. It has been stored for a while in a sealed container made for welding rods.
I used stranded wire that was too thin and got overloaded.
My second failure involved wrapping too tightly and cutting the insulation on a sharp corner of the transformer. This caused a short circuit. I fixed it by filing down the sharp edges around the transformer's hole and re-winding it.
I've made two of these welders. They both work but can only use thin rods (around 1/16") and they still trip the circuit breaker after a few seconds. Also they get pretty warm.
I used three smaller transformers in my first welder and two larger ones in my second welder.
The primaries (connected to the wall plug) are in parallel and the secondaries (the ones we rewind with thick wire) are in series. You should have 30 volts minimum.
Practice the one hand always in a pocket rule. This is probably the most dangerous configuration of scrap electrical components possible. Play it safe and get some help like T Bomber.
To everyone--> because I'm forcing myself to stop reading more comments on this intructable, out of the need for less worry in my life-- PLEASE understand that this instructable is intrinsically very SIMPLE, and yet there are a few key aspects of it that are dangerous to anyone who would be working on the circuit, be they professional or amateur. Get someone's help who at least kinda sorta knows what they are doing. Discharge that large capacitor in the microwave and test it with a multimeter to ensure that you got rid of all the voltage. Sometimes there is quite a bit remaining after the first "pop!" Be CAREFUL and fully understand the phase (think of it kinda like polarity) of the transformers, and if you don't have a clue what that means then just skip this build. You might spend a lot less time finding someone who will gladly show you how to weld, than you would on this project BTW.
I waited and watched craigslist (for a long time) until a Miller Dialarc 250 AC/DC came up for $300.....plus the $350 co-pay when my Dad threw his back out helping me. Don't lean over when you're man handling 180 pounds (1/2).
alwaysusually careful not to use my back when I'm lifting heavy loadsOur electricity in South Africa is 220v, and we also have a different frequency as well, which throws a big spanner in the works for me trying to follow the american guys' calculations. At the current moment I have lost interest in the project, when i am more motivated again I will try to "cool it down". For now I have made quite a few useful things with it, like a motorbike stand, and various tools.
Try thicker gauge wire, and then try another MOT or two and see what happens. Don't spend money on stuff!...That defeats the whole point of DIY... I put adverts up on gumtree asking people for their broken microwaves, and in a week, I had six microwaves! The copper i chopped out of the secondary windings, earned me enough money at the scrap yard, that I could buy all the wire I needed for my new secondaries, plus stuff like rod holders and clamps etc. I also bought my wire from a scrapyard, which meant I paid 1/10 of what it would cost me new.
How have you got your 6 transformers wired? Multiple MOT designs are usually a combination of series and parallel connections of secondaries.
Also did you leave the shunts in the MOTs. The shunts are to limit the power through the MOT, without them the MOT can draw too much power and overheat.
To reduce the welding current you actually may need to have more turns on your secondary, that means slightly thinner wire. This will give you higher voltage with less amps. You probably won't need as many transformers.
Tim had 20 windings to get 20V from each transformer. With two 1000W MOTs he got 40V at 50A for welding. That's a fairly low powered welder.
Your voltage and frequency should not cause any trouble with calculations.
Basically with a transformer Power in = Power out and Power = V x A
So if your secondary winding gives you 20V and you have a 1000W MOT then you get P / V = 1000 / 20 = 50 Amps.
As you can see if your secondary voltage goes up you current goes down and vice versa because the maximum power stays constant.
To calculate the maximum current on the primary 1000 / 220 = 4.5 Amps
To work out your turns ratio on the MOT just put 10 turns on the secondary using any thin insulated wire, we aren't going to draw current from it. Connect the mains to the primary and measure the voltage on the secondary, divide the voltage by 10 and you get your turns ratio.
EG secondary measures 12V that gives you 1.2V per turn.
Remove the wire afterwards.
Also you need to find the output voltage when tied together in series vs individually. They should add together (say 12V from one and 14V from the other gives 26V, which is low, but ok to weld with). If they seem to subtract (say you get 2V) you need to swap the wires on one of the MOT's. This is also very crucial to check if you plug in the two plugs into different circuits, as the may be on the same phase or opposite phase.
If you wired the output of the MOT's in Parallel, that requires a little more attention as to how you wire your MOT's
Also, you said I should measure the voltage output, but is it alright to use a multimeter?
As for measuring the voltages, by all means use a multimeter (just have it set for AC voltage..)