Build a Microwave Transformer Homemade Stick/Arc Welder


Step 5: Schematic

Picture of Schematic
It's a pretty simple circuit.
In fact there's nothing in it except wire!

We'll take two transformers and wind low-voltage secondary windings on them with thick wire.

We'll put the secondaries in series with our welding rod and workpiece.
We'll plug the primaries into the wall.

I really like the way aaawelder put it: "do not include yourself in this circuit"
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OVERLOADED2 years ago
wouldnt wiring the sec in parallel give you double the amps?
tmelnik3 years ago
so..... i just wanna know this... does the ends of the secondarys (where the actual welding is being done), does the secondary connect anywhere!? like how do you get power to the secondary if the ends are just the welding stick, and the ground?
dph84 tmelnik3 years ago
Listen very carefully--if you don't understand how power gets to the secondary--then DO NOT attempt to build this device. (at least not at this time) Because that is extremely evident to anyone qualified to build this. I'm not trying to sound rude. I'm simply stating that it is basic electrical theory. The answer to your question is that in an AC circuit, a coil creates an electromagnetic field which expands and can induce a voltage on another coil. The primary coils being energized make an electromagnetic coupling which is the basis of how ALL transformers work. You may have some experience with DC cirucits and I want to encourage you to learn your way up to the point where this instructable is obvious to you, too. But as far as now, be SAFE, and don't mess around with this circuit. If you want proof, check out the extremely sad story that young man's mother wrote on a previous page.

timmy3005 years ago
Hi guys. im from the uk. i want to use two MOT's for my welder, but i dont undeerstand how to wire them up correctly and safely. Ok so in everyones elses MOT arc welder are the transformers with in series to each other or in parralel? How to i connect all the primary wires into a 13amp three pin UK wall socket?
I havent got my MOT's yet but does anyone know what kind of current i can get out of 10 turns of thick wire on both transformers with an input of 230v @ 50hz? Also i heard that somone used 10awg wire and it melted can anyone recomend a good thickness and a supplier?

if you have a 3 pin wall socket... the third one must be a ground wire... connect the earth wire/ground wire to the casing of your MOT welder....

Its better to make a welder, using thicker wires on the secondary, even with lesser turns.You just need to add another transformer..

I tried 2 transformers, 10AWG 10 turns each... secondaries in series, primary in parallel.

then 3 transformers 8AWG 7 turns each... secondaries in series, primary in parallel. (this works better)

I'm also thinking of making a 4 transformer welder, as soon as I find one more...

Anyway, as added cooling, i used the fan found in the microwave, to cool of the unit from heat. a little aluminum heat sink would also help..

charlieb0004 years ago
why is there no DC rectifier in your circuit? (do note you will need a large number of diodes to cope with the current, and will drop the output power by a bit), i thought it was better to DC weld...
natcrazz4 years ago
Can I use only one transformer if I intend to weld only thin metal for small jobs and artistic purposes?
if the one primary is connected to the mains, and the other open-circuited, then NO damage, short-circuiting or quenching will result. However, current will be induced in both of the secondaries, AND in the primary of the second transformer (with the O/C transformer). Due to the shape of the transformer core layout now being unconventional, the efficiency will be reduced, as will the output. The cores are likely to create eddy currents (of magnetism) and, thus, get hot. Another thing to watch out for, is the direction of windings (are they wound clockwise or anticlock?) If the transformers are close together, and the primaries and/or secondaries are connected in opposing phases, they will try cancel out and burn up. Output current should be matched to the primary value. If the output is rated higher than the input (by using lacquered wire, which allows a greater diameter of conductor, for example), then the primary will overheat/burn out. A fan in the cabinet would help reduce a heat problem, and increase reliability and duty cycle. I hope this is of help.
In fact if one transformer primary is connected and the other transformers primary is kept open circuited , its secondary however connected , then in this case the transformer whose primary is connected to the supply source will get loaded heavily at the beginning . This is because of two parameters , one being the welding load and the other being the inrush current for the o/c transformer's primary . The primary here is being fed from the secondary . So the magnetising current required on the lv side would be much higher since it has to induce 220 V on the primary side . This would cause immense loading oin the connected transformers primary thereby causing it to overheat .
jules154 years ago
my microwave is 120volt. cant i just use a 120 socket with one transformer?
dylanz3334 years ago
Is it possible to run a 110v line for each transformer?  Just like your schematic, but in the end it would be 220v total?  If this is possible, can I connect them to a standard wall outlet? (one plug over the other)
Okay well im confused so  how do i wire the transformers to the wall?? Do i use the existing plugs for the transformers?? Does it matter which way the windings are and hoe does all this wiring work???
What 2 plugs!!??!
dtvercon5 years ago
can two 110-volt welding transformers be connected in series and plugged into a 220 volts mains outlet?
TimAnderson (author)  dtvercon5 years ago
Yes. Mine is set up that way now. I was blowing the circuit breaker too much. So I wired it up for 220 and made a long extension cord with 220 volt connectors.
Hi Tim, Q: How did you wired the two PRI to connect to 220v?
TimAnderson (author)  taino15 years ago
if your microwaves were made to be plugged into 220v, do it just as in this diagram. If you're wiring a pair of 110v primaries for a 220v socket, 1: connect the adjacent wires of the two primaries together. 2: connect the two other wires from the primaries to your 220v source. 3: If something bad happens or nothing happens, disconnect it and switch around the wires from one of the primaries.
Thanks, Tim. I was thinking more of 2 separate complete units (each one with its own primary/secondary windings and electrode holder) so 2 welders can weld at the same time. Can the 2 units, if 110v, be connected in series to a 220v power line?
TimAnderson (author)  dtvercon5 years ago
I don't know. Maybe it would probably be better to wire them both for 220. Or maybe the electrons wouldn't notice the difference between those two options.
thomas61495 years ago
I built one similar to this with two pairs of transformers in parallel for double the amperage. One pair had an off on switch and the other pair was controlled by an incandescent light bulb dimmer switch to control the output. If you plug in each pair and they growl, it is out of phase, reverse the input wires on one transformer. If the two pairs wired together growl, reverse the output wires on one pair.
larze5 years ago
So if you connect two transformers primaries in series (for 220V) then wouldn't it just be all the same use just one transformer? Because, with 2 x windings on both sides it makes the ratio equal to 1 x windings, for example 2:20 = 1:10. Right?
the primaries aren't actually connected in series. the 2 primaries are separate circuits since they're plugged into separate outlets and aren't connected at all. you connect the *secondaries* in series to double the voltage going through the weld. if each transformer with a power of 1,000 watts (total of 2,000 watts) outputs 20 volts at 50 amps individually (for the sake of argument), you won't get a decent arc unless you put the secondaries in series to give you 40 volts with 50 amps. using just one transformer won't give you high enough voltage to arc well (which usually requires 30+ volts)... nor would it give you sufficient amperage to sustain the arc. in short, one transformer couldn't supply enough power... and if you tried, you'd probably melt the insulation on your secondary and end up frying the whole transformer.
So uhm I don't think I'm getting this does the primary connect to the secondary at all?
Nope. In a transformer, the primary and secondary windings are completely separate circuits. When a current runs through the primary coil, it produces a strong electromagnetic field that induces a current in the secondary coil. Same concept the makes generators work (magnet passes by a coil) and radios as well (coil in the transmitter connected to an antenna produces an electromagnetic field, which is picked up by the reciever's antenna causing a current to be induced in its own coil). RFID uses this concept too... the tag or card doesn't need its own power source because its power is induced by the reader's coil interacting with the card's coil. Sorry for the extraneous information... I just think this stuff is cool.
thorning5 years ago
I am building the welder but am a little confused about your schematic. It shows 2 plugs for the primaries. I thought they were wired into a single 110 volt plug. Also you dont show a grounding wire in any of the diagrams from the 110 volt side. Isnt this necessary as all the outlets in modern wiring in the USA use a 3 prong plug with the 3rd round prong being the green ground wire. Also there is no fan shown. I intend to put a 110 volt fan into place to cool the transformers. It came out of the microwave anyway when I took it apart to use the transformer. I also hope to use some sealer around the secondary windings to keep them in place and a 110 volt indicator light and a switch on the 110 volt side. The switch would be OK if I dont need to use 2 plugs. Any comments ? Tom H
im in the uk and here you dont need to earth devices that have an insulated case or have two layers of insulation to a metal case. while i cant gaurantee anything, it sounds like it would be the same in the usa. reegardless, you need to earth these transformers. just run a wire from the earth pin and bolt it FIRMLY to each transformer. and you can wire it to one plug. just link the 2 wires from one trasformers primary(the side connected to the power) to the others and wire to one plug. also the fans would be a good idea.
welder guy5 years ago
is it possible to hook up the transformers 120-110 volt house end into each other? like in parallel or something where they both share the voltage? or do you need two outlets? please reply someone
TimAnderson (author)  welder guy5 years ago
You can do it either way. I wired mine in parallel. It's one less wire to put away. When it was running on 110 that is. I now have it wired for 220 with the primaries in series.
eric m5 years ago
didn't explain the parallel & series part well enough.

220 = one outlet so you need to go series.

110= less hassle to rewire the transformer. just use the original plugs. Looks less commercial and pro and more GHETTO but it's less work.

kixter015 years ago
my question is do have to conect the secodary coils to the prim or just leave them un conected..
jdpower6 years ago
If you bare the tops of the transformers.(removing the clear coat) place them top to top, then power one PRI. You will fiend that the unpowerd transformer has an out put. My ? . Is the field from the powered PRI. strong enuf to support two seconderys?
jdpower jdpower6 years ago
Thinking a little . The power from the single PRI. would be shared buy the secondery wiendings. Just kinda hit me like that.