Build a Microwave Transformer Homemade Stick/Arc Welder

Step 5 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"

Comments

[OVERLOADED]

wouldnt wiring the sec in parallel give you double the amps?

[oskymike]

yup,ya got that one right,push pull sort of thing,wire them up then check the voltage on the output,(careful,currant ,not voltage kills)

[OVERLOADED]

yes thats right thanks i got zapped by 60kv and didint die lol but its funny im a welder and i can zap myslef with sparks of about 3/4 inches from the tig machine on my finger and not feel any jolting ? can you explain why?

[timmy300]

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?

THANKS

[clayfigur]

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..

[microedit]

About the three prongs...one is ac electricity always on, the next is used only if there is a short to it... i.e. bad wiring....the third the government added for the housings of appliances, so a short would not get to a person touching the appliance. But ...a double short would still get you (very rare!). Also, the second wire is necessary to complete the AC circuit but never has juice...its just a conductor (unless a short).

[dph84]

The first prong is the "hot" conductor, which represents one end of a single-phase "edison style" power distribution transformer out at the street... the second prong is the center tap of that transformer...(it has 240v overall, the center tap is a difference of 120v, and when you use both "ends" of the transformer out at the street --both "hots"--it gives you 240v.) The only reason the second prong does not "have juice :?" on it is because it is connected (bonded) to the third prong--the bonding electrode conductor--at the breaker box. Effectively telling the power distribution transformer where ground is. However the second prong DOES "have juice" during half of the cycle of AC...Its just that it has no potential to ground because they are the same point, provided you are close enough to the point where they meet. The bonding electrode is to give a low resistance path back to the breaker box in the event of a short, in order to trip the breaker--but you can and do get the living daylights shocked outta you before the very SLOW tripping of breakers occurs. That's why breakers are there to prevent fires, but GFCI protected circuits are to protect personnel. Just wanted to get that all corrected. Thanks :)

[dph84]

Note: I gave voltage for the U.S. by mistake. In the U.K. the voltage in the uk is 230, but the real distiction to be made is that it is 50hz instead of 60hz.

Frequency change affects transformers like this: raising the frequency (more than the nameplate value) causes the transformer to "fight itself" more--i.e. more heat, due to less effeciency...though this is not considered unsafe as long as it can be dissipated. Lowering the frequency, on the other hand, causes the transformer to "not restrict itself enough" (to understand that one, take an AC power class...) thus causing TOO MUCH CURRENT to flow through the windings themselves... which can cause meltdown. Its not simply a heat thing, though it becomes heat. it is an overcurrent thing.

[tmelnik]

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]

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.

--DH

[larze]

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?

[stayputnik]

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.

[lenny25]

Aaaaaaaaaaah....*lightbulb* .Thanks so much that answers a lot of my questions. So it's not just high amps that you need you also need a fair amount of volts. I tired it with one. I thought i had blown my wall plug, cos it didnt want to work, but then i just reset my earth leakage and now its back to normal, I got another transformer, so i will give it a bash now. So the way to wire it is: Primaries in parallel and secondaries in series.

[agb6]

No . The reason being welding demands high current and low voltage . The primaries need to be wound in series considering that you are having a 220 V wall socket . The secondary here needs to be connected in parallel , since by doing so you'll be able to supply a greater value of current into the welding joint at a much lower voltage which you wpouldn't be able to achieve when the secondaries are connected in series

[ac-dc]

If you are in an area where wall outlets are 220V, odds are any microwave transformer you find will also have a primary meant for 220V. If that is the case, and you can tell easily enough by what power cord plug is on the microwave, then you would still wire the primaries in parallel, and still wire the secondaries in series.

Whether the secondaries are in series or parallel depends on how many wraps around the transformer you can get, it will vary based on how large the transformer was. I had a microwave like the one pictured which had a much larger transformer than what you find today in the sub- $100 models even if the newer one is rated similarly like 1200W.

As someone mentioned already, if you are below 30V or so you will need to wire secondaries in series. It is not really true that welding "demands" low voltage, it is simply that it does demand fairly high current. Higher voltage is more dangerous, and to have both high voltage AND high current would raise the cost quite a bit, but if you make the voltage too low not only will it not arc, but the impedance of certain metals will in itself limit how much current you can pass unless the clamp is nearer the working area.

Easiest would be to just wind the transformers, do connect the primaries in series for a moment, and measure the output from each transformer's secondary with them not connected, to determine what the voltage is of each.

It is important to note that you do not want to connect the secondaries in parallel if they are not VERY near the same voltage, otherwise you have power going from the one which is higher voltage to the one which is lower.

[charlieb000]

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...

[evza134]

from what i understand and have been told by my boilermaking teacher, its almost always better to stick weld AC that way you avoid arc blow.

[natcrazz]

Can I use only one transformer if I intend to weld only thin metal for small jobs and artistic purposes?

[clayfigur]

make a spot welder, use bigger wire, lesser turns... its ideal for thin sheet metal..
use a copper or carbon rod instead of welding rod...

I am also thinking of making one my self... already have 3 stick welder and a migwelder.. I need to make a spot welder for thin sheets...

[englishmanjsz]

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.

[agb6]

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 .

[jules15]

my microwave is 120volt. cant i just use a 120 socket with one transformer?

[dylanz333]

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)
Thanks.

[jonathandirtbiker]

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???

[sthealthraider]

What 2 plugs!!??!

[dtvercon]

can two 110-volt welding transformers be connected in series and plugged into a 220 volts mains outlet?

[TimAnderson]

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.

[taino1]

Hi Tim, Q: How did you wired the two PRI to connect to 220v?

[TimAnderson]

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.

[inserbot]

Thanks.

[dtvercon]

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]

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.

[thomas6149]

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.

[xBrainstormerx]

So uhm I don't think I'm getting this does the primary connect to the secondary at all?

[stayputnik]

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.

[thorning]

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

[matroska]

Well I think there's 2 power outlet probably because one wouldn't supply enough power. I haven't built it yet, I'm in the careful process of understanding and planning. I also believe that the ground clamp is the way for the circuit to be completed, for the electricity to make a loop, otherwise hey it won't work :). I think that in this case, it's unrelated to the walls power outlet. I'm not sure about this, but I think walls outlet ground is only a safety (I repeat, I'm not sure), as many device don't have the third prong. However, I've noticed that sensitive deviced and heavy duty devices (e.g: microwave oven, power bars, high end gaming console) have one, although it's not a rule.

[markthsmallth]

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 guy]

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]

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.