Step 4: Wind the new transformer secondaries

We wound 20 turns of 10-guage wire on each transformer. That's just about how much wire would fit into the available space. It took a little over 20 feet of wire each.

tip: draw tally marks on your table to keep track of the number of windings.

How does a transformer work?
The primary winding is an electromagnet connected to alternating current.
The humming magnetic field of the primary induces a current to flow in the secondary winding. If both windings have the same number of turns, the output voltage is the same as the input.
(minus a smidgin due to eddy currents, resistance, etc.)
If the secondary has more turns than the input, its output voltage is higher. That's the type of transformer you started out with.


Our primary has 100 turns and gets connected to 100 volts AC. We're winding 20 turns on the secondary, so we'll get about 20 volts out.

The available POWER STAYS THE SAME regardless of what the output VOLTAGE is.

If the primary is made take 1000 watts (100 volts * 10 amps) out of the wall, we'll be able to take 1000 watts out of the secondary. With 1/5 of the windings, we can draw 50 amps out of the secondary.

That's the cartoon version with play numbers anyway.
Over here in our shed full of reality we've got two of these beasts in series and plan to short the outputs through a welding rod like Jennifer Beals.

Let's just say we're going to pull a whole lot of amps, which is why we need to wind our secondary with such thick wire.

The copper conductor in ten-guage wire happens to be 1/10" (0.1") in diameter.

Here's a table of conductor diameter, guage, and current rating.

In the process of removing my secondaries i bent the primaries on one of my transformers. Should i keep going with it or scrap it and find another junk microwave? They look to be fine and dont look like they will short out but looks can be deceaving. Is there any way to test the primary coils to see if they are junk?
this is stolen from Grant Thompson, who made a much prettier one
<p>to be fair, people have been making these for ages. Also its includes her experiences with the project so it is not the same thing.</p>
<p>Please send us a link to the stolen one.</p>
Would there be a problem if I used two different sized transformers?
100% honest, I ran 2 plugs in a series and I thought I was running them each on a separate fuse in my garage but I wasn't, then I turn it on and the power goes out. I tried resetting the breaker box but I still haven't gotten any power. Im almost positive I made a mistake when I tried to run an extra plug
<p>if you didwire 2 plugs to 1 transformer than your house=Fried</p>
just a quick question for better understanding when you wrap the 10g wire around for the secondary winding do you strip any insulator from it or leave it on?
I left it on and it works alright
<p>I would highly recommend a larger wire than 10 AWG. My 70A welder has what looks like 8AWG and it gets so hot that it actually melts during long welds. Its helps to use the same exact wire on the electrodes that you've used around the transformers, because you can at least feel when it is getting too hot before it melts and causes a fire, but the minimum is not recommended.</p><p> I've looked at many of these DIY welders and the reason that they are a fire hazard is that many of them use a smaller wire around the transformers than they use on the transformer. If you do that, you will never know when the wire inside is getting overloaded. At that point, it will get so hot that it can ignite a wooden enclosure, or short to the case and melt the steel.</p>
<p>Quick question, How dumb is it to try and run one of these with no power controller like a VARIAC?</p><p>(or the SCARIAC from grant thompson)</p>
<p>Its either full on, or completely off. You'd melt the metal!!!!!!!!!!!!!</p>
<p>But melting metal i is what you want to do. Correct this is full on, but that doesn't mean it can't do a range of work. By selecting the rod size and adjusting the technigue used</p>
<p>Not dumb at all. As is this can do fairly large range of welding jobs depending on the skill of the operator.. Using multiple transformers one can create a unit with selectable heat ranges. Multiple heat ranges cane be created depending on how one winds the secondary on a sing transformer frame. Basic commercially available welders don't have very sophisticated power controllers. Simple is less expensive and trouble free for years</p>
<p>Its either full on, or completely off. You'd melt the metal!!!!!!!!!!!!!</p>
<p>Why dont my posts stay, so I follow this website for the dimmer,</p><p>scr-based switching circuitry to vary the power,</p><p><a href="http://www.dansworkshop.com/2008/03/homebuilt-arc-welder/" rel="nofollow">http://www.dansworkshop.com/2008/03/homebuilt-arc-...</a></p><p>I hope this isnt gunna cost more then $100 cuz I coulda just bought a welder.</p>
<p>Where does one buy a Solid State Dimmer for Inductive Loads??????????</p>
<p>Would this work?</p><p><a href="http://www.avdweb.nl/arduino/hardware-interfacing/spot-welder-controller.html" rel="nofollow">http://www.avdweb.nl/arduino/hardware-interfacing/...</a></p>Arduino spot welder controller / solid state relay <p>I bought it, and the parts and its all soldered. I found some different transformers. Ones out of a 1100W output unit, I will try to find something similar to double it up.</p>
<p>&quot;A solid-state dimmer that's rated for inductive loads does the same thing and costs a lot less.&quot;</p><p>Where does one buy one of these? I have seen other web-pages where they use a regular wall dimmer switch, but lights/ceiling fans use 1A. Im sure using 2 Transformers you need a dimmer rated for much higher.</p>
<p>I doubt this will get responded too in time, I just scored 3 transformers, one huge one out of a Frigidaire 1400W, things heavy and big. I will go to to a appliance part store and buy a second if the price is right. Otherwise can I use a different transformer, like from a 1100W microwave. Maybe I should have just bought a hobby welder.</p>
<p>Hey yeah, so that regular household wall dimmer is put on the input of the transformer, so it would work. Would need to be rated for 25A or more for UL rating. Each light is usually rated for 1A, usually 12-15 put on a circuit to the panel. Might work better that way.</p>
<p>These are simple enough, but one thing I have not been able to come across is a DIYer addressing the current limiting. 10 gauge wire, even at 1000 feet is less than an ohm impedance, which would put your primary at 120Amps - way too much for a household circuit. Secondary windings should use even greater gauge and have even less resistance, that it becomes negligible. So the only room left to bring down the amperage must be the inductance/reactance from the transformer itself and the resistance of the metals you are welding, which is not much either. Unfortunately, I have not studied transformers in depth yet, and do not know what kind of impedance the transformer would have on the circuit. If anyone could help, I would appreciate it. I'm looking to make a 300A welder with a ratio of somewhere between 50:1 and 37.5:1 </p>
<p>I guess I don't understand what you are asking for . 300A is pretty high output for a welder . Of all of my experience welding , ( 40 years ) I have never needed that much current . You don't clearly explain what you mean by &quot; ratio &quot; ( voltage ratio ? ) . If you want the welder to function , you will need 35-40 volts output . At a 37.5:1 voltage ratio , you would need to feed the primary with somewhere around 1300 to 1500 volts . ???? Anyway , try studying electrical theory , such simple things as Ohms law , Watts law , and Kirchoffs law , basic transformer theory is not that difficult once you get a handle on it . </p><p>Cheers !</p>
<p>yes, I am familiar with all of the basic circuitry laws. I have been collecting microwave transformers and have 4 or 5 now that I can use to build an arc welder. Your 35-40V rule helps. My predicament lies with the fact that professional grade welders (~$500 range) seem to go up to around 250A on a 120VAC (RMS) rail, which I want to duplicate.</p>
<p>Less voltage on sec = more amps.</p><p>But author says 30-40V is sweet spot for some reason.</p>
<p>My original comment was inquiring as to what reactance (which I have not studied much about) was limiting the power draw from the household outlet. 120V*15A=1800Wmax from standard circuit breaker. This translates in a perfect world to 1800W/35V=51.42A left for the transformer. This is where my problem lies - not enough.</p>
<p>But again, the 1800W is only acquired by some form of impedance (reactance, capacitance, resistance, etc.) which must come straight from the imperfections of the microwave transformers in every DIY arc welding tutorial, thus making values unpredictable. Else, the Amperage could be infinite.<br>Also, sorry to hijack this thread.</p>
<p>Duty cycle is an important consideration with welding machines , which would be really difficult to predict with a homebrew handwound transformer . In this article , the author checked to see if the transformer was getting hot . I guess it depends on how you plan to use the welder .This guy explains duty cycle pretty well for commercially made machines :</p><p><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/X0ut4KRwP44" width="500"></iframe></p><p>Things to take into consideration . When welding , depending on what you are working on , chances are that you would &quot; burn &quot; a rod and lay down a bead , then let the metal cool and chip the slag . 30% duty cycle or even less should be adequate for most home projects . The authors transformers were in open air , if you put them in an enclosure ( recommended ) you may want to add a cooling fan . The temperature rating of the insulation on the secondary winding would be important too . Varnish coated &quot; magnet wire &quot; might be a better choice for the secondary winding rather than plastic insulated wire ( better heat transfer ) . But this project appears to work just fine , without a lot of cash outlay , I like it !!</p><p>Cheers , take care , and have a good day !...73</p>
<p>OK,</p><p> This may be tricky but doable. Source two identical pair of transformers. Two of &quot;type A&quot; and two of &quot;type B&quot; will be fine. Convert each as described and assemble into two welders. Use one &quot;type A&quot; and one &quot;type B&quot; for each. You should now have two welders with IDENTICAL open circuit output voltage. Now, after the following tests, place them in parallel. CAUTION, TEST PHASING AND VOLTAGE FIRST!!!!!!! Phase test - - place ground clamps together and measure between rod holders - - - should be at or near ZERO volts! If not, place ground clamp on other end of one welder and test again! ZERO - -? GOOD. NOW, in steps, increase the sensitivity of your volt meter to ensure that the voltage is indeed ZERO between the rod holders. If not Zero, subtract one turn at a time from one transformer until you have ZERO Volts between rod holders. THEN and ONLY THEN, clamp a rod holder to each clean end of a rod. It should NOT even start to get warm! NOW, and ONLY NOW, clamp both rod holders to the same end of a rod and start welding. You have a two level welder now.</p><p>Open circuit voltage of a transformer is the ratio of input turns to output turns times input voltage so any two, three, or more transformers can be voltage matched by changing output turns, one at a time! </p>
<p>Caution Caution Caution !!!!!! </p><p>For safety DO NOT USE separate line plugs for each transformer. Once tested, use a single plug! If, after testing you manage (AND YOU WILL!!!!) to reverse a plug, or worse plug into different wall circuits, YOU WILL GET SMOKE or WORSE.. Place a fuse in EACH wire going to each transformer primary as well!!</p><p>If you are too poor to place a switch in the primary of each transformer pair, at least plug them into a single POLERIZED duplex outlet, itself having a single cord and SINGLE plug to the mains (wall).</p><p> Also, it is safer to not parallel the rod holders if one is not turned on. </p><p>I speak from Experience HERE!!! </p>
<p>If a microwave transformer is used, and the magnetic shunt is not removed, then there is current limiting. The magnetic shunt adds an effective series inductance which will limit current even if the secondary is short-circuited.</p>
<p>Hope you have had a chance to study up on Transformers. You will find that it is the 'Turns Ratio' that determines the voltage and current of the Secondary. </p>
For most transformer 'problems' like this, it's ok to consider PowerIn = PowerOut. So Vin x Iin = Vout x Iout.
<p>You are right but you MUST first have the specifications of the transformer secondary winding wire gauge to ascertain maximum load carrying capacity. You don't want a situation of the secondary overloading resulting in fireworks !</p>
<p>Voltage yes, Current is dependent on a lot of factors such as transformer inductance, resistance, frequency and magnetic flux coupling</p>
<p>hi i want to have a complete specification for the the secondary wire </p><p>please give the diameter of copper inside insulation </p><p>if possible a clear picture </p><p>any help from anyone is much appreciated</p>
<p>Naw, as Nike like to say &quot;Just Do It&quot;</p>
<p>This is very nice BUT, this isn't as efficient as an actual stick welder. I have took apart tons of microwaves and a few welders. So I know what's going on with this. Nice how you rigged the wiring to make it work. But EVERY stick welder has a bigger transformer than a microwave roughly 30%. So granted this works great for you especially just using spare parts! But if you wanted something that does every job and have proper circuit protection I'd recommend buying one for only $100 from Harbor Freight. So don't get me wrong I still like this project especially if someone who doesn't have a budget and make something from nothing! </p>
<p>&quot;</p><p>But if you wanted something that does every job and have proper circuit <br>protection I'd recommend buying one for only $100 from Harbor Freight.&quot;</p><p>$100 or free, and are they comparable in terms of what you can weld? I doubt it. Hooking up multiple transformers in series you can weld thicker metal, the thickest Ive seen for the cheap hobby welders is very thin.</p>
<p>I have two transformers, a big one and a smaller one, can I use them together, or they must have the same type?</p>
<p>Ideally you want them to be both the same, but maybe you could use different ones, but maybe they cant be too far different in terms of winding turns guage, length etc. I dont really know though.</p>
I'm hoping you could help with a solution or anyone reading the comments as I am trying to figure out my dilemma. My homemade welder is ran off 120v/20a circuit with nothing else sharing it. I have 12 gauge feeding the two transformers and 6 gauge for the secondary(10 wraps for one and 12 for the other). The transformers currently are wired in parallel since that's the only way to get a good arc, when in series there's not enough current to start one. I've checked the secondaries to make sure they're not out of phase but after I get one bead or if the rod sticks then the breaker trips. What exactly am I missing?
<p>your breaker is tripping because the plugs that your welder are plugged into are in the same circuit you need to have them 180 degrees from eachother so they a re on diffrent circuits King of random talked about it pretty good honestly and yes this will require lots of extension cords I know I wasn't happy about having cords running through my house either </p>
<p>Yes, from other videos you need one from one side (left) and another from other side of the panel. Look on the panel, what the switch is. Panel outlet is on its own circuit, central vac, microwave outlet, garage outlet, deck outlet.</p><p>&quot;</p><p>A solid-state dimmer that's rated for inductive loads does the same thing and costs a lot less.&quot;</p><p>Where does one buy this? is it a regular wall dimmer, there is no elboration on this at all, makes me wonder sometimes!</p>
<p>hi! this is my welder from transformer. </p><p>secondary 50v </p><p>weld 25v 120a </p><p>( sorry my poor english) </p>
<p>solid-state dimmer that's rated for inductive loads</p><p>What should I look for in rating or whatever for a dimmer? Looks like a great project! I have the transformers and the #10 wire on hand now. My granddaughter wants to do a little welding...</p>
<p>This is pretty hairy, and I know next to nothing about welding: Why not use the 240V dryer hookup for power? Of course that may prove impractical. It must be accommodated differently.... </p>
I have a variable speed control for rotary tools, would that work for the power contol?

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