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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.

OUTPUT VOLTAGE = INPUT VOLTAGE * (NUMBER OF SECONDARY TURNS) / (NUMBER OF PRIMARY TURNS)

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.
POWER (WATTS) = AMPS * VOLTS

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.

Ahsan...sorry that you ran into so much trouble...I wish they were as wasteful over there as they are here (I have 8 transformers that I pulled from microwaves thrown to the garbage....free.....hahasad but true.<br><br>Anyhow you have to limit the current...a 5 pound transformer can only handle about 5 amps for a minute or so before the wire insulating the loops in the coil melts and shorts out... the problem is also that as it gets hotter it becomes easier for the insulation to melt (in the coils of the transformer especially....), so you need more experience then this to make a properly grounded setup before you do this, (and it isn't even safe WITH such a setup....but one way that I have sloppily thrown together a cooler is by putting the transformer inside acontainer and then putting that container into something shallow like a cookie pan or maybe just put mesh in the bottom of a bigger container to allow water to contact the bottom of the container that the transformer is in (metal is good for conduction of heat...but it makes it more dangerous)....then the outside of the transformer will not get much hotter than 100 Celsius (that is the boiling point of water.....assuming you keep it with water in it contacting the whole bottom surface....that will help the overall heat to disipate faster...but at a cost of safety more or less....sorry I cant be of more help....not too much time these days.
<p>What about putting transformer in large container filled with mineral oil?</p>
<p>good thinking...oil is used as a coolant...but it might be harder to get then water and also the fact that oil has higher viscosity (oil is more has more stickiness than say, 'water', it doesn't transport the heat away as well as something that is 'less viscous' (like water)...so it will end up cooling it...but won't dump the heat as easily as something that is thin like water...still you could use it if you had it....(more is better (MOST OF THE TIME)....overdesigned things NEVER BREAK....anyone who tells you different is a moron</p><p>;) good luck man.</p>
I made two transformers 1 with 28 turns other with 20 turms then center tap both of them, have check series several times, still i can only get 17.89 volts, can any one help?
<p>In general, if you add the two sources in series then you add the voltage....BUT...also you have to take into account that IF the transformers are different sizes and or different number of turns, or different size wiring, then the impedances of the individuals dont add together like 1volt + 1 volt = 2 volts...but rather 1 + 1 = 1.3 volts (a made up example).<br><br>Can you do anything about it....well if you want more voltage, more turns of wire and perhaps smaller wire if needed...or....if you want and can get another transformer of the same size and make them identical in design, then the theoretical voltage should add up like the 1 volt + 1 volt = 2 Volt example above.....so another words, to simplify things you should have the same transformers because the impedance will be the same in each respectively.<br><br>I am not an electrical engineer (I am a mechanical engineer), but I think that is the information you need. Hope it helps.</p>
thanks brother for your help it is very useful information for me but i already have bought 3 old transformers and waisted almost 30 meters of wire. here we already have 220 voltage so i think i don't to make two sources.<br><br>But as i was trying to resolve it I gave both primary coils 220, 220 volts from different sources and centre tap the secondary coils and it actually worked, but soon after 10 seconds secondary coils were smoked, i used insulated 8 gauge stranded copper wire. Then i did same with three transformers together and power was enormous but they could only survive 15 max.<br>
I made these transformer with 1 having 25 turns and other having 20 turns but i can only get 17.68 volts max, i had check series and all connections but still unable to get 38 or above volts, can any one help?
<p>Where N is the number of turns on transformer &ldquo;x&rdquo; or &ldquo;y&rdquo;<br>respectively, you can create two equations and two unknowns and solve for the<br>number of turns that you made and then check to see if the voltages 120V X Nx&hellip;out<br>of transformer X is what it theoretically should be (or close to it)&hellip;if not,<br>then think about why&hellip;</p><p>25/Nx (240)+20/Ny (240)=17.68 volts and</p><p>Nx(120) + Ny(120) =240 volt</p><p>6000/(Nx)+ 4800/(Ny) = 17.68 volt</p><p>120(Nx) + 120(Ny) = 240 Volt</p><p>Divide the 2 equations gives -&agrave;<br>((120(Nx)^2)/6000) + ((120(Ny)^2)/4800) = (240 Volt/17.68 Volt)</p><p>(3(Nx)^2/150) + (3(Ny)^2/120) = 13.575Volt/Volt&hellip;.--&gt;</p><p>Then solve for nx or ny and plug it back into one or the<br>other equation to get the other then check the voltage in each transformer to<br>make sure that it is somewhat close to the values you got (it wont be exact<br>because of impedance and nothing is theoretically perfect (resistence and<br>losses will make sure of that&hellip;., but it should be near the values&hellip;.</p>
I wired in series and used 220vac and it works great...before i had it wired 110vac and had them wired in parallel and it worked but kept tripping the breaker but, it worked.
<p>in uganda we use 240v instead of 110v power mains, would i still need to connect the transformers in series</p>
<p>It depends on the breakers for the circuits...I assume that with a 240 volt mains, it would be be connected to a 50 amp breaker.....so that means that the mains will dump 240 Volts at 50 amps...ie 240*50 Volt Amps....or 1200 Volt amps...ie 1.2KVa....if the breaker was a 30 amp breaker off your mains then it would be 240 Volts times 30 Amps to equal 720Volt Amps or 0.72KVa.....</p><p>That means that with the same voltage ...bigger breaker is better....so 50 amp would be better than 30 amp....now comes the safety part...</p><p>In order for the TRANSFORMERS to handle MORE AMPS they have to be bigger (the weight of the metal has to be bigger ....that way it doesn't over heat (the metal in the transformer can distribute the heat better if it is more massive...more surface area to get rid of the heat faster and more volume to take up the created electric flux field....</p><p>Also the wires need to be bigger to handle more amps....there are rules of thumb, but if you get 10 gauge wire...and just make sure that it doesnt get much hotter than will burn you, then you should be okay...you just make sure to turn it off before it gets that hot....(also remember that just because the surface is not hot enough to burn you doesnt mean that the wires in the inside of the transformer (the ones you cant touch) are not getting hot enough to burn you. </p><p>The heat burns through the insulation creating a short so dont destroy your transformer by letting it get to hot...</p><p>there is much more too it, but hopefully that helps....</p><p>more transformers are better than less....and also if your stick wont start an arc, then it is likely too low of a voltage (so add another transformer in series....and if </p><p>the welder sounds more like it is cooking bacon in grease, then that means that your amperage is too low for what you are welding...so increase it...(one way to increase it would be by using less wraps of thicker wire...</p><p>good luck man.</p>
<p>hey, do you think 4 (or less, it's just the amount of them that i have) beat up CRT televisions would be any good as to do something as this? Great Instructable :)</p>
How would you lower current to weld thinner material like a bought one. Is there a circuit to reduce it
<p>Hi, I've added your project to <em style="">&quot;</em><em style="">The Ultimate Collection of DIY Workshop Tools</em><em style="">&quot; </em>Collection</p><p>Here is the link If you are interested:</p><p><a href="http://www.instructables.com/id/The-Ultimate-Collection-of-DIY-Workshop-Tools/">http://www.instructables.com/id/The-Ultimate-Colle...</a></p>
<p>Is it possible to use amplifier power cable (8 AWG) with this project?</p><p>Also if i put a light switch dimmer on the 240v input would this be able to control the power?</p>
<p>Just curious, how did the 10 AWG wire work for you? I've got some 8 AWG and some 1 AWG, might test both out</p>
<p>I really like the information. I have started my own project and have the transformers both wound with 20 turns of 10 awg insulated wire. I have 23 vac out one transformer and 22 ac v out the other. Will these voltages be ok? </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?
<p>Leave it insulated, transformers work off of the magnetic flux running through the windings; if they are not insulated the path is much shorter, and not wound at all. </p>
I left it on and it works alright
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?
I actually dropped my core and it did slightly damage my primary. but it was still usable. I say keep going and if it doesn't work then use another one
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>
<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>

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