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Transformer Technicalities?

Hey guys I need some help from the experts. I am building the microwave transformer ark welder instructable. I have acquired my microwave transformer, and rewound the secondarys. Now here's where it get interesting. I stay in South Africa, and we have 220v, 15amps coming out of the wall. So I figured with so much wall power I probably only need one transformer, cos I already have too many amps (on paper). So from what I understand, I will be putting 3300watts(220v*15Amps) into this transformer. Another interesting detail is that I think my transformer has 200 turns! I put 16 turns on the secondary (although there is space for more, I just don't have a piece of wire long enough). Which means that my out put voltage will be 17.6v, and 187Amps! Ahhhhhh!!!! If I wind a few more turns on the secondary, I could probably squeeze 25 on there, that will bring my output voltage to 27.5v and 120 amps. Which seems like quite a lot? So here's my question: Will this work? If not, and things go bad, what will happen? Is there any chance that the primary coils will melt, or is it only the secondarys that will do that? I don't really want to destroy my transformer, because they are really hard to get here. South Africans won't give you snow in winter. I had to buy a broken microwave! One idea I had: I have a single coil wrapped around a plate iron core, it looks just like a transformer but with only one set of windings. The thing is as big as the microwave transformer, its wire is of a slightly thicker gauge, and it probably has about 600 turns on it (it belonged to a florescent light setup). I thought I could connect this up to the secondary winding, maybe it will bring the amps down, and also serve as an inductor/ark stabilizer. But I'm just guessing, I'm a complete noob to electronics!?

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appolo7 years ago
Hi, you don't have 220v, 15 amps coming out of your wall socket. This is the maximum amount of load current you can draw from it! You can't overload your transformer with power, the transformer will only take enough power it requires to work. So say the transformer when completed requires 6 amps_ then that's all the current it will draw from the wall socket... Not 15 amps. The item that looks like a transformer is probably what's known as a choke. I haven't seen this instructable but be judged by the authors experiments. If the secondary windings are not connected to anything then they are basically known as open circuit so nothing nasty will happen. Only when you strike an arc will you draw a heavy current through you added winding. If you allow the welding rod to stick to the work piece in an attempt to strike an ark, then you basically have what's known as a short circuit. Under these conditions the transformer will draw a heavy current and get extremely hot so practise striking an arc while avoiding the weld rod sticking onto the work piece.
lenny25 (author)  appolo7 years ago
Cool thanks for the advise so far. So I connected the primary coils up to the mains and the secondaries to a welding rod and the other clamped to a piece of steel. I tried to strike an ark, but nothing happened, no sparks, no sticking, zip. My mains did not trip, but for some reason the wall plug no longer worked. Being slightly clueless and fearing the wrath of my wife, I reset our earth leakage and switched the mains on and off, and hey presto, the plug works again. But that still leaves me quite puzzled as to what to do to get this thing to arc. Do you think if I add some more windings it will work? I now have another transformer, do I add this one into the equation? Will it help, If so in parallel or in Series. Also does anyone know which one of the secondary wires must be clamped to the workpiece and which one connected to the rod?
snotty lenny255 years ago
If you want to reduce your voltage, I'm pretty sure you can put a big chunk of steel in series with your secondary wires and this will act as a high wattage resistor.

Also I think that since these are AC welders, there is essentially no difference which of the secondary wires you connect to the rod. AC does not have a designated plus or minus wire BUT there is a "hot" wire which is usually black and a white wire as well as a green ground wire.

I suggest grounding the body of your welder.
in welding its all about the current for the most part, but if the voltage is too low then you will not be able to strike the arc.  get a volt meter and measure the output of the transformer, you will need about 40 volts to stick weld, so you may need to add another transformer
40V? I had my microwave welder running pretty well at a little around ~32V. That was in Japan where the wall voltage is about 100V.