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Can a 28-0-28 amplifier toroidal transformer like this be practically used as a high current supply at low voltages? I plan to put a couple of turns of 4 gauge wire through the centre. I want to use the power supply for heating metals to red-hot temperatures fairly quickly, so the current output has to be pretty high. I would use the stock primary.

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  • \$\begingroup\$ Do you mean 2A instead of 2V ? \$\endgroup\$
    – efox29
    Sep 30, 2014 at 18:32
  • \$\begingroup\$ No, I don't. I want high current (>20A) at any voltage (even half a volt will do). I want to use this to heat metals to red hot temperatures. \$\endgroup\$
    – AvZ
    Sep 30, 2014 at 18:33
  • \$\begingroup\$ What VA rating is the transformer? \$\endgroup\$
    – Andy aka
    Sep 30, 2014 at 22:44

3 Answers 3

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You may be able to do that. A better setup: using a microwave oven transformer (MOT) from an old microwave, with the secondary removed, and a new secondary from a few turns of very heavy gauge wire (as heavy as would physically fit). This tends to produce on the order of 1500-2000VA, for example 200A at 10V with ten turns, or 1000A at 2V with two turns, depending on the MOT. One especially nice feature is the magnetic shunt which regulates the peak current, unlike your toroidal. That means the current is appropriate for the primary, ie it won't trip the mains breaker; however it does NOT mean the new secondary won't melt down :) Check this out: http://mad-science.wonderhowto.com/how-to/turn-microwave-oven-transformer-into-high-amperage-metal-melter-0140772/ or just google "microwave oven transformer welder" for lots of examples.

Do be careful, as this is a mains powered circuit. It is good to put it in a grounded metal box, with a safe way to connect and disconnect from the mains (a switch rated for mains voltage and heavy current). The hazards on the output side are less about electrocution and more arcing and fire. Needless to say, when shorted, this produces enough heat to melt itself down, as well as potentially set nearby stuff on fire. This kind of device is very hazardous, you have been warned.

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Yes, certainly. I would guess you might need four or five turns to get 2V which could be a bit of a tight squeeze.

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You can do that. It would be more efficient if you take off the stock secondary first. If you then want a specific minimum voltage you can either count those, or test how much 10 windings of the thinner, easier stock wire will give you.

Once the stock secondary is gone, you can use very thick wire to fill up the entire window, but it'd work better if you use multiple thinner wires, as even at 50Hz or 60Hz AC at very thick wires there will be at least some current fringing and/or skinning. Basically a current at some frequency likes the surface of a conductor more than the middle, the higher the frequency the sooner a 1mm dia wire will stop conducting altogether, but for 50Hz it is already advised not to go much thicker than 10AWG or copper foil. But copper foil is difficult with torroidials.

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