Microwave transformer mods

Discussion in 'General Electronics Chat' started by danbob, Dec 18, 2010.

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  1. danbob

    Thread Starter New Member

    Nov 30, 2007
    Objective: 90 to 100 volts dc at 25 to 30 amps

    Could I take 2 microwave transformers cut the tops off . then throw them in the mill and machine the cut surfaces. ( to make a variable current welding transformer they cut the top off, machine the two sides and then slide the top off center to lessen the current ) Then wind a new secondary and weld them together. I would double the core and more than double the secondary window.

    I only need about 70 volts ac to achieve my objective. But how much would the voltage drop at 30 amps? Would a large amount of filtering capacitance help eliminate some of the voltage drop?

    I have a little Forney 100 amp inverter dc welder and when you get down to 25 to 30 amps it is hard to start and maintain an arc. At these currents my welder puts out about 20 volts. I figure if I had one that put out 90 to 100 volts it would be a lot easyer to start and maintain a arc.

    Any thoughts on the feasibility of my plan would be appreciated.

    Last edited: Dec 18, 2010
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    You are at the limit of a standard household outlet for power. Most are rated for 15A Max, some 20A.

    I'd suggest getting a 220V Welder. You wouldn't be snapping a breaker all the time, and I may as well state that the safety is greatly improved.

    When working with those power levels, a regulated welder gives better results as well.

    Ever tried a MIG? I am in love with mine.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    The transformer idea was novel, but flawed. The metal core is made up of plates or sections that are stacked to form the core. If you weld across them you turn them into a large single piece of metal by that welded connection and that allows massive amounts of eddy currents to flow in the core while in operation. This will create large amounts of heat and eventually the core will 'smoke' the insulation off the wires and short out the circuit. You would have to disassemble and weld each individual plate, then grind it flat and varnish the bare metal before reassembly.

    One can connect the primary sides in parallel on multiple transformers and then connect the secondary sides in series for higher voltage. A second transformer wired in such a way would boost your output voltage, but as pointed out it will draw more current than a house outlet will allow.
  4. bertus


    Apr 5, 2008

    I think the safety can not be garanteed.
    We do not want you to get hurt by shock or fire.

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