Step down transformer from MOT

Discussion in 'The Projects Forum' started by kriksis, Mar 2, 2016.

  1. kriksis

    Thread Starter New Member

    Feb 23, 2016
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    0
    Hello,

    People may start to think, that my only problems in life are all related to transformers..
    I disassembled a microwave oven and got the transformer. Since I am not big fan of arch welding, and I don't need 2100 vac output, I thought of rewinding it to something more useful. Has anyone done it? Maybe share some experience please? Is there any obvious downsides? (except the weight, of course).
    Now, if I can trust the internet, then 1.65mm² (15 gauge for American fellows) can hold approx 15 Amps with wire length of ~7.5m. (Or maybe I have I have gotten this completely wrong)
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
    948
    You are on the right track following wire gauge sizes.

    You will find that based on current times voltage = power, that larger wires give more current but also take up more room so you get fewer turns and therefore a lower voltage.

    No matter what size wire you choose, your power output will always be about the same.

    If it handled 1000 watts in its first life, you can reliably bet that 1000 watts is all you can ever get no matter what amp and volt combo you end up using.

    The size limit for your secondary winding will keep you from overloading the wire you choose.
    It will not prevent a short circuit or other problems from ruining your day but in normal use what ever wire you choose will be just fine.
     
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  3. SLK001

    Well-Known Member

    Nov 29, 2011
    820
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    What does "MOT" mean in your title?

    Does the transformer break down easily? (Probably "no").

    Have you ever rewound a transformer before?

    Instead of rewinding, you may be able to start removing windings from the secondary to get to where you want to be (provided that the secondary is on top of the primary, which they usually are).

    What is the voltage in your country?
     
  4. kriksis

    Thread Starter New Member

    Feb 23, 2016
    21
    0
    Hi, thanks for heads up. I'll try to poke around. Anyways, worst thing, is that I could blow my fuses.
     
  5. kriksis

    Thread Starter New Member

    Feb 23, 2016
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    0
    MOT stands for microwave oven transformer. No, it definitely does not break down easy. It has two welds on each side. Disassemble would require cutting open the ribs.
    I have not done this before. My first experiment. About the removing the secondary, well I am pretty sure I will damage some of windings. Also I want to rewind it with center tap.
    It's 230vac outlets here, where I am from.
     
  6. #12

    Expert

    Nov 30, 2010
    16,316
    6,818
    Theoretically, the window size for the primary and secondary are equal. The fatter the wire, the less number of turns because the more amps, the less voltage. Theoretically, it comes out as equal areas for equal power. You won't achieve that by trying to stuff the wire through the window, one turn at a time, because you can't match the nice, neat windings that can be had when everything is apart and easy to get at.

    I just use a Variac on mine to get enough voltage for vacuum tube circuits. The core is designed for a kilowatt, and I only need a tenth of that for some serious vacuum tube experiments.
     
  7. kriksis

    Thread Starter New Member

    Feb 23, 2016
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    0
    Yea, I am aware of fact, that I wont get the same power ratio with this technique, but as long as I have this heavy piece of gizmo, and stopping doors from closing is the next best thing I can think of, as use of it, I may as well try to do my best.

    I thought of buying a variac, but well, the price quickly made me change my mind. This transformer in fact, is meant to power tube circuit.
     
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
    948
    There is also plenty of room to make three separate secondary windings of the proper voltage for tube circuits.
    6.3 V, 90 V, and 400 V for one example.

    Also a variac is worth the price. There are so many ways it can be of use in design and troubleshooting as well as one off quick test rigs. Once you own one you'll wonder how you got along without it.
     
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