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automated variac o0-220Vac

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Discussion in 'General Electronics Discussion' started by missk, Aug 12, 2011.

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  1. Aug 12, 2011 #1
    missk

    missk

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    Apr 7, 2011
    Hi

    I need to use an Atmega MCU to vary the voltage from 0-220Vac on the primary of a 220V//2000V transformer. I was looking into using a stepper motor to control a variac using a pulley/belt system. But considering that this is only a part of the bigger picture, it seems complex as I need to take into account torque considerations and such.Any chance that somebody may have a better or different idea?
     
  2. Aug 13, 2011 #2
    poor mystic

    poor mystic

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    Apr 8, 2011
    Hi Missk :)
    there are a lot of good things to say about a stepper-motor-controlled variac in a power supply, but as you say they aren't always the best solution for a given problem.
    There are as many other ideas as you want to think about and lots more, too! Eg proportionally controlled triacs, phase-cutting triacs, series resistances, series reactances, pulse-width modualtion, dot dot dot.
    Perhaps you could give us a few more details?
     
  3. Aug 15, 2011 #3
    missk

    missk

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    Apr 7, 2011
    Hi Poor Mystic

    I have been considering the options and I got a suggestion to use my MCU and a DAC to generate a variable ac waveform...then use a high power om amp....and then a step up transformer to get this to 0-220Vac for my transformer primary. I think this could work. Do you think this solution would work? Using a motor controlled variac would be too costly...
    Thanks for the reply
     
  4. Aug 15, 2011 #4
    poor mystic

    poor mystic

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    Apr 8, 2011
    There's plenty of good potential in that idea.
    Of course the amplifier that feeds the step-up transformer has to provide all the power required by the load. What is the load please?
     
  5. Aug 15, 2011 #5
    missk

    missk

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    Apr 7, 2011
    Let me give you the bigger picture, Im trying to build a Hi Pot tester, using a commercial microwave oven(220:2000). I've got to vary my input voltage from 0-220V ac automatically using my MCU to the device under test. Ive got to detect a leakage current of 50mA.

    Now im apologising in advance if Im not answering the question you are specifically asking me, because im still a bit hazy with the specific details....I'd use ohms law for the resistance on my transformer secondary right?2000/50mA=40k..... is that it? or are you asking me about the transformer primary?
     
  6. Aug 15, 2011 #6
    poor mystic

    poor mystic

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    Apr 8, 2011
    Hi Missk
    I'm wondering how much power you'll need on the 2000V side, and I'm very doubtful that an op-amp can supply it, whatever it is.
     
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