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automated variac o0-220Vac

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

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  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. poor mystic

    poor mystic

    1,061
    30
    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. missk

    missk

    3
    0
    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. poor mystic

    poor mystic

    1,061
    30
    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. missk

    missk

    3
    0
    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. poor mystic

    poor mystic

    1,061
    30
    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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