Rectified AC across transformer

Discussion in 'General Electronics Chat' started by apurvmj, Oct 27, 2013.

  1. apurvmj

    Thread Starter New Member

    Sep 28, 2012
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    It happen to be working with rectifiers (full & half wave) I observed that I could get half wave rectified wave transfer from primary of isolation transformer to secondary but couldn't with full wave rectified AC wave (filters not used).
    Could someone pls answer it how.
    Thanks
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    How are you connecting the rectifiers in question?
    Max.
     
  3. apurvmj

    Thread Starter New Member

    Sep 28, 2012
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    normal bridge rectifier & in other case a single diode, then feeding it to isolation transformer (1:1) & checking the output at secondary. Hope this time I'm clear.
    Thanks.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    You can't feed DC (rectified AC) through a transformer. They are AC only. You need to put the rectifiers at the output of the last transformer in the chain.
     
  5. ian field

    Distinguished Member

    Oct 27, 2012
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    ..........unless you're driving a saturable reactor.
     
  6. apurvmj

    Thread Starter New Member

    Sep 28, 2012
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    I know.But have you ever tried it with half wave rectified wave form. It does get transferred from primary of transformer to secondary. Which baffles me.
    As the theory goes transformers works on changing filed of electromagnetic induction. So shouldn't it work with rectified AC; half as well as full wave. But it seems it works with half wave rectified only.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Your using it as a pulse transformer, it is not what it is designed for.
    But what are you trying to achieve here?
    Max.
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    To attach your circuit will help the discussing.
     
  9. apurvmj

    Thread Starter New Member

    Sep 28, 2012
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    Pls find attached photo. No definite purpose but just an observation.
     
  10. Ramussons

    Active Member

    May 3, 2013
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    Measure with an oscilloscope - there will be an output; but much less than with a half wave input.

    Ramesh
     
  11. apurvmj

    Thread Starter New Member

    Sep 28, 2012
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    Ya I didn't checked it on oscilloscope but on voltmeter. But I wonder why are full wave rectified waves are blocked. Checked it on 50 hz power supply.
     
  12. Ramussons

    Active Member

    May 3, 2013
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    The rectified wave has a DC and an AC component. It's the AC part that causes magnetic flux variation resulting in a "transfer" of voltage across the transformer windings.

    In a full wave rectifier, the AC component is less than in the case of half wave rectifier, and the transfer is less.

    See what happens when you load the secondary.

    Ramesh
     
    anhnha likes this.
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    One of the early methods used on mobile equipment such as automobile radios that required a DC of around 200vdc, in order to produce AC was to use a mechanical vibrator, this switched or alternated the primary between battery -ve and +ve.
    The secondary was rectified in the usual way.
    There was also a synchronous vibrator that switched both primary and secondary in sync, so that no rectifier was required.
    Google should turn up examples.
    http://www.youtube.com/watch?v=Fp6PkRTmb8U
    Max.
     
  14. ScottWang

    Moderator

    Aug 23, 2012
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    The frequency of full wave rectified AC wave are 120Hz, so you have to make sure that your multimeter is a real rms multimeter.

    Does it shows any brand of the multimeter, any infos?

    Take the 1:1 transformer away and measuring the voltage of output of diodes bridge, does the multimeter shows any voltage?
     
  15. apurvmj

    Thread Starter New Member

    Sep 28, 2012
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    at above,
    " Take the 1:1 transformer away and measuring the voltage of output of diodes bridge, does the multimeter shows any voltage?"
    -Yes it does.

    -I don't want to find RMS value, finding peak is enough for me.
    My problem is, in rectified ac wave emf goes from 0 to max. and then to 0 thus a varying magnetic field. so shouldn't it (transformer) give rectified ac wave at secondary of transformer ?
     
  16. ScottWang

    Moderator

    Aug 23, 2012
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    When you used the half wave rectified, the width of waveform of the low voltage was enough to drive the transformer, but when you used the full wave rectified, the width of waveform of the low voltage was not enough, you can see the waveform of full wave.

    The most of the iron cores for the 50/60hz transformers, their frequency of response almost < 400hz, when the width of waveform of the low voltage is too narrow, it means that the frequency is too high, so you can't get the voltage from the output of the isolation transformer.
     
    Last edited: Oct 28, 2013
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