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Centre tapped Transformer

Discussion in 'Power Electronics' started by Srinivasa Rao Beera, Jun 26, 2018.

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  1. Srinivasa Rao Beera

    Srinivasa Rao Beera

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    Apr 7, 2017
    We are using centre tapped transformer - 9V-0-9V /500mA for power supply. Circuit I made as below. For 200mA load , I am getting Vload is "4.5V" only. Let me know where is the issue , it has to work for load 9A/500mA right.

    Or transformer is faulty, tried with two transformer , result is same.
    upload_2018-6-26_9-25-2.png
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I assume you used a multimeter in DC range to measure? Your supposed DC is superimposed by a large AC ripple. You need to apply a smoothing capacitor.
     
  3. Srinivasa Rao Beera

    Srinivasa Rao Beera

    5
    0
    Apr 7, 2017
    I have added electrolytic capactor , sorry it has missed in circuit. still it is "4.5V" .
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Have you verified that the AC output of the transformer is 9-0-9 VAC?
     
  5. Srinivasa Rao Beera

    Srinivasa Rao Beera

    5
    0
    Apr 7, 2017
    Yes , it is coming around 10Vac measured with multimeter in AC mode.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    So therefore about 20V across the ends of the windings?

    What does it measure with the load connected
     
  7. kellys_eye

    kellys_eye

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    Jun 25, 2010
    The readings you give are consistent with a 4.5-0-4.5V (i.e 9V centre-tapped) transformer. This is NOT THE SAME as a 9-0-9V transformer.

    Have you checked that the primary voltage is correct i.e. you're not running a 240V primary on a 120V supply?
     
    SOLARWIND01 likes this.
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    And your mains voltage is 230V?
     
  9. WHONOES

    WHONOES

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    May 20, 2017
    Is the phasing of the transformer secondary's correct?
    Using the notation: S = Start of winding and F = Finish of winding, the secondary must be connected in the order:
    S, F, S, F. Otherwise the secondary's will effectively be in parallel which means that it is giving half wave rectification rather than full wave. If this is so, your output voltage will be 9V - forward drop of diodes, assumed to be 1V x 0.637 which calculates to 5.096V.
     
  10. 73's de Edd

    73's de Edd

    3,070
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    Aug 21, 2015
    That transformer construction automatically has the wiring done by the manufacturer, so that its going to have proper series phasing relationships.
    Any chance that you made a boo-boo on one diodes polarity of installation, or that you have one open diode ?
    How much capacitance is the main filter and is your load resistor in the order of 20 Ω' s ?
     
  11. WHONOES

    WHONOES

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    May 20, 2017
    Are your measurements with or without a load?
     
  12. davenn

    davenn Moderator

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    Sep 5, 2009

    when measured where ??


    you should be getting ~ 18V across the transformer
    or ~ 9V between the centre tap and either winding end
     
  13. WHONOES

    WHONOES

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    May 20, 2017
    What diodes are you using and what value is you smoothing capacitor?
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    As best I can tell, he is posting from a place that has 220V (ish) mains.

    Or more accurately "is no longer posting from..."
     
    SOLARWIND01 likes this.
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