Mains Transformers

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  • barry wilkins
    Senior Member
    • Aug 2009
    • 172
    #1

    Mains Transformers

    Does anybody have any info on the impedance and inductace of mains transformers ?
    I did some rough calculations on a 100va transformer kit with a 240v primary ,it had a turns ratio of 4.21 ,this would make the primary turns close to 1000.
    According to info on Wiki. the impedance of a transformer is N squared.
    This equates to 1MegOhm ,using 2x pi x f ,I got about 3.2 mH.
    This seem a bit high to me ?
    Any help with this query would be appreciated.

    Barry Wilkins
    Tags: None
    • Th3_uN1Qu3
      Believe in
      • Jul 2010
      • 6031
      • Romania
      #2
      Re: Mains Transformers

      There are meters for this you know. Inductance depends on the magnetic material used, there is no general formula.
      Originally posted by PeteS in CA
      Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
      A working TV? How boring!

        Comment

        • barry wilkins
          Senior Member
          • Aug 2009
          • 172
          #3
          Re: Mains Transformers

          Yes I know you can ring transformer to see if it has shorted turns,some meters for flyback transformers work like this.Not sure you can do it at 50hz though.
          Checking an old transformer about 200W gave an inductance of 0.7 mH ,so the formula Z=N2 is way out ,so perhaps you need to divide it by a reluctance factor .

          Barry Wilkins

            Comment

            • lifthanger
              Member
              • Dec 2010
              • 10
              #4
              Re: Mains Transformers

              This is almost impossible to calculate because you'd have to know the exact permeability of the core material. This can vary a lot. According to Wikipedia ferrite has values ranging from 4 to over 10000. In Physics we always calculated with a given permeability noone told me I'd be licked in the real world .

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