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transformer inductance 16000H??

Discussion in 'General Electronics Discussion' started by komalbarun, May 18, 2013.

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  1. komalbarun

    komalbarun

    67
    0
    Nov 25, 2011
    Am a bit confused...

    20:1 step down transformer, 240V to 12V @ 0.3 A 3.6VA.

    what is the indcutor's primary coil's and secondary coil's inductance?

    I get 16000H for primary and 40H for secondary coil !!?

    pls help..I think my calculus is wrong or maybe it's my concept about the transformer itself which is wrong xD
     
    Last edited: May 18, 2013
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    16000H sounds a little high. How did you measure it?

    The ratio is correct though: the square of the ratio of the windings.

    Bob
     
    Last edited: May 18, 2013
  3. komalbarun

    komalbarun

    67
    0
    Nov 25, 2011
    well...
    V = -L I ?

    Pin = Pout, so ,
    240V x I = 3.6VA
    I = 3.6/240 V = 0.015A

    240 = -L 0.015
    -L = 240/0.015 = 16000

    am I making a mistake somewhere?
     
    Last edited: May 18, 2013
  4. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    Not V = I * L but V = I * Xl

    Xl = 2*pi*F*L

    You are too high by a factor of about 300.
     
  5. komalbarun

    komalbarun

    67
    0
    Nov 25, 2011
    how do I calculate the Xl if I don't know the L or vice-versa?

    how do I use 12V @ 0,3A 3.6 VA to calculate the L (if possible)?
     
  6. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    You measured Xl NOT L as I pointed out in the first equation.

    Transposing the second equation (can you do this?)

    L = Xl/(2*pi*F)

    The 0.3A is the maximum current that the transformer can provide in the load without getting too hot or dropping too much voltage. It has nothing to do with inductance.
     
  7. Raven Luni

    Raven Luni

    798
    8
    Oct 15, 2011
    Is it just me or are transformers much easier to understand than plain inductors?
     
  8. komalbarun

    komalbarun

    67
    0
    Nov 25, 2011
    thnx for that, its good to know ;)
     
  9. komalbarun

    komalbarun

    67
    0
    Nov 25, 2011
    lol I just understood what you meant by this xD, so if am understanding right :

    16000 = 2 * pi * f * L?

    16000 = 2 * pi * 50 * L

    L = 16000/ approx. 314
    L = 50H ?
     
    Last edited: May 19, 2013
  10. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    That looks right to me.

    Raven
    A simple transformer is relatively easy to understand but as soon as non linear effects or energy transfers are included, my mind boggles. Inductors can be used in so many ways.
     
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