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How to work out the turn ratio on a transformer

  1. Jun 4, 2008 #1
    I would like to know how to work out the turn ratio on a transformer from having just the input and output voltages.
    Last edited: Jun 4, 2008
  2. jcsd
  3. Jun 4, 2008 #2
    For an ideal transformer (that is, no losses in the windings or in the core), the turns ratio is just N = Vp/Vs where
    N = turns ratio
    Vp = primary Voltage (rms)
    Vs = secondary Voltage (rms)

    In real transformers, the turns ratio will be slightly higher (typically about 2%) than what is calculated by this formula. One way to improve the accuracy of the calculation is to use a primary Voltage that is only about 10% of the rated Voltage.
  4. Jun 4, 2008 #3
    For example = 244 / 9.88 = 24.6

    So the turn ratio is 24 - 6
    Last edited: Jun 4, 2008
  5. Jun 4, 2008 #4
    There are two types of transformers,step-up transformer(sut) and step-down transformer(sdt),the turns ratio for (sut)is bigger than 1 and for (sdt) is less than 1.
  6. Jun 4, 2008 #5


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    what? isn't it 246 to 10? or 24.6 to 1?
  7. Jun 4, 2008 #6


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    There are quite a few more types of transformers than just step-up and step-down (e.g. autotransformers, buck-boost, isolation).

  8. Jun 5, 2008 #7
    Thank you

    How do you calculate the out put voltage of a transformer when you only know the input voltage
  9. Jun 5, 2008 #8
    its based on the ratio as stated
  10. Jun 5, 2008 #9
    Is there a formula for working this out please
  11. Jun 5, 2008 #10
  12. Jun 5, 2008 #11
    The formula is in post #2. But, you can only solve for one unknown when you have only one equation. If you don't know the turns ratio, you must measure the primary and secondary Voltages.
  13. Jun 5, 2008 #12
    thank you
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