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Turns ratio

Discussion in 'Homework Help' started by FramedShirt, Oct 3, 2015.

  1. FramedShirt

    FramedShirt New Member

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    Guys, I have an assignment here which I have been trying to calculate for almost an hour but I still didnt get the answer. Heres the problem.

    If Ep=120 VAC and Es=25.2 VAC, determine the turns ratio (NS:NP) of the transformer.

    Quick and appropriate response will be highly appreciated. Thank you.
     
  2. Inquisitive

    Inquisitive Super Moderator

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    [​IMG]

    Where P = Primary, S = Secondary
     
  3. Ratchit

    Ratchit Well-Known Member

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    Why are you having a problem with this? Es/Ep = Ns/Np gives an answer of 25.2/120 = 0.21
     
  4. dave

    Dave New Member

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  5. FramedShirt

    FramedShirt New Member

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    What I need obviously is the ratio .. and yeah BY the Way I already got the answer.. and its 21:100.
     
  6. Inquisitive

    Inquisitive Super Moderator

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    Np = Number of turns in the primary
    Ns = Number of turns in the secondary
    Ep = Voltage of primary
    Es = Voltage of secondary
    Ip = Current in primary
    Is = Current in secondary

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]


    [​IMG]

    So, the ratio is:

    [​IMG]

    There are 4.76 turns in the primary to 1 in the secondary.
     
    • Informative Informative x 1
  7. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Turns ratio is usually expressed as a ratio of two integers, so 476:100, so factor the numerator and denominator and reduce it.

    e.g if it were 15:5 = (3*5)/5 = 3:1
     
  8. mvs sarma

    mvs sarma Well-Known Member

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    in general
    they wont wind a transformer at 1turn per volt. Instead they use 4Turns per volt for a good trafo.
    worst case cheap ones use 2.5turns /V. Such ones core gets dam hot even at 10% loading.
     
  9. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Anyway 476 = 2*2*119
    and 100 = 2* 2* 5 * 5
    So 120/25.2 = 4.6:1 = 476:100 = 119:25; They are all right, but typically it's expressed in a ratio of integers.
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I have a Chinese transformer that came with a cheap product. Its output is rated at 9VDC/100mA but is about 19V with no load. It gets very hot even with no load. With a 100mA load its output is its rated 9VDC.
     
  11. tunedwolf

    tunedwolf Well-Known Member

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    Must be one of those magical Chinese ones, I don't think I have ever seen DC make it out of a transformer, alive at least :p
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    My cheap Chinese "transformer" (wall wart adapter) transforms the 120VAC into 9VDC.
     
  13. tunedwolf

    tunedwolf Well-Known Member

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    I knew what you meant bud, I was just joking with you :D
     

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