Turns ratio

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

1. FramedShirtNew 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. InquisitiveSuper Moderator

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Where P = Primary, S = Secondary

3. RatchitWell-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

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5. FramedShirtNew 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. InquisitiveSuper 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

So, the ratio is:

There are 4.76 turns in the primary to 1 in the secondary.

• Informative x 1

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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 sarmaWell-Known Member

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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.

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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.

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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. tunedwolfWell-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

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

13. tunedwolfWell-Known Member

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