transformer question - how to calculate?

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dacflyer
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transformer question - how to calculate?

Post by dacflyer » Thu Oct 18, 2012 12:20 pm

i have no clue of transformer math.,,well just enough to be dangerous..lol

here's the question..
transformer has 120v in - 12v out with 1 amp load.

what is the input load ma.?
and what is the ratio of turns

how do i solve this ?

i looked online for transformer calculator, but there is no way for me to enter the info i have.
i looked at transformer load calculator.. still not finding what i want to know..

is there information missing in the question or ????

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Bob Scott
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Re: transformer question - how to calculate?

Post by Bob Scott » Thu Oct 18, 2012 3:17 pm

Turns ratio should be almost identical to the voltage ratio: 10:1
In the real world, the transformer manufacturer probably adds a few more secondary turns to compensate for resistance losses in the primary and secondary windings when the transformer is under its rated load.

Input and output VA should be the same. Input load current will be 10 times lower that the output load current of 1 Amp. Input: 100mA.

EDIT: Actually the primary current also has the (small) magnetisation current. Probably too small to be concerned with, and its 90 degrees out of phase with the load current so that makes it even less significant with the input current reading.
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Re: transformer question - how to calculate?

Post by dacflyer » Sat Oct 20, 2012 6:14 pm

thanks.. that will help me now :) for that part..

but is there an equation for this or math of some sort...or would it be complicated ?

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Re: transformer question - how to calculate?

Post by Bob Scott » Sat Oct 20, 2012 11:19 pm

dacflyer wrote:but is there an equation for this or math of some sort...or would it be complicated ?
er... What are you trying to do? Are you investigating regular 60 Hz sine wave power transformers with laminated cores? Or are you wondering about high frequency power supplies using ferrite cores?

Are you planning to build one or modify one? Are you familiar with flux density?
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dacflyer
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Re: transformer question - how to calculate?

Post by dacflyer » Sun Oct 21, 2012 7:44 pm

phuu.. already too many questions..lol
i am just trying to prepare of a test..i remembered it had 1-2 questions on transformers.
they did not specify what make they were., but i am assuming they are
laminated iron core 60hz variety.
i think i have enough info to pass them few.
next i need to brush up on resistor math... one over type math...measuring current or voltage in series or parallel or both, ughhhhh...

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Bob Scott
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Re: transformer question - how to calculate?

Post by Bob Scott » Mon Oct 22, 2012 8:32 am

Test Questions! Why didn't you say so!

God luck with the test. :grin:
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Re: transformer question - how to calculate?

Post by gerty » Mon Oct 22, 2012 9:26 am

Turns ratio = Np/Ns
Where Np = number of turns in primary and Ns = number of turns in secondary.

Voltage ratio Vp/Vs = Np/Ns

wher Vp is voltage on the primary and Vs is voltage on the secondary.

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