Hi,
I was asked to determine the voltage on the primary side of the transformer and i was stuck. The data is given below:

Turns Ration (Ns/Np) is 2/5 and the secondary current is 700mA.

How to calculate primary voltage? Any help will be appreciated. Thank you!

 

If that is all the information you have then it is impossible to know.

 

Hello,

With the given information, only a ratio can be given.
Read this wiki page:
https://en.wikipedia.org/wiki/Transformer

Bertus

 

Thank you!

 

Thank you!

At zero current, and within the range of the transformer, the voltage ratio is the same as the turns ratio, which makes it easy. But real transformers are seldom perfect, but good ones are fairly close. This sounds like a homework problem without passing us all of the information. In that case the information to get the desired answer was either in the lesson or in the textbook, neither of those is available to me.

 

At zero current, and within the range of the transformer, the voltage ratio is the same as the turns ratio, which makes it easy. But real transformers are seldom perfect, but good ones are fairly close. This sounds like a homework problem without passing us all of the information. In that case the information to get the desired answer was either in the lesson or in the textbook, neither of those is available to me.

Thank you!
If more information was given, i would have calculated it myself. Moreover, it was not a homework problem.

 

The what IS the problem? If it's not homework, then it had to come from somewhere? If you provide the full context of where it DID come from, perhaps we might at least be able to help you figure out what questions you need to ask whoever asked you to do it.

 

Hi WBahn,
The question is still the same one and it has been answered i believe.

Thank you!

 

Okay. I didn't see the answer.

So... what IS the voltage on the primary side?

And how was it determined from the information given?

Or are you saying that you agree that the "answer" is that no answer can be determined?

 

Thank you!
If more information was given, i would have calculated it myself. Moreover, it was not a homework problem.

Thanks for the clarification. My comment about a homework problem is because I see some posts that are homework questions where the individual has not provided the description of the circuit that is being used for the question.

One more thought is that in a perfect transformer, one with 100% coupling and no losses, the current ratio is close to the reciprocal of the turns ratio. So that could provide an estimate of the primary current. BUT still, there is not enough information to know the voltages. If the secondary load resistance were known, approximate values could be calculated.

 

RE:""Turns Ration (Ns/Np) is 2/5 and the secondary current is 700mA.""
1) It means it is trafo increasing the voltage ie diminishing the current. It means the primary current will be 0,7A * 5/2. But as we dont know any of voltages or Wattage, there is impossible to speak about voltages.
2) For rough tumbrule of any trafo calc, use the formula turns for each Volt = 48/Sc where cross section area Sc is given in cm2. Formula works only for 50Hz. Thus, if You find as an example that t/V=20, then 220Volt demands 4400 turns and 12 Volts demand a 240 turns etc.
Ampearage You find out of the formula J=i/A(w)=3,5 A/mm2. Where A(wire)=pi()/4*D^2=78,4% of D^2.
The max power You find measuring the window cross section and applying the P=U*i where U=1/(turns to Volt) and i=J*A(w)=3,5*Q/2 (mm2)*k(cu) where coeff of filling the window of copper will be between 0,2 at small diameter wires and 0,4 at rather thick.
So:
t=48*V/S(c), cm2;
wire D=sqrt(i/0,784/3,5), mm;
gabarite-power P(W)=S(c)/48*Q/2*3,5*k(cu), cm2 and mm2 respectively.