How to Calculate Currents in a Simple Transformer?

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Homework Help Overview

The discussion revolves around calculating currents in a simple transformer, specifically focusing on a transformer with a primary coil of 2000 turns and a secondary coil of 150 turns, with an applied AC voltage of 240Vrms to the primary. The secondary is connected to a resistor of 300 ohms.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between primary and secondary voltages and currents using transformer equations. There is an attempt to calculate the secondary voltage and current based on the given values, while questioning the correctness of the approach. One participant raises a concern about the method used to find the primary current, suggesting that power balance should be considered instead.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem. Some guidance has been offered regarding the power balance between the primary and secondary circuits, and there is a general agreement on the calculations presented, though no explicit consensus has been reached.

Contextual Notes

Participants are operating under the assumption that the transformer has negligible losses, which is a critical point in their calculations. There is also a note about the resistor being in the secondary circuit, which affects how the primary current is determined.

mogley76
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Homework Statement



A simple transformer with negligable looses has a primary coil of 2000 turns and a secondary coil of 150 turns. if an AC current of 240Vrms is applied to the primary, calculate the secondary and primary currents if the secondary is connected across a resistor of 300 ohms.

Homework Equations


none given


The Attempt at a Solution



i Know this much : vs/vp = Ns/Np
so..
150/2000 * 240 = 18vrms which is vs
then v=ir so
Is = 18/300 : 0.06A
Ip = 240/300 : 0.08A

is all this right or am i horribaly wrong?
 
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The resistor is in the secondary circuit, not the primary, so you can't just divide the primary voltage by that value to find the primary current.

What you can do is recognize that the power delivered to the resistor in the secondary must ultimately be coming from the primary current source, and if there are no losses in the transformer, then the power should balance on both sides.
 


so secondary wattage= Is * Vs : .06A*18Vrms which is 1.08 w
and primary current = 1.08/primary vrms of 240 which is 4.5E-3 A?
 


Looks reasonable. You might convert your current values to mA for clarity.
 


great! thanks!
 

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