# The Maximum current in a transformer

1. May 1, 2012

### claybrow

I have attached the problem. This is a practice exam and the answer Imax = (N2/N1)^2 * (Emax/R) but I have no idea why. I have been trying to manipulate the transformer equation I2/I1 = N1/N2 = V1/V2 but to no avail. Thanks

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2. May 1, 2012

### Staff: Mentor

Welcome to the PF.

To derive the equation to transform the load impedance from the secondary to the primary, start with the two equations for how voltage and current are transformed going through the transformer:

I2 = ?? * I1

V2 = ?? * V1

And then take whatever ratios you need to in order to see how the secondary resistance transforms to the primary side (that it, what load resistance the primary voltage drive source sees, based on the turns ratio)...

3. May 1, 2012

### Andrew Mason

Just to add to what Berkeman has said, use the clue that there is no energy lost in the transformer. What does that tell you about the product EI in the primary and secondary?