# Homework Help: Transformers Current and Voltage

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1. Apr 30, 2015

### xvivi

1. The problem statement, all variables and given/known data
A transformer has a turns ratio of 5 : 1. It is connected to a 230 V supply and an output (secondary) current of 2.7 A is measured. If the transformer is 90% efficient, calculate:
1. Secondary voltage
2. Input (primary) current

2. Relevant equations
Pout/Pin*100=efficiency

3. The attempt at a solution
I dont think it can be solved as most of the equations dealing with transformers assume an ideal transformer.

2. Apr 30, 2015

### Noctisdark

Hi Xvivi,
The ratio is 5:1, just to remind that even the tronsformer isn't 100% efficient the output is yet the same, the only thing that changes is the ouput current,
You can pull out the ouput voltage, use the fact of thethe 90% efficiency to determine the input current, good luck !

3. May 2, 2015

### Staff: Mentor

In your analysis here you do include an ideal transformer, then add an external resistance to it to account for its non-ideality.

4. May 2, 2015

### CWatters

Work out the secondary voltage assuming an ideal transformer.
Work out the output power
Work out the input power allowing for the efficiency being 90%
Work out the input current.