# Transformer Construction

1. Jan 8, 2013

### Hardik Batra

WHY in step up transformer, the number of turns are less in primary and copper wire is thick. Whereas in secondary number of turns are more and copper wire is thin.

In step-down transformer the situation is reversed.

I want the reason for this?

2. Jan 8, 2013

### Staff: Mentor

Fewer turns -> lower voltage -> higher current at the same power -> thicker cables required

3. Jan 8, 2013

### Hardik Batra

For in step up transformer, the frequency of the A.C. Voltage induced in the secondary has the frequency as that of the voltage in primary-----confusing why?

4. Jan 8, 2013

### Staff: Mentor

Why do you expect the frequency to change?
The magnetic field oscillates with the same frequency as the coils - they cannot have a different frequency.

5. Jan 8, 2013

### Hardik Batra

how the voltage be increase in step up transformer?

6. Jan 8, 2013

### Staff: Mentor

More turns -> higher voltage

Those two are proportional to each other.

7. Jan 8, 2013

### Hardik Batra

Your mean that more turn --> more resistance --> from v = IR --> more voltage ?

8. Jan 8, 2013

### sophiecentaur

How could it be a different frequency? 1. What possible mechanism could cause it and.
2. Which frequency would it choose to be?

What's confusing about that, if the only conclusion must be that it's the same.

9. Jan 8, 2013

### sophiecentaur

Did you think of looking up transformers / transformer theory on Wiki? You could avoid all these odd questions by just reading about it.

10. Jan 8, 2013

### Low-Q

Step up transformers are frequently used in SMPS for audio amplifiers in cars for example. The 12V from the battery cannot deliver much energy through a 4 Ohm load. Here comes the frequency you might be wondering about. In such SMPS the DC voltage from the battery is "sliced" into pulses by some electronics. This pulsed voltage is has a frequency at several 100 kHz. Thus the transformers are small and efficient with a few turns of very thick wire at the primary side, and a thinner (But still relatively thick) wire on the secondary side. The resistance in the windings are often less than 0.001 Ohm - on both sides, even though the secondary winding might have 10 times the resistance, but still very low. These power supplies (SMPS stands for Switch Mode Power Supply) are much more efficient than 50Hz transformes which is designed to transfer as much energy as the smaller high frequency transformer.