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Q & A: Transforming Transformers

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Most recent answer: 10/22/2007
why is it incorrect to connect the mains supply to the secondary coil of a step-down transformer so as to obtain a voltage higher than the input voltage?
- steven (age 14)
Braddell secondary school, singapore

As you know, here's how a transformer works. You have 2 coils of wire. Inside the primary coil (the one with a current from the power supply), there is a magnetic field caused by the current. An iron ring is usually used move this magnetic field over through the secondary coil. This magnetic field creates a current in the second circuit.

The voltage in the secondary circuit is related to the voltage in the primary circuit by the ratio of loops in the secondary to the number of loops in the primary (in other words, if there are more less loops in the secondary than in the primary then the output voltage will be smaller that the input voltage).

If you hook it up backwards you can (in principle) get the opposite effect, in other words instead of reducing the voltage you will be increasing it. The catch in all this is that most transformers are designed to work best in one direction, so that in practice you may not get it to work that well "backwards". The best thing is always to buy the right transformer for the job.


(published on 10/22/2007)

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