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Look around your house and you will see lots of small transformers. Whether it's your laptop, telephone or printer - they all use transformers.

Household appliances need electrical transformers because mains electricity is at a much higher voltage (the actual voltage depends upon where you live in the world). As a result we need a device capable of stepping down the mains voltage; this device is called a transformer.

A transformer is an electrical device used to convert AC power at a certain voltage level to AC power at a different voltage, but at the same frequency.

How does a transformer work?

A transformer has a central ferromagnetic core around which a number coils, or windings of insulated wire are wrapped. The input power line is connected to what is known as the primary coil, while the output power line(s) are connected to secondary coils.

Transformers utilise two basic phenomena:-

  • When an electric current flows, electro-magnetism is generated around the wires.
  • Whenever a magnetic field changes (by moving or by changing strength) a voltage is generated.

AC in the primary coil induces an alternating magnetic flux that 'flows' around the ferromagnetic core, changing direction during each electrical cycle. The alternating flux in the core in turn induces an alternating current in each of the secondary coils which have fewer windings. Note each transfer may have more than one secondary coil.

Secondary coils have fewer windings than the primary coil in a step down transformer. Consequently, less coils means less voltage, so the voltage is 'stepped down'.

Output voltage at each of the secondary coils is directly related to the primary voltage by what is known as the turns ratio. This equates to the number of turns in the primary coil divided by the number of turns in the secondary coil.

For example, if the primary coil consists of 90 turns and carries 240v and the secondary coil consists of 30 turns, then the transformer will step the voltage down as below:

240v x 30/90 = 80v. This is known as the secondary voltage.

You may notice that transformers in your home get 'hot', this is because transformers are not totally efficient and lose energy due to a number of reasons including, eddy currents, the resistance of the material that makes up the windings and a phenomena known as 'hysteresis'.

Transformers are available in a variety of forms including 'step-up' transformers. Some of the more common types are listed below:-

  • Audio Transformers
  • Auto Transformers
  • Current Transformers
  • Constant Voltage Transformers
  • High Frequency Transformers
  • High Voltage Transformers
  • Inductors
  • Relays
  • Soleniods
  • Three Phase Transformers
  • Toroidal Transformers
  • Variable Transformers
  • Voltage Transformers

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Guide Written by Paul Wilson

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