How The Transformer Works

A typical transformer
A transformer

With detailed explanation of how the step up and step down transformers works. You will learn what happens inside the transformer during voltage step up and step down. This is how the transformer works made simple.

For long distance power transmissions, high voltage and as small a current as possible is the best; this reduces energy loss in the transmission lines, and smaller wires can be used, saving on material costs.  Certain areas or appliances need a smaller or larger amount of voltage than the one in the transmission lines. The transformer does the necessary work of converting the voltage received to the required voltage which will be used in homes or appliances.
The transformers near our homes convert to the voltage required by our homes and the transformers in our appliances convert the voltage at home into the amount required by the appliance housing it. A typical phone charger may receive 120V or 240V from the home supply, (note that household voltage varies from country to country) but the transformer in the charger converts it to around 5V required to charge the phone. Let’s see how the conversion occurs.

How a transformer works
You probably remember opening up an electronic device (like a radio or charger) and then not being able to put it back the way it was, sometimes you got out the transformer and wondered what it is and what it does inside the electronic device. Transformers use the principle of electromagnetic induction and they work only with Alternating Current (AC): they do not work with Direct Current (DC).

A transformer raises or lowers the voltage (or current) according to need. As shown in the image above, the transformer is made up of primary, secondary coil and a ferromagnetic material (core). When the primary coil is connected to source of electrical power (AC Current), it produces fluctuating magnetic field around it. The core effectively links the magnetic flux produced by the primary coil to the secondary coil. This magnetic field induces a motion of electrons at the secondary coil producing another voltage and current at the output (secondary coil), due to electromagnetic induction.

If an ordinary conductor is used in place of the core, it would just conduct the voltage received by the primary coil straight to the secondary coil. Also, if there is no material for the core, that is, if the magnetic flux is transferred through space, the flux movement will be less effective because flus travels 1000 times better in metal than in air.

The net EMF (Es) at the secondary coil (output) is the sum of individual EMFs per turn.

EMF (Electromotive force) is what makes the electrons move from atom to atom. How much electromotive force is present between two points in a circuit is measured in units of Volts. Voltage is a "Unit of Measure". If you were to apply enough electromotive force to move 3.25*10^18 electrons through a resistance of 1 ohm in one second, your voltmeter would read 1 volt.

How do you get a particular voltage at the primary and then produce a different voltage at the secondary?
This is simply achieved by increasing or lowering the number of turns at the secondary keeping the primary steady. When the two coils have the same number of turns, the EMF at the primary will equal the EMF produced at the secondary. This is true because the same magnetic flux is passing through them.

Lowering Voltage is achieved by decreasing the number of turns at the secondary, which gives a Step Down transformer. Increasing voltage is achieved by increasing the number of turns at the secondary, which gives a Step Up transformer. Current involves movement of electrons so if you have more turns, it means increased wire length and thus more electrons which will result in more current. Also if you have less turns, it means reduced wire length which will ultimately reduce the amount of moving electrons resulting in less current.

This is confirmed by the formula;
Transformer calcuations formula
Transformer formula

Where; Es is the EMF produced at the secondary,
Ep is the EMF at the primary,
Np is the number of turns at the primary,
Ns is the number of turns at the secondary.
So for a transformer of 960 turns (Np) at the primary coil receiving 240V (Ep) to produce 5V (Es), you need 20 turns (Ns) at the secondary coil. As you have properly guessed, this is a Step Down transformer.

Also a transformer receiving 50V (Ep) at the primary with 100 turns (Np) at primary coil and 1000 turns at secondary coil will produce 500V. What kind of transformer do you think this is?

Visit electronicstutorials for more formulas and calculations on transformers.

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  1. excellent ... but i want more details and photos ... i read this
    its good article also ... i want a lot of information about transformer ... i must write educational report about transformer

  2. Okay I see what you mean. I will do something about that. Thank you.
    Our post on Electric Motors is also very interesting and easy to understand.

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