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Electromagnetic Relay Tutorial

The electromagnetic relay consists of a multi-turn coil, wound on an iron core, to form an electromagnet.  When the coil is energised, by passing current through it, the core becomes temporarily magnetised.


The magnetised core attracts the iron armature. The armature is pivoted which causes it to operate one or more sets of contacts. When the coil is de-energised the armature and contacts are released.

The coil can be energised from a low power source such as a transistor while the contacts can switch high powers such as the mains supply. The relay can also be situated remotely from the control source.

Relays can generate a very high voltage across the coil when switched off. This can damage other components in the circuit. To prevent this a diode is connected across the coil. The cathode of the diode is connected to the most positive end of the coil.


The springsets (contacts) can be a mixture of n.o  n.c and  c.o.

Look at the page on switches to see how they can be used in circuits.

Various coil operating voltages (ac and dc) are available.

The actual contact points on the springsets are available for high current and low current operation.

The REED RELAY has a much faster operation than the relays described above.

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