# Relay  (magnetically operated switch)

Relay is a magnetically operated switch. It opens or closes a contact or contacts when an electric current passes through out an electromagnetic coil. This coil is part of the relay.

Its main operation is accomplished by the coil, making an attraction or repulsion of an armature. This armature connects or disconnects the relay terminals.

## How a Relay works?

• If an electric current passes through the coil, it pulls the armature and connects points C and D.
• If no electric current passes through the coil, the connection is made on points D and E.

This way we can connect one device when the coil is active and another one when it is not active.

It is important to know what is the resistance of the coil winding. The coil is connected is between terminals A and B. and what is the necesary voltage to activate it.

The voltage tells us the necesary signal magnitude that is going to activate the relay and the resistance tells us how much current we need to supply to the relay in order to be activated. The current is obtained using the Ohm’s law: I = V/R, were:

• I is the electric current required to activate the relay
• V is the voltage to activate the relay
• R is the resistance of the winding

• The relay allows us to control a device a long distance. There is no need to be close to the device to make it work.
• The relay is activated with little electric current, but it can trigger large machines that consume large amount of current.
• With a single control signal, we can control several relays at once.
• It can switch direct current or alternating current.

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