Electromagnetic relay Simple description of the relay

Description Electrically controlled switch Current through coil Magnetises soft iron core Soft iron armature moves Contacts join Come in many different sizes…speed of operation….number of contacts to be made maximum current

Normally Open [NO] Relay No current flowing through the coil Contacts are not made Coil must be energised for switched circuit to work Self explanatory!

Normally Closed [NC] Relay No current flowing through the coil Contacts are made Coil must be energised for switched circuit to stop working Self explanatory!

In a circuit Low current flows through coil Attracts armature Switched circuit connected Lamp lights BUT Coil is an inductive load Add protection diode Prevent high voltage spike The diode is reverse biased…when the switch is opened dI/dt is big so the voltage across the coil is big [damage the coil by driving big current] the diode allows the gradual change in current flow so dI/dt is small.

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