11) Relays

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Electromagnetic Switch or Electricity powered switch

Relay

Electromagnet

• A coil of conducting wire wrapped around a piece of metal

• Example: Copper winding around an iron nail

• Pass current through any conductor and it generates a magnetic field

• Provide supply at two ends of coil and it starts attracting iron pieces

Inside Relay

• A coil with two supply terminals and a SPDT Switch with terminals: COM, NO and NC

• COM: Common, NO: Normally Open and NC: Normally Close

• No supply: COM and NC are connected

Supply given to coil

• Lever comes down due to magnetic effect of coil

• COM and NO gets connected

No supply given to coil

• Disconnect supply: COM and NC gets reconnected

• Lever comes back due to an internal spring

Relay

Schematic SymbolSchematic Symbol

Working of Relay

Relay is connected across two halves (lower & upper) of BB

All legs of relay should be inserted in different columns

Note: Please look at next slide before you start

Connect Relay on BB

Connecting Relay on BB

Providing supply to relay

• Every Relay needs a certain voltage to activate

• Relay in the kit will activate at a voltage ≥ 12V

• To make ≥ 12V, connect two batteries in series

• When supply is connected, relay gets activated and produces a click sound

• Click Sound: Lever shifts from NC terminal to NO terminal

Connecting batteries in series

Connecting 2 batteries in series on BB

Giving supply to relay

Wrong Connection Right Connection

Note: In case of wrong connection, relay is not connected to Vcc

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