Magnetic Relay: A relay is used where we need to isolate a load circuit from switching circuit. Suppose we want to switch ON or OFF a 220v 100Watt lamp automatically at evening and morning without human activity. we can do it easily with the help of LDR circuit. Depending on the presence of Light LDR switching circuit produce a dc voltage, say 5 volt.
Operation: As shown in the figure normally a magnetic foil placed between two connectors N/O and N/C. In normal state middle foil mechanically attach with the N/O (normally open) terminal.
Relay circuit consist of a magnetic Coil of low voltage (5/6/9/12 volt etc). When relay coil has been energized with control voltage signal, magnetic foil attracted by coil magnet and tach with N/O terminal. Thus connect Pole terminal with N/O. So we found 2 state..
- When control voltage to Relay coil is Zero volt, Pole terminal Connected to N/C
- When control voltage to Relay coil is v/6/12 volt (depending on the operating voltage of relay) , Pole terminal Connected to N/O
Application: A light source can be switch ON or OFF automatically with this relay. Relay is placed between 220 volt AC Power Supply and load.
Neutral terminal of power supply directly connected to load terminal and Line terminal of power supply have to be connected with N/O of the relay. Another terminal of load have to be connected with Pole terminal of relay.
When Input to Relay coil is Zero volt, Pole terminal will be Connected to N/C terminal and load will be disconnected from Power Supply.
When control Signal activate Relay coil, Load will be connected with main Power Supply through N/O terminal.