Relay Seminar Report with PPT and PDF Free Download: An electrical switch which uses an electromagnet to move a switch from off position to on position instead of using a person to move switch is called as a relay. Very less amount of power is utilized in turning on a relay and it also has the ability to control something which draws a huge amount of power. For example, AC i.e. air conditioner in our home is controlled by a relay. The coil which controls relay pull the contacts together by utilizing few watts. Schematic representation of relay is mentioned below:

Fig1: Schematic Representation of Relay

Contacts which are present at top are not connected i.e. they are open. When we pass current through coil then a magnetic field is created by it which connects the contacts that are present on top i.e. the switch will be closed. When power is removed from coil then a spring pull the switch to make it open once again.

Relay selection:

Switches and relays come it distinct configurations. Most common configurations of relays are shown in below diagram:

Fig2: Distinct Configurations of Relay

1. SPST: Full form of SPST is Single Pole Single Throw. It is the simplest configuration which has only two configurations.
2. SPDT: Full form of SPDT is Single Pole Double Throw. This configuration has three contacts.
3. DPST: Full form of DPST is Double Pole Single Throw.
4. DPDT: Full form of DPDT is Double Pole Double Throw.

Double pole versions are similar when compared with single pole versions and only difference between single pole and double pole is that double pole versions have two switches open together and close together.

Practical considerations:

If a relay is not used much and it is only used like thrice per day then lifetime such a relay will be about eighteen years. Few relays are availed to control air conditioners in home, such relays are used many a times and lifetime such type of relay is only a few years. There are few relays which have lifetime of a million cycles.

Fly back diode:

Relay coil not only acts as an electromagnet but also as an inductor. When we apply power to coil, current in coil levels off and build up at its rated current. A magnetic field of coil has some stored energy. When we turn off of the current in coil then this stored or saved energy has to go somewhere. At this time, there will be a fast increase in coil which tries to keep current in coil flowing in similar direction. This spike of voltage can reach hundreds of volts and thousands of volts. Voltage spike can even damage or destroy electronic parts. By including a flyback diode, current will have a path to continue flowing via coil until energy which is saved or stored is totally used. This flyback diode clamps voltage across coil to about 0.7V and saves the electronic parts. Dissipation of stored energy will be very fast in the diode. Flowing of the current will be stopped and relay gets to turn off. Diode handles current in the coil for a short time period. Inductive kickback from load reduces the lifetime of contacts of relay if we don’t use the diode.

Content of the Seminar and PDF Report for Relay

• Introduction
• History
• Types