Introduction to Relays - The Working Principle

Summary

A relay is an electrically-operated switch that controls a secondary circuit using a small current. The primary circuit energizes an electromagnet, which closes a switch and activates the secondary circuit. The process is reversed when the current is cut off, with a spring returning the switch to its original position. This video explains how relays work, including types such as normally open and normally closed relays, and SPST, SPDT, and DPST configurations. It emphasizes the role of electromagnets and springs in controlling the flow of current through different relay types.

Takeaways

• 😀 A relay is an electrically operated switch that controls a larger circuit with a smaller one.
• 😀 When Circuit 1 is activated, it energizes an electromagnet that closes the switch in Circuit 2.
• 😀 A relay works by using a small current to control a larger current in a separate circuit.
• 😀 The electromagnet in a relay generates a magnetic field, which causes a metal armature to move and close the switch.
• 😀 A spring in the relay mechanism ensures the switch returns to its original position when the current is deactivated.
• 😀 In a normally open (NO) relay, Circuit 2 is initially open until Circuit 1 is energized.
• 😀 A normally closed (NC) relay starts with Circuit 2 closed and opens when Circuit 1 is activated.
• 😀 SPST (Single Pole Single Throw) relays control a single circuit with one on/off position.
• 😀 SPDT (Single Pole Double Throw) relays can toggle between two different circuits.
• 😀 DPST (Double Pole Single Throw) relays control two independent circuits, each with one position.
• 😀 DPDT (Double Pole Double Throw) relays allow for two circuits, each with two positions for more complex switching operations.

Q & A

What is a relay and how does it work?

A relay is an electrically operated switch that uses a small current to control a larger current in a secondary circuit. It operates through an electromagnet that, when energized, closes a set of contacts to complete the circuit.

What are the two circuits in a relay system?

The relay system consists of two circuits: the primary circuit (Circuit 1) which controls the relay, and the secondary circuit (Circuit 2) which is controlled by the relay and typically powers a load, such as a light bulb.

What is the role of the electromagnet in a relay?

The electromagnet in a relay is a coil of wire through which current flows. When energized, it creates a magnetic field that pulls the armature, closing the contacts in Circuit 2, which activates the secondary circuit.

How does the spring in a relay work?

The spring in a relay helps return the armature to its original position when the current is cut off. When the electromagnet is de-energized, the spring's restoring force causes the armature to snap back and open the contacts, deactivating the secondary circuit.

What happens when the switch in Circuit 1 is closed?

When the switch in Circuit 1 is closed, current flows through the electromagnet, energizing it and creating a magnetic field that pulls the armature down. This closes the contacts in Circuit 2, allowing current to flow and turn on the connected load (e.g., light bulb).

What occurs when the current is cut off from Circuit 1?

When the current is cut off from Circuit 1, the magnetic field in the electromagnet collapses, causing the armature to return to its original position due to the spring's restoring force. This opens the contacts in Circuit 2 and deactivates the load.

What is a normally open relay?

A normally open relay is a type of relay where the contacts are open by default. They close only when the electromagnet is energized, allowing current to flow in Circuit 2.

What is the difference between a normally open and a normally closed relay?

In a normally open relay, the contacts are open when not energized and close when energized. In a normally closed relay, the contacts are closed by default and open when the electromagnet is energized.

What is an SPST relay?

An SPST (Single Pole Single Throw) relay has one switch that can be in one of two positions: open or closed. It controls a single circuit in one on/off state.

What is an SPDT relay and how is it different from an SPST relay?

An SPDT (Single Pole Double Throw) relay has one switch that can connect to two different circuits. Unlike the SPST relay, which has only one output (on/off), an SPDT relay can switch between two outputs, allowing for more versatile control.

How does a DPST relay work?

A DPST (Double Pole Single Throw) relay has two switches that operate simultaneously. It allows you to control two separate circuits at the same time, either turning both on or off together.

What is a DPDT relay and what advantage does it offer?

A DPDT (Double Pole Double Throw) relay has two switches with two outputs each. It can control two separate circuits and switch between two different outputs, offering more complex control compared to SPDT or DPST relays.