The relay is a fundamental electrically operated device in the world of electronics and automation. Its main function is to control the opening or closing of an electrical circuit via a control signal, often of low power, which triggers an electromagnetic field.
This allows much higher electrical loads to be handled without the need for direct interaction with high-voltage components. The relay provides a practical and efficient solution for automating processes, protecting circuits and ensuring safety in applications ranging from residential to industrial.
Index:
How does a relay work
To understand how the relay works, it is useful to imagine a manual switch, the difference being that the relay is operated electrically rather than manually. The relay consists mainly of three key components: the coil, the anchor and the contacts.
The Coil
The coil consists of a copper wire wound around an iron core. When an electric current flows through the coil, a magnetic field is generated. This magnetic field is the force that allows the relay to function, as it attracts the moving anchor, causing the contacts to move.
The Anchor
The anchor is a moving part of the relay, connected to the contacts. When attracted by the magnetic field generated by the coil, it moves to open or close the circuit contacts. The anchor returns to its rest position (when there is no current in the coil) thanks to a spring.
The Contacts
Contacts are the conductive elements that actually open or close the main circuit. There are different configurations of contacts, including normally open (NO) contacts, which close when the coil is energised, and normally closed (NC) contacts, which open when the coil is energised. In addition, there are relays with changeover contacts, which act as diverters, changing the connection from one circuit to another.
Types of Relays
There are numerous types of relays, each designed to meet specific needs. The main categories include impulse relays, monostable and bistable relays, twilight switches, staircase timers and printed circuit board relays.
Impulse Relay
Impulse relay is used to control a circuit through successive electrical pulses. This type of relay maintains the position of the contacts (open or closed) until a new impulse is received. It is particularly useful in applications such as staircase lighting, where a single light point needs to be controlled from several locations without the need to physically connect switches.
Monostable Relays
Monostable relays have only one rest position, which is the position the contacts assume when the coil is de-energised. When voltage is applied to the coil, the contacts change position, and return to their initial condition as soon as the voltage ceases. This type of relay is ideal for applications where temporary control is desired, such as switching on lights or handling signals in low-voltage circuits.
Bistable Relays
Bistable relays has two stable positions, which means that the contacts can remain in either state even when the voltage on the coil is removed. This is possible due to the presence of two separate coils that each control one of the stable positions. Bistable relays are useful in situations where it is necessary to maintain the state of the circuit without having to keep the relay constantly energised, such as in storage or selection systems.
Twilight Switches
Twilight switches are designed to control lighting according to the amount of ambient light. These devices are equipped with a photocell that detects outdoor light and automatically switches lighting on or off as the sun sets or rises. They are commonly used in residential and commercial settings to ensure that outdoor lights turn on at dusk and off at dawn, contributing to energy savings and safety.
Staircase timers
Staircase timers are devices that switch on or off after a predefined time frame from the moment voltage is applied to the coil. They are widely used to manage lighting in communal areas such as staircases, corridors and garages, where lights need to stay on for a limited period after someone has pressed the switch.
PCB Relays
PCB relays, are designed to be mounted directly on electronic boards. They are used to control significant electrical loads within a circuit board, protecting both the circuit and components from overvoltage or short circuits.
These relays are essential in industrial applications and advanced electronic equipment, where component protection is crucial for system safety and reliability.
Relay applications
Relays are used in a wide range of applications due to their ability to control power circuits via low-voltage control signals. Their applications range from domestic to industrial, and include:
Home automation
In the domestic environment, relays are used for automating lights, managing heating and air conditioning, and controlling electronic devices through home automation. Twilight switches, for example, automate outdoor lighting in homes, while step relays allow the control of lights in corridors and staircases from multiple locations.
Industry and automation
Industrial relays play a key role in the control of machinery, production lines and automation systems. They are used to handle high loads, protect circuits from overvoltage and short circuits, and ensure that industrial processes operate safely and efficiently. Staircase timers, for example, are essential for synchronising operations in assembly lines or for sequential control of equipment.
Safety and security
Relays are key components in Anti-theft systems, such as alarm systems, surge protectors and emergency systems. Bistable relays, due to their ability to maintain state even in the absence of power, are particularly useful in alarm systems where it is essential that the circuit remains activated until manually deactivated.
Applications in vehicles
In vehicles, relays are used to control components such as headlights, horns, windscreen wipers and cooling fans. Their ability to handle high currents without overheating makes them ideal for automotive applications, where safety and reliability are essential.
Relays are extremely versatile and essential devices in many electronic and electrical applications. Their ability to control high-power circuits with low-power control signals makes them indispensable in many areas, from home automation to heavy industry.
Understanding the different types of relays and how they work is crucial to choosing the right device for each specific application, thus ensuring safety, efficiency and reliability in any electrical system.
You might also be interested in: