Types of Relay - Which One Should You Use

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1. Types of Relay - Which One Should You Use?

We use relays for a broad range of applications like industrial, automobiles, DIY projects,
home automation applications, test, and measurement equipment, and much more. A single
relay module commonly includes a coil, and two contacts such as normally open (NO) and
normally closed (NC). This article discusses what a relay is, its different types, and its
applications.
What is a Relay?
Relay is one type of electro-mechanical element which works as a switch. While you use
normal switches to open or close a circuit manually, a Relay refers to a switch that connects
or disconnects two circuits. It uses an electrical signal to manage an electromagnet that in
return connects and disconnects another circuit.
How Does a Relay Work?
The following steps show a simplified working of a relay.
• The electromagnetic induction principle is followed by relays.
• When the electromagnet is applied using some current, it induces a magnetic field
around it.
• A switch is operated to apply DC to the load.
• In the relay, the iron core and copper coil function as an electromagnet.
• When the coil is used along the DC, it begins attracting the contact. This is known as
energizing of a relay.
• When the supply is removed it retrieves back to the original status. This is known as
the de-energizing of a relay.
Understanding About Single Channel 5V Relay Module
A single relay module is used to handle high voltage, current loads such as AC load & lamps,
motor, and solenoid valves. This relay is commonly developed to interface via different
microcontrollers such as Arduino, PIC, and others.

2. A digital signal is used to activate and deactivate the relay module. This signal is applied over
a control pin of the relay module. A single relay module includes transistors, resistors-2, a 5V
relay, and LEDs-2. Two types of relay modules are available depending on the control signal
type used for the relay activation.
Types of Relay
• Electromechanical Relay: They are built using mechanical, electrical, and magnetic
elements. They are designed using a coil that induces a magnetic field when
energized. The magnetic field helps to attract any movable contact that opens or
closes the contacts.
De-energizing of the coil, causes it to lose its magnetic field, and a spring is used to
retract the armature to its normal position that then again, closes or opens the contacts.
Electromechanical relay can withstand large inrush currents, carry high voltage and
high current load, and is cheap and cost-effective. Moreover, it has high mechanical
structure reliability which is not susceptible to external electromagnetic environment.
• Solid State Relay (SSR): They are usually a circuit with several electronic elements
which has the same functioning as an electromechanical relay. They use solid-state
elements to perform the switching operations without any moving elements.
SSR switches on or off when a small external voltage is utilized across its control
terminals. They utilize semiconductor devices to switch the conduction and
disconnect high-voltage loads. Some common advantages of SSR are:
➢ The switching speed is rapid, and it depends on how quickly the LED can be
powered on and off, approximately taking 1 ms and 0.5 ms respectively. For
example, the G3MC202p serial SSR we utilize has a switching time of half the
load power source cycle plus 1 ms.
➢ It operates silently with minimal noise.
➢ The absence of physical contact eliminates sparking, making it suitable for use in
explosive environments.
➢ It has an extended lifespan as there are no moving parts or contacts that would
accumulate carbon, even after multiple activations.
➢ The SSR is designed with a compact, thin profile Monoblock structure that
incorporates a PCB, terminals, and heat sink in a single lead frame. This design is
significantly smaller than mechanical relays and allows for more integrated
channels.
➢ It is resistant to physical shocks.

• Reed Relay: It comprises a pair of magnetic strips (known as reed) which is sealed
within a glass tube. This reed functions as both a contact blade and an armature. The
magnetic field applied over the coil is wrapped around this tube which makes these
reed shift such that a switching operation is performed.
Depending upon dimensions, relays are categorized as miniature, sub-miniature, and
micro-miniature relays. Moreover, depending on the construction, they are
differentiated as open, sealed, and hermetic-type relays. Lastly, based on the load
operating range, they are classified as high, intermediate, low, and micropower types.
Applications of Different Types of Relays

3. Relays are used to safeguard the electrical system and to reduce the harm caused to the device
linked with the system because of overvoltages or currents. The relay is used to protect the
device connected to it. Relays are used to manage the high voltage circuit with the low
voltage signal in the use of audio amplifiers and some other forms of modems.
These are applied to manage a high current circuit by a low current signal in the applications
such as starter solenoids in automobiles. They can detect and isolate the defects which occur
in distribution and power transmission systems. Key applications areas of the relay include:
• Lighting control systems
• Industrial process controllers
• Motor drives control
• Computer interfaces
• Home appliances
• Telecommunications
• Traffic control
• Protection systems of electrical power system
• Automotive
In Conclusion
Overall, a relay is an electrical switch that is operated by an electromagnet. It is used to
control the flow of electric current in a circuit by opening or closing the switch contacts in
response to a signal. The choice of the relay module depends on the specific requirements of
the application, including voltage and current ratings, switching speed, reliability, and
environmental considerations.
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