Solid State Relay vs. Mechanical Relay: Which is Better?

In the world of electronics and automation, relays are extremely valuable. These devices enable low-power signals to control high-power circuits. Hence, they are important in numerous industrial and household systems applications. There are two major types of relays: Mechanical relays and solid-state relays. That is why choosing between two- and three-wheels may seem complicated since each has advantages and disadvantages. Throughout this blog, we explain these relays, how they are constructed, and which one may be the more suitable option for your application.

What is a Mechanical Relay?  

A mechanical relay is a piece of electrical hardware designed to manage the stream of electricity. Its working can be explained by an electromagnet opening or making contacts, making or breaking the circuit. Through the coil, when current passes, it induces a magnetic flux, which causes a lever to make a circuit and close or otherwise open the contacts.

Mechanical Relay Working Principle  

Relay working based on the mechanical relay working principle takes place due to the procedure of an electromagnet. When a weak signal is applied to the coil, it causes a magnetic force to happen that shifts the contacts between two positions. This physical movement gives the relay a label of “mechanical”. When the coil is de-energized, a spring moves the contact back to a position that is out of contact with the other contact.

This operation is quite straightforward, although proven very effective; mechanical relays have been used in the market for many years due to their mechanical construction, which efficiently addresses high loads.

Mechanical Relay Circuit  

A mechanical relay circuit typically consists of the following parts:

• Coil: Generates the magnetic field.

• Armature: One of the parts predefined by both locking and unlocking movement and activated by the magnetic field.

• Contacts: They make or open the circuit. Contacts can be normally open (NO) or closed (NC contacts).

• Spring: This returns the armature to its original position if the relay lacks power or energy.

What is a Solid State Relay? 

An SSR stands for solid state relay, and the difference between an SSR and a mechanical relay is that the latter has no moving parts. It can turn the circuit ON or OFF using electronic components like transistors, triacs or thyristors. Due to the absence of mechanical components in the operation of the solid state relays, they are faster, offer no noise and are more durable.

Solid State Relay Working Principle  

The solid-state relay can be activated remotely from any location using a telephone or other means of communication. The working principles of solid-state relays are based on the ability of semiconductor parts to control the switch. When a low-power signal is connected to the input terminal, it draws the internal electronics, e.g. an optocoupler, which in turn turns on or off a high-power load. Since no mechanical movement is involved, they can switch much faster than mechanical relays.

Solid State Relay Circuit  

A solid-state relay circuit includes components such as:

• Input Circuit: Usually coupled with an optocoupler applied to isolate the low power control signal with the high power load of the output circuit.

• Switching Device: Often a triac, thyristor, or transistor that does the real switching job; besides the above, the circuit also contains a.

• Output Circuit: Carries the load current and its connection or off is controlled by turning the internal semiconductor elements on or off.

Solid state relays find their application where noiseless and fast switching, with high operational life, is desirable in such fields as automation and temperature control.

Comparison of SSR: SSR vs Mechanical Relay  

In the comparison between SSR and mechanical relay, fundamental differences appear, making each relay appropriate for different utilization.

Durability and Lifespan 

Mechanical Relay: The physical movement of parts is bound to result in wear and tear at a certain time. Mechanical relays are assumed to operate for a limited number of switches because contact wears down.

Solid State Relay: The fact that specific selection resistors, SSRs, do not possess moving parts makes the duration of service longer. They are long-lived and can switch without signal falling from millions of operations.

Switching Speed 

Mechanical Relay:

Compared with electronic switches, mechanical relays are slower because of mechanical motion in switching, and the duration of the switching can be in the millisecond range.

Solid State Relay:

SSRs can switch in microseconds, and therefore, the device is useful where response time is paramount because it can instantly switch between max and min.

Noise 

Mechanical Relay:

Each time the contacts open or close, mechanical relays emit a click sound to the human ear. This can, however, be a disadvantage in situations where the absence of noise is necessary.

Solid State Relay:

Composed of no moving parts, SSRs work without noise, which explains why they are useful in noise-critical applications such as medical equipment or home appliances.

Power Consumption 

Mechanical Relay:

In the mechanical relay, the coil consumes more power to produce the magnetic field, which will open or close the contacts.

Solid State Relay:

One major advantage of the consumption of SSRs is that they use semiconductor components, which are more economical in power than mechanical ones.

Cost

Mechanical Relay:

Mechanical relays are usually cheaper initially, which may be important for many users’ projects.

Solid State Relay:

In general, SSRs are costlier than mechanical relays. But, in most cases, they last longer, and their maintenance cost is relatively low compared to other types of engines.

Load Capacity 

Mechanical Relay:

Mechanical relays can tolerate higher surge currents and are for applications where a high power switch is needed, for instance, in use in industrial equipment.

Solid State Relay:

As contemporary SSRs are also able to provide high loads, they often need more heat sinks or cooling systems to manage heat during their operation.

Solid State Relay and Electromechanical Relay Main Differences 

The difference between solid state relay and electromechanical relay can be summarized as follows:

• Switching Mechanism: In a mechanical relay, circuits are switched by physical contact, while in a solid-state relay, there are semiconductor devices.

• Longevity: For similar reasons, mechanical relays are less reliable and less lasting than solid-state relays because the contacts wear out with use.

• Switching Speed: SSRs are way faster than mechanical ones when switching.

• Noise and Vibration: Mechanical relays generate audible noises from the contact's motion, while solid-state relays are noise-free.

Application Areas of Mechanical Relay  

Mechanical relay is used when there is a need to separate signal processing circuits from power circuits.

A mechanical relay is ideal for applications where:

• A high surge current is required, which results from a large amount of surge energy stored in the capacitor bank.

• Price is very important.

• Interferences from other subsystems are not sensed in the environment.

Real-time Applications of a Solid State Relay  

A solid-state relay is better suited for:

• High-speed switching applications are one of the application opportunities for circuit switches.

• For instance, operations that need low noise production include medical equipment and home appliances.

• For applications that require equipment longevity, for instance, in the use of apposite control systems like automated systems or lighting control systems.

Also Read - What is Relay? All Types, Applications, Working Principle?

Conclusion: Which One is Better? 

The decision of whether to go for the SSRR or the mechanical relay will depend on the characteristics of the specific application. An ordinary solid-state relay is preferable if one needs more reliability, faster turn-on/OFF, and virtually no sound. The said circuit solid state relay is intended for high performance with a long life span and little maintenance.

On the other hand, in cases where your application requires high load capacity, does not strongly require high speed, has a low concern about noise and is cost-sensitive, the mechanical relay is still an acceptable solution in today's market. The mechanical relay circuit is simple, effective in connecting high loads, and has been widely used for a considerable period.

Both solid-state relays and electromechanical relays play an important role in electrical systems today, and learning the difference or the similarity between the two may be useful to you on your next project.