Solid State Relay VS Mechanical: 12 Key Differences

While deciding between solid-state relays (SSRs) and electromechanical relays (EMRs), it is critical to know the working principle of each device, their benefits, and their ideal operating conditions. This article will cover the comparisons in switching speed, power consumption, lifespan and other important details of solid state relay vs mechanical relay.

4 Things You Need To Know About The Solid State Relay

What Is A Solid State Relay?

An SSR relay is an electrical device that can be switched electronically with a built-in semiconductor, meaning there are no moving parts unlike a mechanical relay. Instead of traditional electromechanical relays, SSRs employ electrically controlled semiconductor devices such as triacs or thyristors to manage and regulate the high power electrical signals through low power control signals.

Are Solid State Relays Only For AC?

Solid-state relays cater to both AC and DC circuits. Nonetheless, the majority of assortments of solid-state relays are purpose-built for AC switching because of their ability to control voltage variations which are characteristic of alternating current systems.

What Are The Three Types Of Solid State Relays?

There are generally three main types of solid state relays:
AC-AC SSRs: Control AC loads with AC control signals.
AC-DC SSRs: Control DC loads with AC control signals.
DC-DC SSRs: Switch DC loads using DC control signals.

Do Solid State Relays Fail Open Or Closed?

When solid state relays fail, they are usually rendered inoperable, which means they do not conduct. Because they fail like this, SSRs provide an extra layer of protection against overcurrent situations which is very helpful.

What Is The Life Expectancy Of A Solid State Relay?

SSRs are ‘rated for’ long life due to the higher reliability achievable with no moving parts. They are considered to not be damaged by repetitive cycles of switching on and off.

What Is Electromechanical Relay?

What Does An Electromechanical Relay Do?

An electromechanical relay (EMR) is a device that makes or breaks a circuit using one or more sets of mechanical contacts which are controlled with an electromagnet’ coils. EMRs utilize moving parts to complete the circuits, in contrast to solid state relays EMRs use mechanical parts.

Are Electromechanical Relays Reliable?

Electromechanical relays are applicable for a wide range of systems but they are less durable due to their mechanical contacts wearing out from repeated cycles. They are also prone to damage from shocks as well as vibrations.

What Is The Difference Between Electromechanical Relay And Solid State Relay?

Now let’s compare solid state relay vs mechanical relay across different criteria to determine which might be the best choice for your application.

Criteria	Solid State Relay (SSR)	Electromechanical Relay (EMR)
Principle of Operation	Uses semiconductors for switching without movement	Uses electromagnetic force to open/close physical contacts
Size	Compact, ideal for space-limited installations	Larger due to mechanical components
Switching Speed	Very fast, microsecond range	Slower, 5-15 milliseconds due to mechanical movement
Power Consumption	Low, milliwatt range	Higher, due to electromagnetic components
Noise Generation	Minimal noise	Generates noise due to mechanical movement
Isolation	Superior electrical isolation	Less effective isolation, contacts wear over time
Shock & Vibration Resistance	High, ideal for harsh environments	Low, moving parts are vulnerable to damage
Cost	Higher initial cost, but cost-effective long-term	Lower initial cost, but higher long-term maintenance cost
Lifespan	Millions of cycles, long-lasting	Limited, several hundred to thousand cycles
Applications	Automation, medical devices, high-speed tasks	High power tasks like motor drives, heaters
Performance in Harsh Environments	Performs better in vibration, dust, and explosive environments	Struggles in harsh conditions
Positional Sensitivity	Not position sensitive	Position sensitive, requires proper orientation

Principle Of Operation

Solid State Relay: Uses semiconductors to switch circuits without physical movement.
Electromechanical Relay: Uses electromagnetic force to open or close physical contacts.

Size

SSR: Typically smaller and more compact, making them ideal for installations with space limitations, such as PCBs and control panels.
EMR: Requires more space due to the mechanical components involved, including contacts and coils.

Switching Speed

SSR: Extremely fast, with switching times often in the microsecond range, ideal for high-speed automation.
EMR: Slower switching, typically taking 5-15 milliseconds due to mechanical contact movement.

Power Consumption

SSR: Low power consumption, often requiring just milliwatts to operate.
EMR: Typically consumes more power due to the electromagnetic components.

Noise Generation

SSR: Minimal noise generation, including electrical and mechanical noise, thanks to the lack of moving parts.
EMR: Generates noise during operation due to the mechanical movement and electrical transients.

Isolation

SSR: Superior electrical isolation since no physical contact exists between the input and output, enabling efficient switching of high-power circuits with low-power signals.
EMR: Provides isolation but less effectively because physical contacts can wear out and cause degradation over time.

Shock And Vibration Resistance

SSR: These are exceptionally shock and vibration resistant which enables these to be used in harsh conditions in the automotive or aeronautics industry.
EMR: With moving components, mechanical shock and vibration can easily damage the device, causing it to malfunction.

Cost

SSR: Solid-state relays are more expensive than traditional ones, but they tend to be cheaper after taking the long term value into account because of their durability and reliability.
EMR: While the upfront cost is lower with EMR, the cost will increase over time because of the need for more frequent replacements due to the decrease in performance caused by wear and tear.

Lifespan

SSR: Typically lasts for millions of cycles without degradation.
EMR: Has a limited lifespan, typically around several hundred or thousand cycles, depending on load and usage.

Applications

SSR: Dreamlike in its utility for automation systems, medical devices, and other high-speed switching applications espoused by potential mechanical failures.
EMR: More appropriate for high power demanding tasks like motor drives or heaters when cost is a more deciding factor than relays operated with higher speeds.

Performance In Harsh Environments

SSR: Performs better in environments with high vibration, dust, and explosive risks due to their lack of moving parts.
EMR: Struggles in such environments as vibrations or environmental conditions can affect mechanical parts.

Positional Sensitivity

SSR: Positional insensitive, allowing for flexible installation in various orientations.
EMR: Positional sensitive, requiring proper orientation to ensure reliable operation.

Solid State Relay VS Mechanical: Which Is The Best?

Choosing between a solid state relay and a mechanical relay should be based on the requirements of your application:
For the quick switching, long life span, high energy efficiency and resistance to harsh vibrations and environments, Solid State Relays work best.
For high-load cost-efficient applications with significant starting currents, such as motors and other industrial equipment, Electromechanical Relays may be better.

Conclusion

Even if both solid state relays and electromechanical have their pros, SSR is usually better than EMR in switching speed, lifespan, and endurance to hostile conditions. Nonetheless, EMRs still have slightly more value in situations where high load capacity and lower initial costs are of greater importance.

References

Crydom Solid State Relays vs Electromechanical Relays
Solid State Relay vs Mechanical Relay: What is Different?

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