Difference Between Solid State Relays (Ssr) And Mechanical Relays

Difference Between Solid State Relays (Ssr) And Mechanical Relays

Relays are necessary parts of electrical systems because they control the flow of electricity by working like switches. In the past, mechanical relays were the most popular choice. They work on electrical principles and have moving parts like coils and contacts. However, solid-state relays (SSRs) have become more popular as technology has improved. Since SSRs are built on semiconductors, they have benefits like faster switching speeds, less noise, and higher reliability because they don’t have any moving parts. This piece details the differences between mechanical relays and SSRs, looking at their features, how they can be used, and how they can be used in different electrical and electronic circuits.

What are Mechanical Relays?

What are Mechanical Relays?

Electrical and mechanical devices, called mechanical switches, are used to manage the flow of electricity in a circuit. An electromagnet, contacts (usually made of metals like silver or copper), and a spring system are some of the most important parts.

An electrical signal must be presented to the coil for a mechanical relay to work. When electricity runs through the coil, it makes a magnetic field that pulls the contacts together. Depending on the type of relay, this makes the contacts close or open. This action either lets current flow through the main circuit linked to the relay or stops it.

One thing that makes mechanical switches stand out is their reliability and longevity. Because they can handle high currents and voltages, they can be used in a wide range of industry and automotive settings where strong performance is needed. Control panels, motor starts, lighting systems, and safety circuits in machinery are all common places where mechanical relays are used.

Mechanical relays are widely used and reliable but have some problems. For example, they can’t switch as quickly as other relays, they can break down over time because of mechanical wear, and mechanical shocks or noises can damage them. Because of these problems, solid-state relays (SSRs) were created and are now widely used in situations where dependability and faster response times are very important.

Understanding Solid State Relays

Understanding Solid State Relays

Solid state relays (SSRs) are computer switches that work like mechanical relays but don’t have any moving parts. They work with semiconductors and have parts like optocouplers, transistors (mostly MOSFETs or thyristors), and control circuits that manage switching electrical loads.

An optocoupler separates the control signal, usually a low-voltage signal, from the high-power circuit. This is how SSRs work. The input signal turns on the optocoupler, which turns on the semiconductor switching parts. This lets the current run through the SSR and turns the connected load on or off.

There are several reasons why SSRs are better than mechanical switches. To begin with, their change speeds are much faster, which makes them perfect for users who need quick responses. SSRs also don’t have any working parts, so they don’t get mechanical wear and tear. This means they last longer and are more reliable. Because of this, SSRs work great for high-frequency switching tasks like handling complicated electronic circuits where accuracy and dependability are very important or controlling inductive loads like motors and solenoids.

With their solid-state design, SSRs use less power, make less noise, and are more resistant to things like vibrations and shocks in the environment than mechanical switches. Because of these benefits, SSRs are popular in many fields, such as automation, telecommunications, medical devices, and green energy systems.

Comparison of Features

Reliability and Durability

Because they are solid-state, solid-state relays (SSRs) are known for being very reliable and long-lasting. This is because they don’t have any moving parts like mechanical relays do. In comparison to mechanical relays, this means that SSRs last longer and need less upkeep.

Switching Speed

Because they are solid-state, solid-state relays (SSRs) are known for being very reliable and long-lasting. This is because they don’t have any moving parts like mechanical relays do. In comparison to mechanical relays, this means that SSRs last longer and need less upkeep.

Noise and EMI

Compared to mechanical relays, SSRs produce less noise and electromagnetic interference (EMI). Because SSRs don’t have moving parts, they are noise-free and ideal for sensitive electrical circuits where EMI can negatively impact operation.

Size and Weight

Generally speaking, SSRs are lighter and more portable than mechanical relays. Because of their solid-state design, they can have smaller form factors, making them perfect for applications that need to reduce weight or space, like control panels with many people on them or portable electronic devices.


SSRs may initially cost more than mechanical relays, but they are frequently more economical over time. Because SSRs are solid-state devices, they have lower failure rates and require less maintenance, resulting in fewer downtime and replacement expenses. Furthermore, SSRs’ energy efficiency can lead to cheaper operating costs than mechanical relays, particularly in high-frequency switching applications.

The comparison shows that solid-state relays (SSRs) are a better option for many contemporary electrical and electronic systems due to their improved performance, dependability, and efficiency over mechanical relays in several different areas.

Applications and Suitability

Solid state relays (SSRs) are great for many uses where dependability, accuracy, and quick switching are important. Some examples are

  1. HVAC Systems:In HVAC systems, SSRs are often used to precisely handle heating elements, fans, and compressor motors so that the right amount of heat and humidity is maintained.
  2. Industrial Automation:SSRs are very important because they power actuators, solenoids, and motor drives in robotic assembly lines and other manufacturing processes that must be controlled quickly and accurately.
  3. Electronic Switching Circuits:For electrical switching circuits in medical devices, aerospace, and telecommunications, where low noise, high-speed switching, and dependability are very important, SSRs are the best choice.

Because they can handle high currents and voltages, mechanical relays may still be better for high-power uses like heavy machinery, electric cars, or power distribution systems. There are also times when mechanical relays may be more cost-effective, especially if the original investment is high.


In conclusion, mechanical and solid-state relays (SSRs) have pros and cons. SSRs offer faster switching, reliability, and lower noise, albeit with a higher initial cost. Mechanical relays excel in high-power situations and may be cheaper upfront. Choosing the right relay is crucial for performance and economy. For more information and affordable electronic components, contact Rantle East Electronic today for the best products.

Last Updated on April 9, 2024 by Kevin Chen

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