Solid State Relay Vs. Mechanical Relay – What Is Different?

SSR and mechanical relays offer different benefits. If you’re torn between the two, you might want to read this solid state relay vs. mechanical relay comparison post. It outlines the differences and provides the advantages of each type.

Solid State Relay

The solid state relay, also commonly abbreviated SSR, is an electronic switching device that has no moving parts. It consists of a control circuit (or input), a drive circuit, and an output circuit, which also acts as the switch.

The main advantage of using a solid state relay is that there are no physical contacts that can generate sparks/arc and wear out over time. That also means a fast switching action, low resistance, and immunity to shock and vibration.

Electromechanical Relay

A mechanical relay, on the other hand, is an electro-mechanical device that uses the working of an electromagnet to open or close a switch. It mainly consists of a coil of wire (the electromagnet), a spring, and one or more sets of contacts.

These relays can handle large loads, such as those found in industrial applications. However, they are slower to switch than the electronic solid state relay and can be more prone to wear and tear since physical contacts are involved.

Solid state relays are smaller and more compact
Resource: https://www.youtube.com/watch?v=4BMJRzKlw0Y

Solid State Relay Vs. Electromechanical Relay

A solid state relay differs from an electromechanical relay in many ways. One of their biggest differences is their principle of operation. While a solid state relay uses semiconductor devices for switching, mechanical relays use electromechanical contacts. Other differences, and which matter when choosing between the two types of relays, are explained next.

1. Solid State relay Vs. Mechanical Relay: Size

SSRs are generally smaller. This is because there are no physical contacts or coils, which take up space. In situations where space is limited, such as in PCBs and panels, SSRs are often the better option.

Speaking of solid state relay dimensions, you may want to know how big or small an SSR can be. The size of an SSR will vary depending on its specifications, but can be so small that it mounts on a PCB.

2. Solid State Vs. Mechanical Relay: Speed

The solid state relay speed when switching loads is way higher than that of the mechanical relay. In fact, it is almost instantaneous and many times that of an EMR. That’s because there are no physical contacts to move.

The superior switching speed of SSRs makes them ideal for loads that need to be switched quickly and repeatedly. These include automated systems such as the servo motors of CNC machinery and similar tools.

3. Solid State relay Vs. Mechanical Relay: Power Consumption

Solid state relays use semiconductor devices for switching, which means that they consume very little power. In fact, they can operate on as little as a few milliwatts.

Mechanical relays, on the other hand, use electromechanical contacts to switch the current. This process requires more power. For example, a mechanical relay can consume up to 30 times more power than an SSR relay of similar capacity.

4. Solid State relay Vs. Mechanical Relay: Noise

Solid state relay operation generates very little noise when switching because there are no moving parts. This also includes electrical noise or EMI noise, since the relay switches off at lower amp levels, especially when zero cross switching is implemented.

Mechanical relays, on the other hand, can generate a fair amount of noise when switching. This is caused by the moving parts and transients, especially when the cushioning is not adequate among other measures.

5. Solid State relay Vs. Mechanical Relay: Isolation

Isolation means that there is no electrical connection between the input and output of the relay. This is important in applications where you don’t want the input voltage to affect the output voltage (or vice versa).

Both SSRs and EMRs can provide isolation. However, the solid state relay isolation is much better since there is no physical contact between the input and output. That allows the relay to switch much larger currents using very small currents.

6. Solid State relay Vs. Mechanical Relay: Shock and Vibration

Since SSRs have no moving parts, they are not affected by shock and vibration the way EMRs are. This makes them ideal for applications where these factors are present.

These include automotive applications, where the engine vibrations can cause problems for mechanical relays. This explains the popularity of automotive solid state relay.

7.Solid State Vs. Mechanical Relay: Cost

When it comes to price, solid state relay modules are generally more costly than mechanical relay. That’s because the manufacturing process is more complex and requires more precision.

However, the price difference between the two types of relays has been decreasing over the years as SSRs become more and more popular. Plus because SSRs last longer than mechanical they turn out to be a more cost-effective option in the long run.

8.Solid State Vs. Mechanical Relay: Lifespan

The solid state relay lifespan, when compared to that of the mechanical relay, is much longer. With no physical contacts or arc generation, there’s nothing that can physically wear out over time.

Mechanical relays, on the other hand, have a shorter lifespan. The constant opening and closing of the contacts causes them to slowly degrade until they eventually fail. This usually happens after a few hundred or thousand cycles.

9.Solid State Vs. Mechanical Relay: Applications

Because SSR and EMR relays have different characteristics, they are each better suited for different applications. For example, solid state relay applications suit situations where high speed and long lifespan are important, such as critical systems and automation.

Mechanical relays are better suited for applications where lower cost and higher load-carrying capacity are more important.

Solid State relay Vs. Electromechanical Relay: Summary

Which type of relay is best for your application? Based on the above solid state relay vs. mechanical relay comparisons, solid state relays perform better in most cases. They are smaller, have a longer lifespan, generate less noise, and are not affected by shock and vibration.

However, there are still some applications where EMRs are the better choice. These include situations where lower cost and higher load-carrying capacity are more important factors than the others. A good example of such use is when a relay is needed to control a large load, such as an industrial electric motor or heater. We recommend the following uses for solid state relays and electromechanical relays.