Solid State Relay Applications, Advantages over Normal Relay

Solid State Relay Applications, Advantages over Normal Relay

Hey, in this article we are going to discuss about the Solid State Relay which is mostly known as SSR. Here we will discuss the applications of Solid State Relay, what are the amazing advantages of solid-state relay over a normal electromagnetic relay. SSR not have only advantages it also has some disadvantages and limitations we will discuss, so let's start.

What is Solid State Relay(SSR)?

Solid State Relay or SSR is a static semiconductor switching device that provides the same function as a conventional relay or electromagnetic relay means to switch the electrical power.

SSR does not have any Moving mechanical contact mechanism inside it. SSR is mainly constructed with an Infrared LED(which takes input supply) and a phototransistor connected with MOSFET or Thyristors(these control output).

It is an electrically operated switching device, it gets turned on when an electrical supply (generally 3 to 32 volts DC) is applied to its input and gets turned off when the power supply is removed.

What is Electromagnetic Relay(EMR)?

Electromagnetic Relay or EMR is also an electrically operated switching device that works on the principle of electromagnetic attraction. It is also used to switch electrical power.

If we see the construction of a normal relay, there is an electromagnetic coil, and there are some moving and fixed iron or copper strips. During the operation, those strips contact each other and switch the electrical power. To get more knowledge about electromagnetic relays read the article, Relay Function

Difference between Solid State Relay and Electromagnetic Relay

The main differences between SSR and EMR are,

1. EMR works on the principle of electromagnetic attraction whereas SSR works on the principle of Photoconduction or optical coupling.

2. EMR has a mechanical movement contact mechanism in its construction whereas SSR is a static device having no moving contacts.

3. EMR is an Electromechanical device whereas SSR is a static semiconductor device.

4. EMR has an electromagnetic coil whereas SSR does not have any electromagnetic coil.

5. The range of the electromagnetic relay is high which means it requires a comparatively high input voltage for its operation than a solid-state relay.

Solid State Relay Advantages over Electromagnetic Relay

Actually, the main objective of using any relay is to control or switch a large amount of current, voltage, and power using low current or voltage, so both SSR and EMR provide the same function. In fact, both of them provide isolation between the input and output circuits. But there were so many advantages of SSR over an EMR,

1. A Solid State Relay or SSR can handle more current and voltage than an electromagnetic relay.

2. Solid State Relay provides a much faster switching than an electromagnetic relay, for this reason, SSR is most suitable for pulse signals, and digital signals, so it can be used with microprocessors, PLC, etc.

3. One of the biggest advantages of SSR over an EMR is, it provides a zero-current turn-off switching facility in case of AC supply.

That means when we use an SSR for the switching of AC supply, it only gets turned off when the current goes to zero, this helps to eliminate ARC, load distortion, and production of back emf in case of inductive loads.

4. Most of the time electromagnetic relay shows a latching problem when it operates with a high current, but in the case of SSR there is no metal strip, it is a static device so it does not show any latching problem.

5. An SSR can be operated with a very low current and voltage as its input is connected with a single infrared LED only. An SSR can be operated at a minimum of 3V DC with a few milliampere currents.

However, an electromagnetic relay needs more current and voltage to be operated because its input is connected to an electromagnetic coil which takes more current than an LED to perform properly. An electromagnetic relay can be operated perfectly at a minimum of 5V DC.

For this reason, SSR can be used with small sensors, and transducers because they produce very low current as output.

6. As solid-state relays have no mechanical parts, so they have a larger life span, higher reliability, and smooth operation.

7. There is no noise, surges happen in Solid State Realy but in the case of the electromagnetic relay, reverse surge happens when the input signal is removed from the relay.

8. When an EMR is used with inductive loads, back current, noise, surge, etc happens but in the case of SSR nothing back current, noise occurs.

9. As SSR is a static device, so there is nothing operating sound occurs, but in an EMR contact sounds occur.

Solid State Relay Disadvantage and Limitation

Although Solid State Relays have so many advantages but their drawback also there,

1. SSRs are so much costly than a normal relay or EMR, for this reason, EMR only most usable device nowadays also.

2. Almost all the electromagnetic relays provide both NO and NC functions simultaneously but most of the SSRs are provide only one function either NO or NC. In fact, NC SSRs also very rarely available in the market.

3. SSRs are solid-state semiconductor devices so it produces so much heat during operation, extra heatsink arrangement is required.

4. SSRs are not suitable for high-impedance circuits.

5. There is leakage current occurs in the SSR when it is in the off condition, but there is no leakage current occurs in the EMR.

6. SSRs are cannot provide linear voltage-current characteristics as there is transient occurs during operation.

7. It offers high resistance in its output circuit than a normal electromagnetic relay.

Solid State Relay Applications and Uses

1. The main application of SSR is to switch the high amount of AC power using a low-power DC signal.

2. SSRs are used for automatic heater control in baking ovens.

3. SSRs are used in the hydraulic system with the electronic control mechanism.

4. SSRs are used in Lift circuits, and automatic sliding door circuits.

5. SSRs are used for motor control using PLC, microprocessors, etc.

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Solid State Relay Applications, Advantages over Normal Relay Solid State Relay Applications, Advantages over Normal Relay Reviewed by Author on October 23, 2020 Rating: 5
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