Relays are integral parts of any circuit-be it simple or complex. Rather than a switch, they can be replaced. Or they can be used for purposes suited exclusively for them. There are two main types of relays based on the method of working: Electromechanical Relays (EMR) This is the most widely used relay and is based on the principle of electromagnetism. This has a mechanical influence by the electromagnet field created, which regulates the movement of contacts to allow or suppress the flow of current in a circuit. They are strong but may be slower and noisier than SSR. Nirrmally, the solid-state relays are the ones that do not have an electromagnet and apply the know-how of semiconductors to regulate the switch-open and switch-close systems. The power of semiconductor operation allows them to become more sensitive and faster compared to electromagnets. These relays rely on semiconductors and have no moving parts. That makes them more wear-resistant than electromechanical relays. They have a faster switching speed, higher reliability, and longer life duration than the electromechanical relay. They are compact, silent, and low power consumption. Electromechanical relay vs Solid state relay So, unless you need electromechanical relays for specific reasons or prefer them for cost-effectiveness reasons, solid-state relays are certainly the better alternative. To get a better idea of what you're getting yourself into, let's explore exactly how the relay works.

How Solid State Relays Work

A solid-state relay contains solid components like the semiconductor to control the flow of a circuit's current. The basic operation of a solid-state relay is essentially described by two major components: an input control circuit and a switching output circuit. The input circuit is normally an optocoupler, being an LED, that will trigger upon receiving a low voltage input. It will emit light for the photo-sensitive device to sense. There then follows isolation between input and output circuits. The output circuit consists of a photo-coupler, which captures light and turns it into electrical energy to activate the load circuit, possibly containing elements such as triacs, diodes, transistors, or thyristors. It permits the device to conduct and block the flow of current. The most common control signal is the one that usually controls the operation of a solid-state relay. When its control signal is on, the input circuit will allow the current to go to the LED of the optocoupler, causing it to initiate the photosensitive device, and thus, current is now permitted to flow in the main circuit. In other words, if the control signal is not present or has been disabled, the input circuit no longer allows the current to flow through the LED of the optocoupler. The light-sensitive component becomes desensitized and therefore the output circuit's power semiconductor device is switched off, and the flow of current in the main circuit is interrupted. It is the opto-coupling technology that makes the switching extremely fast and sensitive, with high levels of insulation. The output voltage could be digital or analog, depending on the input and load-drive circuit.

Types of Solid State Relays

Now that you understand what makes SSRs different from EMRs and how they work, let's talk about the various types of SSRs available. This will enable you to determine which one will best suit your particular application. The two most common forms of SSRs are as follows: Non-zero crossing Zero Crossing

Non-Zero Crossing SSR

Also called Random Turn ON-OFF relays, they immediately turn on the output voltage when the input voltage is turned on. In consequence, no synchronization with the AC waveform is necessary. They work best in applications where management over the power in the load has to be very precise. This can cause a surge in the current or voltage spikes when the SSR turns on during the high-voltage phase of the AC cycle. It may interfere with the equipment and sometimes even damage the appliances.

Zero Crossing SSR

The zero crossing SSRs are specially designed to combat the downside of the random turn on-off SSRs. They turn on and off only when the AC voltage crosses zero (as their name indicates). Therefore, regardless of whether input voltage is applied when the AC waveform is in between phases or at a high-voltage phase, it will only turn on when it crosses zero. This reduces electrical noise and voltage spikes that are generated due to switching transitions. This, therefore, reduces the likelihood of electrical disturbances taking place. Solid state relays can also be categorized by the isolation method used for control input circuit and output switching circuit. Two types of SSRs based on isolation methods are: triac-based SSRs, and transformer-isolated SSRs.

Triac-based SSR:

In this type of circuit, the switching device for output is a triac. The majority of the SSRs use triacs for applications where AC needs to switch. It is cost-effective, compact, and very good for using in resistive loads or inductive with moderate current surges during inrush. However, they might not so well when using on the highly inductive or highly capacitive loads since it may cause voltage spikes or current surges. Transformer-isolated SSR Transformer-isolated SSRs employ a miniaturized transformer to isolate the control input circuit with the output circuits. It can either be a step up or a step-down as required. Although quite similar in working compared to triac-based SSRs, it may also act as an electrical noise protector, and voltage spikes and transient events can be safeguarded against. Thus, they can be used in conjunction with all types of loads, inductive or capacitive loads.

Applications

Solid state relays are used in various fields as they possess useful properties like high switching speed, reliability, long lifetime and immunity from electrical noises. Let's discuss a few of them here:

Industrial Automation

They are used in motor control, heating and cooling systems, lighting control, and power distribution panels, where one can find some of their biggest applications in industrial automation. Most the products have dedicated inputs for connecting SSRs.

HVAC Systems

They play an important role in Heating, Ventilation, and Air conditioning applications. They are used on the control of electric heaters, fans, pumps, and compressor motors for the efficient and precise regulation of temperature.

Energy Management

In its application, SSR is used in power management systems that govern the switching of power to a variety of loads based on demand. Consequently, energy consumption is optimized and costs are minimised.

Automotive Industry

SSRs are used for application Several applications of automotive systems are realized through the use of SSRs, including lighting controls, electric window motors, wiper control, and power seat adjustments. Through their use, SSRs ensure efficient switching and reliability in demanding situations presented by the automotive environment.

Advantages of SSR

SSRs switch very fast with tight control. There is no other component that can perform this function and neither can SCRs, EMRs, contactors do. They do not require any gating or control signals to maintain conduction, whereas SCRs do They provide full-wave switching for AC loads, although SCRs can only control one half-cycle of the AC waveform SSRs contain no moving parts so have longer life-span and more reliable. They do not emit much electrical noise and are also free from the contact bounce problem. They work almost noiselessly and do not give any kind of humming or buzzing sounds. SSRs are usually smaller in their dimension As compared to their counterparts, the solid-state relays can serve a number of conditions and are extremely efficient. They even come in economical ranges, as per their rating. Here at DA, we currently provide 25A, 40A, 50A, and 70A and are planning to extend this range in the future. They also come with various mounting methods, if you choose so, such as din rail, PCB, bracket, and panel for your convenience.