Advantages of Using a Solid State Relay

Solid state relays are typically used for power control applications. They are designed to provide safe, low-voltage switching of AC load voltage.

An SSR has an internal coupling circuit to connect its input and output terminals without a direct electrical connection. This is usually achieved by using a light sensor (phototransistor, phototriac…) and an LED.

High Reliability

Solid state relays offer high reliability compared to electromechanical relays. They don’t have movable mechanical parts which means they are less sensitive to mechanical shock and vibration as well as external magnetic fields, which helps improve their lifespan and dependability. This helps eliminate failure caused by contact wear between contacts, action noise and mechanical arcing.

The input and output circuits in solid state relays are isolated using either an opto-isolator or a transformer. The opto-isolator uses one infra-red LED light source which optically couples through a gap to an adjacent photo sensitive device such as a Darlington pair, triac or transistor. When a voltage is applied to the control terminal of the opto-coupler, it triggers the output circuit which switches on and off as needed to control the load.

Alternatively, the DC output circuit of an SSR uses power MOSFET output chips which are current regulated to minimize power dissipation and can be driven direct from CMOS or TTL. The AC output circuit uses two thyristors or a triac and is isolated with a diode D1 to prevent damage due to reverse connection of the input drive voltage, and a 56 ohm resistor (R3) shunts any di/dt currents when the output is OFF, eliminating false triggering and ensuring the triac shuts off completely.

Finder’s solid state relays are manufactured to the highest standards, gate driver ic achieving international certifications from Underwriter Laboratories (UL), Canadian Standards Association (CSA), British Approvals Board of Telecommunications (BABT), Verband Deutscher Elektrotechniker (VDE) and Technischen Uberwachungs Vereine (TUV). They have a lifetime of 10 million cycles and have high resistance to inrush currents making them ideal for applications with resistive loads such as electric motors, valves, actuators and electromagnets.

High Durability

Input and output terminals of solid state relays have high dielectric strength, which is able to withstand the voltage value that is more than the rated operating voltage. The dielectric strength can be further increased by using a fast fuse or air breaker in the circuit to prevent excessive current that may damage the Solid State Relay.

Unlike electromechanical relays (EMR), there is no movable mechanical part in the internal structure of a solid state relay and thus it has less action noise, less mechanical wear, and is more reliable and durable. Solid state relays are also more resistant to electromagnetic interference than EMR.

Depending on the application and power requirements, you can choose either DC-SSR or AC-SSR. The difference is that DC-SSRs can only be used to control DC power supply or motor and AC-SSRs can be used to control AC power supply or transformer.

For applications with a constant or pulsed voltage input signal, a snubber circuit can be added to the SSR output to filter out certain frequency signals. RC circuits can also be used to reduce the rise rate of the output voltage (dv/dt), absorb the input surge current, suppress excessive transient voltage / current, and ensure that the Solid State Relay does not break down due to overvoltage. Besides, a varistor can be added to protect the input terminals of the SSR and provide the maximum protection level.

Low Power Consumption

Solid state relays consume less power to energize than electromagnetic (EM) relays because they don’t have moving parts and don’t dissipate any heat during the switching process. In addition, they require very little voltage to operate and are much less affected by electromagnetic interference than their counterparts.

Solid-state relays have lower arcing resistance and don’t produce any contact bounce during the switching process, which makes them safer than EMRs and are compatible with logic circuits. Additionally, they have high input-output isolation voltage, can handle varying voltages between the power supply and load, and are highly resistant to mechanical shock and vibration.

SSRs also feature low switching voltage and current, making them more compatible with the lower analog divider signal outputs found on temperature controllers. In addition, they’re inherently more reliable than mechanical relays and have a longer lifespan with no wearing parts, making them more durable than traditional relays.

While it is possible to damage SSRs by applying too much surge current, this can be avoided by analyzing the characteristics of the controlled load and selecting an appropriate rated current value. If the selected current is greater than the rated current, a resistor or inductor can be connected in series to reduce the excess current. Excessive inrush current can also be prevented by connecting a varistor between the SSR output and the control device.

Low Maintenance

Unlike electro-mechanical relays, solid state relays have no mechanical parts and require very little power to switch. This allows them to operate silently, making them ideal for commercial and medical applications which favor noiseless operation. However, the lack of a “click” sound can make it difficult to detect problems, such as faulty switching. This can lead to malfunction and unexpected heat generation, resulting in derating or even failure.

The robust design of solid state relays means they can withstand a variety of environmental conditions. They can withstand shock and vibration, which is perfect for industrial machinery or other harsh environments. Furthermore, they can work in high temperature environments, which makes them well suited to electronics industries such as photovoltaics, semiconductors and the manufacture of computer components.

Solid state relays also have very low maintenance requirements. They are easy to install and operate, with no arcing or sparks, as they switch between on and off states. This can reduce downtime and save on labor costs, as they do not require regular servicing.

Solid state relays are available in a variety of configurations to meet different needs and application requirements. These include bracket and panel mount, as well as both zero-cross and random relays. They also have 6.3mm Fast-On terminals, which allow easy clip connections without the need for screws. They can also handle a wide range of load currents, from heating to single-phase random motor control.