Why choose Solid State Relays?

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Relays are simple switching device that control high power electrical devices with low power signals. Functionally wise, electromechanical relays and solid state relays behave similarly. The difference lies in that solid state relay do not need moving parts to perform the task of opening or closing contacts in the circuit.

Solid state relays are often seen as the poster child of the semiconductor industry. They use the electrical and optical properties of semiconductors such as silicon-controlled rectifiers (SCRs), triodes for alternating current (TRIACs) and switching transistor outputs to perform the input to output isolation and switching functions.

What are some key advantages that might tip the scales in favor of the choice of solid state relays over electromechanical relays?

  • Long lifetime: Since there are no moving parts inside solid state relays, they are not subject to any contact failure, mechanical strain or corrosion. Solid state relays can operate for millions of cycles with no deterioration in performance and the lifetime is said to be 50-100 times that of electromechanical relay. Hence solid state relays are ideal for repetitive applications and when low maintenance is preferred.
  • Fast switching: Due to the absence of movable parts, solid state relays have a very fast response time. This means power to a load can be applied and removed very quickly and precisely, which is especially important for applications that requires quick on-off switching.
  • Shock and Vibration resistant: Without movable parts, solid state relays will not bounce electrically or mechanically. This makes them highly susceptible to erratic conditions in demanding and high vibration environments. For instance, Schneider Electric’s SSD solid state relays complies with IEC 61373 for railway & rolling stock application.

The above benefits make solid state relays highly suited for applications involving heating control, lighting control and motion control. Some of the main target segments include HVAC, packaging, furnace, food and beverage.

Of course, nothing is perfect. There are some limitations of solid state relays.

But fret not, there are also solutions to overcome it with Schneider Electric’s Harmony solid state relays .

  • Thermal management: Semiconductors are never completely on or off. In the on-state, the presence of substantial resistance in the solid state relays can cause significant heat generation when current is flowing. As thermal stress can reduce the lifetime of the solid state relay drastically, it is necessary to ensure the solid state relay is protected against excessive heat.

    To ensure proper heat dissipation, Schneider Electric’s Harmony solid state relays offer DIN rail mount options which are integrated with heatsink as well as panel mount options with a variation of heatsinks to select while considering the ambient temperature and load current of your application.

  • Product size: In general, solid state relays are bigger in size compared to electromechanical relays due to the heatsink. This becomes a concern faced by many technicians during installation as control panels are becoming more compact in size. Not to worry, Schneider Electric can help you to save panel space with these product offers from Harmony solid state range : slim design SSL range which is only 6.2mm in width; SSM2 range with two inputs and two outputs in a singular relay that is 18mm in width; SSD range with high power density packed inside 22.5mm in width (up to 35A) and 45mm in width (up to 60A) models.
  • Silent operation: This is a double edged sword. Due to the absence of moving contacts, solid state relays do not generate any noise, making it ideal in commercial and medical applications which favor noiseless operation. However, the “click” sound of contacts switching can be useful at times, especially to alert of malfunction when you do not hear the “click” sound in the case for electromechanical relays. As solid state relays operate silently, it is challenging to identify fault conditions unless manual testing is carried out.

    To ease trouble shooting and avoid reactive maintenance, Schneider Electric has developed a smart diagnostic solid state relay with embedded visual indication LEDs and debugging test button to monitor the operation and provide immediate response to abnormalities.

Industrial factory maintenance engineers woman inspect relay protection system of machinery and holding digital tablet with copy space.

There is no clear answer to the commonly asked question: are electromechanical relays or solid state relays better? The answer is neither, as each has its merits and demerits. The choice depends on the specific application requirements. If you are considering the service of the equipment, solid state relays will be the most cost-effective choice as you rarely need to worry about maintenance, repairing or replacement after installation.

Schneider Electric’s Harmony solid state relays boosts a wide range of products for you to select from. Need help in choosing the ideal solid state relay for your application? Refer to our catalog or use the product selector to ease your selection today.

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