Solid-state relays are often seen as a textbook example of the semiconductor industry. They take advantage of the electrical and optical properties of semiconductors, such as a triode that can switch current in both directions and transistor outputs that are faster, more reliable and therefore can handle higher frequencies.

In the world of electronic circuits, there are two prominent players: solid-state relays and electromechanical relays. Each has its own unique characteristics and applications. Below, we dive deeper into the advantages of solid-state relays and how they differ from their electromechanical counterparts.

• Long service life: Because there are no moving parts in a solid-state relay, they are not subject to contact wear, mechanical stress or corrosion. Solid state relays can operate millions of cycles without a reduction in performance. The service life is 50-100 times longer than that of electromechanical relays. Solid-state relays are therefore ideal for repetitive applications and when low maintenance is desired.
• Fast switching: As there are no moving parts, solid-state relays have a very fast response time. This means that current to a load can be added and removed very quickly and accurately. This is especially important in applications that require rapid switching on and off.
• Resistant to shock and vibration: Solid-state relays are well suited to demanding environments with a lot of vibration. They do not receive electrical or mechanical shocks because there are no moving parts inside. Harmony solid-state relays for panel mounting comply with, among others, the international standard IEC 61373 for railways and similar guided transport. This makes this series highly suitable for shock and vibration tests.

Long life, fast response time and shock resistance make solid-state relays well suited for applications involving heating control, motor control, lighting control, medical devices and automobiles. Some key industry segments include HVAC, railway and transport, packaging and food & beverage.

But rest assured, there are also specific solutions and functionalities to overcome these with Schneider Electric's Harmony solid-state relays.

• Thermal management: It is important to understand that semiconductors are never completely on or off. When they are in the ‘on’ position, the resistance within the solid-state relay can generate significant heat as current flows through it. This heat can significantly shorten the life of the solid-state relays. Therefore, it is essential to protect these relays from overheating.

  Schneider Electric's Harmony solid-state relays offer a solution for this. They have DIN-rail mounting options that are integrated with a heat sink (heatsink). This helps dissipate the heat generated. They also offer panel-mount options with a range of heat sinks to choose from. When selecting a heatsink, you should consider the ambient temperature and current of your application. This ensures effective thermal management and extends the life of your solid-state relays.

• Product size: In general, solid-state relays are larger than electromechanical relays due to the fact that they have a carbon body (heatsink). This is a problem for many panel builders during installation, as control panels and cabinets become increasingly compact. For this, Schneider Electric has specific ranges. that provide a solution for this challenge. For example, the SSL range. Save panel space with selected products in the Harmony solid-state relay range. The SSL series has a slim design that is only 6.2mm wide. The SSM2 range comes with two inputs and two outputs in a single relay that is only 18mm wide.The SSD range comes in models of 22.5mm wide (up to 35A) and 45mm wide (up to 60A) and comes with high power density.

• Silent operation: Solid-state relays produce no noise, making them ideal for commercial and medical applications, where silent operation is desired. However, the ‘’click sound‘’ of contacts switching can sometimes be useful, especially to warn of a fault. Because solid-sate relays operate silently, it is challenging to indentifcate faults or damage unless hand-mating tests are performed.

To facilitate troubleshooting and avoid reactive maintenance, Schneider Electric has developed a smart diagnostic solid-state relay with built-in visual LEDs and a debugging test button. This is to monitor the operation of the solid-state relays and react immediately to anomalies.