Thermal Protection Prevents SSR Failure

Solid State Relays (SSR) are replacing conventional electromagnetic relays for load control applications in the industry, as they hold several advantages over the latter. However, SSRs often face overheating causing them to fail. Newer designs now come with integrated thermal protection that improves longevity, efficiency, and system safety by preventing overheating and failure of SSRs.

Machinery driven by large motors requires a system to switch off the power supply to the motor on sensing higher than normal heat, thereby preventing expensive damage. Usually, this is accomplished by an electrical relay accomplishes this by interrupting the power supply to the motor. Presently, the industry uses two main types of electrical relays for the purpose—an electromagnetic relay (EMR) or a solid-state relay (SSR). Although EMRs are the tried and trusted solution for load circuit management, SSRs are now making successful inroads into their market share.

One of the major drawbacks of EMRs is their limited life span, and their susceptibility to external influences such as shock, vibration, and magnetic noise, among others. This causes wear and reduces the life cycle. On the other hand, the all-solid-state construction of the SSR, without any moving parts, makes them highly tolerant of external disturbances. As there is no wear to reduce accuracy, SSRs enjoy longer life cycles and offer predictable operation. For instance, while an EMR may work reliably for hundreds of thousands of cycles, an SSR continues to perform satisfactorily even after five million cycles of operation.

SSRs carry a several-fold entry price hike over their similarly rated electromechanical counterparts, which are priced considerably lower. Therefore, unless the application demands exclusive seclusion from positioning, vibration, shock, and/or magnetic interference, using an EMR is often more economical. SSRs are more suited to harsh operating environments, and their longer lifespan soon provides their return on investment.

Unlike EMRs, SSRs generate heat when conducting current. Unless managed by a thermal component, overheating can damage an SSR, resulting in an outage of the manufacturing system or assembly line, leading to expensive repair expenses.

To address the challenge of overheating, designers now integrate a thermostat within the SSR. This prevents the device from overheating and ensures the relay always operates within its safe operating area (SOA). Furthermore, it protects the operation of the system and components from potential outages and/or damage.

The user can set the maximum operating temperature depending on the application. If the internal temperature of the SSR crosses the set threshold, the integrated thermostat embedded within cuts off power to the input circuit. The internal power-switching device mounts a metal plate, whose temperature the thermostat constantly monitors. If the temperature of the metal plate exceeds the normal range, the power-switching device signals the SSR to turn off the power.

By providing a trip during overheating conditions, the built-in thermal protection ensures   near-absolute equipment damage. This translates into reduced maintenance expenses and production downtimes. The user can choose to turn on power automatically when the temperature has returned to normal, or opt for an inspection before switching on the power manually. The second option helps to troubleshoot design issues in the system.