What do conveyor belts, assembly lines, medical, energy, industrial/commercial HVAC and refrigeration systems, heavy-duty transport and construction vehicles, and other complex manufacturing systems all have in common? Electrical Motors.
Big and expensive electrical motors that, if they overheat, can be damaged or even destroyed. Motors can overheat from a variety of different causes—too much weight being moved, jams in a conveyor belt, working in high temperature environments, and fluctuations in supply voltage—all can contribute to the possibility of overheating. Thermally protected solid-state relays (SSRs) can also help protect against cyberattack by preventing rogue instructions from forcing a machine to run extra fast, stressing its components, and causing serious damage from overheating.
Many of these large machines require a system attached to the motor’s power supply that can sense overheating and will turn off the power to the motor, thus preventing this damage. In many cases, this device is an electrical relay that turns the power on and off. There are two main types of these relays—electro-mechanical (EMRs) and SSRs.
What Is The Difference Between An EMR And SSR?
For more than 150 years, electro-mechanical relays were the standard solution for managing these load circuits providing power to big machines. However, in the last 30 years or so, SSRs have captured a great deal of market share because of increased operational life, reliability, and design flexibility.
There are significant differences between EMRs and SSRs, especially in terms of life span and performance.
EMRs are mechanical based and have moving parts, making them highly susceptible to magnetic noise, vibration, shock, and other outside influences that can affect wear and life cycle. In contrast, SSRs offer a durable, all-solid-state electronic construction with no moving parts to affect wear or accuracy, thereby offering predictable operation and longer life.
The average life span of EMRs is in the range of hundreds of thousands of cycles compared to five million hours for three-phase SSRs. With such maintenance-free durability, SSRs can often outlast the equipment in which they are installed.
In addition to a longer life span that provides greater reliability and replacement cost savings, SSRs provide faster switching than EMRs, making them adaptable to a wider range of high power load applications.
SSRs operate silently (without the undesirable clicking sound emitted by EMRs) with low input power consumption and produce little electrical interference. Both shock and vibration resistant, SSRs can withstand harsh environments and continue to operate accurately and reliably, whereas EMRs need frequent replacement, making them very undesirable in harsh conditions.
SSRs excel over EMRs in other areas as well.
They are compatible with control systems, immune to magnetic noise, and encapsulated to protect critical components. Their solid-state design enables them to be position insensitive and provides design engineers more flexibility to mount SSRs anywhere within an application—whether sideways or upside down.
Because they are solid-state without any moving parts, SSRs can be safely used in industrial locations where there is heavy vibration with no interference in performance, whereas mechanical-based EMRs are very sensitive to positioning, shock, and vibration, thereby restricting design options.
With all the advantages SSRs provide, it is understandable that they are more expensive than EMRs. Though significant, this price point disparity becomes a non-issue when factored in over the five million hours of life SSRs provide.
SSRs and Thermal Management
As SSRs generate heat when conducting current, there is a thermal management component to their operation, just like the motors they control.
Should overheating occur, diagnosing and replacing a damaged SSR can take time while the assembly line or manufacturing system is down and out of service, cutting into operations and running up expenses.
When the SSR turns on to generate current, it also generates heat. Failure to adequately protect the SSR can cause damage to the relay or to the load.
So how do you protect the SSR itself from overheating?
To address this overheating challenge, Sensata has developed a new SSR technology that integrates a thermostat into the SSR itself to ensure that the relay always operates in a safe or protected mode. This new design is differentiated by its ability to prevent the SSR from overheating, thus protecting component and system operation from potential damage or shut down.
The new SSR cuts off input circuit power when the temperature goes beyond the specified maximum as determined by the application requirements. Power is automatically turned on again when the temperature has cooled down to within the normal operating range. The cool down and re-start phase usually takes only a few minutes.
This automatic thermal protection is accomplished by means of an integrated thermostat embedded in the SSR. The thermostat senses the internal temperature of a mechanical interface with a metal plate where the internal power-switching device is mounted. If the heat exceeds the normal range, it sends a signal to the SSR to turn off the power. This built-in thermal protection completely prevents overheating conditions by providing a trip before equipment damage can occur, thereby saving time and money.
In addition to preventing overheating, this integrated thermal protection function can help troubleshoot design issues in the system. It can help identify incorrect heat sinking capacity in the SSR or system, poor installation resulting in insufficient heat sinking contact, heat dissipation efficiency of the system, and other issues.
While developed for use in a commercial refrigeration application, this SSR design can be adapted to other industrial and manufacturing applications. For example, consider a conveyor belt application where a motor could stick, causing overload and potential damage to the system. In this case, the SSR with integrated thermal protection would prevent overheating from occurring by shutting down the conveyor belt once a pre-determined heat threshold was met within the SSR’s thermostat.
In injection molding applications, where limited space can cause the temperature in the cabinet to rise, thermal protection prevents the SSR from overheating if the heatsinking is not adequate, thus avoiding costly repairs. For heating systems, the thermally protected SSR can help shut down the heating element if there is a problem with the temperature controller that causes a temperature runaway, thereby protecting the entire system.
SSRs provide robust solutions for electronic switching in load control applications and hold many advantages over EMRs. New, emerging SSR designs offer integrated thermal protection that can prevent overheating and improve system safety, efficiency, and longevity. This product evolution will undoubtedly change the game in thermal protection for a wide range of applications.
