A solid state relay produces heat while carrying load current. Heat-sink selection should be based on calculated power loss and the complete thermal path, not only on the current printed on the relay.
Review the model-specific on-state voltage drop and expected RMS load current. Their product provides an initial estimate of conduction loss. Switching losses may also matter in high-frequency applications.
Include continuous current, duty cycle, inrush current and the expected load profile. A relay used intermittently may have different thermal requirements from one operating continuously.
The temperature inside an electrical enclosure can be significantly higher than room temperature. Nearby heat sources, enclosure ventilation and seasonal conditions must be considered.
Heat moves from the semiconductor through the relay base, thermal interface material, heat sink and surrounding air. Poor surface contact or incorrect mounting pressure can increase thermal resistance.
Natural convection depends on fin orientation and clear space around the heat sink. Forced airflow can improve cooling, but fan reliability and filter maintenance then become part of the design.
A heat sink does not replace overcurrent, short-circuit or overvoltage protection. Select protective devices according to the SSR, load and system requirements.
Check the model data in the XURUI solid state relay range before deciding the permissible current and heat-sink arrangement.
