How the Heat Sink works

How the Heat Sink works

The role of the heat sink is to dissipate the heat generated by the solid state relay or module to ensure that the solid state relay or module will work stably and reliable at optimum conditions and not be burned and damaged due to high temperatures. The heat dissipation effect of the heat sink is not only related to its specification (size, shape), but also related to external environmental factors, such as the ambient temperature (season), ventilation conditions (natural cooling or forced cooling, and ventilation volume), and installation density. In addition, it is also necessary to consider whether the volume of the solid state relay or the module itself and the installation space of the heat sink in the equipment matches the specifications of the heat sink.

The cooling method of the solid state relay/module can be divided into Air Cooling method and Water Cooling method. And the air cooling heat sink can be farther divided into the Heat Sink (natural cooling) and Air Cooled Radiator (forced cooling by fan). Normally, if the load current of the solid state relay/module reaches 10A, a heat sink must be equipped; if the load current is 40A or more, an air-cooled radiator or a water-cooled radiator must be installed. When the module is used for the load with load power greater than 15 KW, it is recommended to use a suitable heat sink, and apply thermal grease between the heat sink and the SCR backplane, as well as cold air to cool down. If the current is below 350A, the module is cooled by forced air cooling; if the current is more than 400A, the cooling method for the module can be either air-cooling or water-cooling.

Heat dissipation reference standard: The temperature of the bottom plate (the side in contact with the heat sink) of the solid state relay or module does not exceed 80 °C.

In practical applications, we recommend installing a 75°C temperature switch (with a pair of normally closed contacts) on the mounting surface of the heat sink where near the edge area of the solid state relay or module (within 20mm), and then connecting the control signals of the solid state relay or module in series with the normally closed contacts. In this way, when the temperature of the detection point exceeds 75 °C, the normally closed contact will trip and cut off the control signal, and the output terminal of the solid state relay or module will be forcibly turned off to get protection. Generally, if the solid state relay or module is installed to the place with the actual current of each phase exceeding 50A, the high installation density and ambient temperature, it is better to apply a temperature switch for protection to ensure that the temperature of the bottom plate of the solid state relay or module does not exceed 80 ° C under severe conditions.