As an Automotive Relay Manufacturer, we have the following recommendations for the selection of solid state relays.
1. The steady state current at the output of the solid state relay must not exceed the rated output current. Almost all loads have surge currents, such as so-called purely resistive electric heating elements, but they have a positive temperature coefficient, and the resistance at low temperatures is small, so the instantaneous current is just large when starting up.
2. Solid state relays have input characteristics of 3 to 32V DC, which has a wide control range. The input current to the control loop of a single-phase DC/AC solid state relay is typically around 10 mA. The control loop input current of the three-phase solid state relay is generally around 30 mA.
3. The control operating frequency of the AC solid state relay should not exceed 10 Hz. The control signal period of the DC solid state relay should be greater than 5 times the sum of the on and off times of the relay.
4. The load capacity of a solid state relay is directly related to the ambient temperature. As the ambient temperature increases, the load capacity of the SSR also decreases. At the same time, there is sufficient room for selecting the rated current of the SSR. Pay more attention to this when the ambient temperature is high.
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