How to Maintain Solid State Relays

1. When selecting a solid state relay for a printed circuit board with a small current specification, since the lead terminal is made of high thermal conductivity material, it should be soldered at a temperature of less than 250°C and a time of less than 10S. The load current is generally controlled within 1/2 of the rated value.
2. The controlled load will generate a large inrush current at the moment it is turned on. Since the heat is too late to dissipate, it is likely to damage the thyristor inside the SSR. Therefore, users should analyze the surge characteristics of the controlled load when selecting a relay, and then select the relay. In order to enable the relay to withstand this surge current under the premise of ensuring steady-state operation, please refer to Table 2 for selection of derating factors for various loads (at room temperature).
If the selected relay needs to work in an occasion with high operating frequency, long life and high reliability requirements, it should be multiplied by 6.2 on the basis of Table 0 to ensure reliable operation.

Generally, the above principles are followed when choosing. When low voltage requires small signal distortion, DC solid-state relays using field effect transistors as output devices can be used; for AC resistive loads and most inductive loads, zero-crossing relays can be used. Extend the service life of loads and relays, and reduce their own radio frequency interference. If it is used for phase output control, a random solid state relay should be selected,

3. The load capacity of the solid state relay is greatly affected by the ambient temperature and its own temperature rise. During installation and use, ensure that it has good heat dissipation conditions. Products with a rated working current above 10A should be equipped with a radiator, and products with a rated operating current above 100A should be equipped with a radiator. Equipped with radiator and fan for forced cooling. When installing, pay attention to the good contact between the bottom of the relay and the heat sink, and consider applying an appropriate amount of heat-conducting silicone grease to achieve the best heat dissipation effect.
If the relay works at high temperature (40°C~80°C) for a long time, the user can consider derating according to the maximum output current and ambient temperature curve data provided by the manufacturer to ensure normal operation.

4. When using a relay, the internal output thyristor of the SSR solid state relay will be permanently damaged due to overcurrent and load short circuit. Consider adding a fast fuse and an air switch in the control loop to protect it (the relay should be selected for product output protection, the built-in varistor absorption loop and RC snubber can absorb surge voltage and improve dv/dt tolerance) ; An RC snubber loop and a varistor (MOV) can also be connected in parallel at the relay output for output protection. The selection principle is to use 600V-220V varistors for 500V and 900V-380V varistors for 800V. .

5. When the input voltage is too high or the input current exceeds its specified rated parameters during use, it can be considered to connect a voltage divider resistor in series at the input end or connect a shunt resistor in parallel at the input port so that the input signal does not exceed its rated parameter value.

6. In specific use, the control signal and load power supply should be stable, and the fluctuation should not exceed 10%, otherwise measures should be taken to stabilize the voltage.

7. During installation and use, keep away from electromagnetic interference and radio frequency interference sources to prevent the relay from malfunctioning and out of control.

8. When the solid state relay is disconnected and there is voltage at the load terminal, there will be a certain leakage current at the output terminal, which should be paid attention to when using or designing.

9. When the solid state relay cannot be replaced, a product with the same original model or technical parameters should be selected as much as possible to match the original application circuit and ensure reliable operation of the system.