1. When using the solid state used in the printed circuit board with small current specifications, because the lead terminal is made of high thermal conductivity material, the welding should be carried out under the condition that the temperature is less than 250 °C and the time is less than 10S.
2. The selection of SSR for solid state relay with various load surge characteristics
The controlled load will generate a large inrush current at the moment of switching, and because the heat cannot be dissipated in time, it is likely to damage the internal thyristor of the SSR, so the user should analyze the surge characteristics of the controlled load when selecting the relay, and then select the relay. To make the relay be able to withstand this inrush current under the premise of ensuring steady-state operation, you can refer to the derating coefficient (at room temperature) of various loads in Table 2 when selecting.
If the selected relay needs to work in the occasion with high requirements for more frequent work, life and reliability, it should be multiplied by 0.6 on the basis of Table 2 to ensure reliable operation.
Generally, the above principles are followed in the selection, and the DC solid-state relay using the FET as the output device can be selected when the signal distortion is small at low voltage; For example, for AC resistive loads and most inductive loads, zero-crossing relays can be selected, which can prolong the life of the load and relay, and also reduce its own radio frequency interference. If it is used as a phase output control, a random solid state relay should be selected.
3. The influence of the ambient temperature
The load capacity of the solid state relay is greatly affected by the ambient temperature and its own temperature rise, in the process of installation and use, it should be ensured that it has good heat dissipation conditions, the rated working current of more than 10A products should be equipped with radiators, and products above 100A should be equipped with radiators and fans for strong cooling. During installation, attention should be paid to the good contact between the bottom of the relay and the radiator, and an appropriate amount of thermal grease should be considered to achieve the best heat dissipation effect.
If the relay works at high temperature for a long time (40°C-80°C), the user can consider derating to ensure normal operation according to the maximum output current and ambient temperature curve data provided by the manufacturer.
4. Over-current and over-voltage protection measures
When the relay is used, due to overcurrent and load short circuit, the internal output thyristor of the SSR solid state relay will be permanently damaged, and the fast fuse and protection type can be considered in the control loop (the product output protection should be selected for the selection of relay, with built-in varistor absorption circuit and RC buffer, which can absorb surge voltage and improve dv/dt resistance); Output protection can also be achieved by connecting an RC absorption loop and a varistor (MOV) at the output of the relay. The selection principle is 500V-600V varistor for 220V, and 800V-900V varistor for 380V.
5. Relay input loop signal
When the input voltage is too high or the input current is too large to exceed the rated parameters specified in the input, it can be considered to connect the voltage divider resistor in series at the input terminal or connect the shunt resistor at the input port in parallel, so that the input signal does not exceed its rated parameter value.
6. In specific use, the control signal and load should be stable, and the fluctuation should not be greater than 10%, otherwise voltage stabilization measures should be taken.
7. When installing and using, it should be kept away from electromagnetic interference and radio frequency interference sources to prevent the relay from malfunctioning out of control.
8. When the solid state relay is open and there is voltage at the load end, there will be a certain leakage current at the output end, which should be paid attention to when using or designing.
9. When the solid-state relay fails to be replaced, the original model or the product with the same technical parameters should be selected as far as possible to match the original application line and ensure the reliable operation of the system.
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