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Will you keep the maintenance of solid state relay?

pk_hits:       date:2018-10-26

Solid State Relay (SSR) is a non-contact switch consisting of microelectronic circuits, discrete electronic devices, and power electronic power devices. The isolation between the control terminal and the load terminal is realized by the isolation device. The input of the solid state relay uses a small control signal to directly drive a large current load.


1. When using the solid state relay used in the small current specification printed circuit board, the lead terminal is made of high thermal conductivity material, and the welding should be carried out under the condition of temperature less than 250 ° C and time less than 10 S, for example, considering the ambient temperature. If necessary, derating can be considered. Generally, the load current is controlled within 1/2 of the rated value.

2. Selection of solid state relay SSR for various load surge characteristics

The controlled load will generate a large inrush current at the moment of turning on, and the internal thyristor of the SSR may be damaged due to the inability to dissipate heat. Therefore, the user should analyze the surge characteristics of the controlled load when selecting the relay, and then analyze Select the relay. The relay can withstand the surge current under the premise of ensuring steady state operation. For the selection, please refer to the derating factor (at normal temperature) of various loads in Table 2.

If the selected relay needs to work in a place with more frequent work, long life and high reliability requirements, it should be multiplied by 0.6 on the basis of Table 2 to ensure reliable operation.

Generally, the above principle is followed in the selection. In the low voltage requirement, the signal distortion is small, and the MOSFET can be used as the DC solid-state repeater of the output device; for the AC resistive load and most inductive loads, the zero-crossing relay can be selected. Extends load and relay life and also reduces its own RF interference. For phase output control, a random type solid state relay should be used.

3. Effects of using ambient temperature

The load capacity of solid state relays is greatly affected by the ambient temperature and temperature rise. During installation and use, it should be ensured that it has good heat dissipation conditions. Products with rated working current above 10A should be equipped with heat sinks. Products above 100A should be used. With radiator and fan strong cooling. Pay attention to the good contact between the bottom of the relay and the heat sink during installation, and consider applying proper amount of thermal grease to achieve the best heat dissipation.

If the relay is working in high temperature for a long time (40 °C ~ 80 °C), the user can consider the derating to ensure normal operation according to the maximum output current and ambient temperature curve data provided by the manufacturer.

4. Overcurrent and overvoltage protection measures

When the relay is used, the overcurrent and load short circuit will cause permanent damage to the SCR solid state relay internal output thyristor. Consider adding a fast fuse and air switch to the control circuit to protect it. (Selecting the relay should select product output protection, built-in The varistor absorption circuit and RC snubber can absorb surge voltage and increase dv/dt tolerance. It can also be connected to the RC absorption circuit and varistor (MOV) at the output of the relay for output protection. The selection principle is that 500V selects 500V-600V varistor for 220V, and 800V-900V varistor for 380V.

5. Relay input loop signal

In use, when the input voltage is too high or the input current is too large to exceed its specified rated parameters, consider connecting the voltage divider resistor at the input terminal or connecting the shunt resistor at the input port so that the input signal does not exceed its rated value. .

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

7. Keep away from electromagnetic interference and RF interference sources during installation and use to prevent the relay from malfunctioning.

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, so be careful 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 much as possible to match the original application line to ensure the reliable operation of the system.

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