1. Selection of voltage level and overvoltage protection of solid-state relay
When the voltage peak value added to the AC end of the solid state relay exceeds the highest voltage peak that the AC solid state relay can bear, the components in the solid state relay will be damaged by the voltage breakdown and cause the AC solid state relay to be damaged.
a. When the AC load is a resistive load of 220V, the AC solid state relay with a voltage level of 220V can be selected.
b. When the AC load is 220V inductive load or the AC load is 380V resistive load, the AC solid state relay with 380V voltage level can be selected.
c. When the AC load is an inductive load of 380V, an AC solid-state relay with a voltage level of 480V can be selected (the AC solid-state relay with 480V level also has a higher static DV/DT index); Other occasions with special requirements and high reliability requirements, such as power compensation, capacitor switching, motor forward and reverse rotation, etc., must choose AC solid state relay with 480V voltage level.
d. When the voltage of the AC load is less than 100VAC, it is best to consult our company for customization when choosing a solid state relay. AC solid-state relay overvoltage protection: In addition to the AC solid-state relay itself has RC absorption loop protection, it can also take parallel metal oxide varistor (MOV), MOV area size determines the absorption power, MOV thickness determines the protection voltage value. Generally, 500V-600V varistors can be selected for 220V series AC solid state relays, 800V-900V varistors can be selected for 380V series AC solid state relays, and 1000V-1100V varistors can be selected for 480V series AC solid state relays.
2. Selection of current level and overcurrent protection of solid state relay
Overcurrent (in the most severe case, a short circuit under load) is the most common cause of permanent damage to the thyristors inside the output of AC solid state relays. Fast fuses and air switches are one of the methods of overcurrent protection, and fuses can also be used for small-capacity AC solid state relays; Many loads will generate a large inrush current at the moment of turn-on, and the inrush current is one of the most important causes of damage to the internal output thyristor of the AC solid state relay as well as overcurrent. Therefore, when selecting a solid state relay, it is extremely important to ensure a certain amount of current margin.
a. When resistive load, the current level of the AC solid state relay should be greater than or equal to 2 times of the load rated current.
b. When the load is an AC motor, the current level of the AC solid-state relay must be greater than or equal to 6-7 times of the rated current of the motor.
c. When AC solenoids, intermediate relay wire protection, inductance coils and other loads, the current level of AC solid state relay should be greater than or equal to 4 times of the load rated current, and the transformer requires greater than or equal to 5 times the primary rated current of the transformer, and the current margin of the AC solid state relay should be amplified according to the actual experience for special inductive and capacitive loads.
d. When the power compensation capacitor load, the current level of the AC solid state relay must be greater than 5 times the load rated current.
3. Heating and heat dissipation of AC solid state relay
The maximum heat value of single-phase AC solid state relay when it is turned on is calculated according to the actual working current ×1.5W/a, and the ambient temperature, ventilation conditions (natural cooling, fan cooling) and AC solid state relay installation density should be taken into account in the heat dissipation design. A thin layer of thermal grease must be applied between the solid state relay and the mounting surface of the radiator.
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