Selection Of Current Specifications And Safety Precautions For Solid-state Relays

Based on the nature of the load and rated current, the maximum output current IT value of the solid-state relay is selected as follows:

(1) Resistive load: The current specification of solid-state relays should be more than twice the rated current of the load.

(2) Inductive load: The current specification of solid-state relays should be more than 3 times the rated current of the load.

(3) If the load current changes significantly, increase the current multiple appropriately.

(4) Ensure that the actual working current of the load during the entire operation process does not exceed the nominal maximum output current of the solid-state relay.

Product application:

The SSR series solid-state relay adopts a flame-retardant engineering plastic shell, epoxy resin encapsulation, and threaded lead out terminal wiring. It has high structural strength, impact resistance, strong vibration resistance, and low input driving current, making it convenient to interface with computer terminals and various digital programmable circuits. It is widely used in petrochemical equipment, food machinery, packaging machinery, textile machinery, CNC machine tools, plastic machinery, and fitness equipment, Automation control fields such as entertainment facilities.

Especially suitable for harsh environments such as corrosion, humidity, dust prevention, explosion-proof requirements, and frequent switching situations, it is a replacement product for AC contactors.

Safety precautions:

1. When the load current is higher than 5A, a heat sink must be used or installed on a metal base plate with corresponding heat dissipation effect, and thermal conductive silicone grease must be coated between the heat dissipation base plate and the installation surface of the solid-state relay. If the load current is above 40A, a fan forced cooling or water cooling should be added.

2. When used in inductive loads, high transient voltage and surge current may be applied to the output terminal, which may cause the solid-state relay to mislead or damage. Usually, voltage control devices with specific clamping voltage, such as bidirectional voltage regulator diodes or varistors (MOVs), need to be connected to the output terminal. Varistors are recommended to be 1.6 to 1.9 times the rated voltage.

3. When controlling a small load current load that is close to the minimum load current, a virtual load resistor must be connected in parallel on the load to reduce the output leakage current and generate a higher residual voltage on the load.

4. In order to avoid the temperature rise of solid-state relays exceeding the allowable value, the design and application should consider the heat dissipation effect and installation position. When two or more solid-state relays are installed side by side, appropriate spacing should be left.

5. The output terminals of multiple solid-state relays should not be used in parallel to attempt to increase the output current. But the output terminal can be used in series to adapt to higher working voltages.

6. When multiple solid-state relays share a common control power supply, the input terminals can be used in series or in parallel.

7. Please use capacitive loads with caution and choose solid-state relays specifically designed for capacitive loads.