How to Use CG Solid State Relay SSR-25DD: Examples, Pinouts, and Specs

The CG SSR-25DD is a solid state relay (SSR) designed for reliable and efficient switching of DC loads. Unlike mechanical relays, the SSR-25DD uses semiconductor components to provide electrical isolation and control, ensuring fast and silent operation with no moving parts. This relay is capable of handling up to 25A of current and operates with a low control voltage, making it ideal for automation, industrial control systems, and other high-performance applications.

• Industrial automation and process control
• Motor control and DC load switching
• Heating element control
• LED lighting systems
• Robotics and embedded systems

The SSR-25DD has four terminals, as described below:

1. Control Signal Connection: Connect the control signal source (e.g., microcontroller, PLC, or switch) to the input terminals (Pin 1 and Pin 2). Ensure the control voltage is within the range of 3V DC to 32V DC.
2. Load Connection: Connect the DC load to the output terminals (Pin 3 and Pin 4). The load voltage must be between 5V DC and 60V DC, and the current should not exceed 25A.
3. Power Supply: Ensure the power supply for the load matches the load voltage and current requirements.
4. Mounting: Secure the SSR-25DD to a heat sink or panel using screws to ensure proper heat dissipation during operation.
5. Testing: Apply the control signal to the input terminals and verify that the load is switching on and off as expected.

• Heat Dissipation: The SSR-25DD can generate heat during operation, especially at high currents. Use a heat sink or cooling fan to prevent overheating.
• Overcurrent Protection: Use a fuse or circuit breaker to protect the relay and load from overcurrent conditions.
• Voltage Spikes: For inductive loads, use a flyback diode across the load to suppress voltage spikes and protect the relay.
• Polarity: Ensure correct polarity when connecting the input and output terminals to avoid damage to the relay.
• Isolation: Verify that the control and load circuits are electrically isolated to prevent interference or damage.

Below is an example of how to control the SSR-25DD using an Arduino UNO to switch a DC motor.

• Input (+): Connect to Arduino digital pin (e.g., D9) through a 220-ohm resistor.
• Input (-): Connect to Arduino GND.
• Output (+): Connect to the positive terminal of the DC motor.
• Output (-): Connect to the negative terminal of the DC motor.

// Define the pin connected to the SSR input
const int ssrPin = 9;

void setup() {
  pinMode(ssrPin, OUTPUT); // Set the SSR pin as an output
}

void loop() {
  digitalWrite(ssrPin, HIGH); // Turn on the SSR (motor ON)
  delay(5000);               // Keep the motor ON for 5 seconds
  digitalWrite(ssrPin, LOW);  // Turn off the SSR (motor OFF)
  delay(5000);               // Keep the motor OFF for 5 seconds
}

1. Can the SSR-25DD switch AC loads?

   • No, the SSR-25DD is designed specifically for DC loads. For AC loads, use an AC-rated SSR.

2. What happens if the control voltage exceeds 32V DC?

   • Applying a control voltage higher than 32V DC can damage the relay. Always stay within the specified range.

3. Is the SSR-25DD polarity-sensitive?

   • Yes, both the input and output terminals are polarity-sensitive. Ensure correct polarity during installation.

4. Can I use the SSR-25DD without a heat sink?

   • While it is possible for low-current applications, a heat sink is recommended for currents above 10A to prevent overheating.

By following this documentation, users can effectively integrate the CG SSR-25DD into their projects for reliable and efficient DC load switching.