How to Use SSR DC - DC: Examples, Pinouts, and Specs

The Fotek SSR DC - DC is a Solid State Relay (SSR) designed specifically for DC applications. Unlike traditional mechanical relays, this SSR uses semiconductor switching technology, enabling faster operation, silent switching, and a significantly longer lifespan. It is ideal for controlling high-voltage DC loads using low-voltage control signals, making it a reliable and efficient choice for various applications.

• Industrial automation systems
• Motor control in DC circuits
• Battery management systems
• Solar power systems
• LED lighting control
• Robotics and IoT projects

The following table outlines the key technical specifications of the Fotek SSR DC - DC:

The Fotek SSR DC - DC has four terminals, as described in the table below:

1. Connect the Control Signal:

   • Attach the positive control signal (3-32 V DC) to the + (Input) terminal.
   • Connect the ground of the control signal to the - (Input) terminal.

2. Connect the Load:

   • Connect the positive terminal of the DC load to the + (Load) terminal.
   • Connect the negative terminal of the DC load to the - (Load) terminal.

3. Power the Circuit:

   • Ensure the control signal voltage is within the specified range (3-32 V DC).
   • Apply the load voltage (5-220 V DC) to the load terminals.

4. Switching:

   • When the control signal is applied, the SSR will switch on, allowing current to flow through the load.
   • Removing the control signal will turn the SSR off, stopping current flow.

• Heat Dissipation: Ensure proper heat dissipation by mounting the SSR on a heat sink if the load current is high.
• Polarity: Observe correct polarity for both the control signal and the load connections.
• Voltage and Current Ratings: Do not exceed the specified voltage and current ratings to avoid damage to the SSR.
• Isolation: The SSR provides electrical isolation between the control and load sides, but ensure proper grounding for safety.
• Switching Speed: The SSR is designed for fast switching, but avoid rapid on/off cycles that could lead to overheating.

The following example demonstrates how to control a DC load using the Fotek SSR DC - DC and an Arduino UNO.

• Connect the Arduino's digital output pin (e.g., pin 9) to the + (Input) terminal of the SSR.
• Connect the Arduino's ground (GND) to the - (Input) terminal of the SSR.
• Connect the DC load to the + (Load) and - (Load) terminals of the SSR.

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

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

void loop() {
  // Turn the SSR on (control signal HIGH)
  digitalWrite(ssrPin, HIGH);
  delay(5000); // Keep the load on for 5 seconds

  // Turn the SSR off (control signal LOW)
  digitalWrite(ssrPin, LOW);
  delay(5000); // Keep the load off for 5 seconds
}

1. SSR Not Switching On:

   • Cause: Insufficient control signal voltage or current.
   • Solution: Verify that the control signal voltage is within the 3-32 V DC range and the current is sufficient (≥ 7.5 mA).

2. Load Not Receiving Power:

   • Cause: Incorrect load connections or insufficient load voltage.
   • Solution: Check the polarity and ensure the load voltage is within the 5-220 V DC range.

3. Overheating:

   • Cause: Excessive load current or rapid switching.
   • Solution: Use a heat sink and avoid rapid on/off cycles.

4. SSR Stuck in On/Off State:

   • Cause: Damaged SSR due to overvoltage or overcurrent.
   • Solution: Replace the SSR and ensure the voltage and current ratings are not exceeded.

Q: Can the SSR DC - DC be used for AC loads?
A: No, this SSR is designed specifically for DC loads. For AC loads, use an AC-rated SSR.

Q: Does the SSR require an external power supply?
A: No, the SSR operates directly from the control signal voltage (3-32 V DC).

Q: Can I use the SSR for PWM control?
A: While the SSR can handle fast switching, it is not ideal for high-frequency PWM control due to potential heating issues.

Q: How do I mount the SSR?
A: The SSR is panel-mounted. Use screws and ensure proper heat dissipation with a heat sink if necessary.