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. It enables the control of high-voltage DC loads using low-voltage control signals. Unlike traditional mechanical relays, the SSR DC-DC offers fast switching, high reliability, and no mechanical wear, making it ideal for applications requiring frequent switching or high durability.

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

The Fotek SSR DC-DC is engineered to handle a wide range of DC control and load voltages. Below are the key technical details:

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

1. Control Signal Connection:

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

2. Load Connection:

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

3. Power Supply:

   • Ensure the load voltage and current do not exceed the SSR's rated specifications (5-200 V DC, 40 A max).

4. Mounting:

   • Secure the SSR to a heat sink or panel to ensure proper heat dissipation during operation.

5. Testing:

   • Apply the control signal to the input terminals and verify that the load is powered correctly.

• Heat Dissipation: Use a heat sink or cooling fan if the relay operates near its maximum current rating to prevent overheating.
• Polarity: Ensure correct polarity for both the control signal and load connections to avoid damage.
• Isolation: Verify that the control and load circuits are properly isolated to prevent electrical interference.
• Switching Speed: The SSR is designed for fast switching, but avoid exceeding the rated switching frequency to maintain reliability.
• Protection: Use appropriate fuses or circuit breakers to protect the SSR and connected components from overcurrent or short circuits.

The SSR DC-DC can be controlled using an Arduino UNO. Below is an example circuit and code to toggle a DC load using a digital pin.

1. Connect the Arduino's digital pin (e.g., pin 9) to the + (Input) terminal of the SSR.
2. Connect the Arduino's ground (GND) to the - (Input) terminal of the SSR.
3. Connect the DC load to the + (Output) and - (Output) terminals of the SSR.
4. Ensure the load has a separate power supply within the SSR's rated voltage and current.

// 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 (and load) ON
  digitalWrite(ssrPin, HIGH);
  delay(1000); // Keep the load ON for 1 second

  // Turn the SSR (and load) OFF
  digitalWrite(ssrPin, LOW);
  delay(1000); // Keep the load OFF for 1 second
}

1. The load does not turn on:

   • Verify that the control signal voltage is within the specified range (3-32 V DC).
   • Check the polarity of the control signal and load connections.
   • Ensure the load voltage and current are within the SSR's rated specifications.

2. The SSR overheats:

   • Ensure proper heat dissipation using a heat sink or cooling fan.
   • Verify that the load current does not exceed the maximum rating (40 A).

3. The SSR does not switch off:

   • Check for residual voltage on the load side. Some SSRs may have a small leakage current.
   • Ensure the control signal is completely removed when turning off the SSR.

4. The SSR fails to operate:

   • Inspect for physical damage or signs of overheating.
   • Test the SSR with a known working control signal and load.

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

Q: Is the SSR polarity-sensitive?
A: Yes, both the control signal and load connections must follow the correct polarity.

Q: Can I use the SSR for PWM control?
A: While the SSR supports fast switching, it is not ideal for high-frequency PWM control. Use a dedicated DC motor driver or MOSFET for such applications.

Q: How do I know if the SSR is working?
A: Apply a control signal and measure the voltage across the load terminals. If the load voltage matches the expected value, the SSR is functioning correctly.