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 long operational lifetimes.

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

Below are the key technical details for the Fotek SSR DC-DC:

The SSR DC-DC typically has four terminals, as described 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 + (Load) terminal.
   • Connect the negative side of the DC load to the - (Load) terminal.

3. Power Supply:

   • Ensure the load voltage and current do not exceed the SSR's rated output voltage (5-220 V DC) and current (40 A).

4. Mounting:

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

5. Testing:

   • Apply the control signal voltage to the input terminals. The SSR should switch the load on or off depending on the control signal.

• Heat Dissipation: Use a heat sink or cooling fan if the SSR operates near its maximum current rating to prevent overheating.
• Voltage Spikes: For inductive loads, use a flyback diode across the load to suppress voltage spikes and protect the SSR.
• Polarity: Ensure correct polarity for both the control signal and load connections to avoid damage.
• Isolation: Verify that the control circuit and load circuit are properly isolated to prevent electrical interference.

The SSR DC-DC can be controlled using an Arduino UNO. Below is an example circuit and code:

• 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.

// Example code to control a Fotek SSR DC-DC with an Arduino UNO
// This code toggles the SSR on and off every 1 second.

#define SSR_PIN 9  // Define the Arduino pin connected to the SSR input

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

void loop() {
  digitalWrite(SSR_PIN, HIGH);  // Turn the SSR on (control signal HIGH)
  delay(1000);                  // Wait for 1 second
  digitalWrite(SSR_PIN, LOW);   // Turn the SSR off (control signal LOW)
  delay(1000);                  // Wait for 1 second
}

1. SSR Does Not Switch the Load:

   • Cause: Insufficient control signal voltage.

   • Solution: Ensure the control signal voltage is within the specified range (3-32 V DC).

   • Cause: Incorrect wiring.

   • Solution: Double-check the connections for both the control signal and load.

2. Overheating:

   • Cause: Excessive current through the SSR.
   • Solution: Verify that the load current does not exceed the SSR's maximum rating (40 A). Use a heat sink if necessary.

3. Load Flickering:

   • Cause: Noise or instability in the control signal.
   • Solution: Use a decoupling capacitor near the SSR input terminals to stabilize the control signal.

4. No Isolation Between Control and Load Circuits:

   • Cause: Faulty SSR or incorrect wiring.
   • Solution: Test the SSR's isolation using a multimeter. Replace the SSR if necessary.

Q1: Can the SSR DC-DC be used with AC loads?
A1: No, the SSR DC-DC is designed specifically for DC loads. For AC loads, use an AC-rated SSR.

Q2: What happens if the control signal exceeds 32 V DC?
A2: Applying a control signal above the specified range may damage the SSR. Always ensure the control voltage is within 3-32 V DC.

Q3: Can I use the SSR without a heat sink?
A3: For low-current applications, a heat sink may not be necessary. However, for high-current loads, a heat sink is essential to prevent overheating.

Q4: How fast can the SSR switch?
A4: The SSR has a switching speed of ≤ 10 ms, making it suitable for most DC applications.