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

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

The Fotek 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 + (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, especially for high-current applications.

5. Testing:

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

• Heat Dissipation: Use a heat sink or cooling fan to prevent overheating during high-current operation.
• Isolation: Ensure proper electrical isolation between the control and load circuits to avoid damage.
• Polarity: Observe correct polarity for both the control signal and load connections.
• Surge Protection: Use a flyback diode across inductive loads to protect the SSR from voltage spikes.
• Switching Speed: The SSR is not suitable for high-frequency switching applications due to its switching speed limitations.

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 - (Input) terminal of the SSR to the Arduino's GND.
• Connect the DC load to the + (Load) and - (Load) terminals of the SSR.
• Ensure the load voltage and current are within the SSR's specifications.

// Example code to control a Fotek SSR DC-DC with an Arduino UNO
// This code toggles the SSR on and off every 2 seconds.

#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 (load powered)
  delay(2000);                  // Wait for 2 seconds
  digitalWrite(SSR_PIN, LOW);   // Turn the SSR off (load disconnected)
  delay(2000);                  // Wait for 2 seconds
}

1. Can the SSR DC-DC be used for AC loads?

   • No, this SSR is designed specifically for DC applications. For AC loads, use an AC-AC SSR.

2. What is the maximum switching frequency of the SSR?

   • The SSR has a switching speed of ≤ 10 ms, making it unsuitable for high-frequency switching.

3. Do I need an external resistor for the control signal?

   • No, the SSR has an internal current-limiting circuit for the control signal.

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

   • For low-current applications, a heat sink may not be necessary. However, for high-current loads, a heat sink is essential to prevent overheating.

5. How do I protect the SSR from inductive load spikes?

   • Use a flyback diode across the load to suppress voltage spikes caused by inductive loads.