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 lifespans.

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

3. Power the Circuit:

   • Ensure the control signal voltage is within the specified range (3-32 V DC).
   • When the control signal is applied, the SSR will switch the DC load on.

4. Mounting:

   • Secure the SSR to a heat sink or panel to ensure proper heat dissipation, especially for high-current applications.

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

The following example demonstrates how to control a DC motor using the SSR DC-DC and an Arduino UNO:

// Example: Controlling a DC motor with Fotek SSR DC-DC and Arduino UNO

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

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

void loop() {
  digitalWrite(ssrPin, HIGH); // Turn the SSR (and motor) ON
  delay(5000); // Keep the motor ON for 5 seconds

  digitalWrite(ssrPin, LOW); // Turn the SSR (and motor) OFF
  delay(5000); // Keep the motor OFF for 5 seconds
}

Note:

• Connect the ssrPin (pin 9) to the Input (+) terminal of the SSR.
• Connect the Arduino ground (GND) to the Input (-) terminal of the SSR.

1. SSR Not Switching On:

   • Cause: Control signal voltage is too low.
   • Solution: Ensure the control signal voltage is within the 3-32 V DC range.

2. Overheating:

   • Cause: Excessive current or insufficient heat dissipation.
   • Solution: Use a heat sink or cooling fan, and ensure the load current does not exceed the SSR's maximum rating.

3. Load Not Operating:

   • Cause: Incorrect wiring or polarity.
   • Solution: Double-check all connections and ensure correct polarity for both the control and load circuits.

4. Voltage Drop Across SSR:

   • Cause: Internal resistance of the SSR.
   • Solution: Verify that the voltage drop is within acceptable limits for your application.

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

Q2: Is the SSR DC-DC suitable for PWM control?
Yes, the SSR can handle PWM signals, but ensure the switching frequency is within the relay's response time (≤ 10 ms).

Q3: How do I protect the SSR from voltage spikes?
For inductive loads, use a flyback diode across the load to suppress voltage spikes and protect the SSR.

Q4: 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 strongly recommended to prevent overheating.