How to Use SSR-25DA 25A 250V Solid State Relay Module: Examples, Pinouts, and Specs

The SSR-25DA is a solid state relay (SSR) manufactured by HiLetgo (Part ID: 3-01-1247-25A). This relay is designed to switch AC loads of up to 25A at 250V using a low-voltage DC control signal. Unlike traditional mechanical relays, the SSR-25DA uses semiconductor devices for switching, offering faster response times, silent operation, and a longer lifespan.

• Industrial automation and control systems
• Heating, ventilation, and air conditioning (HVAC) systems
• Motor control and lighting systems
• Home automation projects
• Arduino and microcontroller-based projects for controlling high-power AC devices

The SSR-25DA has four terminals, divided into two sections: the control side and the load side.

1. Control Side Connection:

   • Connect the positive control signal (e.g., from a microcontroller or Arduino) to the + terminal.
   • Connect the ground of the control signal to the - terminal.
   • Ensure the control voltage is within the range of 3V to 32V DC.

2. Load Side Connection:

   • Connect one terminal of the AC load to one of the ~ terminals on the SSR.
   • Connect the other ~ terminal to the AC power source.
   • Ensure the load does not exceed the maximum rating of 25A at 250V AC.

3. Powering the Circuit:

   • When the control signal voltage is applied (≥ 3V DC), the SSR will switch ON, allowing current to flow through the load.
   • When the control signal voltage is removed (≤ 1V DC), the SSR will switch OFF, stopping current flow.

• Heat Dissipation: The SSR-25DA generates heat during operation. Use a heatsink or mount the relay on a metal surface to ensure proper heat dissipation, especially for high-current loads.
• Isolation: Ensure proper electrical isolation between the control and load sides to prevent damage to the control circuit.
• Zero-Crossing Switching: The SSR-25DA uses zero-crossing technology, which minimizes electrical noise and extends the lifespan of connected devices.
• Overcurrent Protection: Use a fuse or circuit breaker to protect the relay and load from overcurrent conditions.
• Avoid Inductive Loads: For inductive loads (e.g., motors), use a snubber circuit to suppress voltage spikes.

Below is an example of how to control an AC light bulb using the SSR-25DA and an Arduino UNO.

• Connect the Arduino's digital pin (e.g., pin 9) to the + terminal of the SSR.
• Connect the Arduino's GND to the - terminal of the SSR.
• Connect the AC light bulb to the load side of the SSR as described above.

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

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

void loop() {
  digitalWrite(ssrPin, HIGH); // Turn ON the SSR (AC load ON)
  delay(5000);               // Keep the load ON for 5 seconds
  digitalWrite(ssrPin, LOW);  // Turn OFF the SSR (AC load OFF)
  delay(5000);               // Keep the load OFF for 5 seconds
}

Note: Ensure proper safety precautions when working with AC mains voltage. Disconnect power before making any connections.

1. Can the SSR-25DA be used with DC loads?

   • No, the SSR-25DA is designed for AC loads only. For DC loads, use a DC-specific SSR.

2. What happens if the load exceeds 25A?

   • Exceeding the rated current can damage the SSR. Always use a fuse or circuit breaker for protection.

3. Is the SSR-25DA suitable for dimming applications?

   • No, the SSR-25DA is not designed for phase control or dimming. Use a dimmer-specific SSR for such applications.

4. Can I use the SSR-25DA without a heatsink?

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

By following this documentation, you can safely and effectively use the SSR-25DA in your projects.