How to Use NVF4-2 12 V SPDT Automotive Relay (Bottom View): Examples, Pinouts, and Specs

The NVF4-2 is a Single Pole Double Throw (SPDT) automotive relay manufactured by Ningbo Huaguan. It is designed for 12 V systems and is commonly used to control high-current loads, such as motors, lights, and other automotive devices, using low-current control signals. Its robust design and reliable switching capabilities make it ideal for automotive and industrial applications.

• Automotive lighting systems (e.g., headlights, fog lights)
• Electric motor control (e.g., fans, pumps)
• Horn circuits
• Power window and door lock systems
• Industrial control systems requiring high-current switching

The NVF4-2 relay has five pins, as shown in the bottom view. The table below describes each pin:

1. Power the Coil: Connect pin 85 to ground and pin 86 to a 12 V DC control signal. This energizes the relay coil and switches the contact from NC (87a) to NO (87).
2. Connect the Load:
   • Connect the power source to pin 30 (COM).
   • Connect the load to pin 87 (NO) if you want the load to be powered only when the relay is energized.
   • Alternatively, connect the load to pin 87a (NC) if you want the load to be powered when the relay is not energized.
3. Ensure Proper Ratings: Verify that the load current does not exceed the relay's contact rating of 40 A.

• Diode Protection: Add a flyback diode across the coil terminals (85 and 86) to protect the control circuit from voltage spikes when the relay is de-energized.
• Secure Connections: Use appropriate connectors or soldering to ensure reliable connections, especially in automotive environments where vibrations are common.
• Heat Dissipation: Ensure adequate ventilation or heat sinking if the relay operates under high current for extended periods.

Below is an example of how to use the NVF4-2 relay to control a 12 V LED using an Arduino UNO:

// Define the relay control pin
const int relayPin = 7; // Connect Arduino pin 7 to relay pin 86 (Coil +)

void setup() {
  pinMode(relayPin, OUTPUT); // Set relay control pin as output
}

void loop() {
  digitalWrite(relayPin, HIGH); // Energize the relay (LED ON)
  delay(5000); // Keep the LED ON for 5 seconds
  digitalWrite(relayPin, LOW); // De-energize the relay (LED OFF)
  delay(5000); // Keep the LED OFF for 5 seconds
}

Wiring Notes:

• Connect pin 85 of the relay to the Arduino GND.
• Connect pin 86 of the relay to Arduino pin 7 (via a transistor if needed for current amplification).
• Connect the 12 V LED's positive terminal to pin 87 (NO) and its negative terminal to ground.
• Connect a 12 V power source to pin 30 (COM).

1. Relay Not Switching:

   • Cause: Insufficient voltage or current to the coil.
   • Solution: Ensure the control signal provides 12 V DC and sufficient current (typically ~133 mA for this relay).

2. Voltage Spikes Damaging the Control Circuit:

   • Cause: Lack of a flyback diode across the coil terminals.
   • Solution: Add a diode (e.g., 1N4007) across pins 85 and 86, with the cathode connected to pin 86.

3. Load Not Receiving Power:

   • Cause: Incorrect wiring of the load or power source.
   • Solution: Verify that the load is connected to the correct pins (30 and 87/87a) and that the power source is properly connected to pin 30.

4. Relay Overheating:

   • Cause: Exceeding the contact current rating.
   • Solution: Ensure the load current does not exceed 40 A. Use a heat sink or cooling mechanism if necessary.

Q1: Can the NVF4-2 relay be used with a 5 V control signal?
A1: No, the NVF4-2 is designed for a 12 V DC control signal. Using a 5 V signal will not provide sufficient current to energize the coil.

Q2: Is the relay suitable for AC loads?
A2: While the relay can switch AC loads, it is primarily designed for DC automotive applications. Ensure the AC load does not exceed the relay's contact rating.

Q3: Can I use the relay without a microcontroller?
A3: Yes, the relay can be controlled using a simple switch or any 12 V DC control signal.

Q4: What is the purpose of the NC (87a) terminal?
A4: The NC terminal allows the load to remain powered when the relay is not energized, providing flexibility in circuit design.