🔧 How to Make a DIY 12V AC/DC Fan for a 12V Battery Pack

📅 Project Overview

Do you want to automatically power a 12V fan using both AC and DC power? This DIY project is perfect for inverter systems, battery backup setups, and cooling applications. In this tutorial, I will demonstrate how to create a 12V AC/DC fan system that intelligently switches between mains power and a 12V battery using a smart circuit and a few electronic components.

🌟 Features

✅ Automatically uses AC power when available.

• ✅ Automatically uses AC power when available.

✅ Automatically switches to battery backup when AC is off.

• ✅ Automatically switches to battery backup when AC is off.

✅ Includes buck converter, LED indicator, and fan control.

• ✅ Includes buck converter, LED indicator, and fan control.

✅ Ideal for battery packs, solar systems, and DC appliances.

• ✅ Ideal for battery packs, solar systems, and DC appliances.

📷 Circuit Diagram

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🧰 C omponent List (Line by Line)

LM2596 Buck Converter Module – 1 pc

• LM2596 Buck Converter Module – 1 pc

1N5822 Schottky Diode – 3 pcs (D5, D6, D8)

• 1N5822 Schottky Diode – 3 pcs (D5, D6, D8)

1N5819 Diode – 1 pc (D3)

• 1N5819 Diode – 1 pc (D3)

1N5408 High-Current Diode – 2 pcs (D1, D2)

• 1N5408 High-Current Diode – 2 pcs (D1, D2)

LED (Red) – 1 pc (for power indication)

• LED (Red) – 1 pc (for power indication)

1kΩ Resistor – 1 pc (for LED current limiting)

• 1kΩ Resistor – 1 pc (for LED current limiting)

10kΩ Resistor – 1 pc (MOSFET gate pull-down)

• 10kΩ Resistor – 1 pc (MOSFET gate pull-down)

IRF9540N P-Channel MOSFET – 1 pc

• IRF9540N P-Channel MOSFET – 1 pc

880μH Inductor – 1 pc

• 880μH Inductor – 1 pc

220μF Capacitor (Electrolytic) – 2 pcs (C1, C2)

• 220μF Capacitor (Electrolytic) – 2 pcs (C1, C2)

Switch (SPST or jumper type) – 1 pc (manual control)

• Switch (SPST or jumper type) – 1 pc (manual control)

12V DC Fan (2-pin or 3-pin) – 1 pc

• 12V DC Fan (2-pin or 3-pin) – 1 pc

Battery (12V Lead-Acid or Li-ion pack) – 1 pc

• Battery (12V Lead-Acid or Li-ion pack) – 1 pc

Terminal Block (2-pin or 3-pin) – As needed for AC input, battery, and load

• Terminal Block (2-pin or 3-pin) – As needed for AC input, battery, and load

Wires (AWG 20 or thicker) – As needed

• Wires (AWG 20 or thicker) – As needed

PCB or Perfboard – 1 pc (for assembly, optional)

• PCB or Perfboard – 1 pc (for assembly, optional)

Heatsink (for LM2596 if needed) – Optional

• Heatsink (for LM2596 if needed) – Optional

Soldering Iron and Solder – For connections

• Soldering Iron and Solder – For connections

🧠 Circuit Explanation (Step-by-Step)

🔌 1. A C Input and Rectification

D1 & D2 (1N5408): These diodes form a rectifier to allow AC to be safely converted to DC.

• D1 & D2 (1N5408): These diodes form a rectifier to allow AC to be safely converted to DC.

C1 (220μF): Smooths out the ripples from the rectified voltage.

• C1 (220μF): Smooths out the ripples from the rectified voltage.

LED1 + R3: Indicates AC power is ON.

• LED1 + R3: Indicates AC power is ON.

🔋 2. D C Voltage Regulation

LM2596 Buck Converter (X1):

Converts high DC voltage (from rectified AC) down to a stable 12V.

• Converts high DC voltage (from rectified AC) down to a stable 12V.

Pinout:

VIN: Input Voltage

• VIN: Input Voltage

GND: Ground

• GND: Ground

OUTPUT: Regulated 12V Output

• OUTPUT: Regulated 12V Output

ON/OFF & FB: Control and Feedback pins for operation

• ON/OFF & FB: Control and Feedback pins for operation
• Pinout:VIN: Input VoltageGND: GroundOUTPUT: Regulated 12V OutputON/OFF & FB: Control and Feedback pins for operation
• LM2596 Buck Converter (X1):Converts high DC voltage (from rectified AC) down to a stable 12V.Pinout:VIN: Input VoltageGND: GroundOUTPUT: Regulated 12V OutputON/OFF & FB: Control and Feedback pins for operation

🔄 3. A uto Switching Control Logic

D5 (1N5822): Allows current flow from the buck converter to the fan only when AC is present.

• D5 (1N5822): Allows current flow from the buck converter to the fan only when AC is present.

D3 (1N5819): Prevents backflow from the battery when AC is ON.

• D3 (1N5819): Prevents backflow from the battery when AC is ON.

D6 (1N5822): Ensures one-way flow from battery to the MOSFET gate.

• D6 (1N5822): Ensures one-way flow from battery to the MOSFET gate.

⚙️ 4. MOSFET Auto Switching

Q2 (IRF9540N P-Channel MOSFET):

Acts as an electronic switch to allow battery power to the fan when AC is off.

• Acts as an electronic switch to allow battery power to the fan when AC is off.

Gate Control:

R1 (10kΩ) pulls the gate high to keep the MOSFET OFF when not triggered.

• R1 (10kΩ) pulls the gate high to keep the MOSFET OFF when not triggered.

When AC is off, the gate is pulled LOW via D6, turning the MOSFET ON.

• When AC is off, the gate is pulled LOW via D6, turning the MOSFET ON.
• Gate Control:R1 (10kΩ) pulls the gate high to keep the MOSFET OFF when not triggered.When AC is off, the gate is pulled LOW via D6, turning the MOSFET ON.
• Q2 (IRF9540N P-Channel MOSFET):Acts as an electronic switch to allow battery power to the fan when AC is off.Gate Control:R1 (10kΩ) pulls the gate high to keep the MOSFET OFF when not triggered.When AC is off, the gate is pulled LOW via D6, turning the MOSFET ON.

🌬️ 5. F an Output

Fan Output is connected to the drain of the MOSFET and receives power either from:

AC Source (via Buck Converter and D5) when AC is available

• AC Source (via Buck Converter and D5) when AC is available

Battery (via D8 and MOSFET Q2) when AC is not available

• Battery (via D8 and MOSFET Q2) when AC is not available
• Fan Output is connected to the drain of the MOSFET and receives power either from:AC Source (via Buck Converter and D5) when AC is availableBattery (via D8 and MOSFET Q2) when AC is not available

🛠️ Assembly Tips

Double-check diode polarity.

• Double-check diode polarity.

Use heatsinks on the LM2596 if the fan draws high current.

• Use heatsinks on the LM2596 if the fan draws high current.

Test the output using a multimeter before connecting the fan.

• Test the output using a multimeter before connecting the fan.

🎥 Video Tutorial

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🔺 Final Thoughts

This project is a must-have for any DIY enthusiast working on battery systems or off-grid setups. With just a few inexpensive components, you can create a smart 12V AC/DC fan system that’s perfect for inverters, solar systems, or any power backup configuration.

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