🔌 Automatic AC Changeover for Inverter – DIY Circuit Guide

Are you tired of manually switching between main electricity supply and your inverter system whenever there’s a power cut? An Automatic AC Changeover Switch is the perfect solution for you. It ensures uninterrupted power to your home appliances by automatically shifting the load from main AC supply to inverter backup and back when the main supply returns.

In this post, I’ll explain how you can build your own AC Changeover for Inverter using a simple relay-based circuit, as shown in the provided circuit diagram.

⚡ What is an AC Changeover Switch?

An AC Changeover Switch is an electrical circuit that automatically transfers your house load from the utility power (AC mains) to the inverter power supply during a power outage. When the main power returns, it switches back to the grid automatically.

This saves time, protects your appliances, and ensures that your devices keep running smoothly.

🛠 Components Required

1. To build the Automatic AC Changeover, you’ll need the following components:
2. Step-down transformer (for relay driving voltage)
3. 1N5822 diodes (rectifier)
4. LM7805 Voltage Regulator (for 5V DC supply)
5. Relay SPST (for switching the AC load)
6. 1N4007 Diode (flyback protection for relay)
7. Capacitors (1000µF & 220pF) (filtering)
8. Resistor (1kΩ)
9. LED (power status indicator)

📘 Broad Description of the Circuit Diagram

Let’s break down the main working parts of the provided circuit diagram:

1. AC Step-down Transformer → Converts high-voltage AC mains (220V/110V) into a low-voltage AC supply.
2. Rectifier Section (D1, D2 - 1N5822 diodes) → Converts the AC voltage into DC.
3. Filter Capacitor (C1 - 1000µF) → Smooths the rectified DC output to reduce ripples.
4. Voltage Regulator (U2 - LM7805) → Regulates the voltage to a stable 5V DC required to power the relay.
5. Relay (U1 - SPST) → Acts as the automatic switch that toggles between Main AC and Inverter AC.
6. Protection Diode (D4 - 1N4007) → Protects against voltage spikes from the relay coil.
7. Status LED (LED11 with R3 - 1kΩ resistor) → Indicates when the main supply is available.

🔌 Practical Connection Explanation

Here’s how to connect this circuit in real life:

1. AC(M) terminal → Connect to Main AC supply (Grid Power).
2. AC(INV) terminal → Connect to the Inverter AC output.
3. LOAD terminal → Connect to your home appliances (fan, light, socket, etc.).
4. When main power is ON, the relay is energized, and the load is powered from the mains supply.
5. When main power goes OFF, the relay switches automatically, connecting the load to the inverter output.
6. When mains return, the relay switches back to the grid power without manual intervention.
7. This makes it a fully automatic inverter changeover system for home use.

🖥 How to Convert This Circuit into a PCB

Designing a PCB (Printed Circuit Board) for this circuit makes it compact, reliable, and suitable for permanent installation. Here’s the step-by-step process:

1. Circuit Schematic to PCB Layout
2. Use PCB design software like Proteus, EasyEDA, KiCAD, or Altium Designer.
3. Import the circuit schematic and arrange the components.
4. Component Placement
5. Place high-voltage AC terminals (AC-M, AC-INV, LOAD) at one side for easy wiring.
6. Keep low-voltage DC section (rectifier, capacitor, regulator, relay driver) separate from the AC side.
7. Routing the Traces
8. Use thick copper traces for the AC lines (load carrying).
9. Use thin traces for the low-voltage DC control section.
10. Provide isolation distance between AC and DC tracks.
11. Safety Precautions
12. Add a fuse on the AC input line.
13. Maintain creepage distance between AC and DC areas to avoid short circuits.
14. Use proper connector terminals for input and output.
15. Fabrication
16. Export Gerber files and get the PCB manufactured from any PCB fabrication service.
17. Solder components carefully and test before use.

🔋 Advantages of Automatic AC Changeover for Inverter

✅ No need for manual switching

✅ Protects appliances from sudden power cuts

✅ Reliable and efficient operation

✅ Simple & cost-effective DIY project

✅ Ensures uninterrupted power supply

📊 Applications

1. Home inverter systems
2. Small offices and shops
3. Automatic generator changeover
4. Solar inverter backup systems

📝 Conclusion

By following this guide, you can easily build your own Automatic AC Changeover Switch for Inverter. It’s an efficient, low-cost project for ensuring a seamless power supply to your essential appliances during power cuts.

With just a few electronic components and by designing a custom PCB, you can convert this circuit into a professional inverter changeover system suitable for long-term home and office use.