DIY AC Changeover Circuit for Automatic Inverter System ⚡ | Instructables Guide

Have you ever wanted your home appliances to run continuously without interruption when the main electricity supply fails? This simple AC Changeover Circuit solves that problem by automatically switching between Main AC Power and Inverter Power.

In this Instructables-style tutorial, we’ll go step by step to make an Automatic AC Changeover Switch using a relay, rectifier, capacitor filter, and voltage regulator.

Components List

1. 1 × Transformer (AC step-down)
2. 2 × Diode 1N5822
3. 1 × Voltage Regulator LM7805
4. 1 × Relay SPST (5V or 12V depending on design)
5. 1 × Diode 1N4007
6. 1 × Capacitor 1000µF / 25V
7. 1 × Capacitor 220pF
8. 1 × LED (any color)
9. 1 × Resistor 1kΩ
10. Wires, PCB/Breadboard, and AC connectors

✅ Automatic Switching – Load will run on main power (AC) when electricity is available.

✅ Seamless Transition – When electricity goes off, the relay switches to the inverter line automatically.

✅ Indicator LED – Shows when the system is powered.

✅ Safe & Reliable – Diodes and filter capacitors ensure stability.

1. Transformer + Rectifier (D1, D2: 1N5822) → Converts AC to DC for relay control.
2. Filter Capacitors (C1: 1000µF, C3: 220pF) → Smooths voltage.
3. Voltage Regulator (U2: LM7805) → Provides stable 5V DC for the relay.
4. Relay (U1: SPST) → Switches between Main AC and Inverter AC.
5. Diode (D4: 1N4007) → Protects relay from back EMF.
6. Indicator LED (LED11 + R3: 1kΩ) → Shows power ON status.

1. When Main AC Power (AC Mains) is ON:
2. The transformer and rectifier supply DC power.
3. Relay coil energizes and connects the load to main AC.
4. Load runs directly from main electricity.
5. When Main AC Power is OFF:
6. The relay deactivates and automatically shifts to the Inverter line.
7. The load now runs from the inverter backup.
8. No manual switching is required!

This ensures uninterrupted power supply (UPS-like function) for fans, lights, routers, and other essential appliances.

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Step 1: Assemble Power Supply Section

1. Connect the transformer output to diodes (D1, D2) for rectification.
2. Use capacitor C1 (1000µF) for smoothing.
3. Add LM7805 regulator for stable DC output.

Step 2: Connect Relay & Load

1. Connect relay coil to the regulated DC.
2. Wire AC mains to relay’s Normally Open (NO) terminal.
3. Connect inverter AC to Common terminal (COM).
4. Load is connected at relay output.

Step 3: Add Safety Diode & Indicator LED

1. Place D4 (1N4007) across relay coil to prevent back EMF.
2. Connect LED + resistor across DC line for status indication.

Step 4: Testing the Circuit

1. First, power ON main AC → Load runs from mains.
2. Now, switch OFF main AC → Relay auto-switches, and load runs from inverter.

⚠️ This project deals with AC 220V/110V, so handle carefully.

1. Always use fuses and proper insulation.
2. If you’re a beginner, test first with low-voltage AC.
3. Keep PCB design neat to avoid short circuits.

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Home Inverter Automatic Switching

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Fan & Light Emergency System

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This AC Changeover Circuit is a low-cost and reliable way to make your inverter system automatic. Once installed, you’ll never need to manually switch between main electricity and inverter backup.