This article explains how to make an AC over voltage protection circuit using Arduino. The AC over voltage protection circuit is an essential project for electronics learners. We will cover the AC over voltage protection circuit design, required components, working principle, step-by-step construction, testing procedure, and FAQs. The AC over voltage protection circuit helps protect electrical devices from supply fluctuations. Learn everything about AC over voltage protection circuit today.

AC Over Voltage Protection Circuit Using Arduino

Protecting household and industrial appliances from voltage surges is essential. High AC voltages can damage sensitive equipment, shorten their lifespan, or even cause fire hazards. An AC over voltage protection circuit automatically disconnects the load when voltage crosses a set threshold.

In this article, we’ll design and build a practical AC over voltage protection circuit using Arduino with simple components such as LM358 IC, resistors, a relay, a BC547 transistor, and an LCD for monitoring.

Introduction

AC mains voltage often varies due to power distribution imbalances or sudden load changes. Such fluctuations can lead to overvoltage conditions. Without protection, devices like refrigerators, TVs, computers, and lab instruments risk permanent damage.

An AC over voltage protection circuit disconnects the appliance when the supply voltage exceeds the safe range. Using Arduino, we can set threshold values, monitor them on an LCD, and control the relay for automatic disconnection.

Circuit Overview

• Input: AC mains supply.
• Sensing: Voltage divider with resistors feeding the LM358 comparator.
• Control Unit: Arduino Nano.
• Display: 16×2 LCD via I2C.
• Output Switching: Relay module driven by BC547 transistor.
• Safety: Diode protection across relay coil.

The circuit continuously checks the input voltage. When it crosses the set overvoltage limit, Arduino signals the transistor to cut relay supply, disconnecting the load.

 Materials for the Project

Useful Tools 

Circuit Diagram Explanation

• The voltage divider (using multiple 470k resistors) scales down the AC supply for safe sensing.
• The LM358 IC conditions the input and sends it to Arduino.
• Arduino Nano reads this value, compares it with pre-set overvoltage limits, and drives the output.
• The relay, controlled by BC547 transistor, switches the AC load.
• The LCD displays the live voltage and system status (ON/OFF).
• Push buttons allow setting threshold values.
• The 1N4148 diode protects the transistor from back EMF during relay switching.

Download Circuit Diagram

Step-by-Step Assembly Guide

1. Place Arduino Nano on breadboard/PCB.
2. Connect LM358 IC: Pin 4 → GND, Pin 8 → +5V.
3. Connect resistors as voltage divider (470k series).
4. Attach 10k, 4.7k, and 2.2k resistors to LM358 for proper scaling.
5. Connect divider output to Arduino analog input.
6. Wire LCD (I2C) to Arduino: SDA → A4, SCL → A5, VCC → 5V, GND → GND.
7. Connect push buttons to D3, D4, D5 with pull-down to GND.
8. Wire BC547 transistor: Emitter → GND, Collector → Relay coil, Base → Arduino D2 via 1k resistor.
9. Connect relay coil VCC → +5V.
10. Add 1N4148 diode across relay coil (cathode to +5V, anode to transistor collector).
11. Connect AC line through relay COM → Load → Neutral.
12. Power Arduino and upload code.

Arduino Code

Working Principle of the Circuit

• The resistive divider scales down AC to safe DC equivalent.
• Arduino reads voltage through LM358.
• When voltage > threshold, Arduino signals transistor → relay OFF → load disconnected.
• When voltage ≤ threshold, relay remains ON → load connected.
• LCD displays “Normal” or “Over Voltage.”

Arduino Code Explanation

• Reads analog values from divider circuit.
• Converts reading into actual AC voltage.
• Compares against user-defined threshold.
• Displays real-time voltage on LCD.
• Controls relay ON/OFF accordingly.

(You can adjust limits in code for your region’s voltage supply 220V or 110V.)

Testing and Calibration

1. Power up Arduino with USB.
2. Feed AC supply through divider circuit.
3. Adjust resistor values if voltage scaling is incorrect.
4. Set overvoltage threshold via push buttons.
5. Increase supply with variac or simulated source.
6. Verify relay disconnects at threshold.
7. Observe LCD reading and system behavior.

Applications

• Protecting refrigerators, TVs, and washing machines.
• Industrial machines with voltage-sensitive motors.
• Laboratory and test equipment.
• UPS and inverter input protection.

FAQs

Q1. What is an AC over voltage protection circuit?
An AC over voltage protection circuit disconnects a load automatically when the supply voltage exceeds a safe limit.

Q2. Can I use this AC over voltage protection circuit for 110V systems?
Yes, just recalibrate the resistor divider and Arduino code for 110V supply.

Q3. Why do we need an AC over voltage protection circuit?
Because appliances can be damaged by sustained high voltages. The AC over voltage protection circuit ensures safe operation.

Q4. Which relay rating should I use in an AC over voltage protection circuit?
Choose a relay with a current rating above the load consumption, typically 5A–10A.

Q5. Can this AC over voltage protection circuit be expanded to under voltage protection?
Yes, by modifying the Arduino code to monitor both high and low voltage thresholds.

Q6. Is LM358 essential in the AC over voltage protection circuit?
Yes, LM358 amplifies/conditions the divided voltage for stable Arduino sensing.

Q7. What happens if the AC over voltage protection circuit fails?
If the circuit fails, the load may remain unprotected. Always use good-quality components for reliability.

Conclusion

We successfully built an AC over voltage protection circuit using Arduino that safeguards appliances from high supply voltages. The design is simple, affordable, and easy to implement in homes or labs. By using Arduino, thresholds can be customized, and monitoring becomes straightforward.