AC Overcurrent Protection Circuit Using Arduino and LM358
An AC overcurrent protection circuit is an essential project for protecting electrical devices from current overload. This AC overcurrent protection circuit uses an Arduino, LM358 IC, relay, and current transformer to automatically cut off power when the current exceeds a safe limit. In this article, you’ll learn the step-by-step process of making an AC overcurrent protection circuit, including the required components, wiring details, and circuit explanation.
We’ll also explain how the AC overcurrent protection circuit works, provide the full components list with buying links, and show a simple method to program and test the system. By the end, you’ll understand how to design an AC overcurrent protection circuit for your home or lab to safeguard appliances. This DIY AC overcurrent protection circuit project is perfect for electronics students, hobbyists, and engineers looking for practical circuit-based solutions.
Introduction
An AC overcurrent protection circuit is a safety system that automatically disconnects appliances from the supply when the current exceeds a predefined threshold. Overcurrent conditions often occur due to short circuits, overloads, or faulty equipment. If not protected, devices may overheat or burn out.
In this project, we will build an AC overcurrent protection circuit using Arduino, LM358 IC, and a current transformer (CT). The Arduino monitors the current through the CT and triggers a relay to cut off the AC supply when the current exceeds the set limit.
Why We Need Overcurrent Protection
- Appliance Safety: Prevents damage to fans, motors, refrigerators, and other AC devices.
- Fire Prevention: Avoids wire overheating that may lead to fire hazards.
- Automatic Control: No manual switching required, the circuit disconnects load automatically.
- Cost-Effective: A low-cost protection circuit compared to industrial circuit breakers.
Materials for the Project
| Component | Quantity | Description/Value | Buy Link |
|---|---|---|---|
| Arduino Nano | 1 | Microcontroller board | Buy Here |
| LM358 IC | 1 | Dual Op-Amp | Buy Here |
| Current Transformer (CT) | 1 | 5A / 10A rating | Buy Here |
| 16×2 LCD (I2C) | 1 | Display readings | Buy Here |
| Relay Module 5V | 1 | SPDT Relay | Buy Here |
| BC547 Transistor | 1 | NPN Transistor | Buy Here |
| 10kΩ Resistor | 2 | For feedback and bias | Buy Here |
| 47Ω Resistor | 1 | Load resistor | Buy Here |
| 1kΩ Resistor | 1 | Base resistor | Buy Here |
| Push Buttons | 3 | For settings | Buy Here |
| 1N4148 Diode | 1 | Flyback protection | Buy Here |
| Terminal Blocks | 2 | AC Input/Output | Buy Here |
| Jumper Wires | – | For connections | Buy Here |
| Breadboard / PCB | 1 | Prototyping board | Buy Here |
Useful Tools
| Tool | Quantity | Purpose / Notes | Click & Buy |
|---|---|---|---|
| Soldering Iron Kit | 1 | For making permanent connections | Click & Buy |
| Solder Wire (60/40, 0.8mm) | 1 | Electrical soldering | Click & Buy |
| Wire Stripper & Cutter | 1 | Stripping jumper wires | Click & Buy |
| Mini Screwdriver Set | 1 | For module and relay terminal screws | Click & Buy |
| Multimeter | 1 | Testing voltages and continuity | Click & Buy |
| Hot Glue Gun (optional) | 1 | Securing components in place | Click & Buy |
| Small Pliers | 1 | Holding and bending wires | Click & Buy |
| Heat Shrink Tubing Set | 1 | Insulating exposed wires | Click & Buy |
Circuit Diagram Explanation
The heart of this AC overcurrent protection circuit is the current transformer (CT), which senses the current flowing through the AC line. The CT output is fed into the LM358 op-amp, configured as a current-to-voltage converter.
- LM358 Stage: Converts CT signal into a voltage proportional to load current.
- Arduino: Reads this voltage using the ADC pin, compares it with a threshold, and decides whether to trigger the relay.
- Relay & Transistor: The Arduino drives the BC547 transistor, which switches the relay ON or OFF. The relay controls the AC line connected to the load.
- LCD Display: Shows current values and warning messages.
- Push Buttons: Allow you to set/reset current thresholds or reset the circuit after tripping.
This way, when the load exceeds the set current, the Arduino cuts off power to prevent damage.
Download Circuit Diagram
Step-by-Step Guide
Step 1: Power Supply Connections
- Connect Arduino 5V and GND to the power rails of the circuit.
- Attach a terminal block for AC input and output safely.
Step 2: LM358 IC Connections
- Pin 4 → Ground
- Pin 8 → +5V
- Resistor (10k) between Pin 1 and Pin 2 (feedback)
- Another 10k between Pin 2 and Ground
- 47Ω resistor between Pin 3 and Ground
- CT output to Pin 3
Step 3: LCD Connections (I2C Module)
- VCC → 5V
- GND → GND
- SDA → A4
- SCL → A5
Step 4: Push Buttons
- Button 1 → D3 and GND
- Button 2 → D4 and GND
- Button 3 → D5 and GND
Step 5: Relay & Transistor Connections
- Emitter of BC547 → GND
- Base of BC547 → D2 via 1kΩ resistor
- Collector → Relay coil
- Relay coil other pin → +5V
- Relay common terminal → Live AC line
- Normally Open (NO) → Load terminal
- Neutral AC → Load directly
Step 6: Diode Protection
- Place 1N4148 diode across the relay coil for flyback protection (Cathode to 5V, Anode to transistor).
Step 7: Upload Code to Arduino
- Write Arduino code to measure CT voltage, convert to current, compare with threshold, and control relay.
- Display real-time current on LCD.
Arduino Code
Working of the Circuit
When AC current flows through the load, the CT senses it and produces a small signal. The LM358 amplifies this signal and feeds it to the Arduino ADC. If the measured current exceeds the preset limit, the Arduino turns OFF the relay through the BC547 transistor.
The LCD shows real-time current values and alerts when tripping occurs. To resume operation, the user can press the reset button or reduce the load.
Applications
- Home appliance protection (AC, refrigerator, washing machine).
- Motor overcurrent protection.
- Lab equipment safety.
- Low-cost alternative to industrial MCBs.
FAQs
Q1: What is the role of the LM358 in this circuit?
The LM358 converts the CT current signal into a readable voltage for the Arduino.
Q2: Can this circuit work without an Arduino?
Yes, a comparator-based design is possible, but the Arduino allows flexible thresholds and display features.
Q3: What is the maximum current this circuit can handle?
It depends on the rating of the CT and relay. For higher loads, choose higher-rated components.
Q4: Can I use this for DC loads?
No, current transformers only work with AC. For DC, a Hall-effect sensor like ACS712 is used.
Q5: How do I set the overcurrent threshold?
You can define the threshold value in the Arduino code or use push buttons to adjust it.
Conclusion
The AC overcurrent protection circuit is a simple yet powerful way to safeguard AC devices from overload conditions. By combining Arduino, LM358, and a current transformer, this project ensures automatic disconnection of the load when unsafe current levels are detected. It is low-cost, customizable, and perfect for DIY enthusiasts and engineering students.
This project not only teaches you about current sensing and relays but also provides a practical solution to appliance safety.