Project Hub /Basic Analog & Power Electronics/Discrete & Component Electronics/Overcurrent Relay with IDMT for Motor Protection Using Arduino

Intermediate

ARDUINO

₹500 – ₹1,500

3 – 6 Hours

Partial Kit

Overcurrent Relay with IDMT for Motor Protection Using Arduino

A DIY Arduino-based overcurrent relay project that emulates Inverse Definite Minimum Time (IDMT) protection using an Arduino Nano and an ACS712 current sensor to protect electrical motors and loads.

Originally published on ElectronicsForU

View original tutorial

Parts You'll Need

This project is sourced from another site, not written by us — this list is our best match of their components against what we stock, not a verified bill of materials. Always check the original blog (linked above) for the actual parts list before buying.

Arduino Nano C Type V3 ATMEGA328 with Soldered Headers Rs. 608.00
10pcs 5mm RED Diffused Light Emitting Diodes - LEDs Set Rs. 39.00
10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
2-Slot 18650 Holder with Protective Cover and On/Off Switch – Case Rs. 109.00
5V 1 Channel Relay Module Rs. 45.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
Jumper Wire 10 Pin Male To Female 20cm Rs. 45.00

Selected: Rs. 0.00

This list includes a generic resistor set as a placeholder — it is not matched to the exact value or part number this circuit needs. The correct one is specified on the original source page linked above; check it before buying.

We don't carry yet: Current Sensor ACS712
Transistors (BC547 / 2N2222 / TIP / MOSFET)
Diodes (1N4007 / 1N4148 / Schottky / Zener)
DC Barrel Jack / Power Connector
Header Pins / Terminals / Connectors
Enclosure / Box / Case
LED Bulb / Lamp / AC Load
Transformer

Browse all components

How It Works

The Overcurrent Relay with IDMT for Motor Protection functions by continuously monitoring the current drawn by an AC load or motor using an ACS712-30A current sensor connected to an Arduino Nano board. The ACS712 outputs an analog voltage proportional to the measured current, which the Arduino reads via its analog-to-digital converter. The software implements an Inverse Definite Minimum Time (IDMT) algorithm: the higher the overload current detected, the faster the Arduino triggers a response. When an overcurrent condition persists beyond the calculated time threshold, the Arduino changes the state of a digital output pin connected to a BC547 NPN transistor. This transistor acts as a solid-state switch to drive a 12V SPDT relay coil, powered via a 12V 1A adaptor and protected by 1N4007 rectifier diodes (D1, D2) against back-EMF voltage spikes. Once energized, the relay mechanically disconnects the AC load from the power supply, safeguarding the motor from overheating and winding insulation damage. A 5mm LED driven through current-limiting resistors provides visual status indication, while a push-to-on switch and 2-pin connectors (CON1-CON4) facilitate user control and wiring within the wooden enclosure.

Why Build This

Gain practical undergraduate-level experience in designing microprocessor-based power protection systems for electrical motors and industrial feeders.

Implement time-current characteristic curves programmatically to emulate industrial-grade Inverse Definite Minimum Time (IDMT) protection relays.

Learn to interface analog current sensors and electromagnetic relay switching circuits safely with microcontroller development boards.

Real-World Application

Protecting industrial and domestic induction motors, electrical feeders, and appliances against prolonged overload, overheating, and winding insulation damage.

Skills You'll Learn

analog sensor interfacing

microcontroller ADC reading

transistor-based relay driving

inductive load protection with flyback diodes

IDMT algorithm implementation

Safety Precautions

Exercise extreme caution when working with mains AC voltage for connected loads and motor circuits to avoid electric shock.

Technology Tags

ARDUINO

ACS712

CURRENT SENSOR

OVERCURRENT PROTECTION

IDMT RELAY

MOTOR PROTECTION

HARDWARE

RELAY

Frequently Asked Questions

Why is an IDMT algorithm used instead of an instant trip mechanism?

IDMT allows the system to tolerate harmless momentary current spikes (like motor startup surges) while tripping faster during severe, sustained overloads.

What is the purpose of the 1N4007 diodes in this circuit?

The rectifier diodes act as flyback diodes to dissipate voltage spikes generated when the 12V SPDT relay coil de-energizes, protecting the BC547 transistor and Arduino from damage.

Can this project directly control high-voltage AC motors?

The Arduino and ACS712 handle low-voltage control and sensing, while the onboard 12V SPDT relay acts as the physical switch to interrupt the higher-voltage AC motor circuit.

This page is part of Kitkraft's Project Hub — a curated collection of electronics & robotics projects gathered from the maker community to help students and hobbyists discover and learn to build. Kitkraft does not claim authorship of the original project, and makes no representation as to the accuracy, completeness or safety of third-party source material. The summary and "How It Works" explanation above are AI-generated, rewritten with reference to the original tutorial — not a reproduction of it. Full credit and a direct link to the original source are provided above. If you're the original creator and have a concern about how your work is represented here, please contact us and we'll address it promptly.

Kitkraft Project Hub — curated from the maker community, credited at the source.

PRJ-01453