Power·Jan 1, 2024

Automatic Power Factor Corrector and Monitor Device

Microcontroller-driven power factor corrector that measures AC load behaviour and switches capacitor banks to bring PF closer to unity.

Overview

Low power factor is one of those silent problems — the bill quietly grows and nobody knows why. I built this corrector mostly to understand the problem end-to-end: from sensing voltage and current to actually switching capacitors on an AC load. The device samples the AC line, estimates the load behaviour and switches capacitor stages through relays. An LCD shows the live values so you can watch the correction happen.

Specifications

RoleHardware designer and firmware developer

MicrocontrollerArduino / ATmega328

SensorsVoltage sensorCurrent sensor

ModulesRelay moduleCapacitor bankLCD display

ProtocolsGPIOI2C

Tech tagsPower FactorCapacitor BankRelay ControlAC MeasurementEmbedded

Architecture

Sensors feed electrical data to the controller. Firmware decides the required correction stage and switches capacitors through relays while displaying real-time status.

Project photos

Automatic power factor corrector prototype — Power factor corrector prototype and display

Videos

Implementation details

Firmware

Firmware samples voltage/current inputs, estimates load condition, selects capacitor stages, updates LCD values, and prevents rapid relay chatter through timing logic.

PCB

Prototype wiring separates measurement, relay switching, and display/control sections for easier debugging.

Power

AC measurement and capacitor switching require proper isolation, fusing, discharge paths, and safe enclosure design for field use.

Components / BOM

Arduino / ATmega328 controller, Voltage sensing stage, Current sensing stage, Relay module, Capacitor bank, LCD display

Engineering challenges

Sensing on a noisy AC line, and switching capacitors safely without making the relays chatter and burn themselves out.

Solutions

Staged correction with hysteresis so the relays only move when the load actually changes, and a clear LCD readout to make the behaviour explainable.

Results & metrics

Demonstrates automatic correction on a bench load with visible PF improvement on the display.

Future improvements

Move to a dedicated metering IC, add data logging over RS485, build a properly enclosed unit with protection circuitry for small workshops.