Design of a Microcontroller-Based Automatic Generator Transfer Switch for Residential Use in Akwa Ibom State

Frequent power outages in Akwa Ibom State, South South Nigeria, make standby generator operation essential in most households, yet manual transfer between mains and generator power is inconvenient and carries electrocution risks if performed incorrectly. This project designed a microcontroller-based automatic transfer switch that seamlessly switches between mains and generator power sources without manual intervention. An ATmega328P microcontroller continuously monitored mains voltage through a sensing transformer. When mains voltage fell below 180V or was absent for more than 5 seconds, the controller sent a start signal to the generator's automatic starter via a relay and waited 10 seconds before transferring the load. On mains restoration above 210V, the controller waited 30 seconds for stable mains supply before transferring the load back and shutting down the generator. Neutral interlocking relays prevented both sources being connected simultaneously. A buzzer and LED indicator panel displayed the active source and fault conditions. The system was bench-tested over 100 simulated mains failure and restoration cycles. Transfer from mains failure to generator supply was completed in 11.8 seconds on average. Back-transfer to mains on restoration took 32.4 seconds on average, within the 35-second design target. No simultaneous source connection event occurred across all test cycles. Load voltage during transfer was interrupted for less than 1 cycle at 50Hz. Total component cost was 31,200 naira. The study recommends adding generator fuel monitoring with SMS alert functionality and extending the design to handle three-phase power for commercial premises.