Design of a Microcontroller-Based Automatic Changeover Switch for Seamless Power Transition Between Grid and Generator in Residential Buildings in Enugu State

The instability of grid electricity supply in residential areas of Enugu State, South East Nigeria, forces households to rely on generators as backup power sources. Manual changeover switches require homeowners to physically intervene each time grid power is lost or restored, which is inconvenient and risks unsafe electrical practices. This project presents the design of a microcontroller-based automatic changeover switch that detects grid power status and seamlessly transfers the electrical load between the utility grid and a standby generator without manual intervention. An ATmega328P microcontroller continuously monitors the grid supply voltage using a voltage divider and AC rectifier circuit. Upon detecting grid failure, the microcontroller activates the generator start relay after a programmable delay, then transfers the load via a double-pole double-throw contactor once the generator reaches stable voltage. Grid restoration triggers an automatic transfer back to grid supply and a generator cool-down and shutdown sequence. The system was installed in a residential building in Independence Layout, Enugu, and evaluated over three months of normal habitation. A total of 47 grid outage events were recorded, with the automatic changeover responding correctly to 45 events, yielding a 95.7 percent reliability rate. The two failure events were attributed to generator non-starting due to fuel exhaustion. Changeover time from grid loss to generator load transfer averaged 22 seconds including generator start time. Total system cost was approximately 58,000 Naira. Keywords: automatic changeover, power transfer, generator control, grid failure, Enugu State