Design and Testing of an Automatic Voltage Stabilizer and Surge Protector for Household Appliances in Enugu State

Erratic power supply and voltage fluctuations pose serious risks to household electrical appliances across Nigeria, with Enugu State consumers frequently experiencing voltage surges and brownouts that damage refrigerators, televisions, and air conditioning units. This project presents the design and testing of an automatic voltage stabilizer combined with a surge protection circuit for household application. The stabilizer uses a toroidal autotransformer with multiple tap positions selected by electromechanical relays driven by a comparator circuit. An ATmega8 microcontroller monitors output voltage and adjusts relay switching to maintain a regulated output of 220 volts AC within a tolerance of plus or minus 5 percent across an input range of 140 to 260 volts. A transient voltage suppression diode array and a metal oxide varistor are incorporated at the input stage to clamp surge voltages. The system was bench-tested with resistive and inductive load profiles representative of typical Nigerian household appliances. Performance tests showed a voltage regulation accuracy of 97.3 percent under varying input conditions. Thermal behaviour was assessed under continuous load to ensure safe operating temperatures within the enclosure. A comparison study of repair bills from appliance service centres in Enugu documented the typical financial losses caused by voltage irregularities, providing economic justification for the device. This study contributes a locally manufacturable and affordable power protection solution relevant to the Nigerian residential context. Keywords: voltage stabilizer, surge protection, power regulation, household appliances, Enugu State