Design and Analysis of a Low-Cost Uninterruptible Power Supply for Domestic Applications

Abstract

Reliable domestic electricity is important for lighting, communication equipment, fans, routers, computers, and other low-power household loads. Commercial online uninterruptible power supplies (UPSs) offer excellent regulation but are often unnece=ssarily complex and expensive for homes where the main requirement is short-to-medium duration backup during supply interruptions. This paper presents a methodology for the design and analytical evaluation of a low-cost 600 VA domestic UPS based on an offline/line-interactive architecture. The proposed system uses a 12 V lead-acid battery, a four-switch MOSFET full-bridge inverter, a 12/230 V step-up transformer, sinusoidal pulse-width modulation (SPWM), a 10 A constant-current/constant-voltage charger, a mains-sensing transfer relay, and basic over-current, under-voltage, over-temperature, and short-circuit protection. Component ratings are derived from load power, battery current, transformer volt-ampere capacity, switching stress, and required backup time. An LC output filter is selected to attenuate the switching carrier while preserving the 50 Hz fundamental. Analytical results indicate that, for a 400 W design load, the battery-side current is approximately 38 A at 88% inverter efficiency, and a 12 V, 100 Ah battery can provide about 1.2–1.5 h of practical backup at high load or substantially longer at 200 W. The selected architecture emphasizes low component count, repairability, galvanic isolation through the transformer, and acceptable domestic power quality. The methodology provides a reproducible basis for constructing and testing a cost-conscious household UPS without claiming laboratory measurements that have not yet been performed.