ABSTRACT

This uninterruptible power supplies device has the capability of converting from 12volts D.C to 220volts alternating current at the frequency of 50Hz with the help of a step-up transformer. The main importance of this device is its ability to ensure absolute continuity of power to the computerized control system thereby protecting a critical equipment from electrical supply failure. Ups system achieve this by rectifying the mains supply, using the direct current to charge the standby battery and to produce a “clean” alternating current by passing through an inverter and filter system. The output produced is free of sags of services in the line voltage, frequency variation, spikes and transients. 

CHAPTER ONE

1.0 INTRODUCTION
A DC-AC Inverter is basically a device which converts direct to a sinusoidal current. There are different ways of doing this conversion to achieve better performance and reliable system.. This system is designed to generate 50Hz sinusoidal and 220volts alternating current and a total power of 200watts to provide power to sensitive equipment like computer, communication equipment, and/or to provide emergency light and power to some essential household appliances when there is power failure in the house. The desire to embark on the project was born out of the knowledge of the problem and discomfort that Nigerians faced when there is power failure in their homes or offices.
Even with generating sets, the user load will not pick-up power instantly when the failure occurs and where sensitive equipments like biomedical equipment and telecommunication equipment, where a momentary loss of power could result in equipment breakdown or data loss which could cause more labour to recreate (in the case of computer) or death in hospitals where such equipment were on power supply.

1.1 PROJECT OBJECTIVE
To overcome some of these shortcomings, a n uninterrupted power supply has been designed and constructed. This, we realized with rectifiers and inverter with a back-up power source. One interesting aspect of this system is that the unit is always in circuit when the supply authority is delivering power. The only requirement needs is a battery charger, automatic control system, inverter unit, battery (dc-source) and a step- up transformer. The mains charges the battery where the supply is ON and in the event of power failure, the load none derives its power from the battery via an automatic changeover switch.