In the previous tutorial, Online UPS was assembled from its basic building blocks like Lead Acid battery Charger, Square Wave Inverter and Modified Sine Wave Inverter. Now in this tutorial, offline UPS will be designed. The Offline UPS is one of the topologies of UPS (Uninterruptible Power Supply). In UPS system, the term topology refers to the switching mechanism of the UPS system.  Contrary to online UPS, in offline UPS, the load circuit is initially directly powered by the AC mains. On the failure of power supply, the power failure is detected by a switching circuit and the power is provided to the load through the battery and inverter after the power failure has already occurred. So, in the offline UPS, the load experiences the power cutoff once before it receives the power backup from the UPS.

An uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power [[wysiwyg_imageupload::]]source, typically mains power, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries or a flywheel. The on-battery runtime of most uninterruptible power sources is relatively short (only a few minutes) but sufficient to start a standby power source or properly shut down the protected equipment.There are different types of UPS such as On line UPS, OFF line UPS and  a Line interactive UPS.This project details in creating an offline project with PIC microcontroller. Off Line UPS the load is connected directly to the mains when main supply is available and it is not too high or not to low. Continue reading to find out how PIC microcontroller is utilized and how the project is put to work.