Design and Construction of a Low-Cost Automatic Single-Phase Transfer Switch

Irregular power supply poses a serious problem in many developing countries with power outage usually experienced on a regular basis. Thus, this challenge necessitates the need for an automated method of power change over to an alternative source during power failure that will be an improvement over the manual change over system. This study aims to design and construct a microcontroller-based Automatic Transfer Switch (ATS) for a single-phase system. Atmega8 microcontroller was programmed to automatically switch power supply between a primary source and a secondary power source through the aid of relays. A modular approach was used in the design of this ATS, which incorporates Atmega8 microcontroller, diodes, resistors, L7805 voltage regulator, PC817 optocouplers, a buzzer alarm, NPN transistors, and a Liquid Crystal Display (LCD) that indicates which power source was available. This design is limited to 30A on full loading due to the power relay used in the design. The testing showed that the design was able to automatically switch power between two supply sources with no external aid and it performed optimally even when loaded to 90% of its maximum bearing-capacity. Keywords: Automatic Transfer Switch, Atmega8 Microcontroller, Liquid Crystal Display, NPN Transistors, PC817 Optocouplers, Relays