FUOYE Journal of Engineering and Technology (FUOYEJET), Volume 6, Issue 1, March 2021 ISSN: 2579-0625 (Online), 2579-0617 (Paper) © 2021 The Author(s). Published by Faculty of Engineering, Federal University Oye-Ekiti. 55 This is an open access article under the CC BY NC license. (https://creativecommons.org/licenses/by-nc/4.0/) http://dx.doi.org/10.46792/fuoyejet.v6i1.579 engineering.fuoye.edu.ng/journal Design and Construction of a Low-Cost Automatic Single-Phase Transfer Switch Abiodun E. Amoran, Gerald K. Ijemaru, Olaitan Akinsanmi and Waston Agbramu Department of Electrical and Electronics Engineering, Federal University, Oye-Ekiti, Nigeria {abiodun.amoran|gerald.ijemaru|olaitan.akinsanmi}@fuoye.edu.ng Received: 18-SEP-2020; Reviewed: 22-OCT-2020; Accepted: 27-NOV-2020 http://dx.doi.org/10.46792/fuoyejet.v6i1.579 Abstract- 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, NPN Transistors, PC817 Optocouplers, Relays —————————— ◆ —————————— 1 INTRODUCTION An Automatic Transfer Switch (ATS) is an electrical and electronic device that senses when public utility supply is interrupted and starts up a secondary supply, if the utility remains unavailable. ATS also known as “Generator Transfer Switches” has an additional circuit component in which a computer monitors the incoming power supply (Agbetuyi, Adewale,Ogunluyi & Ogunleye, 2015). Automatic switching eliminates the problem associated with manual switching mechanism which includes interrupted power supply, device damage due to frequent commutations, possible causes of fire outbreak due to switching sparks, wear & tear of mechanical parts and high maintenance cost (Amuzuvi & Addo, 2015) and as a result of these problems, the need arises for automation in switching of loads. ATS is to maintain constant supply to the loads that are being supplied by eliminating time delay that usually accompanies manual switching from one source to another, wherever continuity of supply is necessary. The switching between the mains supply and the generator occurs in milliseconds. The opto-coupler serves as a monitoring or sensing mechanism that detects voltage and triggers the microcontroller process in the allocation of load. If the mains supply is switched off, the generator automatically comes ON and load is transferred back to the house. Also, if the mains supply comes back on, the load switches from the generator to the mains supply and this initiates generator shutdown. ATS is a technological advancement which makes use of smart electrical and electronic gadgets; and the need for its development arises especially at critical places such as hospitals, business premises, Universities, research institutes, and diagnostic centers where uninterruptible power supply is highly needed. There is therefore the need for a seamless and reliable transfer system in the event of power outage. *Corresponding Author This paper presents the design and construction of ATS with the use of Atmega8 microcontroller that automatically switches ON or OFF a secondary source of supply in the presence or absence of the public utility supply, and it is low cost with higher switching speed. 2 RELATED WORK Osaretin, Ibhadode, & Igbinovia (2016) in their work identified the pertinent problem faced in the society today due to the instability in power supply and thought of the need for alternative sources of power to enable the switching of load between two or more sources. The automatic changeover eliminates the need for manual or human intervention by sensing mains supply and switching to an available source. Automation eliminates the delay and the cost of inefficiency associated with manual operation. The device automatically switches between the power sources and indicates if utility power is restored when an alternative power is in use. They designed a system that automatically changes over with step loading for renewable energy systems with the aid of an 8052 microcontroller. (Amuzuvi & Addo, 2015) designed a microcontroller based Automatic Transfer Switching System to overcome the problem of manual switching to alternative source of energy in case of power outrage from mains. The microcontroller PIC16F877A coordinated the other circuits namely a voltage sensing circuit (which monitors continuously utility supply and alternative supply and communicates with microcontroller accordingly), a Hall Effect current sensor (responsible to feed load current to the Transfer Switch), relays (which help in starting fuel flow pump and engine), Light emitting Diodes and a Liquid crystal display. GCG basic programming software was used to program the hardware while proteus design suite software was used to simulate the proposed circuit. It has the advantage of having a time lag of 20s but the rating of the proposed ATS was not specified and it was not also stated whether it could work for single or three phases.