1.1 Introduction
The PSU is a device that supplies electrical power to a device or group of devices (Wikipedia, 2012). The term ‘PSU’ is commonly applied to units that are integrated with devices the supply power to such as computers and household electronic appliances. The PSU used in the laboratory for experimental purposes is called a laboratory bench supply (Shoewu et al., 2011). It is usually a variable power supply unit which can either supply a uni- or bi- polar power to the load connected. Aside the aforementioned, there are cases when the need to power other electrical appliances using a very low AC source either for domestic use or laboratory experimentation arise. In these situations, the DC output is less useful. Hence, the need to design and develop a simple, cost effective, functional and reliable multi-output power supply that can serve a dual purpose of providing DC and AC outputs of different magnitudes for satisfying the desired need.
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Limitations of the Study and Definition of technical terms.
1.2 Background of Study
Over the years, there had been epileptic power supply due to uncontrollable factors such as vandalization of electric cables, drop in volume of water flows in dams, heavy rainfall overloading of transformers, bridging of power cables. The converted voltage, 12V AC gets to the transformer via the switching stage, the signal will be stepped up from 12V AC to 220V AC before the output will be supplied to the load and small to a low input charger that converts the AC voltage to DC by bridge rectifier circuit that charges the 12V battery. The relay switches to the DC operators to power the load connected to the inverter. Many inverters of different types have been developed such as square wave modified sine wave, multilevel and pure sine wave inverters. The square wave inverters were the simplest, least expensive and early incarnation of inverter technology. They are seldom seen because of the low quality power.
In this design, transistors, comparators and regulators have been used as the basic building blocks in order to facilitate a robust design to give the desired multi-output required. Hence, reducing the number of components used in circuit design and also increases the functionality of the power supply unit. Modified sine wave inverters produce similar square wave output except that the output goes to zero volts for a time before switching positive or negative. They are simple low cost and suitable for many electronic devices except for sensitive or specialized equipment such as computers, laser printers, microwave, ovens, and fluorescent lighting audio equipment. A pure sine wave inverter produces nearly perfect sine wave output (typically below 3% total harmonic distortion) that is essentially the same as utility supply grid power thus it is compatible with AC electronic devices.
A self-charging power inverter serves this purpose not only as a back-up for power failure but as an uninterrupted supply of electricity for 24/7 on daily basis. It is a device used to convert direct current (dc) to alternating current (ac) by converting 12 volt DC power source into 220 volt AC. A few of most widely used applications of selfcharging inverters includes television sets, microwaves, printers, radio sets, and other household appliances and charging of cell phones, laptops from a car cigarette lighter outlet and running power tools from a 12volt battery on jobsite where electricity isn’t available. Self charging inverter can be built in modules of 5kVA up to the load capacity.
All equipments sold in the market are designed for a sine wave hence sine wave inverter will guarantee that the equipment work to its full specification. Sine wave inverters are the most expensive but they also deliver the most consistent wave output. The multi level inverter is a power electronic system that synthesis a desired voltage from several levels of a desired voltage from several level of direct current voltage as inputs. The advantages of using multilevel topology include reduction of power rating of power devices and lower cost. There are three topologies: diode clamped inverter, flying capacitor inverter and cascaded inverter.
Electrical power interruptions are quite common in every place especially after a power outage, heavy down pour or a severe storm. In response to this power outage, a more economical, noiseless and emission free, alternative source of electricity -surpassing the use of the generators, solar and more recently the inverters is both the self-charging inverter. Both the generators and inverters come with their adverse problems such as cost of fuelling, the noise, emissions and the need to recharge the inverter’s batteries after use. However, these different types of inverter require charging of the batteries after depletion (use) and this call for a self-charging inverter that constantly recharges its battery when in use. Therefore, in Nigeria where the research was carried out, the activities that was conducted is to design and construct a Constant Power Supply from a DC Source.
1.3 Statement of Problems
Investigation reveals the problems of the Design and Construction of AC-DC Power Supply Trainer which entails that, the existing system is not ideal for inductive AC and motor loads, sensitive electronic devices can be damaged by poor wave forms by low batteries, and reduced efficiency, more complexity, increased cost. Although basic switching regulator technology and its advantages have been known for years, a lack of the necessary switching transistors, rectifier diodes, and filter capacitors caused certain performance problems that were costly to minimize.
As a result, these supplies were used only in airborne, space, or other applications where cost was a secondary consideration to weight and size. However, the advent of high-voltage, fast switching power transistors, fast recovery diodes, and new filter capacitors with lower series resistance and inductance, have propelled switching supplies to a position of great prominence in the power supply industry.
1.4 Aim and Objectives of Study
The aim of the study is to design and construct a system that will generate a Constant Power Supply from a AC-DC Source. In achieving this aim, the following specific objectives were laid out as follows to design and construct a system that will:
- Help reduce our reliance on the burning of fossil fuels;
- Produce a constant and efficient electricity supply; and
- Generate a Constant Power Supply from a AC-DC Source;
1.5 Significance of Study
The developed AC-DC output power supply is much useful in measurements, laboratory works and general applications requiring power supply. This study will also be of immense benefit to Electrical Engineers, PHCN Company and other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.
1.6 Scope of Study
The scope of this research is focused on the Design and Construction of AC-DC Power Supply Trainer.
1.7 Limitations of the Study
During the course of this study, many things militated against its completion, some of which are:
- Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
- Research material: availability of research material is a major setback to the scope of the study.
- Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
- Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).
