THE DESIGN AND CONSTRUCTION OF AN AUTO CUT-OFF CAR BATTERY CHARGER

ABSTRACT

This project is divided into several chapters that thoroughly address the design and construction of a battery charger equipped with an auto-cut-off feature, capable of charging a 12-volt battery. In the course of this construction research, various designs were developed. A historical research approach was employed to break down and analyze the system to a detailed level of understanding of what an auto-cut-off charger entails, how it can be constructed, and the primary purpose of the project.

The charging current, along with the power supply for the circuit, is derived from a 0–18 volt, 2-ampere step-down transformer. The low-voltage AC is rectified by a bridge rectifier consisting of diodes D1 through D4 and smoothed by capacitor C1 to eliminate ripples for charging purposes. For charging the battery, 18V DC is utilized, while 9 volts regulated DC (obtained from IC1) powers the control circuit. IC2 (CA 3140) functions as a simple voltage comparator to control the relay. Following the series of rectification and smoothing stages, pure DC is obtained that can effectively charge a specified DC battery. The relay serves as the tripping mechanism to automatically disconnect the charger when the battery reaches full charge and to manage operations when the battery is weak.

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

In the realm of renewable energy sources, a battery is defined as a device comprising electrodes and electrolytes that stores chemical energy and facilitates a reaction between its electrodes and the electrolyte, resulting in the flow of electrons through an external circuit. The circuitry responsible for recharging batteries in portable devices forms a crucial component of any power supply design. The complexity and cost of the charging system largely depend on the type of battery and the required recharge time.

The lifespan of batteries commonly used by automobile drivers can be significantly extended by preventing overloading, overcharging, and supplying charging currents that exceed the manufacturer’s recommended value (Bangaru et al., 2013). Observations over time have shown that most commercial battery charging service centers in towns such as Enugu, Nigeria which are frequently patronized by automobile drivers rely on conventional battery chargers that lack an automatic charging cut-off circuit. The absence of this automatic cut-off feature requires operators to manually monitor the charging process to determine when the connected battery is fully charged (Baker, 2014).

Regardless of the battery’s initial discharge level, service center operators typically connect the battery and leave it charging overnight without supervision. This common practice frequently results in overcharging of the battery. Additionally, in an effort to provide faster service and meet customers’ urgent needs, operators sometimes increase the charging current by adjusting the charger settings to shorten the charging duration. Such practices ultimately reduce the battery’s lifespan. These recurring issues have highlighted the need for the development and construction of a 12V portable battery charger with a built-in automatic charging cut-off circuit. This innovation would promote domestic usage and enable automobile drivers to avoid the problems associated with commercial charging centers (Bangaru et al., 2013).

During the development of this device, protective components such as a fuse and a reverse current prevention diode were incorporated to safeguard against issues arising from short-circuit currents and reverse polarity.

Given the compact design of the battery charger and its limited ventilation, an extractor fan was integrated to expel hot air and moisture generated inside the charger enclosure during operation (Bangaru et al., 2013).

1.2 Statement of the Problem

A basic 12-volt charger operates by delivering a constant DC or pulsed DC power source to the battery under charge. This type of charger does not adjust its output according to time or the battery’s state of charge. Its simplicity makes it relatively inexpensive to produce. The circuit of a battery charger is designed to convert voltages from one form to another (typically from AC to DC). This conversion is achieved using essential components such as rectifiers, capacitors to filter and remove ripples from the AC source, and a voltage regulator (IC).

However, this project focuses on the construction of a 24V/12V simple battery charger using locally available materials to minimize costs. The proposed design is intended for use with 24V/12V batteries. A resistor is included in the circuit to limit short-circuit current.

1.3 Aim and Objectives of the Study

The aim of this project is to design and construct an auto cut-off car battery charger.

The specific objectives are as follows:

• To design a device capable of recharging 24V/12V lead-acid batteries when they are discharged.

• To design a device that can indicate the charging process, low battery level, and full charge status through LED indicators.

• To design and construct a battery charger suitable for charging various types of 24V/12V rechargeable batteries, including alkaline, NiCad, and lead-acid batteries.

1.4 Significance of the Study

A simple 24V/12V battery charger is a basic circuit composed of various electronic components soldered onto a circuit board to perform the required charging function. The importance of this project lies in its ability to guide technicians and students on how to construct a simple battery charger circuit and understand its working principles. It is anticipated that upon completion, the charger circuit will be housed in the laboratory for practical battery charging, academic demonstrations, and other educational purposes.

1.5 Scope of the Study

This project is limited to the design and construction of an auto cut-off car battery charger. The circuit accepts an input voltage of 240 volts from the AC mains supply, which is stepped down by a transformer to 12 volts. The resulting 12-volt AC is rectified using a bridge rectifier and filtered by a capacitor connected in parallel to the positive terminal of the rectifier. The output voltage is then used to charge the battery. The project is specifically designed for 24V/12V batteries and is not recommended for use with rechargeable batteries outside this voltage range.

1.6 Limitation of the Study

During the execution of this project, the researcher faced several challenges that delayed timely completion. These included financial constraints, time limitations, and the unavailability of certain materials, which required traveling long distances to source textbooks and other essential resources.

1.7 Relevance of the Study

a) It helps to extend the lifespan of the battery.

b) It minimizes damage to the battery and other connected components.

1.8 Report Organization

This project report is structured in the following sequence:

Chapter One: This chapter introduces the research/project. It discusses the problems the project seeks to address and the approaches to solving them. It also covers the relevance of the project, its scope, and its limitations.

Chapter Two: This chapter presents the literature review. It examines relevant works by other researchers in the field of battery protection systems, the challenges they encountered, available technologies for realizing the project, and the characteristics of the components used.

Chapter Three: This chapter addresses the methodology and design of the system. A key element is the block diagram of the system. Mathematical analysis is also performed here to determine appropriate components for each section.

Chapter Four: This chapter focuses on system implementation and the results of tests conducted on the completed system. The Bill of Engineering Measurement and Evaluation (BEME) is also presented in this section.

Chapter Five: This final chapter provides the conclusion and recommendations. It summarizes the research conducted and the results obtained.

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