DESIGN AND IMPLEMENTATION OF VARIABLE BATTERY CHARGER

DESIGN AND IMPLEMENTATION OF VARIABLE BATTERY CHARGER

ABSTRACT

The present of battery charger is of great important in today’s technology advancement. Charger serves as the live wire of the backup power supply system in our day to day technological development. “The variable battery charger” is a device design to build up electrical energy in wet cells through the help of a transformer that takes in 220/230V and rectifier circuit which contain diodes to convert the alternating current[AC] from the transformer to direct current[DC], the output from the rectifier was being smoothen by a capacitor and then regulated by an integrated circuit(IC), the output is varied to the desire voltage by the use of variable resistor. The components as stated above were carefully arranged and soldered part by part together and coupled in a metal casing of 40*30*20cm. finally it was tested and work perfectly well. “This variable battery charger” can be used to charge automobile and portable equipment batteries with voltage ranging from 6-36 volt. To charge a battery, the charger voltage has to be greater than the terminal voltage of the battery. When a battery is connected to this charger, the dial of the ammeter will read to the near current require by the battery to start charging. The charger ammeter begins to draw until when it finally drop to zero indicating that the battery is fully charged. 

CHAPTER ONE

1.0       INTRODUCTION

The variable battery charger is an electrical device that is used to charge a rundown lead acid battery in automobile and other equipment with different voltage level requirement. The battery charger converts the A.C. from the power line into D.C. suitable for the battery voltage requirement. The circuitry to recharge the batteries in portable equipment is an important part of any power supply design.  The complexity of the charging system is primarily dependent on the type of battery and the recharge time. Lead acid battery cells have low energy density and relatively low life-cycle, yet because of their cost effectiveness they are still considered the preferred choice by many electric vehicle (EV) developers and are likely to continue to be so for the next 5-10 years. One method of improving the performance of a battery powered EV is to improve the battery charging methodology, since EV performance and range is largely determined by the capacity, weight and charge/discharge characteristics of the on-board batteries. This project describes a method for fast charging lead acid batteries using current pulses of controllable magnitude and duty called ‘pulse charges’. It is used together with constant voltage/current profiles to increase charge acceptance, improve the charging time, and to potentially increase the life cycle of lead acids cells. A step-down transformer is use to reduce the high mains voltage to a low A.C. voltage, a half wave rectifier for converting the alternating current into direct current, a charger current limiting element for preventing battery from damage.

1.1       BACKGROUND OF STUDY

In the realm of battery charging, charging methods are usually separated into two general categories:  Fast charge is typically a system that can recharge a battery in about one or two hours, while slow chargeusually refers to an overnight recharge (or longer). Slow charge is usually defined as a charging current that can be applied to the battery indefinitely without damaging the cell (this method is sometimes referred to as a trickle charging). The maximum rate of trickle charging which is safe for a given cell type is dependent on both the battery chemistry and cell construction.  When the cell is fully charged, continued charging causes gas to form within the cell.  All of the gas formed must be able to recombine internally, or pressure will build up within the cell eventually leading to gas release through opening of the internal vent (which reduces the life of the cell). This means that the maximum safe trickle charge rate is dependent on battery chemistry, but also on the construction of the internal electrodes.  This has been improved in newer cells, allowing higher rates of trickle charging. The big advantage of slow charging is that (by definition) it is the charge rate that requires no end-of-charge detection circuitry, since it cannot damage the battery regardless of how long it is used.  This means the charger is simple (and very cheap). The big disadvantage of slow charge is that it takes a long time to recharge the battery, which is a negative marketing feature for a consumer product. In the case of fast charging, the charge rate is higher than or equal to 1 C in practice.

This means that the maximum charge time is just over one hour. The actual charge time will depend on the battery’s temperature before charging and on the amount of overcharging resulting from the chosen end-of-charge trigger. For example, a 120% charge with a 1 C charge rate implies a charge time of 1 hour and 12 minutes when the charging is started with a completely empty battery. Ultra-fast chargers with charge rates over 4 C, hence with charge times less than 15 minutes, have been reported for NiCd batteries. It should be noted that the charged capacity will be lower than 100% in this case. Proper end-of-charge triggers based on voltage and temperature measurements have to be implemented for fast charging of both NiCd and NiMH batteries to prevent the risk of serious damage to the batteries.

 1.2       AIM AND OBJECTIVE

The aim of this project is to construct a variable battery charger with the output voltage ranging from 6-36V. In order to charge batteries with different voltage requirement between 6, 12, 24 and 36, thereby making battery available for use at all time.

1.3       PROBLEM STATEMENT

Mostly portable hand held equipments and automobiles need external DC source for effective operation and this is always supply from battery, as a result of that there is always the need to re-energize the cells after being discharged in order to protect the cells from damage there by leading to short life-cycle Variable battery charger is to make available different voltage to charge different battery of different voltage requirement.

1.4       SIGNIFICANCE OF STUDY

The significance of this project can never be over emphasized, variable battery charger make available four voltage level (6v, 12v, 24, and 36v) to select between to charge different battery. This can be used in industries to charge the battery of portable equipment; it is also very useful to automobiles battery and even at homes to power back up batteries.

1.5       SCOPE OF STUDY

The project employs the principle that when battery energy is used up, an electrical energy can be forced into the battery to replace the lost energy through a means known as charging. The energy gradually stores up in the battery until the battery current capacity is reached. The variable battery charger has four different voltage output to choose between whenever the need arise, this to create flexibility and comfort ability. It has a step-down transformer, a rectifier, a capacitor; a resistor and a voltage selector to make available a stable variable DC supply to charge batteries.

 1.6       LIMITATION OF THE PROJECT

The performance and effectiveness of the project is affected if it is operated in an area where there is no electricity.  It requires longer charging time to fully charge a battery.