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DESIGN AND CONSTRUCTION OF A 12 VOLTS AUTHOMATIC BATTERY CHARGER

CHAPTER ONE

INTRODUCTION

BACKGROUND OF THE STUDY

A battery charger is an electrical device employed in charging batteries that are usually charged by battery charges are the storage batteries also known as “accumulators”. The charger is made up of various electrical and electronics component which for the purpose of clanty are group into your basic unit they are:

The power supply units

The smoothing circuits

The regulating unit and

Regulated D.C charging units

          Battery chargers comes in various designs and voltage.  The choice of a particular and of charger that depends largely int eh size of battery or battery or batteries which on mterds to charge the mini battery changer could be used to charge batteries whose voltage ranges from 6 – 12 volts. The bigger battery changes are for batteries with voltage ranging from 12 – 48 volts.  These are the heavy duty batteries.

          The battery charge is builts in such a way that it delivers a constant value of d.c current into the battery it is charging in the opposite direction from which current flows on the batteries during discharge one cannot successfully design a battery charge with out a fundamental understanding of the accumulator because it also makes up the operation.

          Thus chapter two aimed at a brief study of the accumulator (battery).  Chapter three deals with the power supply units which series as the backbone of the battery charger and how the automatic cut off is achieved.     

          Chapter four fully analysis the operates of the battery charger and its casing which chapter five while happen to be the last chapter aimed at concluding the summarizing what has been achieved at the end of the project.

STORAGE BATTERY

A battery is a group of electrical cells connected in series or series/parallel produces electrical energy as a result of chemical energy stored on it.

Batteries are generally divided into two groups these are the primary cells and secondary cell which are mostly known as a storage batteries or accumulators.

          Primary cell which are usually dry cell for example, touch batteries (the lechanche dry all) the mercury cell etc.  the cannot be re-charged ones their chemical energy is fully utilized.

          The secondary all or storage all can be re-charged ones their chemical energy is fully utilized, hence we will discuss more on these kinds of cells (as they are the ones that will be charged with a battery charger).

          The storage cell are also known as accumulator.  In these types of cells, the chemical althon between the electrode and the electrolytes is trudy reversible.  A current (d.c) passed though it in opposition to its E.M.F reforms the original material of the electrodes and the cell can therefore be sued again and again.  We shall consider two of the most common types of storage cell.

          The nickel – iron (Nike) accumulator, the asteve material in the positive plates in nickel oxide (N12 03) and the negative plates finally divided.  The electrolyte is a solution of potassium hydroxide (K0H) when H2ions movest anode and S04 ions to the cathode.  At anode (Pb02) it combine with oxygen of (Pb02) and H2 S04 attacks lead to forum pbS04.

THE LEAD ACID ACCUMULATOR

The lead acid accumulator is one of the mostly widely used t ypes of storage cell. The negative electrode is of lead and the positive electrode is of lead (iv) oxide (pb02).  The electrolyte is sulphur acid initially of density. 1.21 the initial emf of the battery it about 2.1 volts.  This rapidly decrcoses to 2.0 volts at which figure it remains nearly constant until the battery is almost discharge re-charging should be begin if the emf falls as low as 1.8 volts.

          Those substance of the cell which stake active part in chemical combination and hence absords or produces electricity during charging or discharging are known as active materials of the cell.  The active materials of a lead acid cell are.

1.                 Lead peroxide (Pb02) for positive plate

2.                 Spong lead (Pb) for negative plate

3.                 Delute Sulphorine Acid (H2 S04) as electrolyte

Lead peroxide (pb02) is a combination of lead and oxygen.  Its dure chocolate brown in colour and its quite hard but brittle substance.  It is made up of one atom of lead (pb) and two atoms of oxygen (02) and its chemical formular is Pb02: As said earlier, it posses the positive action material of the accumulator.  The spong lead (pb) is a pure leads in soft sponge or porous conduction, its chemical formualr is Pb and forms the negative alhra material.

          The dilute sulphrine acid is approximately  three parts water and one parts suphurie acid the chemical formular of this is H2 S04.  The positive and negative plates are inversed in this solution known as electrolyte.  The current producers chemical changes in this solution.  Hence the  lead acid cell depend.  For its action of the presence of two plates covered with Pb02and Pb in solution of dilute H2S04 of specific gravity of 1.21 or ne3ar about as earlier stated.  The basically means of discharging and the charging process of the accumulator is known as chemical charger.

          In the process of the accumulator is known as chemical charger.  In the process of dischargings of a battery.  If the cell is fully charged, it s positive plate or anode is Pb02 (dack chocolate brown0 and the negative plate or cathode is pb (slate grey) when the cell discharges, the scorda current through the extend lend, then H2 S04 is dissociated into positive H2and negative S04 ions.  As the current within the cell is flowing from cathode to anode in the process of charging of a battery if the cell is recharged, then hydrogen ions (H2) moves to cathode and S04 ions gas to anode and the following charges would likely placed.

          At cathode

                   Pb S04 + H2          Pb + H2 S04

          At Anode

                   Pb S04 + S04 + 2H20                          Pb02 + 2H2 S04

General, it will be noted that during discharging the following are absorbed:

i.                   Both anode and cathode becomes pb S04 which is whitish in colour

ii.                 The specific gravity and acid is discharged due to the formation of water

iii.              The voltage of the cell decrease

iv.              The cells given out energy

METHOD OF CHARGING

          These are basically four method of charging batteries.   They are includes:

a.                 Constant voltage

b.                 Constant current

c.                  Ride charging and

d.                 Floating charging

But for the purpose of celerity and simplification of works and increase of theirs project it is the constant voltage method that we are going to discuss furt6her.  This method has been employed while testing and constructing the charger.

CONSTANT – VOLTAGE METHOD

In the method of charging the voltage is  maintained at a value which is slightly in excess of the end of fully charged battery, act the beginning of the charging period the current is charged.

          During the charging process the current fails as the emf of the cell rises to approach the charging voltage when the battery is fully charged it up to its maximum 12 volts, the charger will automatically stop charging with the help of the contact relay, the transistor and the zener dioxide which send the current back to the system.

          Then at this moment

          The charging current is usually determined from the formular

IC      =       V – E

                       r

Where         IC      =       Charging current

                   V       =       Output voltage

                   E       =     E.M.F of the battery (at full charged)

                   r        =       Internal resistance of the battery