Batteries: Basics of Electrical & Electronics Engineering PDF

Department of Electrical Engineering Unit No:- 7 Name:- Batteries Basics of Electrical & Electronics Engineering Mr. Nirav Tolia Assistant Professor  Disclaimer It is hereby declared that the production of the said content is meant for non-com...

Department of Electrical Engineering Unit No:- 7 Name:- Batteries Basics of Electrical & Electronics Engineering Mr. Nirav Tolia Assistant Professor  Disclaimer It is hereby declared that the production of the said content is meant for non-commercial, scholastic and research purposes only. We admit that some of the content or the images provided in this channel's videos may be obtained through the routine Google image searches and few of them may be under copyright protection. Such usage is completely inadvertent. It is quite possible that we overlooked to give full scholarly credit to the Copyright Owners. We believe that the non- commercial, only-for-educational use of the material may allow the video in question fall under fair use of such content. However we honour the copyright holder's rights and the video shall be deleted from our channel in case of any such claim received by us or reported to us.   Electric cell  Types of cells  Equivalent circuits  Grouping of cells Outline  Batteries, Important terminologies of battery,  Charging method  Application of battery Prof. Nirav Tolia 3  What is a Cell ?  When a current passes through an electrolyte solution, chemical reaction occurs i.e. electrical energy is converted into chemical energy. Conversely, chemical energy can also be converted into electrical energy. The device which is capable of carrying out these conversions is called a cell.  A cell is a device which provides emf by converting chemical Electric Cell energy into electrical energy. It is made up of two metal plates of different materials immersed in a suitable solution. The plates are called electrodes and the solution is called electrolyte (such as acid or salt solution). The magnitude of emf of the cell depends upon the nature of both the electrodes and electrolyte. Prof. Nirav Tolia 4  What is a Cell ?  Some of the most prominent alloys and materials used as electrode materials are copper, graphite, titanium, brass, silver, and platinum.  When the two electrodes are immersed in the electrolyte, different chemical actions takes place on them and a potential difference is produced between them. Electric Cell  The magnitude of e.m.f. of a cell depends upon : 1. nature and material of the plates used as electrodes 2. nature or type of electrolyte used Prof. Nirav Tolia 5  Types of cells  Electric cells may be of two types 1. Primary cells: The cell in which chemical action is not reversible are called as primary cells. e.g. voltaic cell, denial cell, dry cell etc.  In this type, during discharging one of the plate is consumed which can not recovered by reversing the direction of flow of current. In this case cell is not recharged. Thus chemical action is Electric Cell not reversible. So primary cells are expansive source of energy. 2. Secondary cells: The cells in which chemical action is reversible are called secondary cells e.g. lead acid cell, nickel iron cell, nickel cadmium cell etc.  In these cells, no electrode is consumed during discharging, however chemical composition of the plates is changed. When the direction of flow of current is reversed, the plates regain their original composition. Thus the cells can be recharged. That why the are called as storage cells. 6 Prof. Nirav Tolia  Important terms of a cell E r V  Electromotive force : The energy supplied by a cell to one coulomb of charge is called e.m.f. It is the potential difference Equivalent between two electrodes. circuits  Internal Resistance : The opposition offered to the flow of current by the internal composition of the cell itself is called internal resistance.  Terminal voltage : The potential difference across the terminals of the cells at load is called terminal voltage.  Thus V=E–Ixr Prof. Nirav Tolia 7  Important terms of a cell Equivalent circuits Prof. Nirav Tolia 8  Grouping of cells  The emf of a single cell is very small about 1.2 V to 2 V. In order to get the desired emf, a number of cells are suitably connected. This is termed as grouping of cells. It can be done in the following ways. (1) Series grouping Grouping of cells (2) Parallel grouping (3) Series- parallel grouping Prof. Nirav Tolia 9  Grouping of cells (1) Series grouping:-  When two or more similar cells are connected in series i.e. negative terminal of one cell to the positive terminal of the other cell, then this type of grouping is called series grouping. Grouping of Let us assume, cells E = emf of one cell r = internal resistance of one cell n = total number of cells R = load resistance Prof. Nirav Tolia 10  Grouping of cells (1) Series grouping:- Therefore, Total voltage = nE volts Total internal resistance = nr ohms Grouping of Total resistance of the circuit = (R + nr) ohms cells nE  Current I = amp ( R + nr ) Prof. Nirav Tolia 11  Grouping of cells (2) Parallel grouping:-  When the positive terminals of two or more cells are connected together and their negative terminals are connected together then the combination is called parallel grouping.  E = emf of one cell Grouping of  r = internal resistance of one cell cells  n = no of cells connected in parallel  Total voltage = E volts  Total internal resistance = r/n ohms  r =  R +  ohms  Total resistance of the circuit E  n  Current I = amp  r  +  R 12 Prof. Nirav Tolia  n  Grouping of cells (3) Series-Parallel grouping:-  Few cells are connected in series in one branch, and few such branches are connected in parallel. Therefore this is also called mixed grouping of cells.  n = no. of cells in series Grouping of  m = no. of branches in parallel cells  r = internal resistance of each cell  E = emf of one cell  Total voltage of one branch = nE volts  Total internal resistance of one branch = nr ohms  Total internal resistance of all the cells = nr/m ohms 13 Prof. Nirav Tolia  Grouping of cells (3) Series-Parallel grouping:-  nr  =  R +  ohms  Total resistance of the circuit  m nE  Current I = amp  nr  Grouping of R +   m cells 14 Prof. Nirav Tolia  Grouping of cells  Eight cells, each with an internal resistance of 0.2 and an e.m.f. of 2.2V are connected (a) in series, (b) in parallel. Determine the e.m.f. and the internal resistance of the batteries so formed. Grouping of cells 15 Prof. Nirav Tolia  Grouping of cells  A cell has an internal resistance of 0.02 Ohm and an e.m.f. of 2.0V. Calculate its terminal p.d. if it delivers (a) 5A, (b) 50A Grouping of cells 16 Prof. Nirav Tolia  Grouping of cells  The p.d. at the terminals of a battery is 25V when no load is connected and 24V when a load taking 10A is connected. Determine the internal resistance of the battery. Grouping of cells 17 Prof. Nirav Tolia  Grouping of cells  Ten 1.5V cells, each having an internal resistance of 0.2, are connected in series to a load of 58. Determine (a) the current flowing in the circuit and (b) the p.d. at the battery terminals. Grouping of cells 18 Prof. Nirav Tolia  What is a Battery? A series, parallel or series-parallel grouping of cells is called a battery. Generally, a cell can deliver a small current at low voltage.  If higher voltage is required- a battery containing number of cells connected in series. Battery  If higher current is required – a battery containing number of cells connected in parallel.  If large current at high voltage is required- a battery containing number of cells in series and further connected in parallel. Usually a no. of cells connected in series placed in single container is called a battery. Prof. Nirav Tolia 19  Electrical Characteristics of a Battery  Some important electrical characteristics of batteries are (i) Electromotive force (EMF) (ii) Terminal voltage (iii) Internal resistance (iv) Ampere hour capacity Battery (v) Watt hour capacity Prof. Nirav Tolia 20  Electrical Characteristics of a Battery  Electromotive Force (EMF): It is the potential difference between the terminals of a battery when it is open circuited i.e. when no load is connected across the battery. The value of emf depends on temperature, specific gravity of electrolyte and the time lapsed since it was last charged. The emf increases marginally with an increase in temperature.  Terminal Voltage (V): It is the potential difference between the terminals of a battery when an external load is connected across the battery. This Battery potential difference is always less than the emf of the battery due to the voltage drop in the internal resistance of the battery. V = E – rI where V = terminal voltage of the battery E = emf of the battery r = internal resistance of the battery I = current in the external circuit Prof. Nirav Tolia 21  Electrical Characteristics of a Battery  Internal Resistance (r): It is the resistance offered by the positive plate, negative plate and the electrolyte of the battery. It should be as low as possible. The factors affecting the internal resistance are area of plates, specific gravity of the electrolyte and spacing between the plates.  Ampere-hour Capacity (Ah): The capacity of a battery indicates the ability of the battery to discharge at normal voltage, specific gravity and normal discharging current, and it is expressed in ampere-hours (A-h). Battery  The ampere-hour capacity is the product of rated current during discharging and the time in hours. A-h capacity = Id Td Where Id = rated current during discharging, Td = discharging time in hours  The capacity of the battery depends on the following factors:  Area of plates, Specific gravity of the electrolyte, Discharge rate, Density of the electrolyte, Temperature, Age of the battery. Prof. Nirav Tolia 22  Electrical Characteristics of a Battery  Watt-hour Capacity (Wh):  The terminal voltage of the battery changes during the discharging process. The watt-hour capacity is the product of the average terminal voltage during discharging and the ampere-hour capacity.  W-h capacity = A-h capacity * Average terminal voltage during discharging  W-h capacity = Id Td Vd Battery Where Vd = the average voltage during discharging. Id = rated current during discharging Prof. Nirav Tolia 23  Efficiency of a Battery There are two types of efficiency: (i) Ampere-hour efficiency (ii) Watt-hour efficiency (1) Ampere-hour efficiency: It is the ratio of ampere-hours during Battery discharging to the ampere-hours during charging of the battery. 24 Prof. Nirav Tolia  Efficiency of a Battery (2) Watt-hour Efficiency: It is the ratio of watt-hours during discharging to the watt-hours during charging of the battery. Battery 25 Prof. Nirav Tolia  Charging of a Battery  A battery should be maintained in charged condition to ensure its normal life span. There are two methods of charging of a battery: (i) Constant current method (ii) Constant voltage method (1) Constant current method Battery 26 Prof. Nirav Tolia  Charging of a Battery (1) Constant current method  Here the charging current is kept constant throughout the charging period of the battery. As the voltage of the battery increases gradually during charging, a variable resistance R is used in series. A number of batteries can be connected in series for charging, with the same charging current. Battery  This method has the following disadvantages  It takes longer time as compared to other methods of charging.  The battery charger must have a high voltage rating if a number of batteries are to be charged simultaneously.  Circuit is to be interrupted while removing or connecting any battery with the charging circuit. 27 Prof. Nirav Tolia  Charging of a Battery (2) Constant voltage method Battery  In this method the charging voltage is kept constant during the charging period. The charging current is more initially but decreases as the voltage of the battery increases.  A number of batteries with the same voltage rating can be charged by connecting them in parallel. Due to parallel connection of batteries, the circuit need not be interrupted at any time. This method is faster compared to the constant current method. 28 Prof. Nirav Tolia  Indications of a Fully Charged Battery The indications of a fully charged lead acid battery are: 1. Voltage 2. Specific gravity of electrolyte 3. Gassing 4. Colour of plates a. Voltage: When the battery is fully charged, its terminal voltage ceases to rise. The Battery approximate value of the terminal voltage is 2.1 volts. This voltage depends on the rate of charging, temperature, specific gravity of the electrolyte, etc. b. Specific Gravity of the Electrolyte: When the battery is fully charged, the specific gravity of the electrolyte increases to 1.28. Specific gravity can be measured with a hydrometer which consists of a float, a chamber for the electrolyte and a rubber bulb. c. Gassing: When the battery is fully charged, hydrogen is given off at the cathode and oxygen at the anode. This process is known as gassing. This indicates that the current through the battery produces no chemical action on the plates. d. Colour of Plates: When the battery is fully charged, the positive plate turns chocolate brown in colour and the negative plate turns grey in colour. 29 Prof. Nirav Tolia  Charge Indication  A fully charged battery has a specific gravity of 1.28. However when it falls to 1.15, the battery is fully discharged. To get good life of battery keep the specific gravity more than 1.18. Specific gravity Condition 1.280 to 1.290 100 % charged 1.230 to 1.250 75 % charged 1.190 to 1.200 50 % charged Battery 1.150 to 1.160 25 % charged Below 1.130 Fully discharged 30 Prof. Nirav Tolia  Applications Some important applications of lead acid battery are : 1. Used in automobiles for starting & lighting. 2. For lighting of railway trains. 3. Used at generating station or sub station to operate protective devices 4. Used in telephone exchanges. Battery 5. Used in emergency tube lights 6. Used for lighting purposes in remote rural areas 31 Prof. Nirav Tolia