BATTERY

Capacity of battery is denoted by Amp/hour. = Capacity x hour

                             V-Eb

Cell current (I) =--------

                            R + r

Where V= Emf, Eb = Bach emf, R= outside resistance, r= Internal resistance

Battery charging current = Capacity/hours. *cell charging current should be applied as per manual.

Equalizing Charging: Charge on low rate. Charge up to three same reading of voltage & sp. Gravity.

Battery drawback:

Sulphation:   Active material in the form of sulfur, deposits on +ve & -ve plate and surface of plate is hardened.

Plates buckling: At the time of charging/discharging if it is taking high current then its temperature will also increase. Due to this, plates get bending un-uniformly and there is a possibility of short ckt.

Sensitization: In battery, active material is depositing on the plates. An active material, in the form of powder form deposited at the bottom of cell. So internal resistance of the cell increases and battery loose its capacity.

Ni – Ca Battery Chemical Reaction

+ve Plate: Nickel hydroxide as the active constituent.

-ve Plate: Cadmium hydroxide

Electrolyte: Solution of Potassium hydroxide in DM water with lithium hydroxide as an additive.

2Ni(OH)₃ + 2Cd(KOH)   -> 2Ni(OH)₂ + 2Cd(OH)₂ + 2KOH

The Potassium hydroxide electrolyte takes no parts in these reactions and acts only as a carrier of ions and the lithium hydroxide additive in the electrolyte significantly increases the life of the cell since it has a beneficial effect on the positive electrodes. This beneficial effect is more.

UPS A BATTERY: 350A/h (a) C-10 (T350P) 2V per cell, 180 cells.

UPS B BATTERY: 200 A/h (a) C-10, 12v, 32 CELLS

Chemical effect of electric current: When an electric current is passed through an electrolysis decomposing of electrolyte into its ions takes place. This phenomena is called chemical effect of electric current.

Electrolyte: It is compound, which in solution or in the molten state, conducts an electric current and is simultaneously decomposed by it. Electrolyte may be acids, bases or salts. It is also known as liquid conductor. Current is carried by ions, not by electrons as in metals.

Electrolysis: The process of chemical decomposition or dissociation of certain substances (electrolytes) in a dissolved or molten state by an electric current passed through that substance is known as electrolysis.

Faraday’s laws of electrolysis:

1)            The mass of an ion liberated at an electrode by the chemical action of a current of electricity is proportional to the quantity of electricity which is passed i.e. to the product of the strength of the current and the time during which it flows.

2)             The masses of ions liberated or deposited by the same quantity of electricity passed through several electrolytes are proportional to their chemical equivalents.

Chemical equivalent: Chemical equivalent of an element is this weight of the element which, combines with or replace one part, by weight, of hydrogen by chemical action and is numerically equal to the atomic weight divided by an valency.

Electrochemical equivalent (ECE): The electro chemical equivalent (E.C.E) of an element is the mass of its ions in grams which is liberated or deposited by chemical action by the passage of one coulomb of electricity i.e. by one ampere for one second.

Electrode: It is conductor by which an electric current enters or leaves an electrolyte in electrolysis.

Anode: It is the positively charged terminal or electrode in electrolysis through which current flows into the electrolyte.

Cathode: It is the negatively charged terminal or electrode in electrolysis towards which the current flows in an electrolyte.

Ions: The constituent of the electrolyte associated with an electric charge which are liberated during electrolysis are called ions.

Anions: The negatively charged ions which during electrolysis are attracted towards the positively charged anode are called anions and so the anions area electro-negative.

Electroplating: Electroplating is a process of depositing a layer of metal on any other metal by passing current through an electrolyte containing a solution of a salt of the same metal which is to be deposited. Cathode is polarity of depositing metal in electroplating. Silver plating means the deposition of a layer of metallic silver generally by electrolysis.

Copper sulphate solution (C_uSO₄) and silver nitrate (AgNO₃) solution are generally used for copper plating and silver plating respectively.

Electrotyping: It means the production of copies of printing plates of set up types, engravings etc, by the electrolytic deposition of a layer of metal on a previously prepared mould.

Cell: A cell is a single unit device for producing an electric current by converting chemical energy to electrical energy.

Primary cell: It is a device for producing e.m.f. by chemical reaction in an irreversible way which can not be charged again when the cell once discharged.

Characteristics of primary cells:

i)                    The cell once discharged can not be recharged.

ii)                  Easily portable.

iii)                Initial cost is low.

iv)                Overall cost of supplying energy is high.

v)                  Suitable for intermittent work such as bells, alarms, telephone, telegraph etc.

Local action and polarization are the defects of an primary cell.

Local action and remedy: Due to the impurities like iron, lead etc being present within the electrode particularly in commercial zinc, zinc gets consumed, when the zinc rod is placed within the electrolyte even when it is not connected to the external circuit. These impurities form some tiny cells which are short circuited by the main body of the zinc rod. This uncontrolled action of tiny cells, causing wastage of zinc is called local action.

Local action can be removed by amalgamating the zinc rod or by rubbing the mercury over zinc rod.

Polarization: During operation of primary cell the forming of hydrogen gas bubbles on the copper or carbon plate increases the internal resistance of cell causing voltage drop and power loss. The effect produces a back e.m.f.  which reduces the current produced by the cell. This fact is known as polarization.

To minimize this effect depolarizers are used around the positive plate. In Leclanche cell manganese dioxide is used as depolarizer.

Different primary cells: i) Simple or Voltaic cell, ii) Daniel cell, iii) Leclanche cell, iv) Dry cell, v) Standard cell (Weston cadmium cell)

Battery: When two or more secondary cells are grouped in one unit by connecting either in series or in parallel or in both, the combined unit is called as a battery. Usually cells are connected in series to form a battery.

The number of cells in a battery depends on Voltage of the battery.

Grouping of cells: There are three types of grouping arrangements:

i) Series grouping, ii) Parallel grouping and  iii) Series parallel grouping.

Series grouping of cells:  When the negative terminal of one cell is connected with the positive terminal of the next one after another, the grouping is known as series grouping

Characteristics of series grouping of cells:

i)                    Same current flows through all the cells.

ii)                  Total e.m.f. is the sum of the individual e.m.f.  of the cells.

Series grouping of cells is useful where external resistance is very high in comparison to internal resistance.

Parallel grouping of cells: When all the high potential positive terminals of all the cells are connected together to form a common positive terminal and all the low potential negative terminals of all the cells are connected together to form a common negative terminal, the grouping is known as parallel grouping.

Characteristics of parallel grouping of cells:

i)                    The e.m.f.  of the combination is same as that of individual cell.

ii)                  The current through external resistance is the sum of the current delivered by each cell.

For a strong current, parallel grouping of cells is used where external resistance is very low in comparison to internal resistance of a single cell.

Series Parallel grouping of cells: When the cells are divided into several rows in parallel each row containing several cells in series, the grouping is known as series parallel grouping of cells.

Electromotive force (E.M.F.) of a cell: The potential difference between positive and negative terminals of a cell on open circuit is called the e.m.f.  of a cell. It is denoted by ‘E’.

Factors on which E.M.F. of a cell depends:

i)                    The material of the plates and the electrolyte used in the cell.

ii)                  The temperature of the electrolyte.

Internal resistance of a cell: The opposition offered to the flow of current in a cell is called the internal resistance of a cell. It is denoted by ‘r’. The internal resistance is due to the resistance of plates, electrolyte and the terminals of the cell.

Factors on which the internal resistance of a cell depends:

i)                    The size or area of the plates immersed in the liquid.

ii)                  The distance between them.

iii)                The strength of the electrolyte.

Larger area and closer distance of the plates reduce the internal resistance.

Terminal voltage of a cell: The potential difference between positive and negative terminals of a cell when delivering current to the external circuit is called the terminal voltage of a cell.

Capacity of a battery: The capacity of a battery means the amount of electricity which can be obtained fro a cell and is expressed in ampere hours.

Ampere hour: Ampere hour is the quantity of electricity delivered by a current of one ampere flowing for one hour generally used in rating storage batteries.

Ampere hour of a battery is determined by multiplying the value of the constant current taken from the battery by the number of hours it will supply this current before its voltage drops to 1.8 volt per cell.

Factors on which the capacity of a battery depends:

i)                    Rate of discharge

ii)                  Practical limit of final voltage,

iii)                Design and number of plates,

iv)                Specific gravity of electrolyte,

v)                  Operating temperature

vi)                Age of battery.

Efficiency of battery: The efficiency of a battery is the ratio of the output to the input required to restore it to the initial fully charged condition under specified conditions of discharge and charge rates and temperature.

                                               Ampere hour output on discharge

Ampere hour efficiency = ---------------------------------------------          or

                                                 Ampere hour input to charge.

                                          Watt hour output on discharge

Watt hour efficiency = ------------------------------------------

                                            Watt hour input to charge

Uses of Secondary cells: The secondary cells are generally used in central power station for starting the engine in automobiles, train lighting, telegraph, telephone, booster and emergency lighting etc.

Characteristics of secondary cell:

i)                    Action is reversible

ii)                  E.M.F. is fairly constant

iii)                Internal resistance is low

iv)                Efficiency is high

v)                  Good mechanical strength

vi)                Storage capacity is good

vii)              Durability is satisfactory.

Types of Secondary cell: i) Lead acid cell, ii) Alkaline or Nickel iron cell

Materials are used for different parts of a lead acid cell:

a)      Positive plate                          Lead peroxide (pbO2)

b)      Negative plate                                    Spongy lead.

c)      Electrolyte                               Dilute Sulphuric acid (H2SO4)

d)      Separators                               PVC sheet, treated wood, perforated rubber or celluloid.

e)      Bottom block                           Had rubber, PVC grid

f)       Connecting bars and posts      Lead

g)      Cell cover                                Vulcanized rubber, PVC sheet

h)      Sealing compound                  Semi plastic bituminous compound

i)        Connecting straps                   Lead or non corrosive metal casting

j)        Vent plug                                 PVC, Plastic.

Separators: Separators having one side grooved and the other side smooth are used in such a way that the grooved side faces the positive plate so as to make the electrolyte in good contact with the active material of the plate.

Separators are necessary to avoid short circuiting between positive and negative plates.

In a cell separators are necessary, double the number of positive plates or one less than the total number of the positive and negative plates.

Chemical reaction during charging and discharging:

During Charging :                  PbSO₄ + 2H₂O + PbSO₄ à PbO₂ + 2H₂SO₄ + Pb

                                                    (+)                        (-)            (+)                         (-)

During Discharging               PbO₂ + 2H₂SO₄ + Pb à PbSO₄ + 2H₂O + PbSO₄

                                                   (+)                        (-)         (+)                         (-)

When battery is fully charged, the e.m.f. is 2 volts, and when fully discharged the e.m.f is 1.8 volts.

When the  battery is fully charged, the specific gravity is 1.22 to 1.25, and when fully discharged the specific Gravity is 1.18.

Alkaline cell: Secondary cells in which alkali is used as electrolyte instead of acid is called alkaline cell.

Types of Alkaline cell: i) Nickel-iron cell or Edison cell & ii) Nickel-cadmium cell or Jungner cell.

Parts of Alkaline cell:

I)                    Solid steel container

II)                  A set of positive plates containing nickel hydroxide and metallic nickel flakes.

III)                A set of negative plates filled with powdered iron oxide

IV)               Separators

V)                 Electrolyte (dilute KOH)

VI)               Cell cover

VII)             Gas release valve

VIII)           Filler cap.

Chemical reaction:

During Charging:

Ni(OH)₂ + KOH + Fe(OH)₂ à Ni(OH)₄ + KOH + Fe

    (+)                           (-)                (+)                    (-)

During discharging:

Ni(OH)₄ + KOH _ Fe à NI(OH)₂ + KOH + Fe(OH)₂

    (+)                      (-)           (+)                       (-)

When battery is fully charged, the e.m.f. is 1.75 volts, and when fully discharged the e.m.f is 1.15 volts.

When battery is fully charged, the sp gra. is 1.19 to 1.25, and when fully discharged the sp. Gra. is 1.16.

Applications of Alkaline cell; Alkaline cells are used in mine locomotives, miner’s lamp, aircraft, motor boats, automobiles where high current is not required but there is every possibilities of mechanical shock and vibration etc.

Sulphation: It is the formation of a hard white substance on the plates of a storage battery taking place each time by the electrochemical reaction between the electrolyte and the active material of the plates during discharging.

Indications of a fully charged Lead acid battery are:

i)                    The color of positive plate is dark chocolate brown and that of negative plate is grey.

ii)                  Voltage of each cell is about 2.6 volts which remains constant for about 15 minutes.

iii)                Specific gravity of electrolyte becomes 1.24

iv)                Liberation of oxygen causes gassing.

Boost charging: Boost charging means a method of quick charging at a maximum current rate allowed for an hour or during lunch/rest period of vehicle batteries give in addition to the normal charge.

Trickle charging: Trickle charging is a method of any low rate charge in ampere equal to 0.05 to 0.1 percent of the battery capacity i.e. 0.5 to 1 mA per Ah capacity which is sufficient to balance the internal losses of the battery and therefore keeps the battery in a fully charged condition when it is idle.

 Gassing: Gassing means the liberation of oxygen gas from the cell when it is fully charged.

Ordinary water is not used for topping up of a cell because it has so many minerals and salts which have adverse chemical reaction on plates. The impurities present in the water will in time affect the working of the battery and may eventually cause failure.

Only water should be added to restore the level of electrolyte because the loss of water increases the acid concentration.

Precautions should be observed for using a Lead Acid Battery:

i)                    It should not be left in discharged condition for long time

ii)                  Discharge should be stopped when the battery reaches its minimum voltage.

iii)                The plates should always be submerged in the electrolyte

iv)                Loss of water should be compensated by adding distilled water only from time to time. Ordinary tap water should never be used because its impurities area very much detrimental to the working of the battery.

v)                  The battery should be kept in cool and dry place

vi)                The charge and discharge rate should be normal

vii)              The battery should be charged before use until all the cells are gassing

viii)            While charging vent plugs should be kept loose for passing out of evolved gases

ix)                The flame and sparking should be kept away from the battery while charging

x)                  While preparing electrolyte water should not be poured into the acid.