Download battery - GTU e

Swaminarayan college of
engineering and technology
• Topic: BATTERY
• Prepared by: Anjali Sharma Guide By: Jigna Parmar
Shivani Gupta
BATTERY :
A series, parallel or series-parallel group of cells
is called a Battery.
For a circuit,
 if higher voltage is required - a battery containing
number of cells connected in series.
 if larger current is required- number of cells connected
in parallel
 if larger current and higher voltage is required- a battery
containing number of cells connected in series
parallel(mixed) combination is used.
The following storage batteries are in common use:
 Lead-Acid battery
 Nickel –Iron battery
 Nickel – Cadmium battery
Lead Acid Battery :
• Following are the important materials used in a lead
acid battery :
1. Positive Plate or Anode : It is made up of lead
peroxide(PbO2) plate of chocolate, dark brown
colour.They are of two types :
(i) Plante Plates
(ii) Faure of Pasted Plates.
2. Negative Plates or Cathorde : It is made up of pure
lead(Pb).
3. Electolyate: aqueous solution of sulhuric acid (H2SO4) is
used as electrolyt .
4. Container : containing plates and electrolyte is placed in
a container. Made of hard rubber and bitumen
compound,glass,moulded plastic,ceramic etc.
5. Separators : The separators are used to prevent them
from coming in contact with each other
Continue to Lead Acid Battery…
6.Bottom blocks : Bottom blocks are used to provide a
sufficient clear space for plates internal short circuit.
7. Plate Connectors : To connect the positive plates
together, separate connectors are used. similarly
negative plates are connected together. They are made
of lead and alloy.
8. Vent Plug : made up of rubber and screwed to the
cover of the cell provided for free exit of gas formed
inside the battery and prevent the escape of electrolyte.
9. Partition Wall : for separation two cells.
10.Cell connectors : To connect cells in series together.
They are lead alloy bars.
Working of a Lead Acid Battery :
A Lead – Acid battery is a device for storing
electrical energy in the form of chemical
energy.The active elements in a lead – acid
battery are
(i) Lead- peroxide(PbO2) as positive plate
(ii) Spongy lead (Pb) as negative plate.
Both the plates are suspended in an electrolyte of
sulphuric acid (H2SO4) of specific gravity 1.28. The
function of lead acid battery may be divided in two
parts.
 Discharging
 Charging
Discharging :
• When the external resistance is connected across the
anode and cathode of a fully charged battery,the
current flows through the resistance,the direction of
current is from cathode to anode through the
electrolyte.Thus the external resistance absorbs
electrical energy. This is called discharging.
• The sulphure acid when dissolved, its molecules are
dissociated into hydrogen ions (2H+) and sulphate ions
(SO4--) which move freely in the electrolyte.
• Sulphate ions move towards cathode and hydrogen oins
towards the anode.
H2SO4 --> 2H+ + SO4-• Each sulphate ion (SO4--) moves towards the cathode
and becomes radical SO4.
Discharging Of A Battery:
 At cathode,
SO4-- - 2e --> SO4 (radical)
• Sulphate radical attacks the metallic lead cathode and
form lead sulphate
Pb + SO4 -> PbSO4
 At anode,
• Each hydrogen ion (H+) liberated from sulphuric acid
now moves to the anode and become hydrogen atom.
2H+ + 2e -> 2H
• Since it is directly in contact with anode (PbO2), so it
attacts and forms lead sulphate (PbSO4),
PbO2 + 2H -> PbO + H2O
PbO + H2SO4 -> PbSO4 + H2O
PbO2 + H2SO4 + 2H -> PbSO4 + 2H2O
• Thus during discharging :
 The electrodes are converted into lead
sulphate(PbSO4)
 Voltage of the battery fall from 2V to 1.8V.
 Density of electrolyte decreases from 1.28 to
1.15.
 Chemical energy stored is converted into
electrical energy.
Charging :
• During charging process,
excess electrons are supplied
to the cathode. This creates a
shortage of electrons at the
anode.
• For charging, anode is
connected to the positive
terminal of the d.c. source
and cathode is connected to
the negative terminal of the
sourceas shown in Fig.-->
• During charging, molecules
of sulphuric acid (H2SO4) in
solution again break up into
hydrogen ions (2H+) and
sulphate ions (SO4--).
 At anode,
SO4-- ions move to the anode and give up its
additional 2 electrons and become radical SO4 with the
anode electrode PbSO4 and form lead peroxide (PbO2)
and sulphuric acid (H2SO4).
SO4-- - 2e -> SO4
PbSO4+ SO4 + 2H2O -> PbO2 + 2H2SO4
 At cathode,
Electrons liberated at anode through external
circuit. Each hydrogen ion (H+) on reaching the cathode,
takes one electron from cathode and become hydrogen
atom
2H+ + 2e --> 2H
This atom react with lead sulphate cathode forming
lead and sulphuric acid according to ,
PbSO4 + 2H -> H2SO4 + Pb
• Thus during charging:
 Lead sulphate anode gets converted into Lead
Peroxide.
 Lead Sulphate cathode gets converted into
lead.
 Voltage of the battery increases.
 Density of Sulphuric Acid increases.
 Electrical energy is stored in form of the
chemical energy.
Various Condition during charging & discharging
Capacity Of A Battery :
 It is defined as the product of discharge current and time in
hours.It is measured in Ampere hours(Ah).Mathematically,
the product of discharge current in amperes and the time for
discharge in hours till the voltage falls to a specified value is
called capacity of a battery.
Battery Capacity = ID X TD Ah
Where, ID = Current in ampere
TD = Time in hours
 Sometimes the capacity of the battery is specified in watthour(Wh).
Watt-hour capacity is defined as the product
of the average voltage during discharge and ampere-hour
capacity of a battery.

Watt-hour capacity of a battery,
= Ah capacity x average voltage during discharge
= ID TD x VD Wh
• Where, ID = Discharge current
TD = Time of discharge
VD = Average voltage during discharge
 Capacity of the battery depends on the following :
 Rate of discharge
 Density of Electrolyte
 Rise in temperature
 Size of the plates
Efficiency of a Battery :
Efficiency of a battery is the ratio of output during discharging
to the input to the battery during charging.
 The efficiency of a battery can be defined in following two ways :
1) Ampere-hour (Ah) efficiency :
It is defined as the ratio of output in ampere-hours during
discharging to the input in ampere-hours during charging of the
battery is called ampere-hour efficiency of the battery. It is also called
as quantity efficiency of the battery.
• Mathematically,
Ampere-hour efficiency,
η Ah = Ampere-hours of discharge x 100 / Ampere-hours of charge
= Id Td x 100 / Ic Tc
Where,
Id = Current during discharge (A)
Td = time of discharge (hours)
Ic = current during charging ( A)
Tc = time of charging (hours)
2) Watt-hour (Wh) efficiency :
It is defined as the ratio of energy delivered in watt-hours
during discharge and energy drawn in watt-hours during charging .It
is also known as energy efficiency.
• Mathematically,
• Energy or watt-hour efficiency,
η Wh = Output in Watt-hours x 100 / Input in watt-hours
= current delivered x time of discharge x avg. potential
diff. during discharge / current drawn x time of
charge x avg. p.d.during charging
= Id Td Vd x 100 / Ic Tc Vc
= (Id Td / Ic Tc ) x ( Vd / Vc) x 100
= η Ah x ( Vd / Vc) x 100
• Where,
Vd = average terminal voltage during discharge
Vc = average terminal voltage during charging
 It varies from 72 to 80 %.