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Cells and Batteries
An electrical battery is one or
more electrochemical cells that
convert stored chemical energy
into electrical energy
Cells are portable source of
electrical power.
Cells and Batteries
Since the invention of the first battery in
1800 by Alessandro Volta, batteries have
become a common power source for
many household and industrial
applications.
According to a 2005 estimate, the
worldwide battery industry generates
US$48 billion in sales each year, with 6%
annual growth.
Cells and Batteries
Cells are portable source of
electrical power.
There are two types of
batteries:
Primary batteries (disposable
batteries), which are designed
to be used once and discarded
Secondary batteries
(rechargeable batteries), which
are designed to be recharged
and used multiple times.
Batteries have different shapes
and different voltages they
supply: a 1.5-volt AAA battery
is a single 1.5-volt cell, and a
9-volt battery has six 1.5-volt
cells in series.
Cells and Batteries
Battery consists of a number
of voltaic cells;
Each voltaic cell consists of
two half cells connected in
series by a conductive
electrolyte containing anions
and cations.
Cells and Batteries
One half-cell includes electrolyte
and the electrode to which anions
(negatively charged ions) migrate,
i.e., the anode or negative
electrode;
The other half-cell includes
electrolyte and the electrode to
which cations (positively charged
ions) migrate, i.e., the cathode or
positive electrode.
The electrodes do not touch each
other but are electrically connected
by the electrolyte.
The voltage developed across a cell's
terminals depends on the energy
release of the chemical reactions of its
electrodes and electrolyte.
Cells and Batteries
Primary batteries irreversibly
transform chemical energy to
electrical energy.
Primary batteries can produce current
immediately on assembly. Disposable
batteries are intended to be used
once and discarded.
These are most commonly used in
portable devices that have low
current drain or
well away from an alternative power
source, such as in alarm and
communication circuits.
Cells and Batteries
Disposable primary cells cannot be
reliably recharged, since the chemical
reactions are not easily reversible.
Common types of disposable batteries
include zinc-carbon batteries and
alkaline batteries.
Cells and Batteries
Secondary batteries can be
recharged; that is, they can have
their chemical reactions reversed
by supplying electrical energy to
the cell, restoring their original
composition.
A lead acid accumulator is a
secondary cell – it stores
electrical energy generated in
another source (charger).
As it discharges, Pb (lead) ions
dissolve into the acid and
electrons are left behind. Charging
reverses the process.
Cells and Batteries
Secondary batteries must be
charged before use; they are
usually assembled with active
materials in the discharged state.
Rechargeable batteries or
secondary cells can be recharged
by applying electrical current,
which reverses the chemical
reactions that occur during its
use.
Devices to supply the
appropriate current are called
chargers or rechargers.
Compare current directions
Cells and Batteries
Cells are portable source of
electrical power.
A dry cell is a primary cell –
the electricity is generated
by a chemical reaction and it
is not rechargeable.
A lead acid accumulator is a
secondary cell – it stores
electrical energy generated
in another source. As it
discharges, Pb (lead) ions
dissolve into the acid and
electrons are left behind.
Charging reverses the
process.
Cells and Batteries
Cells are portable source of
electrical power.
A dry cell is a primary cell –
the electricity is generated
by a chemical reaction and it
is not rechargeable.
A lead acid accumulator is a
secondary cell – it stores
electrical energy generated
in another source. As it
discharges, Pb ions dissolve
into the acid and electrons
are left behind. Charging
reverses the process.
A battery comprises several
cells.
Electromotive Force
A cell provides the energy to create
a potential difference to make a
current flow round a circuit.
It can do this because the chemical
action within it creates an
electromotive force (e.m.f.)
using its chemical energy
Cell
alkaline
mercury
NickelCadmium
LeadAcid
e.m.f.
1.5 V
1.35 V
1.2 V
Type
prim.
prim.
sec.
2.0 V
sec.
Electromotive Force
Using an analogy of a water flux and electrical current, a water
pump pushing water through the system mimics a battery which
pushes current through an electrical circuit.
Water energy from the water pump mimics e.m.f., while obstacles
slowing the water down mimic resistance.
Electromotive Force
E.m.f. is the energy created
per unit charge in the cell,
i.e. the units are J/C or Volt.
By contrast, a potential
difference is the electrical
energy delivered per unit
charge.
E.m.f. is
energy created
during this
pumping
1C
e.m.f. is the
energy created
per unit charge
Its unit is the Volt
(V).
Electromotive Force
A cell provides the energy to
create a potential difference
to make a current flow round
a circuit.
It can do this because the
chemical action within it
creates an electromotive
force (e.m.f.).
E.m.f. is the energy created
per unit charge in the cell,
i.e. the units are J/C or Volt.
By contrast, a potential
difference is the electrical
energy delivered per unit
charge.
Cell
alkaline
mercury
NickelCadmium
LeadAcid
e.m.f.
1.5 V
1.35 V
1.2 V
Type
prim.
prim.
sec.
2.0 V
sec.
e.m.f. is the
energy created
per unit charge
Its unit is the Volt
(V).
Internal Resistance
I
A cell or any power supply has an
internal resistance that limits
the current that it can deliver.
Any real voltage source has an
internal resistance, so whenever it
is connected to a real load there is
a potential divider effect.
Since two resistances are in
series, the total resistance of the
load and internal resistance is
Rtotal=R+Ri
Total current I= E/Rtotal=E/(R+Ri)
Voltage on the load Vout=IR
=ER/(R+Ri)<E
Internal Resistance
Voltage generated by a battery is always lower than
e.m.f due to a “lost” voltage on internal resistance
Vout=IR =ER/(R+Ri)<E
+IRi=Vout+IRi
Therefore, the potential
difference appearing on the
output of a cell will be
reduced by the effect of the
internal resistance.
Vout=E-IRi
The term IRi behaves like a
“lost” voltage.
Vout=E-IRi
Using Ohm’s law we can also
write E=IRtotal =I(R+Ri) = IR
Vlost=IRi
Internal Resistance
Internal
resistance limits
the current.
Its Unit is the
Ohm (W).
Internal Resistance
A cell or any power supply has
an internal resistance that
limits the current that it can
deliver.
The potential difference
appearing on the output of a
cell will be reduced by the effect
of the internal resistance.
Vout=E-IRi
The term IRi behaves like a
“lost” voltage.
Internal
resistance limits
the current.
Its Unit is the
Ohm (W).
Cell Characteristics
The internal resistance of a cell
is the thing that determines the
uses to which it may be put.
Vout=E-IRi
 Voltage generated by
current linearly decreases
with current and drops to
zero at I=E/Ri.
 Maximum current E/Ri
occurs for short-cut circuit.
E
E/Ri
Power supplies
must be matched
to the application
using both e.m.f
and Ri
Cell Characteristics
A power supply or battery
must be matched to the
application in both e.m.f.
and internal resistance
(usually actually specified by
operating current).
If your circuit requires high
current, a battery with high
internal resistance is not
appropriate.
Power supplies
must be matched
to the application
using both e.m.f
and Ri
Cell Characteristics
When a cell “discharges”,
the parameter that changes
is the internal resistance, not
the e.m.f. The internal
resistance increases with
time.
Internal
resistance
Cell Characteristics
The internal resistance of a
cell is the thing that
determines the uses to
which it may be put.
A power supply or battery
must be matched to the
application in both e.m.f.
and internal resistance
(usually actually specified by
operating current).
When a cell “discharges”,
the parameter that changes
is the internal resistance, not
the e.m.f. The internal
resistance increases with
time.
Power supplies
must be matched
to the application
using both e.m.f
and Ri