Cells and BatteriesCells and BatteriesAn electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energyCells are portable source of electrical power.

Cells and BatteriesCells and BatteriesSince 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 BatteriesCells and BatteriesCells are portable source of electrical power.There are two types of batteries: Primary batteries (disposable batteries), which are designed to be used once and discardedSecondary 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 BatteriesCells 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 BatteriesCells and BatteriesOne 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 BatteriesCells and BatteriesPrimary 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 inportable devices that have low current drain or well away from an alternative power source, such as in alarm and communication circuits.

Cells and BatteriesCells and BatteriesDisposable 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 BatteriesCells 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 BatteriesCells and BatteriesSecondary 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.

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Cells and BatteriesCells 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 BatteriesCells and BatteriesCells 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 ForceElectromotive 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 e.m.f. Type alkaline 1.5 V prim. mercury 1.35 V prim. Nickel-Cadmium

1.2 V sec.

Lead-Acid

2.0 V sec.

Electromotive ForceElectromotive ForceUsing 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 ForceElectromotive ForceE.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 the energy created per unit chargeIts unit is the Volt (V).

e.m.f. is the energy created per unit chargeIts unit is the Volt (V).

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Pum

pin

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charg

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up

E.m.f. is energy created during this pumping

Electromotive ForceElectromotive ForceA 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.

e.m.f. is the energy created per unit chargeIts unit is the Volt (V).

e.m.f. is the energy created per unit chargeIts unit is the Volt (V).

Cell e.m.f. Type alkaline 1.5 V prim. mercury 1.35 V prim. Nickel-Cadmium

1.2 V sec.

Lead-Acid

2.0 V sec.

Internal ResistanceInternal Resistance

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

I

Internal ResistanceInternal ResistanceVoltage 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

Internal ResistanceInternal Resistance

Using Ohm’s law we can also write E=IRtotal =I(R+Ri) = IR +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.

Internal resistance limits the current.Its Unit is the Ohm ().

Internal resistance limits the current.Its Unit is the Ohm ().

Vlost=IR

i

Vout=E-IR

i

Internal ResistanceInternal ResistanceA 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 ().

Internal resistance limits the current.Its Unit is the Ohm ().

Cell CharacteristicsCell CharacteristicsThe 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.

Power supplies must be matched to the application using both e.m.f and Ri

Power supplies must be matched to the application using both e.m.f and Ri

E

E/Ri

Cell CharacteristicsCell 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

Power supplies must be matched to the application using both e.m.f and Ri

Cell CharacteristicsCell 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 CharacteristicsCell CharacteristicsThe 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

Power supplies must be matched to the application using both e.m.f and Ri