Cell & Cell & BatteriesBatteries

• CELLS AND BATTERIESCELLS AND BATTERIES

• Understand the general features of cells and batteriesUnderstand the general features of cells and batteries

• Describe the relationship between cells and batteries.Describe the relationship between cells and batteries.

• Describe the basic operation of a battery.Describe the basic operation of a battery.

• Compare between primary and secondary cells.Compare between primary and secondary cells.

• List types of cells and batteries.List types of cells and batteries.

• Understand cell connections in series, parallel and series-parallelUnderstand cell connections in series, parallel and series-parallel

• Discuss the effects of different cell connections:Discuss the effects of different cell connections:

• a. Seriesa. Series

• b. Parallelb. Parallel

• c. Series-parallelc. Series-parallel

• Determine the total voltage of series sources with the sameDetermine the total voltage of series sources with the same

• polarities.polarities.

• Determine the total voltage of series sources with oppositeDetermine the total voltage of series sources with opposite

• polarities.polarities.

• Describe the internal resistance of cells connected in seriesDescribe the internal resistance of cells connected in series

• and parallel. Determine the total internal resistance of cells connected inand parallel. Determine the total internal resistance of cells connected in

• series and parallel.series and parallel.

• Identify the relationship between the terminal voltage dropsIdentify the relationship between the terminal voltage drops

• and load current.and load current.

CELLS AND BATTERIESCELLS AND BATTERIES

THE CELLTHE CELL        A cell is a device that transforms chemical A cell is a device that transforms chemical energy into electrical energy. The simplest cell, energy into electrical energy. The simplest cell, known as either a galvanic or voltaic cell, is shown known as either a galvanic or voltaic cell, is shown in figure 2-1. It consists of a piece of carbon (C) and in figure 2-1. It consists of a piece of carbon (C) and a piece of zinc (Zn) suspended in a jar that contains a piece of zinc (Zn) suspended in a jar that contains a solution of water (H20) and sulfuric acid (H2S04) a solution of water (H20) and sulfuric acid (H2S04) called the electrolyte.called the electrolyte.

•Figure 2-1. - Simple voltaic or galvanic cell.Figure 2-1. - Simple voltaic or galvanic cell.

THE CELLTHE CELL

•         The cell is the fundamental unit of The cell is the fundamental unit of the battery. A simple cell consists of the battery. A simple cell consists of two electrodes placed in a container two electrodes placed in a container that holds the electrolyte.that holds the electrolyte.

•         In some cells the container acts as In some cells the container acts as one of the electrodes and, in this case, one of the electrodes and, in this case, is acted upon by the electrolyte. This is acted upon by the electrolyte. This will be covered in more detail later.will be covered in more detail later.

ELECTRODESELECTRODES•         The electrodes are the conductors by The electrodes are the conductors by

which the current leaves or returns to the which the current leaves or returns to the electrolyte. In the simple cell, they are electrolyte. In the simple cell, they are carbon and zinc strips that are placed in carbon and zinc strips that are placed in the electrolyte; while in the dry cell (fig. 2-the electrolyte; while in the dry cell (fig. 2-2), they are the carbon rod in the center 2), they are the carbon rod in the center and zinc container in which the cell is and zinc container in which the cell is assembled. assembled.

ELECTROLYTEELECTROLYTE

•         The electrolyte is the solution that The electrolyte is the solution that acts upon the electrodes. The acts upon the electrodes. The electrolyte, which provides a path for electrolyte, which provides a path for electron flow, may be a salt, an acid, electron flow, may be a salt, an acid, or an alkaline solution. In the simple or an alkaline solution. In the simple galvanic cell, the electrolyte is in a galvanic cell, the electrolyte is in a liquid form. In the dry cell, the liquid form. In the dry cell, the electrolyte is a paste.electrolyte is a paste.

ELECTROCHEMICAL ACTIONELECTROCHEMICAL ACTION•         If a load (a device that consumes If a load (a device that consumes

electrical power) is connected externally electrical power) is connected externally to the electrodes of a cell, electrons will to the electrodes of a cell, electrons will flow under the influence of a difference in flow under the influence of a difference in potential across the electrodes from the potential across the electrodes from the CATHODE (negative electrode), through CATHODE (negative electrode), through the external conductor to the ANODE the external conductor to the ANODE (positive electrode).(positive electrode).

•         A cell is a device in which chemical A cell is a device in which chemical energy is converted to electrical energy. energy is converted to electrical energy. This process is called ELECTROCHEMICAL This process is called ELECTROCHEMICAL action.action.

•       

ELECTROCHEMICAL ACTIONELECTROCHEMICAL ACTION• The voltage across the electrodes depends The voltage across the electrodes depends

upon the materials from which the electrodes upon the materials from which the electrodes are made and the composition of the are made and the composition of the electrolyte. The current that a cell delivers electrolyte. The current that a cell delivers depends upon the resistance of the entire depends upon the resistance of the entire circuit, including that of the cell itself. circuit, including that of the cell itself.

• The internal resistance of the cell depends The internal resistance of the cell depends upon the size of the electrodes, the distance upon the size of the electrodes, the distance between them in the electrolyte, and the between them in the electrolyte, and the resistance of the electrolyte. The larger the resistance of the electrolyte. The larger the electrodes and the closer together they are electrodes and the closer together they are in the electrolyte (without touching), the in the electrolyte (without touching), the lower the internal resistance of the cell and lower the internal resistance of the cell and the more current the cell is capable of the more current the cell is capable of supplying to the load.supplying to the load.

Types of cellsTypes of cells

Cells are classified as either Cells are classified as either primaryprimary or or secondarysecondary..

In a In a primary cellprimary cell, chemical reactions , chemical reactions use up some of the materials in the use up some of the materials in the cell as electrons flow from it. They cell as electrons flow from it. They can’t be recharged.can’t be recharged.

When these materials have been used When these materials have been used up, the cell is said to be discharged up, the cell is said to be discharged and cannot be recharged.*and cannot be recharged.*

Primary cellsPrimary cells

• Primary cells can be further classified Primary cells can be further classified as either as either wetwet or or drydry..

• The The primary wet cellprimary wet cell was first was first developed in 1800 by Italian developed in 1800 by Italian scientist, scientist, Alessandro VoltaAlessandro Volta..

• This cell is This cell is thereforetherefore called the called the voltaic cellvoltaic cell..

Dry cell batteryDry cell battery

Secondary CellsSecondary Cells

Unlike primary cells, a Unlike primary cells, a secondary secondary cellcell can be discharged and can be discharged and recharged many hundreds of times.recharged many hundreds of times.

Secondary cells are often referred to Secondary cells are often referred to rechargeablerechargeable batteries. batteries.

• A car battery consists of a group of A car battery consists of a group of secondary cells.secondary cells.

BATTERIESBATTERIES

•         A battery is a voltage source that uses A battery is a voltage source that uses chemical action to produce a voltage. In chemical action to produce a voltage. In many cases the term battery is applied to many cases the term battery is applied to a single cell, such as the flashlight battery. a single cell, such as the flashlight battery. In the case of a flashlight that uses a In the case of a flashlight that uses a battery of 1.5 volts, the battery is a single battery of 1.5 volts, the battery is a single cell. cell.

• The flashlight that is operated by 6 volts The flashlight that is operated by 6 volts uses four cells in a single case and this is a uses four cells in a single case and this is a battery composed of more than one cell. battery composed of more than one cell. There are three ways to combine cells to There are three ways to combine cells to form a battery. form a battery.

TYPES OF CONNECTION TYPES OF CONNECTION CELLSCELLS• Series cellsSeries cells

• Parallel cellsParallel cells

• Series-Parallel cellsSeries-Parallel cells

• Cells connected in SERIES provide a higher Cells connected in SERIES provide a higher voltage. voltage.

• while cells connected in PARALLEL provide a while cells connected in PARALLEL provide a higher current capacity. higher current capacity.

• To provide adequate power when both voltage To provide adequate power when both voltage and current requirements are greater than the and current requirements are greater than the capacity of one cell, a combination SERIES-capacity of one cell, a combination SERIES-PARALLEL network of cells must be used. PARALLEL network of cells must be used.

Series-Connected CellsSeries-Connected Cells

•         Assume that a load requires a power supply of Assume that a load requires a power supply of 6 volts and a current capacity of 1/8 ampere. 6 volts and a current capacity of 1/8 ampere. Since a single cell normally supplies a voltage of Since a single cell normally supplies a voltage of only 1.5 volts, more than one cell is needed. To only 1.5 volts, more than one cell is needed. To obtain the higher voltage, the cells are connected obtain the higher voltage, the cells are connected in series as shown in figure 2-6.in series as shown in figure 2-6.

Series connected cellsSeries connected cells

Series-Connected CellsSeries-Connected Cells

• Formula ;Formula ;

Total of Internal resistance = n x r (Total of Internal resistance = n x r ())

Where n = total of cells in the circuitWhere n = total of cells in the circuit

Load Resistance = RLLoad Resistance = RL

Total of resistance = (RL + nr)Total of resistance = (RL + nr)

Total of e.m.f = n x E (volt)Total of e.m.f = n x E (volt)

Current, I = Current, I = n E n E (Ampere) (Ampere)

(RL + nr)(RL + nr)

Parallel-Connected CellsParallel-Connected Cells

Parallel-Connected CellsParallel-Connected Cells

• Formula ;Formula ;

Total of Internal resistance = r / n (Total of Internal resistance = r / n ())

Where n = total of cells in the circuitWhere n = total of cells in the circuit

Load Resistance = RLLoad Resistance = RL

Total of resistance = (RL + r/n) (Total of resistance = (RL + r/n) ())

Total of e.m.f = E (volt)Total of e.m.f = E (volt)

Current, I = Current, I = E E (Ampere) (Ampere)

(RL + r/n)(RL + r/n)

Series-Parallel Connected Series-Parallel Connected CellsCells

• Formula ;Formula ;

Total of Internal resistance (in series) = nr (Total of Internal resistance (in series) = nr ())

Total of Internal resistance = nr / m (Total of Internal resistance = nr / m ())

Where m = total of internal resistance in Where m = total of internal resistance in

parallelparallel

Load Resistance = RLLoad Resistance = RL

Total of resistance = (RL + nr / m) (Total of resistance = (RL + nr / m) ())

Total of e.m.f = nE (volt)Total of e.m.f = nE (volt)

Current, I = Current, I = nE nE (Ampere) (Ampere)

(RL + nr/m)(RL + nr/m)

Series-Parallel Connected Series-Parallel Connected CellsCells

Example for series cells Example for series cells connectionconnection

Example for Parallel cells Example for Parallel cells connectionconnection

Example for Series-Parallel Example for Series-Parallel cells connectioncells connection