14 Review of Literature Operation and Maintenance of the 125 VDC Station Battery and Charger System at BCFTPP-I A. HISTORY OF BATTERIES Although Alessandro Volta in Italy is usually credited with being the inventor of the modern battery (Silver-Zinc), ancient cells have been discovered in Sumerian ruins, origin around 250 BC. The first evidence of batteries comes from archaeological digs in Baghdad, Iraq. This first "battery" was dated to around 250 B.C. and was used in simple operations to electroplate objects with a thin layer of metal, much like the process used now to plate inexpensive gold and silver jewelry, one of the first uses for batteries. Batteries were rediscovered much later by a man named Alessandro Volta after which the unit of electrical potential was named, the volt. The jar was found in Khujut Rabu just outside Baghdad and is composed of a clay jar with a stopper made of asphalt. Sticking through the asphalt is an iron rod surrounded by a copper cylinder. When filled with vinegar - or any other electrolytic solution- the jar produces about 1.1 volts. Figure 5. Alessandro Volta In 1859, Gaston Planté invented the lead acid batteries and first demonstrated it to the French Academy of Sciences in 1860. The Lead Acid is the oldest rechargeable battery.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
14
Review of Literature
Operation and Maintenance of the 125 VDC Station Battery and Charger System at BCFTPP-I
A. HISTORY OF BATTERIES
Although Alessandro Volta in Italy is usually credited with being the inventor of
the modern battery (Silver-Zinc), ancient cells have been discovered in Sumerian ruins,
origin around 250 BC. The first evidence of batteries comes from archaeological digs in
Baghdad, Iraq. This first "battery" was dated to around 250 B.C. and was used in simple
operations to electroplate objects with a thin layer of metal, much like the process used
now to plate inexpensive gold and silver jewelry, one of the first uses for batteries.
Batteries were rediscovered much later by a man named Alessandro Volta after which the
unit of electrical potential was named, the volt. The jar was found in Khujut Rabu just
outside Baghdad and is composed of a clay jar with a stopper made of asphalt. Sticking
through the asphalt is an iron rod surrounded by a copper cylinder. When filled with
vinegar - or any other electrolytic solution- the jar produces about 1.1 volts.
Figure 5. Alessandro Volta
In 1859, Gaston Planté invented the lead acid batteries and first demonstrated it to
the French Academy of Sciences in 1860. The Lead Acid is the oldest rechargeable
battery.
15
Review of Literature
Operation and Maintenance of the 125 VDC Station Battery and Charger System at BCFTPP-I
Figure 6. Earliest form of battery
B. BATTERY CONSTRUCTION
The lead-acid battery is one of the most common batteries in use today. Figure 7
shows the makeup of a lead-acid battery. The container houses the separate cells. Most
containers are hard rubber, plastic, or some other material that is resistant to the
electrolyte and mechanical shock and will withstand extreme temperatures. The container
(battery case) is vented through vent plugs to allow the gases that form within the cells to
escape. The plates in the battery are the cathodes and anodes. In figure 8, the negative
plate group is the cathode of the individual cells and the positive plate group is the anode.
As shown in the figure, the plates are interlaced with a terminal attached to each plate
group. The terminals of the individual cells are connected together by link connectors as
shown in figure 7. The cells are connected in series in the battery and the positive
16
Review of Literature
Operation and Maintenance of the 125 VDC Station Battery and Charger System at BCFTPP-I
terminal of one end cell becomes the positive terminal of the battery. The negative
terminal of the opposite end cell becomes the negative terminal of the battery.
Figure 7. Lead-acid battery construction
Figure 8. Lead-acid battery plate arrangement
The terminals of a lead-acid battery are usually identified from one another by
their size and markings. The positive terminal marked (+) is sometimes colored red and is
physically larger than the negative terminal, marked (-).
17
Review of Literature
Operation and Maintenance of the 125 VDC Station Battery and Charger System at BCFTPP-I
C. COMPOSITION AND OPERATION
A battery provides electrical power by converting its stored chemical energy into
electrical energy. This energy conversion is achieved by a chemical reaction in the
battery that releases electrons. The process is reversible in a stationary battery. If a load is
placed across the battery terminals, the chemical reaction produces electrical power. If
electrical energy is directed into the battery (charging the battery), the chemical reaction
reverses and restores the battery to a fully charged condition.
The lead acid battery, in the charged state, is made up of electrodes of lead metal
(Pb) and lead dioxide (PbO2) in an electrolyte of 35% sulphuric acid and 65% water
solution. The electrolyte causes a chemical reaction that produces electrons.
C.1 ELECTROLYTE
The electrolyte in a lead-acid battery is a mixture of sulfuric acid and water.
Sulfuric acid, H2SO4, is a very active compound of hydrogen, sulfur, and oxygen. When
added to water, the sulfuric acid does not stay intact as individual H2SO4, molecules.
Instead, the sulfuric acid molecules split into two ions, hydrogen and sulfate. Each
hydrogen ion carries one positive electrical charge and each sulfate ion carries two
negative electrical charges.
Sulfuric acid is highly reactive and ionizes almost completely in water. The ions
are in constant motion, attracted or repelled by one another. This constant random motion
tends to cause the ions to diffuse throughout the electrolyte. This diffusion process is not
immediate and can take a relatively long time to reach equilibrium throughout the
electrolyte.
18
Review of Literature
Operation and Maintenance of the 125 VDC Station Battery and Charger System at BCFTPP-I
Specific gravity is a measure of the density of a liquid. Pure water has a specific
gravity of 1.0. The specific gravity of other liquids is usually expressed in relation to that
of water. The lead-acid cell electrolyte specific gravity typically varies from 1.210 to
1.300, depending on the particular cell design.
The specific gravity range of 1.210 to 1.240 is usually adequate for vented cells.
The capacity of a vented cell is often limited by the quantity of active material in the
positive or negative plates. A higher specific gravity electrolyte would generally be used
only if the quantity of sulfuric acid in the electrolyte is potentially limiting.
C.2 ELECTROCHEMICAL PROCESS
The generation of electrical current from a cell originates from a difference in
electrochemical potential between two compounds inside the cell that are not in direct
contact, but are electrically connected by a conducting medium. The two compounds are
installed in the cell as positive and negative plates, and the conducting medium between
the two plates is referred to as the electrolyte.
As the plate materials chemically react with the electrolyte, a potential difference
is created between the plates and the electrolyte. The positive plates have a positive
potential in relation to the electrolyte; the negative plates have a negative potential in
relation to the electrolyte. The electrochemical process between the plates and electrolyte
creates a voltage between the positive and negative plates of the cell. This voltage
between the plates constitutes an electromotive force that causes electrons to flow from
the negative plates to the positive plates if the plates are connected together by an
external conductor (a load). The flow of electrons disrupts the electrochemical
equilibrium between the plates and the electrolyte, which initiates further chemical
19
Review of Literature
Operation and Maintenance of the 125 VDC Station Battery and Charger System at BCFTPP-I
reaction as the cell attempts to maintain electrochemical equilibrium. The battery’s
chemical reaction continues to generate electrical current until the materials involved in
the reaction are depleted or the external connection (the load) is removed.
In a lead-acid battery, the positive plate material is lead dioxide (PbO2) and the
negative plate material is lead (Pb). The plate material is often referred to as the active
material. The electrolyte is a sulfuric acid solution (H2SO4). The chemical reaction in a
lead-acid cell can be described in terms of the reaction occurring at each plate:
The above half-cell reactions offer greater insight into the actual processes
occurring at each plate and within the electrolyte. From left to right, these equations
represent the discharge process, and from right to left, the charging process. The sum of
the plus and minus charges on the left side of each equation equals the total charge on the
right side.
C.2.1 NEGATIVE PLATE REACTION
The negative plate reaction during discharge is depicted in Figure 9. When lead
from the negative plate comes into contact with the electrolyte, the chemical interaction
between the two compounds casts lead ions into solution; the ions carry a charge of plus
20
Review of Literature
Operation and Maintenance of the 125 VDC Station Battery and Charger System at BCFTPP-I
2 (Pb+2
). Each positively charged lead ion entering solution leaves behind two negative
charges (electrons). Hence, the chemical reaction gives the negative plate an excess of
electrons and a net negative charge relative to the electrolyte.
Once in solution, the lead ions combine with sulfate ions (SO4-2
), which have
charges of equal magnitude but opposite sign, to form lead sulfate, which has a neutral
charge. The sulfate ions are created when the dilute sulfuric acid disassociates into