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Batteries - Lead - Edison's ( Electrical Engineering )

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Topic includes 


-Lead acid battery
-Construction
-History 
-Discharging
-Charging
-About 
-Application
-Explosion
- Edison nickel iron battery
- Edison nickel cadmium battery
- Advantage and disadvantage

Lead acid battery 

The lead–acid battery was invented in 1859 by French physicist Gaston Planté and is the earliest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by starter motors.

Constructing parts


Positive plate 

Lead peroxide deposited on a grid frame of antimony lead alloy.

Negative plate 

Porous spongy lead deposited on a grid frame
When the battery is in charge co codition the negative iplate is grey in colour.

Electrolyte

Dilute sulphuric acid

Seperator

The function of separator is to keep the positive and negative plates electrically apart.

Container

The container is made of hard glass or hard rubber..

Chemistry 


Negative plate 

It loses two electrons and becomes Pb positive ions. These positive ions do not dissolve into the liquid but remain on the plate and attract SO4 negative ions..

Positive plate

In it each lead particle is lacking four electrons which were given to the oxygen when the plate was formed and each ion takes two electons from external circuit.

In the charged state, the chemical energy of the battery is stored in the potential difference between the pure lead at the negative side and the PbO2 on the positive side, plus the aqueous sulphuric acid. The electrical energy produced by a discharging lead–acid battery can be attributed to the energy released when the strong chemical bonds of water molecules are formed from H+ ions of the acid and O2− ions of PbO2. Conversely, during charging the battery acts as a water–splitting device.

History


The French scientist Nicolas Gautherot observed in 1801 that wires that had been used for electrolysis experiments would themselves provide a small amount of "secondary" current after the main battery had been disconnected.

Discharging


In the discharged state both the positive and negative plates become lead(II) sulfate (PbSO
4), and the electrolyte loses much of its dissolved sulfuric acid and becomes primarily water. The discharge process is driven by the pronounced reduction in energy when 2 H+(aq) (hydrated protons) of the acid react with O2− ions of PbO2 to form the strong O-H bonds in H2O (ca. −880 kJ per 18 g of water).This highly exergonic process also compensates for the energetically unfavorable formation of Pb2+(aq) ions or lead sulfate .

The release of two conducting electrons gives the lead electrode a negative charge.

As electrons accumulate they create an electric field which attracts hydrogen ions and repels sulfate ions, leading to a double-layer near the surface. The hydrogen ions screen the charged electrode from the solution which limits further reaction unless charge is allowed to flow out of electrode.

Charging


In the fully charged state, the negative plate consists of lead, and the positive plate is lead dioxide. The electrolyte solution has a higher concentration of aqueous sulfuric acid, which stores most of the chemical energy.

Overcharging with high charging voltages generates oxygen and hydrogen gas by electrolysis of water, which bubbles out and is lost. The design of some types of lead-acid battery allows the electrolyte level to be inspected and topped up with pure water to replace any that has been lost this way.

About


The lead–acid cell can be demonstrated using sheet lead plates for the two electrodes. However, such a construction produces only around one ampere for roughly postcard-sized plates, and for only a few minutes.

Gaston Planté found a way to provide a much larger effective surface area. In Planté's design, the positive and negative plates were formed of two spirals of lead foil, separated with a sheet of cloth and coiled up. The cells initially had low capacity, so a slow process of "forming" was required to corrode the lead foils, creating lead dioxide on the plates and roughening them to increase surface area. Initially this process used electricity from primary batteries; when generators became available after 1870, the cost of production of batteries greatly declined.[8] Planté plates are still used in some stationary applications, where the plates are mechanically grooved to increase their surface area.

Applications..


Most of the world's lead-acid batteries are automobile starting, lighting and ignition (SLI) batteries, with an estimated 320 million units shipped in 1999.[8] In 1992 about 3 million tons of lead were used in the manufacture of batteries.

Wet cell stand-by (stationary) batteries designed for deep discharge are commonly used in large backup power supplies for telephone and computer centres, grid energy storage, and off-grid household electric power systems.Lead–acid batteries are used in emergency lighting and to power sump pumps in case of power failure.

Explosion


Excessive charging causes electrolysis, emitting hydrogen and oxygen. This process is known as "gassing". Wet cells have open vents to release any gas produced, and VRLA batteries rely on valves fitted to each cell. Catalytic caps are available for flooded cells to recombine hydrogen and oxygen. A VRLA cell normally recombines any hydrogen and oxygen produced inside the cell, but malfunction or overheating may cause gas to build up. If this happens (for example, on overcharging) the valve vents the gas and normalizes the pressure, producing a characteristic acid smell. However, valves can fail, such as if dirt and debris accumulate, allowing pressure to build up.



Edison and nickel storage batteries

These are true long life batteries..

Edison nickel iron battery 

The Edison battery is structurally stronger and lighter in weight than lead cells of the same current rating. The negative plates  consist of a nickel steel grid containing powered  iron with some FeO and Fe(OH)2. The iron is the source of the electrons which are attracted through the external circuit toward nickel ions Ni positive.
The positive plates are nickel plated tubes containing a mixture of nickel oxides and hydroxides with flakes of pure nickel for increased conductivity. 

Advantages and disadvantages

The battery can withstand overcharge, overdischarge and short-circuiting and yet last 20 years or more. The disadvantages however outweigh the advantages. ... Nickel-Iron batteries have lower energy density and lower specific power compared to lead-acid batteries (or in layman's terms are less efficient).

Nickel cadmium battery


This battery followed a line of development that produces a battery not intended for frequent cycling but rather a more general purpose battery that enabled the user to draw as many amperes as possible from a battery of given ampere hour rating, without excessive falling off voltage. The starting of gasoline and diesel engines and the operation of signals, relays and controls are jobs for which the nickel cadmium battery is suited .

Advantage and disadvantage

NiCad batteries are used when long life, high discharge rate, and low price are important hardware features.
...
Disadvantages of today's NiCad batteries
Mature technology with little tolerance for overcharging.
Cadmium is environmentally troublesome.
Noticeable charging memory effect.



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