Construction And Working Of Lead Acid Battery PdfBy Damia C. In and pdf 23.05.2021 at 06:51 8 min read
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All lead acid batteries consist of flat lead plates immersed in a pool of electrolyte. Regular water addition is required for most types of lead acid batteries although low-maintenance types come with excess electrolyte calculated to compensate for water loss during a normal lifetime.
Lead Acid Battery: Construction, Working, Charging
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. As they are inexpensive compared to newer technologies, lead—acid batteries are widely used even when surge current is not important and other designs could provide higher energy densities.
For these roles, modified versions of the standard cell may be used to improve storage times and reduce maintenance requirements. Gel-cells and absorbed glass-mat batteries are common in these roles, collectively known as VRLA valve-regulated lead—acid batteries. 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 PbO 2 on the positive side, plus the aqueous sulfuric acid. The French scientist Nicolas Gautherot observed in 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.
In , Camille Alphonse Faure invented an improved version that consisted of a lead grid lattice, into which a lead oxide paste was pressed, forming a plate. This design was easier to mass-produce. An early manufacturer from of lead—acid batteries was Henri Tudor. This battery uses a gel electrolyte instead of a liquid allowing the battery to be used in different positions without leaking.
Gel electrolyte batteries for any position were first used the s, and in the late s, portable suitcase radio sets allowed the cell vertical or horizontal but not inverted due to valve design. It was discovered early in that lead—acid batteries did in fact use some aspects of relativity to function, and to a lesser degree liquid metal and molten-salt batteries such as the Ca—Sb and Sn—Bi also use this effect.
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. 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.
The net energy released per mol g of Pb s converted to PbSO 4 s , is ca. The sum of the molecular masses of the reactants is For a 2-volt cell, this comes to watt-hours per kilogram of reactants, but in practice a lead—acid cell gives only 30—40 watt-hours per kilogram of battery, due to the mass of the water and other constituent parts.
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. Because of freezing-point depression , the electrolyte is more likely to freeze in a cold environment when the battery has a low charge and correspondingly low sulfuric acid concentration.
The reverse occurs during charge. This motion can be electrically driven proton flow or Grotthuss mechanism , or by diffusion through the medium, or by flow of a liquid electrolyte medium. Since the electrolyte density is greater when the sulfuric acid concentration is higher, the liquid will tend to circulate by convection. Therefore, a liquid-medium cell tends to rapidly discharge and rapidly charge more efficiently than an otherwise similar gel cell.
Because the electrolyte takes part in the charge-discharge reaction, this battery has one major advantage over other chemistries: It is relatively simple to determine the state of charge by merely measuring the specific gravity of the electrolyte; the specific gravity falls as the battery discharges. Some battery designs include a simple hydrometer using colored floating balls of differing density.
When used in diesel-electric submarines , the specific gravity was regularly measured and written on a blackboard in the control room to indicate how much longer the boat could remain submerged. The battery's open-circuit voltage can also be used to gauge the state of charge. IUoU battery charging is a three-stage charging procedure for lead—acid batteries. For a single cell, the voltage can range from 1.
Float voltage varies depending on battery type i. Equalization voltage, and charging voltage for sulfated cells, can range from 2. 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.
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 , the cost of producing batteries greatly declined. In , Camille Alphonse Faure patented a method of coating a lead grid which serves as the current conductor with a paste of lead oxides, sulfuric acid, and water, followed by curing phase in which the plates were exposed to gentle heat in a high-humidity environment.
The curing process changed the paste into a mixture of lead sulfates which adhered to the lead plate. Then, during the battery's initial charge called "formation" the cured paste on the plates was converted into electrochemically active material the "active mass".
The grid developed by Faure was of pure lead with connecting rods of lead at right angles. In contrast, present-day grids are structured for improved mechanical strength and improved current flow.
In addition to different grid patterns ideally, all points on the plate are equidistant from the power conductor , modern-day processes also apply one or two thin fibre-glass mats over the grid to distribute the weight more evenly.
However, high-antimony grids have higher hydrogen evolution which also accelerates as the battery ages , and thus greater outgassing and higher maintenance costs. These issues were identified by U. Thomas and W. Haring at Bell Labs in the s and eventually led to the development of lead- calcium grid alloys in for standby power batteries on the U.
Related research led to the development of lead- selenium grid alloys in Europe a few years later. These metallurgical improvements give the grid more strength, which allows it carry more weight, i. High-antimony alloy grids are still used in batteries intended for frequent cycling, e. Since the s, batteries designed for infrequent cycling applications e. Lead-calcium alloy grids are cheaper to manufacture the cells thus have lower up-front costs , and have a lower self-discharge rate, and lower watering requirements, but have slightly poorer conductivity, are mechanically weaker and thus require more antimony to compensate , and are more strongly subject to corrosion and thus a shorter lifespan than cells with lead-selenium alloy grids.
The open circuit effect is a dramatic loss of battery cycle life which was observed when calcium was substituted for antimony. It is also known as the antimony free effect. Modern-day paste contains carbon black , blanc fixe barium sulfate and lignosulfonate. The blanc fixe acts as a seed crystal for the lead—to— lead sulfate reaction. The blanc fixe must be fully dispersed in the paste in order for it to be effective. The lignosulfonate prevents the negative plate from forming a solid mass during the discharge cycle, instead enabling the formation of long needle—like dendrites.
The long crystals have more surface area and are easily converted back to the original state on charging. Carbon black counteracts the effect of inhibiting formation caused by the lignosulfonates. Sulfonated naphthalene condensate dispersant is a more effective expander than lignosulfonate and speeds up formation. This dispersant improves dispersion of barium sulfate in the paste, reduces hydroset time, produces a more breakage-resistant plate, reduces fine lead particles and thereby improves handling and pasting characteristics.
It extends battery life by increasing end-of-charge voltage. Sulfonated naphthalene requires about one-third to one-half the amount of lignosulfonate and is stable to higher temperatures. Once dry, the plates are stacked with suitable separators and inserted in a cell container. The alternate plates then constitute alternating positive and negative electrodes, and within the cell are later connected to one another negative to negative, positive to positive in parallel. The separators inhibit the plates from touching each other, which would otherwise constitute a short circuit.
In flooded and gel cells, the separators are insulating rails or studs, formerly of glass or ceramic, and now of plastic. In AGM cells, the separator is the glass mat itself, and the rack of plates with separators are squeezed together before insertion into the cell; once in the cell, the glass mats expand slightly, effectively locking the plates in place.
In multi-cell batteries, the cells are then connected to one another in series, either through connectors through the cell walls, or by a bridge over the cell walls. All intra-cell and inter-cell connections are of the same lead alloy as that used in the grids. This is necessary to prevent galvanic corrosion.
Deep-cycle batteries have a different geometry for their positive electrodes. The positive electrode is not a flat plate but a row of lead-oxide cylinders or tubes strung side by side, so their geometry is called tubular or cylindrical.
The advantage of this is an increased surface area in contact with the electrolyte, with higher discharge and charge currents than a flat-plate cell of the same volume and depth-of-charge. Tubular-electrode cells have a higher power density than flat-plate cells. And, less active material at the electrode also means they have less material available to shed before the cell becomes unusable.
Separators between the positive and negative plates prevent short circuit through physical contact, mostly through dendrites "treeing" , but also through shedding of the active material. Separators allow the flow of ions between the plates of an electro-chemical cell to form a closed circuit.
Wood, rubber, glass fiber mat, cellulose , and PVC or polyethylene plastic have been used to make separators. Wood was the original choice, but it deteriorates in the acid electrolyte. Rubber separators are stable in battery acid and provide valuable electrochemical advantages that other materials cannot.
An effective separator must possess a number of mechanical properties; such as permeability , porosity, pore size distribution, specific surface area , mechanical design and strength, electrical resistance , ionic conductivity , and chemical compatibility with the electrolyte.
In service, the separator must have good resistance to acid and oxidation. The area of the separator must be a little larger than the area of the plates to prevent material shorting between the plates.
The separators must remain stable over the battery's operating temperature range. In the absorbent glass mat design, or AGM for short, the separators between the plates are replaced by a glass fibre mat soaked in electrolyte. There is only enough electrolyte in the mat to keep it wet, and if the battery is punctured the electrolyte will not flow out of the mats. Principally the purpose of replacing liquid electrolyte in a flooded battery with a semi-saturated fiberglass mat is to substantially increase the gas transport through the separator; hydrogen or oxygen gas produced during overcharge or charge if the charge current is excessive is able to freely pass through the glass mat and reduce or oxidize the opposing plate respectively.
In a flooded cell the bubbles of gas float to the top of the battery and are lost to the atmosphere. This mechanism for the gas produced to recombine and the additional benefit of a semi-saturated cell providing no substantial leakage of electrolyte upon physical puncture of the battery case allows the battery to be completely sealed, which makes them useful in portable devices and similar roles.
Additionally the battery can be installed in any orientation, though if it is installed upside down then acid may be blown out through the over pressure vent.
To reduce the water loss rate calcium is alloyed with the plates, however gas build-up remains a problem when the battery is deeply or rapidly charged or discharged. To prevent over-pressurization of the battery casing, AGM batteries include a one-way blow-off valve, and are often known as "valve-regulated lead—acid", or VRLA, designs.
Another advantage to the AGM design is that the electrolyte becomes the separator material, and mechanically strong. This allows the plate stack to be compressed together in the battery shell, slightly increasing energy density compared to liquid or gel versions.
Lead Acid Battery — The type of battery which uses lead peroxide and sponge lead for the conversion of the chemical energy into electrical energy, such type of the electric battery is called a lead acid battery. Because it has higher cell voltage and lower cost, the lead acid battery is most often used in power stations and substations. Read my article on how to make your own high ampere large Lead Acid battery , this article also explains what tools you should have and how to use them. The type of devices in which the Chemical Energy is converted into Electrical Energy are called electric cells. When a specific number of these electric cells are electrically connected in Series and Parallel combinations it forms a Battery.
Electrical Academia. The lead-acid battery is the most commonly used type of storage battery and is well-known for its application in automobiles. The battery is made up of several cells, each of which consists of lead plates immersed in an electrolyte of dilute sulfuric acid. The voltage per cell is typically 2 V to 2. For a 6 V battery, three cells are connected in series, and for a 12 V battery, six cells are series-connected.
Lead Acid Battery
A lead acid battery consists of a negative electrode made of spongy or porous lead. The lead is porous to facilitate the formation and dissolution of lead. The positive electrode consists of lead oxide. Both electrodes are immersed in a electrolytic solution of sulfuric acid and water. In case the electrodes come into contact with each other through physical movement of the battery or through changes in thickness of the electrodes, an electrically insulating, but chemically permeable membrane separates the two electrodes.
Almost every portable and handheld device consist a battery. The battery is a storage device where energy is stored to provide the power whenever needed. There are different types of batteries available in this modern electronics world, among them Lead Acid battery is commonly used for high power supply.
Construction of Lead Acid Battery
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