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WIKIBOOKS
DISPONIBILI
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ART
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BUSINESS&LAW
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ARTICLES IN THE BOOK

  1. AAAA battery
  2. AAA battery
  3. AA battery
  4. A battery
  5. Absorbent glass mat
  6. Alessandro Volta
  7. Alkaline battery
  8. Alkaline fuel cell
  9. Aluminium battery
  10. Ampere
  11. Atomic battery
  12. Backup battery
  13. Baghdad Battery
  14. Batteries
  15. Battery charger
  16. B battery
  17. Bernard S. Baker
  18. Beta-alumina solid electrolyte
  19. Betavoltaics
  20. Bio-nano generator
  21. Blue energy
  22. Bunsen cell
  23. Car battery
  24. C battery
  25. Clark cell
  26. Concentration cell
  27. Coulomb
  28. 2CR5
  29. Daniell cell
  30. Direct borohydride fuel cell
  31. Direct-ethanol fuel cell
  32. Direct methanol fuel cell
  33. Dry cell
  34. Dry pile
  35. Duracell
  36. Duracell Bunny
  37. Earth battery
  38. Electric charge
  39. Electric current
  40. Electricity
  41. Electrochemical cell
  42. Electrochemical potential
  43. Electro-galvanic fuel cell
  44. Electrolysis
  45. Electrolyte
  46. Electrolytic cell
  47. Electromagnetism
  48. Electromotive force
  49. Energizer Bunny
  50. Energy
  51. Energy density
  52. Energy storage
  53. Flashlight
  54. Float charging
  55. Flow Battery
  56. Formic acid fuel cell
  57. Fuel cell
  58. Fuel cell bus trial
  59. Galvanic cell
  60. Gel battery
  61. Grove cell
  62. Half cell
  63. History of the battery
  64. Hybrid vehicle
  65. Lead-acid battery
  66. Leclanché cell
  67. Lemon battery
  68. List of battery sizes
  69. List of battery types
  70. List of fuel cell vehicles
  71. Lithium battery
  72. Lithium ion batteries
  73. Lithium iron phosphate battery
  74. Lithium polymer cell
  75. LR44 battery
  76. Luigi Galvani
  77. Manganese dioxide
  78. Memory effect
  79. Mercury battery
  80. Metal hydride fuel cell
  81. Methane reformer
  82. Methanol reformer
  83. Michael Faraday
  84. Microbial fuel cell
  85. Molten carbonate fuel cell
  86. Molten salt battery
  87. Nickel-cadmium battery
  88. Nickel-iron battery
  89. Nickel metal hydride
  90. Nickel-zinc battery
  91. Open-circuit voltage
  92. Optoelectric nuclear battery
  93. Organic radical battery
  94. Oxyride battery
  95. Panasonic EV Energy Co
  96. Peukert's law
  97. Phosphoric acid fuel cell
  98. Photoelectrochemical cell
  99. Polymer-based battery
  100. Power density
  101. Power management
  102. Power outage
  103. PP3 battery
  104. Primary cell
  105. Prius
  106. Proton exchange membrane
  107. Proton exchange membrane fuel cell
  108. Protonic ceramic fuel cell
  109. Radioisotope piezoelectric generator
  110. Ragone chart
  111. RCR-V3
  112. Rechargeable alkaline battery
  113. Reverse charging
  114. Reversible fuel cell
  115. Searchlight
  116. Secondary cell
  117. Short circuit
  118. Silver-oxide battery
  119. Smart Battery Data
  120. Smart battery system
  121. Sodium-sulfur battery
  122. Solid oxide fuel cell
  123. Super iron battery
  124. Thermionic converter
  125. Trickle charging
  126. Vanadium redox battery
  127. Volt
  128. Voltage
  129. Voltaic pile
  130. Watch battery
  131. Water-activated battery
  132. Weston cell
  133. Wet cell
  134. Zinc-air battery
  135. Zinc-bromine flow battery
  136. Zinc-carbon battery

 

 
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    ENGLISHGRATIS.COM è un sito personale di
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    Roberto Casiraghi           
    INFORMATIVA SULLA PRIVACY              Crystal Jones


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BATTERIES
This article is from:
http://en.wikipedia.org/wiki/Lead-acid_battery

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

Lead-acid battery

From Wikipedia, the free encyclopedia

 

Lead-acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable battery. Despite having the second lowest energy-to-weight ratio (next to the nickel-iron battery) and a correspondingly low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large power-to-weight ratio. This, along with their low cost, makes them ideal for use in cars, as they can provide the high current required by automobile starter motors. They are also used in vehicles such as forklifts, in which the low energy-to-weight ratio may in fact be considered a benefit since the battery can be used as a counterweight. Large arrays of lead-acid cells are used as standby power sources for telecommunications facilities, generating stations, and computer data centers.

Electrochemistry

Each cell contains (in the charged state) electrodes of lead metal (Pb) and lead (IV) oxide (PbO2) in an electrolyte of about 37% (5.99 Molar) w/w sulfuric acid (H2SO4). In the discharged state both electrodes turn into lead(II) sulfate (PbSO4) and the electrolyte loses its dissolved sulfuric acid and becomes primarily water. Due to the freezing-point depression of water, as the battery discharges and the concentration of sulfuric acid decreases, the electrolyte is more likely to freeze.

The chemical reactions are (charged to discharged):

Anode (oxidation): \mbox{Pb} (s) +\mbox{SO}_{4}^{2-} (aq) \leftrightarrow \mbox{PbSO}_{4} (s) +2e^- \quad\epsilon^o = 0.356 \ \mathrm{V}

Cathode (reduction): \mbox{PbO}_{2} (s) +\mbox{SO}_{4}^{2-} (aq) +4\mbox{H}^++2e^- \leftrightarrow \mbox{PbSO}_{4} (s) +2\mbox{H}_2\mbox{O} (l) \quad\epsilon^o = 1.685 \ \mathrm{V}

Because of the open cells with liquid electrolyte in most lead-acid batteries, overcharging with excessive charging voltages will generate oxygen and hydrogen gas by electrolysis of water, forming an explosive mix. This should be avoided. Caution must also be observed because of the extremely corrosive nature of sulfuric acid.

Practical cells are usually not made with pure lead but have small amounts of antimony, tin, or calcium alloyed in the plate material.

The following are general voltage ranges for six-cell lead-acid batteries:

  • Open-circuit (quiescent) at full charge: 12.6 - 12.8 V
  • Open-circuit at full discharge: 11.8 - 12.0 V
  • Loaded at full discharge: 10.5 V
  • Continuous-preservation (float) charging: 13 - 13.2 V
  • Typical (daily) charging: 13.2 - 14.4 V
  • Equalization charging (for flooded lead acids): 15 - 16 V
  • Gassing threshold: 14.4 V
  • After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V.

Construction of battery

Plates

The principle of the lead acid cell can be demonstrated with simple sheet lead plates for the two electrodes. However such a construction would only produce around an amp for roughly postcard sized plates, and it would not produce such a current for more than a few minutes.

Planté realised that a plate construction was required that gave a much larger effective surface area. Planté's method of producing the plates has been largely unchanged.

A plate consists of a rectangular lead plate alloyed with a little antimony to improve the mechanical characteristics. The plate is in fact a grid with rectangular holes in it, the lead forming thin walls to the holes. The holes are filled with a mixture of red lead and 33% dilute sulphuric acid (Different manufacturers have modified the mixture). The paste is pressed into the holes in the plates which are slightly tapered on both sides to assist in retention of the paste. This paste remains porous and allows the acid to react with the lead inside the plate increasing the surface area many fold. At this stage the positive and negative plates are identical. Once dry the plates are then stacked together with suitable separators and inserted in the battery container. An odd number of plates is always used, with one more negative plate than positive. Each alternate plate is connected together. After the acid has been added to the cell, the cell is given its first forming charge. The positive plates gradually turn the chocolate brown colour of Lead Dioxide, and the negative turn the slate gray of 'spongy' lead. Such a cell is ready to be used.

Many modern manufacturers use pastes in the plates made directly from Lead Dioxide and Lead, thus avoiding the necessity to form the plates. Once acid is added, the cell is ready for use.

One of the problems with the plates in a lead-acid battery is that the plates change size as the battery charges and discharges, the plates increasing in size as the active material absorbs sulphate from the acid during discharge, and decreasing as they give up the sulphate during charging. This causes the plates to gradually shed the paste during their life. It is important that there is plenty of room underneath the plates to catch this shed material. If this material reaches the plates a shorted cell will occur.

Separators

Separators are used between the positive and negative plates of a lead acid battery to prevent short circuit through physical contact, Dendrites (‘treeing’) most and shredded active material. Separators cause some obstructions for the flow of ions i.e. electricity between the electrodes. Separators therefore must have the following characteristics:

  1. They must be porous—high porosity gives a high rate of flow of ions.
  2. Pore size must be small enough to restrict the flow of colloid particles but not restrict the ions.
  3. They must be as thin as possible.
  4. Electrical resistance must be very high.
  5. They are a little larger than the plates to prevent material shorting the plates.

To balance these criteria, the choice of separator shifted from wood to rubber to glass mat to cellulose based separators to sintered PVC separator to microporous PVC/polyethylene separator. An effective separator must meet a number of mechanical properties. 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.

In the battery service condition the following reaction can be shown :

PbO2 + 2H+ + SO4-2 = PbSO4 + H2O + ½ O2
PbO2 + (oxidizable separator material) + H2SO4 = PbSO4 + (oxidized material)

Moreover, the battery service temperature can be as high as 70 to 80 degrees Celsius. The separator must be capable of resisting thermal degradation as far as possible.

Classification of lead acid batteries

By production technology

  • Flooded/Wet cell batteries
  • VRLA: Valve Regulated Lead Acid batteries
  • AGM: Absorbed Glass Mat batteries
  • Gel cell batteries

By application

  • Starter batteries
  • Stand-by (stationary) batteries
  • Traction (propulsion)batteries

Other applications

Wet cells designed for deep discharge are commonly used in golf carts and other battery electric vehicles, large backup power supplies for telephone and computer centers and off-grid household electric power systems.

Gel cells are used in back-up power supplies for alarm and smaller computer systems (particularly in uninterruptible power supplies) and for electric scooters, electrified bicycles and marine applications. Unlike wet cells, gel cells are sealed, so they are less prone to spilling and do not require maintenance of electrolyte levels.

Absorbed glass mat (AGM) cells are also sealed and used in battery electric vehicles, as well as applications where there is a fairly high risk of the battery being laid on its side or over-turned, such as motorcycles.

Historically, lead-acid batteries were used to supply the filament (heater) voltage (usually between 2 and 12 volts with 6 V being most common) in vacuum tube (valve) radio receivers in areas where no mains electricity supply was available. Such radios typically used two batteries: a lead-acid "A" battery for the filament voltage and a higher voltage (45 V–120 V) "dry" non-rechargeable "B" battery for the plate (anode) voltage. A few sets also used a third (3 V–9 V with several taps) "dry" non-rechargeable "C" battery for grid bias.

Lead-acid batteries are used in emergency lighting in case of power failure.

Starting batteries decay with deep discharges

Lead acid batteries designed for starting service, such as those used in most automobiles, are not designed for deep discharge. They have a large number of thin plates designed for maximum surface area, and therefore maximum current output, but which can easily be damaged by deep discharge. Repeated deep discharges will result in capacity loss and ultimately in premature failure, as the electrodes disintegrate due to mechanical stresses that arise from cycling. A common misconception is that starting batteries should always be kept on float charge. In reality, this practice will encourage corrosion in the electrodes and result in premature failure. Starting batteries should be kept open-circuit but charged regularly (at least once every two weeks) to prevent sulfation.

Deep cycle batteries

Specially designed deep-cycle cells are much less susceptible to degradation due to cycling, and are required for applications where the batteries are regularly discharged, such as photovoltaic systems, electric vehicle (forklift, golf cart and other) and uninterruptible power supplies. These batteries have thicker plates that can deliver less peak current, but can withstand frequent discharging.[1]

Marine batteries are something of a compromise between the two, able to be discharged to a greater degree than automotive batteries, but less so than deep cycle batteries.

MF (Maintenance Free) batteries

The MF (Maintenance Free) battery is one of many types of lead-acid battery.

It became popular on motorcycles because its acid is absorbed into the medium which separates the plates, so it cannot spill, and this medium also lends support to the plates which helps them better to withstand vibration.

The electrical characteristics of MF batteries differ somewhat from wet-cell lead-acid batteries, and caution should be exercised in charging and discharging them. MF batteries should not be confused with AGM (Absorbed Glass Mat) batteries, which also have an absorbed electrolyte but again have different electrical characteristics.

Environmental concerns

Currently attempts are being made to develop alternatives to the lead-acid battery (particularly for automotive use) because of concerns about the environmental consequences of improper disposal of old batteries. Lead-acid battery recycling is one of the most successful recycling programs in the world, with over 97% of all battery lead recycled between 1997 and 2001.[2] Effective Lead pollution control system is a necessity for sustainable environment. There is a continuous improvement in battery recycling plants and furnace designs for greater efficiencies. These recycling plants are ecology friendly as they follow all emission standards for lead smelters, but new methods should be devised or alternatives developed to the lead-acid battery so that lead pollution can be reduced to an essentially negligible amount.

Additives

Many vendors sell chemical additives (solid compounds as well as liquid solutions) that supposedly reduce sulfate build up and improve battery condition when added to the electrolyte of a vented lead-acid battery. Such treatments are rarely, if ever, effective.

Two compounds used for such purposes are Epsom salts and EDTA. Epsom salts reduce the internal resistance in a weak or damaged battery and may allow a small amount of extended life. EDTA can be used to dissolve the suphate deposits of heavily discharged plates. However, the dissolved material is then no longer available to participate in the normal charge/discharge cycle, so a battery temporarily revived with EDTA should not be expected to have normal life expectancy. Residual EDTA in the lead-acid cell forms organic acids which will accelerate corrosion of the lead plates and internal connectors.

Active material (the positive plate lead peroxide and negative plate spongy lead) changes physical form during discharge, resulting in plate growth, distortion of the active material, and shedding of active material. Once the active material has left the plates, it cannot be restored into position by any chemical treatment. Similarly, internal physical problems such as cracked plates, corroded connectors, or damaged separators cannot be restored chemically.

See also

 
  • Car battery
  • Gel battery
  • Absorbed glass mat (AGM)
  • VRLA
  • Rechargeable battery

References

  1. ^ "Battery FAQ" at Northern Arizona Wind & Sun, visited 2006-07-23
  2. ^ Battery Council International. Retrieved on 2006-06-01.
  • U.S. Department of Energy, Primer On Lead-Acid Storage Batteries (pdf)
  • Environment Friendly Battery Recycling

External links

  • Yuasa Lead-acid batteries Turkish
  • Used battery management in Turkey in Turkish
  • BatteryUniversity.com
  • Batteries, charge and Power Units Turkish
  • Case Studies in Environmental Medicine - Lead Toxicity
  • National Pollutant Inventory - Lead and Lead Compounds Fact Sheet
  • ToxFAQs™: Lead
  • Firefly Energy - The next generation of lead acid technologies.
Retrieved from "http://en.wikipedia.org/wiki/Lead-acid_battery"