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Biography

An electrical battery is one or more electrochemical cell s that convert stored chemical energy into electrical energy. Since the invention of the first battery (or " voltaic pile ") in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power source for many household and industrial applications. According to a 2005 estimate, the worldwide battery industry generates United States dollar|US$ 48 1000000000 (number)|billion in sales each year,. Draper Fisher Jurvetson . Retrieved 20 November 2005. with 6% annual growth.Buchmann, Isidor. . Battery University . Retrieved 11 August 2008.

There are two types of batteries: Primary battery|primary batteries (disposable batteries), which are designed to be used once and discarded, and Secondary battery|secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times. Batteries come in many sizes, from miniature cells used to power hearing aid s and wristwatches to battery banks the size of rooms that provide standby power for telephone exchange s and computer data center s.

History

In strict terms, a battery is a collection of multiple electrochemical cells, but in popular usage battery often refers to a single cell., Merriam-Webster Online Dictionary (2009). Retrieved 25 May 2009. For example, a 1.5-volt AAA battery is a single 1.5-volt cell, and a 9-volt battery has six 1.5-volt cells in Series_and_parallel_circuits|series . The first electrochemical cell was developed by the Italians|Italian physicist Alessandro Volta in 1792, and in 1800 he invented the first battery, a "pile" of many cells in series.Bellis, Mary. . About.com . Retrieved 7 August 2008.

The usage of "battery" to describe electrical devices dates to Benjamin Franklin , who in 1748 described multiple Leyden jar s (early electrical capacitor s) by analogy to a artillery battery|battery of cannons .Bellis, Mary. . About.com . Retrieved 11 August 2008. Thus Franklin's usage to describe multiple Leyden jars predated Volta's use of multiple galvanic cells."Memoirs of Benjamin Franklin", Volume 2. Benjamin Franklin, William Temple Franklin, William Duane. "Upon this we made what we called an electrical battery , consisting of eleven panes of large sash-glass, armed with thin leaden plates, pasted on each side, placed vertically, and supported at two inches distance on silk cords, with black hooks of leaden wire, one from each side, standing upright, distant from each other..." It is speculated, but not established, that several ancient artifacts consisting of copper sheets and iron bars, and known as Baghdad Battery|Baghdad batteries may have been galvanic cells.Corder, Gregory W. (PDF). Virginia Journal of Science Education , Vol. 1, No. 1. Retrieved 7 August 2008.

Volta's work was stimulated by the Italian anatomist and physiologist Luigi Galvani , who in 1780 noticed that dissected frog's legs would twitch when struck by a spark from a Leyden jar , an external source of electricity.Asimov, Isaac. Retrieved 3 May 2009. In 1786 he noticed that twitching would occur during lightning storms.Encyclopædia Britannica. Retrieved 3 May 2009. After many years Galvani learned how to produce twitching without using any external source of electricity. In 1791, he published a report on "animal electricity."Bernardi, Walter. . Pavia Project Physics . Retrieved 21 May 2008. He created an electric circuit consisting of the frog's leg (FL) and two different metals A and B, each metal touching the frog's leg and each other, thus producing the circuit A–FL–B–A–FL–B...etc. In modern terms, the frog's leg served as both the electrolyte and the sensor , and the metals served as electrode s. He noticed that even though the frog was dead, its legs would twitch when he touched them with the metals.

Within a year, Volta realized the frog's moist tissues could be replaced by cardboard soaked in salt water, and the frog's muscular response could be replaced by another form of electrical detection. He already had studied the electrostatic phenomenon of capacitance , which required measurements of electric charge and of electrical potential ("tension"). Building on this experience, Volta was able to detect electric current through his system, also called a Galvanic cell . The terminal voltage of a cell that is not discharging is called its electromotive force (emf), and has the same unit as electrical potential, named ( voltage ) and measured in volt s, in honor of Volta. In 1800, Volta invented the battery by placing many voltaic cells in Series and parallel circuits#Series circuits|series , piling them one above the other. This voltaic pile gave a greatly enhanced net emf for the combination,Weinberg, Willie. . The Italian-American Web Site of New York . Retrieved 19 March 2007. with a voltage of about 50 volts for a 32-cell pile.Saslow 338. In many parts of Europe batteries continue to be called piles., Pocket Oxford Spanish Dictionary (2005). WordReference.com . Retrieved 6 August 2008., Pocket Oxford-Hachette French Dictionary (2005). WordReference.com . Retrieved 6 August 2008.

Volta did not appreciate that the voltage was due to chemical reactions. He thought that his cells were an inexhaustible source of energy,Stinner, Arthur. (PDF). Retrieved 11 August 2008. and that the associated corrosion effects at the electrodes were a mere nuisance, rather than an unavoidable consequence of their operation, as Michael Faraday showed in 1834.. The Great Idea Finder . Retrieved 11 August 2008. According to Faraday, cation s (positively charged ions) are attracted to the cathode ,. Dictionary.com . Originally published in ''Webster's Revised Unabridged Dictionary . Retrieved 3 February 2009. and anion s (negatively charged ions) are attracted to the anode .. Dictionary.com . Originally published in Webster's Revised Unabridged Dictionary . Retrieved 3 February 2009.

Although early batteries were of great value for experimental purposes, in practice their voltages fluctuated and they could not provide a large current for a sustained period. Later, starting with the Daniell cell in 1836 , batteries provided more reliable currents and were adopted by industry for use in stationary devices, in particular in telegraph networks where they were the only practical source of electricity, since electrical distribution networks did not exist at the time.. MPower Solutions Ltd . Retrieved 19 March 2007. These wet cells used liquid electrolytes, which were prone to leakage and spillage if not handled correctly. Many used glass jars to hold their components, which made them fragile. These characteristics made wet cells unsuitable for portable appliances. Near the end of the nineteenth century, the invention of dry cell|dry cell batteries , which replaced the liquid electrolyte with a paste, made portable electrical devices practical.. American Chemical Society . Retrieved 3 February 2009.

Since then, batteries have gained popularity as they became portable and useful for a variety of purposes.. ExtremeTech . Retrieved 10 September 2007.

Principle of operation

A battery is a device that converts chemical energy directly to electrical energy."battery" (def. 6), The Random House Dictionary of the English Language, the Unabridged Edition (2nd edition) , 1996 ed. It consists of a number of voltaic cells; each voltaic cell consists of two half-cell s connected in series by a conductive electrolyte containing anions and cations. One half-cell includes electrolyte and the electrode to which Ion#Ions|anions (negatively charged ions) migrate, i.e., the anode or negative electrode; the other half-cell includes electrolyte and the electrode to which Ion#Ions|cations (positively charged ions) migrate, i.e., the cathode or positive electrode. In the redox reaction that powers the battery, cations are reduced (electrons are added) at the cathode, while anions are oxidized (electrons are removed) at the anode.Dingrando 665. The electrodes do not touch each other but are electrically connected by the electrolyte . Some cells use two half-cells with different electrolytes. A separator between half-cells allows ions to flow, but prevents mixing of the electrolytes.

Each half-cell has an electromotive force (or emf), determined by its ability to drive electric current from the interior to the exterior of the cell. The net emf of the cell is the difference between the emfs of its half-cells, as first recognized by Volta. Therefore, if the electrodes have emfs

\mathcal{E}_1

and

\mathcal{E}_2

, then the net emf is

\mathcal{E}_{2}-\mathcal{E}_{1}

; in other words, the net emf is the difference between the reduction potential s of the half-reaction s.Dingrando 666.

The electrical driving force or

\displaystyle{\Delta V_{bat

across the terminals of a cell is known as the terminal voltage (difference) and is measured in volt s.Knight 943. The terminal voltage of a cell that is neither charging nor discharging is called the open-circuit voltage and equals the emf of the cell. Because of internal resistance,Knight 976. the terminal voltage of a cell that is discharging is smaller in magnitude than the open-circuit voltage and the terminal voltage of a cell that is charging exceeds the open-circuit voltage.. Originally from Hutchinson Encyclopaedia . Retrieved 7 April 2007. An ideal cell has negligible internal resistance, so it would maintain a constant terminal voltage of

\mathcal{E}

until exhausted, then dropping to zero. If such a cell maintained 1.5 volts and stored a charge of one coulomb then on complete discharge it would perform 1.5 joule of work. In actual cells, the internal resistance increases under discharge, and the open circuit voltage also decreases under discharge. If the voltage and resistance are plotted against time, the resulting graphs typically are a curve; the shape of the curve varies according to the chemistry and internal arrangement employed.Buchmann, Isidor. . Battery University . Retrieved 14 August 2008.

As stated above, the voltage developed across a cell's terminals depends on the energy release of the chemical reactions of its electrodes and electrolyte. Alkaline and Zinc–carbon battery|zinc–carbon cells have different chemistries but approximately the same emf of 1.5 volts; likewise Nickel–cadmium battery|NiCd and Nickel–metal hydride battery|NiMH cells have different chemistries, but approximately the same emf of 1.2 volts.Dingrando 674. On the other hand the high electrochemical potential changes in the reactions of lithium compounds give lithium cells emfs of 3 volts or more.Dingrando 677.

Categories and types of batteries

Batteries are classified into two broad categories, each type with advantages and disadvantages.Buchmann, Isidor. . Battery University . Retrieved 6 January 2008.

Primary batteries irreversibly (within limits of practicality) transform chemical energy to electrical energy. When the initial supply of reactants is exhausted, energy cannot be readily restored to the battery by electrical means.Dingrando 675.

Secondary batteries can be recharged; that is, they can have their chemical reactions reversed by supplying electrical energy to the cell, restoring their original composition.Fink, Ch. 11, Sec. "Batteries and Fuel Cells."

Some types of primary batteries used, for example, for Telegraphy|telegraph circuits, were restored to operation by replacing the components of the battery consumed by the chemical reaction. Franklin Leonard Pope , Modern Practice of the Electric Telegraph 15th Edition , D. Van Nostrand Company, New York, 1899, pages 7-11. Available on the Internet Archive Secondary batteries are not indefinitely rechargeable due to dissipation of the active materials, loss of electrolyte and internal corrosion.

Primary batteries

Primary batteries can produce current immediately on assembly. Disposable batteries are intended to be used once and discarded. These are most commonly used in portable devices that have low current drain, are used only intermittently, or are used well away from an alternative power source, such as in alarm and communication circuits where other electric power is only intermittently available. Disposable primary cells cannot be reliably recharged, since the chemical reactions are not easily reversible and active materials may not return to their original forms. Battery manufacturers recommend against attempting to recharge primary cells.. Retrieved 10 August 2008.

Common types of disposable batteries include zinc–carbon batteries and alkaline batteries . In general, these have higher energy densities than rechargeable batteries, (PDF). Energizer . Retrieved 25 August 2008. but disposable batteries do not fare well under high-drain applications with electrical load|loads under 75 ohms (75 O).

Secondary batteries

Secondary batteries must be charged before use; they are usually assembled with active materials in the discharged state. Rechargeable batteries or secondary cell s can be recharged by applying electric current, which reverses the chemical reaction s that occur during its use. Devices to supply the appropriate current are called chargers or rechargers.

The oldest form of rechargeable battery is the lead–acid battery .Buchmann, Isidor. . Battery University . Retrieved 2 September 2007. This battery is notable in that it contains a liquid in an unsealed container, requiring that the battery be kept upright and the area be well ventilated to ensure safe dispersal of the hydrogen gas produced by these batteries during overcharging. The lead–acid battery is also very heavy for the amount of electrical energy it can supply. Despite this, its low manufacturing cost and its high surge current levels make its use common where a large capacity (over approximately 10 Ah) is required or where the weight and ease of handling are not concerns.

A common form of the lead–acid battery is the modern car battery , which can, in general, deliver a peak current of 450 ampere s.. Amazon . Retrieved 26 August 2008. An improved type of liquid electrolyte battery is the sealed valve regulated lead–acid battery (VRLA battery), popular in the automotive industry as a replacement for the lead–acid wet cell. The VRLA battery uses an immobilized sulfuric acid electrolyte, reducing the chance of leakage and extending shelf life.. C& D Technologies, Inc. Retrieved 26 August 2008. VRLA batteries have the electrolyte immobilized, usually by one of two means:

Gel batteries (or "gel cell") contain a semi-solid electrolyte to prevent spillage.

Absorbed Glass Mat (AGM) batteries absorb the electrolyte in a special fiberglass matting.

Other portable rechargeable batteries include several "dry cell" types, which are sealed units and are, therefore, useful in appliances such as mobile phone s and Laptop|laptop computers . Cells of this type (in order of increasing power density and cost) include Nickel–cadmium battery|nickel–cadmium (NiCd), Nickel–zinc battery|nickel–zinc (NiZn), Nickel metal hydride battery|nickel metal hydride (NiMH), and Lithium-ion battery|lithium-ion (Li-ion) cells.. Battery University . Retrieved 26 August 2008. By far, Li-ion has the highest share of the dry cell rechargeable market. Meanwhile, NiMH has replaced NiCd in most applications due to its higher capacity, but NiCd remains in use in power tool s, two-way radio s, and medical equipment . NiZn is a new technology that is not yet well established commercially.

Recent developments include batteries with embedded electronics such as USBCELL , which allows charging an AA cell through a USB connector,. Retrieved 6 November 2007. and smart battery packs with state-of-charge monitors and battery protection circuits to prevent damage on over-discharge. Low self-discharge NiMH battery|low self-discharge (LSD) allows secondary cells to be precharged prior to shipping.

Battery cell types

There are many general types of electrochemical cells, according to chemical processes applied and design chosen. The variation includes galvanic cell s, electrolytic cell s, fuel cell s, flow battery|flow cells and voltaic piles.

Wet cell

A wet cell battery has a liquid electrolyte . Other names are flooded cell , since the liquid covers all internal parts, or vented cell , since gases produced during operation can escape to the air. Wet cells were a precursor to dry cells and are commonly used as a learning tool for electrochemistry . It is often built with common laboratory supplies, such as beaker (glassware)|beakers , for demonstrations of how electrochemical cells work. A particular type of wet cell known as a concentration cell is important in understanding corrosion . Wet cells may be primary cell s (non-rechargeable) or secondary cell s (rechargeable). Originally, all practical primary batteries such as the Daniell cell were built as open-topped glass jar wet cells. Other primary wet cells are the Leclanche cell , Grove cell , Bunsen cell , Chromic acid cell , Clark cell , and Weston cell . The Leclanche cell chemistry was adapted to the first dry cells. Wet cells are still used in car battery|automobile batteries and in industry for standby power for switchgear , telecommunication or large uninterruptible power supply|uninterruptible power supplies , but in many places batteries with gel cell s have been used instead. These applications commonly use lead–acid or Nickel–cadmium battery (vented cell type)|nickel–cadmium cells.

Dry cell

1. brass cap, 2. plastic seal, 3. expansion space, 4. porous cardboard, 5. zinc can, 6. carbon rod, 7. chemical mixture.
A dry cell has the electrolyte immobilized as a paste, with only enough moisture in it to allow current to flow. Unlike a wet cell, a dry cell can operate in any orientation without spilling as it contains no free liquid, making it suitable for portable equipment. By comparison, the first wet cells were typically fragile glass containers with lead rods hanging from the open top, and needed careful handling to avoid spillage. Lead–acid batteries did not achieve the safety and portability of the dry cell until the development of the gel battery .

A common dry cell battery is the zinc–carbon battery , using a cell sometimes called the dry Leclanché cell , with a nominal voltage of 1.5 volt s, the same as the alkaline battery (since both use the same zinc – manganese dioxide combination).

A standard dry cell comprises a zinc anode (negative pole), usually in the form of a cylindrical pot, with a carbon cathode (positive pole) in the form of a central rod. The electrolyte is ammonium chloride in the form of a paste next to the zinc anode. The remaining space between the electrolyte and carbon cathode is taken up by a second paste consisting of ammonium chloride and manganese dioxide, the latter acting as a depolariser . In some more modern types of so-called 'high-power' batteries (with much lower capacity than standard alkaline batteries), the ammonium chloride is replaced by zinc chloride .

Molten salt

Molten salt battery|Molten salt batteries are primary or secondary batteries that use a molten salt as electrolyte. Their energy density and power density give them potential for use in electric vehicles , but they operate at high temperatures and must be well insulated to retain heat.

Reserve

A reserve battery is stored in unassembled form and is activated, ready-charged, when its internal parts are assembled, e.g. by adding electrolyte; it can be stored unactivated for a long period of time. For example, a battery for an electronic fuze might be activated by the impact of firing a gun, breaking a capsule of electrolyte to activate the battery and power the fuze's circuits. Reserve batteries are usually designed for a short service life (seconds or minutes) after long storage (years). A water-activated battery for oceanographic instruments or military applications becomes activated on immersion in water.

Battery cell performance

A battery's characteristics may vary over load cycle, over charge cycle , and over lifetime due to many factors including internal chemistry, Electric current|current drain, and temperature.

Battery capacity and discharging

A battery's capacity is the amount of electric charge it can store. The more electrolyte and electrode material there is in the cell the greater the capacity of the cell. A small cell has less capacity than a larger cell with the same chemistry, and they develop the same open-circuit voltage.

Because of the chemical reactions within the cells, the capacity of a battery depends on the discharge conditions such as the magnitude of the current (which may vary with time), the allowable terminal voltage of the battery, temperature, and other factors.. Retrieved 16 April 2007. The available capacity of a battery depends upon the rate at which it is discharged.. Retrieved 10 April 2007. If a battery is discharged at a relatively high rate, the available capacity will be lower than expected.

The capacity printed on a battery is usually the product of 20 hours multiplied by the constant current that a new battery can supply for 20 hours at 68& nbsp;F° (20& nbsp;C°), down to a specified terminal voltage per cell. A battery rated at 100 A·h will deliver 5 A over a 20-hour period at room temperature . However, if discharged at 50 A, it will have a lower capacity.Buchmann, Isidor. . Battery University . Retrieved 14 August 2008.

The relationship between current, discharge time, and capacity for a lead acid battery is approximated (over a certain range of current values) by Peukert's law :
:

t = \frac {Q_P} {I^k}

where
:

Q_P

is the capacity when discharged at a rate of 1 amp.
:

I

is the current drawn from battery ( Amperes|A ).
:

t

is the amount of time (in hours) that a battery can sustain.
:

k

is a constant around 1.3.
For low values of I internal self-discharge must be included.

Internal energy losses and limited rate of diffusion of ions through the electrolyte cause the Efficient energy use|efficiency of a real battery to vary at different discharge rates. When discharging at low rate, the battery's energy is delivered more efficiently than at higher discharge rates, but if the rate is very low, it will partly self-discharge during the long time of operation, again lowering its efficiency.

Installing batteries with different A·h ratings will not affect the operation of a device (except for the time it will work for) rated for a specific voltage unless the load limits of the battery are exceeded. High-drain loads such as digital camera s can result in delivery of less total energy, as happens with alkaline batteries. For example, a battery rated at 2000 mA·h for a 10- or 20-hour discharge would not sustain a current of 1 A for a full two hours as its stated capacity implies.

Fastest charging, largest, and lightest batteries

lithium iron phosphate|Lithium iron phosphate (LiFePO₄) batteries were the fastest-charging and discharging batteries ( supercapacitor s, in some ways comparable to batteries, charge faster).Kang, B. and Ceder, G. (2009) Nature 458 : 190-3. The world's largest battery, composed of nickel–cadmium battery|Ni–Cd cells, was in Fairbanks, Alaska .Conway, E. (2 September 2008) Telegraph.co.uk Sodium–sulfur batteries were being used to store wind power .Biello, D. (December 22, 2008) Scientific American Lithium–sulfur batteries have been used on the longest and highest solar-powered flight.Amos, J. (24 August 2008) BBC News The speed of recharging of lithium-ion batteries can be increased by manufacturing changes.

Battery lifetime

Primary batteries

Disposable (or "primary") batteries typically lose 8 to 20 percent of their original charge every year at room temperature (20°–30°C).. Retrieved 9 September 2007. This is known as the "self discharge" rate, and is due to non-current-producing "side" chemical reactions which occur within the cell even if no load is applied. The rate of the side reactions is reduced if the batteries are stored at lower temperature, although some batteries can be damaged by freezing. High or low working temperatures may reduce battery performance. This will affect the initial voltage of the battery. For an AA alkaline battery, this initial voltage is approximately normally distributed around 1.6 volts.

Discharging performance of all batteries drops at low temperature.

Secondary batteries

Storage life of secondary batteries is limited by chemical reactions that occur between the battery parts and the electrolyte; these are called "side reactions". Internal parts may corrode and fail, or the active materials may be slowly converted to inactive forms. Since the active material on the battery plates changes chemical composition on each charge and discharge cycle, active material may be lost due to physical changes of volume; this may limit the cycle life of the battery.

Old chemistry rechargeable batteries self-discharge more rapidly than disposable alkaline batteries, especially nickel -based batteries; a freshly charged nickel cadmium (NiCd) battery loses 10% of its charge in the first 24 hours, and thereafter discharges at a rate of about 10% a month.Buchmann, Isidor. . Battery University . Retrieved 3 February 2009. However, newer Low self-discharge NiMH battery|low self-discharge nickel metal hydride (NiMH) batteries and modern lithium designs have reduced the self-discharge rate to a relatively low level (but still poorer than for primary batteries). Most nickel-based batteries are partially discharged when purchased, and must be charged before first use.. Energizer . Retrieved 3 February 2009. Newer NiMH batteries are ready to be used when purchased, and have only 15% discharge in a year. http://www.eneloop.info/home/performance-details/self-discharge.html

Although rechargeable batteries have their energy content restored by charging, some deterioration occurs on each charge–discharge cycle. Low-capacity NiMH batteries (1700–2000 mA·h) can be charged for about 1000 cycles, whereas high-capacity NiMH batteries (above 2500 mA·h) can be charged for about 500 cycles.. Retrieved 10 August 2007. NiCd batteries tend to be rated for 1000 cycles before their internal resistance permanently increases beyond usable values. Under normal circumstances, a fast charge, rather than a slow overnight charge, will shorten battery lifespan. However, if the overnight charger is not "smart" and cannot detect when the battery is fully charged, then overcharging is likely, which also damages the battery.. Retrieved 10 August 2007. Degradation usually occurs because electrolyte migrates away from the electrodes or because active material falls off the electrodes. NiCd batteries suffer the drawback that they should be fully discharged before recharge. Without full discharge, crystals may build up on the electrodes, thus decreasing the active surface area and increasing internal resistance. This decreases battery capacity and causes the " memory effect ". These electrode crystals can also penetrate the electrolyte separator, thereby causing shorts. NiMH, although similar in chemistry, does not suffer from memory effect to quite this extent.. Retrieved 10 August 2007. A battery does not suddenly stop working; its capacity gradually decreases over its lifetime, until it can no longer hold sufficient charge.

automotive battery|Automotive lead–acid rechargeable batteries have a much harder life.Buchmann, Isidor. Battery University . Retrieved 3 February 2009. Because of vibration, shock, heat, cold, and Lead–acid battery#Sulfation|sulfation of their lead plates, few automotive batteries last beyond six years of regular use.Rich, Vincent (1994). The International Lead Trade . Cambridge: Woodhead. 129. Automotive starting batteries have many thin plates to provide as much current as possible in a reasonably small package. In general, the thicker the plates, the longer the life of the battery. They are typically drained only a small amount before recharge. Care should be taken to avoid deep discharging a starting battery, since each charge and discharge cycle causes active material to be shed from the plates.

"Deep-cycle" lead–acid batteries such as those used in electric golf carts have much thicker plates to aid their longevity.. Northern Arizona Wind & Sun . Retrieved 3 February 2009. The main benefit of the lead–acid battery is its low cost; the main drawbacks are its large size and weight for a given capacity and voltage. Lead–acid batteries should never be discharged to below 20% of their full capacity,. Rainbow Power Company . Retrieved 3 February 2009. because internal resistance will cause heat and damage when they are recharged. Deep-cycle lead–acid systems often use a low-charge warning light or a low-charge power cut-off switch to prevent the type of damage that will shorten the battery's life.. Energy Matters . Retrieved 3 February 2009.

Extending battery life

Battery life can be extended by storing the batteries at a low temperature, as in a refrigerator or freezer , which slows the chemical reactions in the battery. Such storage can extend the life of alkaline batteries by about 5%; rechargeable batteries can hold their charge much longer, depending upon type.. Retrieved 7 March 2007. To reach their maximum voltage, batteries must be returned to room temperature; discharging an alkaline battery at 250 mA at 0°C is only half as efficient as it is at 20°C. Alkaline battery manufacturers such as Duracell do not recommend refrigerating batteries.

Prolonging life in multiple cells through cell balancing

Analog front ends that balance cells and eliminate mismatches of cells in series or parallel combination significantly improve battery efficiency and increase the overall pack capacity. As the number of cells and load currents increase, the potential for mismatch also increases. There are two kinds of mismatch in the pack: state-of-charge (SOC) mismatch and capacity/energy (C/E) mismatch. Though the SOC mismatch is more common, each problem limits the pack capacity (mAh) to the capacity of the weakest cell.

;Cell balancing principle

Battery pack cells are balanced when all the cells in the battery pack meet two conditions:
# If all cells have the same capacity, then they are balanced when they have the same State of Charge (SOC.) In this case, the Open Circuit Voltage (OCV) is a good measure of the SOC. If, in an out of balance pack, all cells can be differentially charged to full capacity (balanced), then they will subsequently cycle normally without any additional adjustments. This is mostly a one-shot fix.
# If the cells have different capacities, they are also considered balanced when the SOC is the same. But, since SOC is a relative measure, the absolute amount of capacity for each cell is different. To keep the cells with different capacities at the same SOC, cell balancing must provide differential amounts of current to cells in the series string during both charge and discharge on every cycle.

;Cell balancing electronics

Cell balancing is defined as the application of differential currents to individual cells (or combinations of cells) in a series string. Cells in a series string normally receive identical currents. A battery pack requires additional components and circuitry to achieve cell balancing. However, the use of a fully integrated analog front end for cell balancing reduces the required external components to just balancing resistors.

Cell mismatch results more from limitations in process control and inspection than from variations inherent in the lithium ion chemistry. The use of a fully integrated analog front end for cell balancing can improve the performance of series connected Li-ion Cells by addressing both SOC and C/E issues. SOC mismatch can be remedied by balancing the cell during an initial conditioning period and subsequently only during the charge phase. C/E mismatch remedies are more difficult to implement and harder to measure and require balancing during both charge and discharge periods.

This solution eliminates the quantity of external components, as for discrete capacitors, diodes, and most other resistors to achieve balance.

Battery sizes

Primary batteries readily available to consumers range from tiny button cell s used for electric watches, to the No. 6 cell used for signal circuits or other long duration applications. Secondary cells are made in very large sizes; very large batteries can power a submarine . Large secondary batteries have been used to stabilize the electrical grid and help level out peak loads.

Hazards

Explosion

A battery explosion is caused by the misuse or malfunction of a battery, such as attempting to recharge a primary (non-rechargeable) battery, or short circuit ing a battery. Car batteries are most likely to explode when a short-circuit generates very large currents. Car batteries liberate hydrogen , which is very explosive, when they are overcharged (because of electrolysis of the water in the electrolyte). The amount of overcharging is usually very small and generates little hydrogen, which dissipates quickly. However, when "jumping" a car battery, the high current can cause the rapid release of large volumes of hydrogen, which can be ignited explosively by a nearby spark, for example, when disconnecting a jumper cable.

When a battery is recharged at an excessive rate, an explosive gas mixture of hydrogen and oxygen may be produced faster than it can escape from within the walls of the battery, leading to pressure build-up and the possibility of bursting of the battery case. In extreme cases, the battery acid may spray violently from the casing of the battery and cause injury. Overcharging—that is, attempting to charge a battery beyond its electrical capacity—can also lead to a battery explosion, in addition to leakage or irreversible damage. It may also cause damage to the charger or device in which the overcharged battery is later used. In addition, disposing of a battery in fire may cause an explosion as steam builds up within the sealed case of the battery.

Leakage

Many battery chemicals are corrosive, poisonous, or both. If leakage occurs, either spontaneously or through accident, the chemicals released may be dangerous.

For example, disposable batteries often use a zinc "can" both as a reactant and as the container to hold the other reagents. If this kind of battery is run all the way down, or if it is recharged after running down too far, the reagents can emerge through the cardboard and plastic that form the remainder of the container. The active chemical leakage can then damage the equipment that the batteries were inserted into. For this reason, many electronic device manufacturers recommend removing the batteries from devices that will not be used for extended periods of time.

Environmental concerns

The widespread use of batteries has created many Electronic waste|environmental concerns , such as toxic metal pollution.. EPA . Retrieved 11 September 2007. Battery manufacture consumes resources and often involves hazardous chemicals. Used batteries also contribute to electronic waste . Some areas now have battery recycling services available to recover some of the materials from used batteries.. Retrieved 9 September 2007. Batteries may be harmful or fatal if swallowing|swallowed . (PDF, p. 2). Retrieved 9 September 2007. Recycling or proper disposal prevents dangerous elements (such as lead , mercury (element)|mercury , and cadmium ) found in some types of batteries from entering the environment. In the United States, Americans purchase nearly three billion batteries annually, and about 179,000 tons of those end up in landfills across the country."San Francisco Supervisor Takes Aim at Toxic Battery Waste". Environmental News Network (11 July 2001).

In the United States, the Mercury-Containing and Rechargeable Battery Management Act of 1996 banned the sale of mercury-containing batteries, enacted uniform labeling requirements for rechargeable batteries, and required that rechargeable batteries be easily removable. http://www.epa.gov/epawaste/laws-regs/state/policy/p1104.pdf California, and New York City prohibit the disposal of rechargeable batteries in solid waste, and along with Maine require recycling of cell phones. http://www.rbrc.org/consumer/howitallworks_faq.shtml? PHPSESSID=ad1e142bcdd99cd67418f2171794d892 The rechargeable battery industry has nationwide recycling programs in the United States and Canada, with dropoff points at local retailers.

The Battery Directive of the European Union has similar requirements, in addition to requiring increased recycling of batteries, and promoting research on improved battery recycling methods.. European Union . Retrieved 27 July 2009.
In accordance with this directive all batteries to be sold within the EU must be marked with the "collection symbol" (A crossed out wheeled bin). This must cover at least 3% of the surface of prismatic batteries and 1.5% of the surface of cylindrical batteries. All packaging must be marked likewise.

Ingestion

Small button cell s can be swallowed, particularly by young children. While in the digestive tract the battery's electrical discharge may lead to tissue damage http://www.poison.org/battery/; such damage is occasionally serious and very rarely even leads to death. Ingested disk batteries do not usually cause problems unless they become lodged in the gastrointestinal (GI) tract. The most common place disk batteries become lodged, resulting in clinical sequelae, is the esophagus. Batteries that successfully traverse the esophagus are unlikely to lodge at any other location. The likelihood that a disk battery will lodge in the esophagus is a function of the patient's age and the size of the battery. Disk batteries of 16& nbsp;mm have become lodged in the esophagi of 2 children younger than 1 year. Older children do not have problems with batteries smaller than 21–23& nbsp;mm. Liquefaction necrosis may occur because sodium hydroxide is generated by the current produced by the battery (usually at the anode). Perforation has occurred as rapidly as 6 hours after ingestion.

Battery chemistry

Primary battery chemistries

(includes data from the energy density article)

Chemistry !! Nominal Cell Voltage !! Specific Energy & #91;MJ/ kg& #93; !! Elaboration
Zinc–carbon
Zinc–chloride
Alkaline (zinc–manganese dioxide)
Nickel oxyhydroxide battery>Nickel oxyhydroxide (zinc–manganese dioxide/ nickel oxyhydroxide)
Lithium (lithium–copper oxide) Li–CuO
Lithium (lithium–iron disulfide) LiFeS₂
Lithium (lithium–manganese dioxide) LiMnO₂
Mercury oxide
Zinc–air
Silver-oxide (silver–zinc)

Rechargeable battery chemistries

(includes data from energy density article)

Chemistry !! Cell Voltage !! Specific Energy & #91;MJ/ kg& #93; !! Comments
NiCd
Lead–acid
NiMH
NiZn
Lithium ion

Homemade cells

Almost any liquid or moist object that has enough ions to be electrically conductive can serve as the electrolyte for a cell. As a novelty or science demonstration, it is possible to insert two electrodes made of different metals into a lemon battery|lemon ,. Accessed 10 April 2007. potato ,. Accessed 10 April 2007. etc. and generate small amounts of electricity. "Two-potato clocks" are also widely available in hobby and toy stores; they consist of a pair of cells, each consisting of a potato (lemon, et cetera) with two electrodes inserted into it, wired in series to form a battery with enough voltage to power a digital clock.. Accessed 10 April 2007. Homemade cells of this kind are of no real practical use, because they produce far less current and cost far more per unit of energy generated—than commercial cells

A voltaic pile can be made from two coins (such as a nickel and a penny ) and a piece of paper towel dipped in saline water|salt water . Such a pile generates a very low voltage but, when many are stacked in series circuit|series , they can replace normal batteries for a short time.. Accessed 10 April 2007.

Sony has developed a biological battery that generates electricity from sugar in a way that is similar to the processes observed in living organisms. The battery generates electricity through the use of enzymes that break down carbohydrates, which are, in essence, sugar.. Accessed 24 August 2007.

Lead acid cells can easily be manufactured at home, but a tedious charge/discharge cycle is needed to 'form' the plates. This is a process in which lead sulfate forms on the plates, and during charge is converted to lead dioxide (positive plate) and pure lead (negative plate). Repeating this process results in a microscopically rough surface, with far greater surface area being exposed. This increases the current the cell can deliver. For an example, see .

Daniell cell s are also easy to make at home. Aluminium–air batteries can also be produced with high-purity aluminium. Aluminium foil batteries will produce some electricity, but are not very efficient, in part because a significant amount of hydrogen gas is produced.

Copyright Citations

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1. Flashlight 2. Magneto

Undetermined Music Artists

Dry Cell

Biography

History

Principle of operation

Categories and types of batteries

Primary batteries

Secondary batteries

Battery cell types

Wet cell

Dry cell

Molten salt

Reserve

Battery cell performance

Battery capacity and discharging

Fastest charging, largest, and lightest batteries

Battery lifetime

Primary batteries

Secondary batteries

Extending battery life

Prolonging life in multiple cells through cell balancing

Battery sizes

Hazards

Explosion

Leakage

Environmental concerns

Ingestion

Battery chemistry

Primary battery chemistries

Rechargeable battery chemistries

Homemade cells

See also

References

Further reading

External links

Copyright Citations