See also: Accumulating

An electric fencer is a device intended for to store the electrical energy and to restore it later on.

One distinguishes:

1. the accumulators of energy converting electrical energy in another form in order to store it (for example in kinetic Energy) and, which are able to restore it later on. See: Storage of energy.
2. electric fencers functioning according to the principles of the electrostatic : Leyden jar, Condensing S.
3. electric fencers functioning according to the principles of the electrodynamic : circuit wound
4. the electrochemical accumulators , functioning thanks to the electrochemical reactions their electrodes, which ensure the conversion of the chemical energy into electrical energy .
5. the piles which are not electrochemical accumulators, because they are not refillable. electrochemical Piles and accumulators is electrochemical generators. The piles provide the quantity of electricity envisaged to their manufacture (no load, nor preparation is necessary before use).

General information

Electrical energy thus can store various manners:

• In the form of electrostatic energy , by accumulating electric charges in one or more condensing S. the appearance, about 1995, of condensers whose capacity can reach a few hundred farads makes it possible to carry out substitutes with the traditional accumulator batteries. The advantages are a reduction in the weight and a possible operation by very great cold (polar vehicles). With a disadvantage of size the price to the Wh stored definitely higher.

• In the form of electromagnetic energy , by establishing an electric current in a circuit wound around a Magnetic circuit, so that energy necessary to put moving the electric charges can be restored by induction.
  the storage period of energy remains weak even with best conducting metals than are the money and coppers it because of the losses by Joule effect in the circuit; a storage of long life requires thus the use of materials superconductive S. the devices thus carried out are known under the name of SMES: Superconducting Magnet Energy Storage.

• In electrochemical form , which shows the characteristic interesting to provide a power (potential difference) on its terminals not very dependant on its load (quantity of stored energy) or running output. One uses the property which have some Couple S chemical to accumulate a certain quantity of electricity by modifying their molecular structure and this in a reversible way.

• Différents types of chemical couples is used for the realization of electric fencers.

Taking into account the limits of the techniques of direct storage of electricity, the accumulating word indicates in electrotechnical mainly the electrochemical device .

General characteristics of the electrochemical accumulators

• the tension or potential (in Volt) is an important parameter. Fixed by the Potential of oxydoreduction of the couple redox used, it is about a few volts for an element. As in practice of the more raised tensions, typically 12,24 even 48  V and more are required, it is enough to increase the tension to connect elements of the same type in series within an accumulator battery. It is undoubtedly the origin of the term “Batterie” like synonym running of “accumulator” and, in English, of “pile”; however some evoke another possible etymological source: the effect of shock of an electric current, as if the electrical appliance “beat” that which receives the discharge.
• the electric capacity is generally indicated in A.h (Amp (S) during one hour) by the manufacturer. It is measured in practice by reference to the time of load/discharge, in Ah (amp - hour) or mAh (Milli amp - hour), but the official unit (IF) is the Coulomb.

1 Ah = 1  000  mAh = 3  600  C; 1  C = 1  Ah/3  600 = 0,278  mAh.

• the energy stored is usually measured in Wh (Watt - hour) but the official unit (IF) is the joule.

1 Wh = 3  600  J = 3,6  kJ; 1  J = 0,278  MWh.

• the maximum capacity of an accumulator is measured in amp.
• the impedance intern, expressed in Ohm, impedance parasite which limits the current of discharge, as well as the frequency of this current, by transforming into heat by Joule effect part of restored energy. In practice, one often compares the impedance to only the pure resistance.
• the mass density is one of the important characteristics of an accumulator, it corresponds to the quantity of electricity (Ah/kg) or energy (Wh/kg) which it can restore compared to its mass .
• the voluminal density is another characteristic which can have its importance, it corresponds to the quantity of electricity (Ah/m ³) or energy (Wh/m ³) which it can restore compared to its volume.
• the ageing , because the batteries lose of their capacity with time (several years).
• the wear , because the batteries lose of their capacity with the use (several thousands of cycles of load and discharge).

Various technologies

Lead - Acid

See also: Lead-acid battery

The nominal voltage of an accumulating element of this type is of 2  V. It also potentially acts of the system oldest, but one of the more polluting. It is the device of storage of electrical energy used in the majority of the Véhicule S Automobile S.

• the lead accumulator was invented by Gaston Planté which observed the electrolysis acidulous water.

• By testing the Lead in its search for matters more economic than the Platinum, it noticed that its apparatus returned electricity when the supply was cut off; as if the Oxygen and the Hydrogène could return the electricity which had produced them.
• It believed to have invented the Combustible battery, but understood quickly that it was not the Oxygène and the Hydrogène gas which returned the current, but the modification Chimique (oxidation) of the surface of lead.
• Its apparatus was composed of two lead blades maintained drawn aside by insulating tapes. To increase the surface of the electrodes, Planté rolled up concentrically two lead strips separated by two rubber guides to avoid any contact between them, the whole contained in a bottle of glass filled with acidulous water.
• to obtain a capacity of important discharge, G. Planted noted that it was necessary to subject the electrodes a series of cycles charges/discharge which constituted what it called “the formation”.

• the operation of the battery does not disperse lead.
• lead is polluting, on the other hand the Recyclage of the batteries is easy. The transport and the recycling of the batteries are more and more severely regulated, which increases the expenses, decreases the profitability of recycling; consequently the quantity of recycled batteries tends to decrease, the price of the kilogram of batteries becomes lower than the price of the kilogram of scrap.
• the lifespan as well as the performances of a lead-acid battery strongly depends on the use that one makes some. Thus, one saw batteries returning the heart after only 50 cycles whereas others of the same type held more than 500 cycles. This strong disparity is partly due to the fact that these batteries are influenced by the type of cycle charges/discharge that one imposes to them, support the major discharges very badly and require a system embarked of very thorough control in order to provide the best possible performances.

Ni-Cd (Cadmium-nickel)

See also: Accumulating cadmium-nickel

The nominal voltage of an accumulating element of this type is of 1,2   V. This electrochemical couple one of has been most usually used for several decades to manufacture accumulator batteries supplying the portable devices. This type of accumulator has a Ratchet effect, which imposes their storage in a state discharged ( 0,6   V). The end of load is characterized by a variation of the charging voltage (dv/dt) negative. It is this threshold which is detected by the automatic chargers of quality to stop the load.

Compared to Nor-MH, Ni-Cd can support more important points of current in discharge (about 10 times) but its natural discharge is much faster than that of Nor-MH. The Cadmium is very polluting. This type of accumulator allows a number of cycles charges/discharge more important than the accumulators Li-ion and much more important than the Nor-MH (higher lifespan).

Let us note finally that the considerable increase of the courses of nickel these last years started again the market of this type of accumulators in its industrial uses (aeronautical, railway, stationary applications).

Nor-MH (Nickel-metal hydride)

See also: Accumulating nickel-metal hydride

The nominal voltage of an accumulating element of this type is of 1,2   V. This type of accumulator incorporates neither Cadmium nor Plomb and is thus low polluting. Moreover, its mass energy is higher of 40  % with that of Ni-Cd and its Ratchet effect is very weak.

The end of load is characterized by a variation of the charging voltage (δv/δt) very slightly negative. It is this threshold which is detected by the automatic chargers of quality to stop the load.

Ni-Zn (Nickel-zinc)

See also: Accumulating nickel-zinc

NiZn is a couple known for a long time, but which could not have been industrialized significantly, because of a very weak lifespan in cycling.

This problem is completely solved today by a new technology developed in France between 1998 and 2005.

NiZn constitutes from now on a system at the same time energy and of power, with the performances higher than those of NiCd and NiMH. It accepts high modes of load and discharge. Its nominal voltage is of 1,65 V . NiZn is a robust, reliable and perfectly sure accumulator, functioning in mode without maintenance (tight).

Its lifespan in cycling is equivalent to that of NiCd, its autodécharge and its ratchet effect is lower.

NiZn is of manufacture more economic than the other alkaline batteries (NiCd and NiMH). It does not contain any heavy metal, and it is easily and completely which can be recycled at the end of the lifetime.

Lithium

See also: Accumulating lithium

The accumulators containing Lithium are of a Technologie recently put at the point and under development intense, having a very important electrochemical potential .

One distinguishes the technology Lithium metal where the negative electrode is made up of metal lithium (material which presents big problems of safety), and technology lithium ion , where lithium remains in an ionic state thanks to the use of a compound of insertion as well to the negative electrode (generally out of graphite) as with the positive electrode. The security issues remain (taken of fire) in the event of overload, of surdécharge or short-circuit. The accumulators lithium-ion are partially replaced by the accumulators lithium Polymère delivering a little less energy, but much surer.

The lifespan of these accumulators is only from 2 to 3 years after manufacture, independently of the number of cycles of loads.

The potential most widespread of a cell to the Lithium - Ion is of 3,7 V.

Alkaline pile

Contrary to the mentions registered on their Packing S, the alkaline piles “nonrefillable” can they also be regenerated partially. But only with one charger adapted to this use. the standard chargers (Nor-MH or Ni-Cd) use methods of nonsuitable loads which make the operation dangerous , being able to go until the Explosion of the pile or at least the destruction of the Container with escape of the components Acide S.D'ailleurs, by safety and in a general way, each chemistry thus requires a method of specific charge a compatible charger.

Admittedly, the alkaline will undergo a number of Cycle S less large than an accumulating , even while remaining under the ideal conditions of reversibility of the chemical reaction (in particular, by never not discharging the elements with less than 1,25 V), it is possible to regenerate them a few tens of time. Consequently, this possibility is ignored general public, the more so as it is reserved for the informed amateurs of the constraints. Moreover, that can be valid only for certain uses.

Alkaline refillable

There exists since the years a 2000 improved version known as alkaline refillable , specifically intended to be reloaded many times. This product is in particular manufactured by a Canadian company . It is available in the Commerce in an almost confidential way.

This type of alkaline piles is particularly adapted to the apparatuses which discharge neither too quickly, nor too deeply their accumulators. But they can be used as accumulator of help thanks to the long life of conservation of the load except use.

Brominate

Currently at the stage of prototype, the accumulators containing Brome will be probably reserved for the fixed installations because they require the circulation of the electrolyte and that, moreover, bromine is particularly dangerous.

The studied couples are: Sodium - brominates, Vanadium - brominates and Zinc - brominates.

Comparative table of various technologies

The battery Li-Po (lymère) is indeed less powerful than the Li-ion but differently manufactured. It takes less place than the Li-ion. Consequently a battery of the same Li-Po cuts than a battery Li-ion has a more important capacity. Attention the preceding table gives the relationship between stokée energy (Wh) and battery masses it (in kg). However, a battery Li-Po is denser than an Li-ion, from where the difference.

See too

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