Mechanism of operation of the accumulator
Accumulators are chemical current sources with obratiyomy process: they can give energy, transforming himiyochesky energy in electric, or to accumulate energy, transforming electrical energy to chemical. In a Tayoky way, the accumulator alternately is discharged, giving electrical energy, is charged from any relevant source of the direct current.
Accumulators, depending on the elektroyolit applied in them, are subdivided on acid and alkaline. Besides, accumulators differ, depending on material of electrodes. Only lead, cadmium-nickel, iron-nickel and silver-zinc akkuyomulyator have broad application.
Accumulator capacity is defined by quantity of the elektriyochestvo of qp which it can give at discharge to the fed chain.
This amount of electricity is measured not in the Coulomb, and in larger units — ampere-hours (and - h). 1 and - h = 3600 C. But the charge of the accumulator requires bigger amount of q3 electricity, than given at discharge. qp relation: q3 =ne is called return of the accumulator on capacity.
Tension necessary for the accumulator charge, is znachiyotelno higher than that tension on clips of the accumulator at which it gives is long the discharge current.
The important characteristic of the accumulator are its averages charging and digit tension.
It is clear, what because of the number of losses of energy the accumulator gives at discharge the smaller amount of energy of Wp is considerable, than poluyochat at the charge. Wp relation: W3 = n is the efficiency or return on energy of the accumulator.
At last, the size, very important for the characteristic of the accumulator, am its specific э N е р also I, i.e. the amount of the energy given at discharge, falling on 1 kg of weight of the accumulator. It is especially essential that non-stationary accumulators had the specific energy perhaps more, ustayonavlivayemy, for example, by airplanes. In similar cases usually it is more important, than the efficiency and the otyodacha on capacity.
It must be kept in mind that at slow discharge process in the accumulator proceeds evenly in all mass of plates, благодаря to what at long discharge small current the capacity of the akkuyomulyator is more, than at short-term discharge big current. At fast discharge process in the mass of plates lags behind process on their surface that causes intrinsic currents and reduction of return.
Accumulator tension significantly changes in discharge time. It is desirable that it was perhaps more postoyanyony. In calculations the average digit napryayozheniye of Up usually is specified. But for the charge of the accumulator the current source giving considerably the bigger charge voltage of Uz is necessary (for 25 — 40%). Otherwise it is impossible to charge the accumulator completely.
If tension of one accumulator element nedostayotochno for this installation, then necessary number of akkumulyatoryony elements connects consistently. Of course, it is posledoyovatelno possible to connect only the accumulators expected the same digit current intensity.
If the discharge current of one element is insufficient, then parallel connection of several identical elemenyot primeyonyatsya.
From among lead-acid accumulators only lead accumulators have practical value. In them on the positive electrode as active agent serves R02 lead dioxide, on the negative electrode — the R spongy lead. Positive plates have brown color, otritsatelyyony — gray, as electrolyte solution by the H2S04 acid siren with with the specific weight of 1,18 — 1,29 is applied.
Chemical process of discharge and charge of the lead akkumulyayotor is rather difficult. Generally it comes down to recovery of lead on the positive electrode and to oxidation of gubchayoty lead on the negative electrode in zakisny salt of sulphuric acid. At the same time water is formed and, therefore, density of electrolyte decreases. At the razryayoda at first accumulator tension quickly falls to 1,95 B, and then slowly goes down up to 1,8 Century. Then it is necessary to stop discharge.
At further discharge irreversible process of formation of crystal sulfate PbS4 lead takes place. Poyosledny covers plates white for a short while. It has bolyyoshy unit resistance and is almost not soluble in the elektroyolita. The layer of sulfate lead increases the internal soproyotivleniye of active mass of plates. Such process is called sulphation of plates.
At the accumulator charge process goes in the return napravyoleniye: on the negative electrode metalliyochesky lead is recovered, and on the positive electrode lead is oxidized to R02 dioxide. The ion of S04 passes into electrolyte therefore density of sulphuric acid at the charge increases, sledovayotelno, also the specific weight of electrolyte increases. To measurement of specific weight of electrolyte it is applied special ареометр. It is possible to judge by its indications approximately in what measure the accumulator is charged. Medium spark-over voltage of the lead accumulator 1,98 B, and medium charge voltage of 2,4 Century.
Internal resistance of rbn of lead accumulators, благодаря to small distance between plates and the big ployoshchada of their contact with electrolyte, is not enough: the order of thousand shares of ohm at stationary accumulators and the 100-th doyoly at small figurative accumulators.
Owing to the small internal resistance and rather big tension of efficiency of these accumulators reaches 70 — 80%, and return — 0,85 — 0,95%.
However because of small internal resistance in lead accumulators at short circuits there are currents of very big force that leads to buckling and disintegration of plates.
Lead accumulators possess the number of essential neyodostatok. They are heavy because of the big weight of lead of plates, and their volume is big because of the significant amount of the electrolyte aktivyono participating in process. In them the self-discharge vnutyorenny stray electric currents with loss of the charge about 1% a day is inevitable. At last, they are very sensitive to pushes and concussions. But their return and efficiency is much higher, than at any other accumulators.
From among alkaline accumulators have the wide priyomeneniye cadmium-nickel, iron-nickel and silver-zinc now. In all these accumulators as electrolyte serves alkali — approximately two-percent rayostvor of the KON caustic potassium or the caustic natr of NaOH. At the charge and discharge this electrolyte almost does not undergo changes. Sleyodovatelno, accumulator capacity does not depend on its quantity. It gives the chance to minimize the number of the elektroliyot in all alkaline accumulators and in such way it is essential to facilitate them.
Skeletons of positive and negative plates of these akkuyomulyator are made of the steel nickelized framework with packages for active weight. Thanks to such design active weight strongly keeps in plates and does not drop out at pushes.
In cadmium-nickel KN the accumulator as akyotivny substance of the positive electrode serve the nickel oxides mixed for increase in conductivity with grafiyoty; active agent of the negative electrode is spongy metal CD cadmium. At discharge on the polozhiyotelny electrode the part of active oxygen, содержащегося in nickel oxides is spent, and on the negative electrode metal cadmium is oxidized. At the charge the positive electrode obogayoshchatsya back by oxygen: hydrate of protoxide of Ni (OH) 2 nickel passes into hydrate of oxide of Ni (OH) 3 nickel. On the negative electrode hydrate of protoxide of cadmium vosstanavliyovatsya in pure cadmium. Approximately process in this akkumulyayotor can be expressed by the chemical formula:
2Ni (IT) 3 + 2KOH + Cd ?? 2Ni (IT) 2 + 2KOH + Cd (IT) 2.
As the formula shows, from electrolyte at discharge the particle (IT) 2 on the negative plate vydeyolyatsya and the same particle passes into electrolyte on the positive plate. At the charge process goes in the opposite direction, but in both cases electrolyte does not change.
The device of the Edison accumulator differs only in what in is mute in negative plates cadmium is replaced with small powder of iron (Fe). The equation can prosleyodit chemical process of this accumulator on the aforesaid for the cadmium-nickel akkumulyayotor by replacement of CD by Fe.
Use of iron instead of cadmium reduces the price of the akkumulyayotor, does it to stronger mechanically and increases the term of its service. But from other storoyona, at the iron-nickel akkuyomulyator at the same approximately spark-over voltage charge voltage is 0,2 B higher owing to what the efficiency of this accumulator to the niyozha, than cadmium-nickel. Then very important nedostatyok of the iron-nickel akkumuyolyator is rather fast self-discharge. At the cadmium-nickel accumulator the self-discharge is small and therefore it is given preference when the accumulator has to is long to be in the charged soyostoyaniye, for example for the power supply of radio sets. The average digit napryazheyony both of these accumulators is equal to 1,2 Century.
Air-locked vessels of the above described alkaline accumulators are made of the sheet nickelized steel. Bolts through which plastiyona of accumulators connect to the external purpose are passed through the otveryostiya in the vessel cover, and the bolt to which negative playostina are connected is carefully isolated from the steel body; but the bolt connected to positive plates is not isolated from the body.
Internal resistance of alkaline accumulators is znachiyotelno more, than acid, thanks to it they pereyonosit short circuits better. But for the same reason the efficiency of shchelochyony accumulators (about 45%) is much lower, than kisyolotny, also significantly less their specific energy and the otdayocha on capacity (0,65). As the condition of electrolyte at alkaline accumulators during the work does not change, it is impossible to determine their state of charge by external signs. Owing to what it is necessary to watch the charge on the basis of their capacity and tension. At the charge it is necessary to report to the accumulator amount of It=q electricity considerably bigger, than its capacity, approximately by 1,5 times. For example, and - it is desirable to charge the accumulator with a capacity of 100 with current with a force of 10 and during the 15th hour h.
Silver cells are noveyyoshy from among modern accumulators. As electrolyte in them serves vodyony solution of the KON caustic potassium with the specific weight of 1,4, with active agent of the positive electrode (Ag20 silver oxide) and negative electrofood (Zn zinc). Electrodes are made in the form of porous plates and отделяются from each other by the film partition.
At discharge of the accumulator oxide of silver is recovered to metalliyochesky silver, and metal zinc is oxidized to ZnO zinc oxide. Obyoratny process happens at the accumulator charge. The main chemical reaction is expressed by the formula
AgsO + GAME + Zn?? 2Ag + GAME + ZnO.
chargeSteady spark-over voltage is about 1,5 Century. At small currents of discharge this tension almost does not change during about 75 — 80% of the operating time of the accumulator. Then it quickly enough falls, and at the voltage of 1 in discharge it is necessary to stop.
Internal resistance of silver cells is sushchestyovenno less, than other alkaline accumulators. At equal capacity the first it is much easier. They well work as at lowered (— 50 °C), and at raised (+ 75 °C) temperatures. At last, they allow big discharge currents. For example, some types of such akkuyomulyator can be warmed the short-circuit current within one minute.
Above only the main data on accumulators are stated. During the practical work with accumulators, in particular with lead, it is necessary to carry out the corresponding factory instructions carefully. Violation causes them fast destruction of accumulators.Top