Batteries are otherwise called secondary cells, or secondary sources. electrical energy. They differ from galvanic cells in that they cannot release energy immediately after manufacture; they must first be charged.
When charging a battery, electrolysis occurs (the breakdown of electrolyte molecules into positive and negative ions, called cations and anions), accompanied by the conversion of electrical energy into chemical energy. As a result of this process, an emf is created at the battery terminals. After charging, the battery can serve as a source of current. During the battery discharge process, stored chemical energy is converted into electrical energy. Thus, the battery stores (accumulates) electrical energy when charged and releases it when discharged.
Acid batteries
Acid batteries are widely used both to power radio and telephone equipment, and to power electrical equipment of vehicles.
An acid battery cell consists of a vessel filled with electrolyte, in which there are positive and negative electrodes (in the form of plates) separated from one another. Individual elements, called banks, are connected into rechargeable batteries, which are called batteries for short. The structure of an acid battery is shown in Fig. 28. The body of the acid battery is made of electrically insulating and acid-resistant material (glass, hard rubber and special types of plastic).
The positive plates of acid batteries are made from red lead (lead oxide with a slightly higher oxygen content) pressed into a lead grid. Negative plates are made from lead litharge (lead oxide) pressed into a lead grid.
To avoid short circuits, the plates are separated from one another by a porous insulating gasket - a separator. To make separators, wood (alder, pine, cedar), hard rubber with microscopic pores (called mipor), microporous plastic (miplast), etc. are used.
The electrolyte is a solution of sulfuric acid in distilled water. Depending on the ambient temperature During battery operation, the density of the electrolyte should be different.
The density of the electrolyte is measured with a hydrometer, which is a small tube that expands downwards. At the bottom of the hydrometer there is a strictly defined amount of weight, and top part has a scale whose divisions indicate density. When the hydrometer is lowered into the electrolyte, it is immersed to the division that corresponds to the density of the electrolyte.
New factory batteries are sold uncharged, and the duration of their operation depends on the correct first charge. A new battery should be filled with electrolyte with a density of 1.12 at a temperature of +20°C and left for five to six hours so that the active mass of the plates is saturated with the electrolyte. Filling is done through a funnel into a special filling hole. The electrolyte level should be 10-15 mm above the top edge of the plates.
To prepare the electrolyte, use industrial sulfuric acid density 1.83-1.84, which is diluted with distilled water. Concentrated sulfuric acid is very poisonous and must be handled with great care. The electrolyte is prepared in the following sequence. The required amount of distilled water is poured into a glass vessel, and then sulfuric acid is poured into the water in a thin stream and in small portions from the bottle, stirring the solution with a glass rod.
It is strictly forbidden to pour water into sulfuric acid, as this will cause rapid boiling and splashing of the acid in all directions. Drops of acid on your hands and face can cause severe burns.
The battery is charged using direct current from the mains direct current or a special rectifier.
The rectifier must be equipped with a rheostat or autotransformer that allows you to change the amount of charging current. The battery is connected to the charging circuit as follows: the positive terminal of the battery (+) is connected to the positive terminal of the rectifier (mains), and the negative terminal (-) to the negative terminal of the rectifier (mains). The battery charging diagram is shown in Fig. 29.
An ammeter is included in the charging circuit to monitor the current value.
The batteries are charged with a current, the value of which is indicated by the manufacturer in the technical data sheet (for stationary batteries, the charging current is equal to one fifteenth of the battery capacity).
The first charge usually lasts 36 hours continuously. After this, take a break for 3 hours and continue charging with the same current for another 12 hours. Towards the end of charging, the electrolyte “boils” (abundant release of gas bubbles - hydrogen and oxygen) occurs, and the electrolyte level can increase significantly. Excess electrolyte should be sucked out with a rubber bulb.
When the voltage at the terminals of one jar rises to 2.3-2.5 V, you should measure the density of the electrolyte and bring it to 1.285.
After charging is completed, the new battery should be discharged with a current equal to one twentieth of the battery capacity until the voltage on each bank is equal to 1.8 e. Then the battery is charged for 10-12 hours and after that it can be put into operation. The voltage on each bank of a freshly charged battery is 2.6-2.86 V. The voltage on the bank should be measured with a special voltmeter equipped with a load resistance, called a battery probe. In order to prevent the explosion of detonating gas formed during charging as a result of electrolysis of water, the probe can be used no earlier than two to three hours after charging.
The battery voltage can be measured with a conventional DC voltmeter when the battery is loaded with a current equal to Vio its capacity.
Depending on the purpose, there are several types of acid (lead) batteries. To power stationary devices, stationary batteries are used, the housing of which is usually made of glass or wood lined with a layer of lead.
Types of electrical energy batteries
Batteries are an integral part of any system focused on obtaining alternative types energy.
The most widespread to date are electrochemical batteries of electrical energy, in which the conversion of chemical energy into electrical energy when the battery is discharged occurs through a chemical reaction. When charging a battery, the chemical reaction occurs in the opposite direction.
In addition to electrochemical batteries, electricity can be stored in capacitors and solenoids (inductors).
In a charged capacitor, energy is stored in the form of energy electric field dielectric. Due to the fact that specific energy, stored by the capacitor is very small (practically from 10 to 400 J/kg), and the duration of possible energy storage due to its leakage is short; this type of energy accumulator is used only in cases where it is necessary to give electricity to the consumer for a very a short time at short term its storage.
In the solenoid, electrical energy is accumulated in the form of magnetic field energy. Therefore, this type of storage device is called electromagnetic. But the energy output time of electromagnetic batteries is usually measured not even in seconds, but in fractions of a second.
To charge the battery you need external source energy, and energy losses may occur during charging. After charging, the battery may remain in a ready state (in a charged state), but even in this state, some energy may be lost due to random dissipation, leakage, self-discharge, or other similar phenomena. When energy is released from the battery, energy losses may also occur; In addition, sometimes it is impossible to get back all the accumulated energy. Some batteries are designed to retain some residual energy.
Battery characteristics
The main characteristic of the battery is its electrical capacitance. The unit of measurement for this capacity is the ampere hour (Ah), a non-system unit of measurement of electrical charge.
Based physical meaning, 1 ampere hour is electric charge, which passes through cross section conductor for one hour if there is a current of 1 ampere in it. Theoretically, a charged battery with a stated capacity of 1 Ah is capable of providing a current of 1 ampere for one hour (or, for example, 0.1 A for 10 hours, or 10 A for 0.1 hour).
In practice, the battery capacity is calculated based on a 20-hour discharge cycle to the final voltage, which for car batteries is 10.8 V. For example, the inscription on the battery label “55 Ah” means that it is capable of delivering a current of 2.75 amperes for 20 hours, and the voltage at the terminals does not drop below 10.8 V.
Too much battery discharge current results in less efficient power delivery, which non-linearly reduces the battery's operating time at that current and can lead to overheating.
Battery manufacturers sometimes indicate capacity as technical specifications stored energy in Wh. Since 1 W = 1 A * 1 V, then if the stored energy is 720 Wh we can divide this value by the voltage value (say 12 V) and get the capacity in amp hours (in our example 720 Wh / 12 V = 60 Ah).
Lead acid batteries
In the charged state, the anode (negative electrode) of such a battery consists of lead, and the cathode (positive electrode) consists of lead dioxide PbO2. Both electrodes are made porous so that the area of their contact with the electrolyte is as large as possible. The design of the electrodes depends on the purpose and capacity of the battery and can be very diverse.
Chemical reactions during charging and discharging a battery are represented by the formula
РbO2 + Рb + 2Н2SO4<—>2РbSO4 + Н2О
To charge the battery, theoretically, a specific energy of 167 W/kg is required. The same number, therefore, expresses its theoretical limit of specific storage capacity. However, the actual storage capacity is much less, so that when discharged the battery typically produces electrical energy of approximately 30 W/kg. Factors causing a decrease in storage capacity are clearly presented in Fig. 1. Battery efficiency (the ratio of energy received during discharge to energy consumed during charging) is usually in the range of 70% to 80%.
Fig.1. Theoretical and actual specific storage capacity of a lead-acid battery
Various special measures (increasing the acid concentration to 39%, using plastic structural parts and copper connecting parts, etc.) in Lately it was possible to increase the specific storage capacity to 40 W h/kg and even slightly higher.
From the above data it follows that the specific storage capacity of a lead battery (and also, as will be shown later, other types of batteries) is significantly lower than that of primary galvanic cells. However, this disadvantage is usually compensated for
- the possibility of multiple charging and, as a result, an approximately tenfold reduction in the cost of electricity obtained from the battery,
- the ability to compose batteries with very high energy intensity (if necessary, for example, up to 100 MWh).
Each charge-discharge cycle is accompanied by some irreversible processes on the electrodes, including the slow accumulation of non-reducible lead sulfate in the mass of the electrodes. For this reason, through certain number(usually approximately 1000) cycles, the battery loses its ability to charge normally. This can also happen if the battery is not used for a long time, since the electrochemical discharge process (slow self-discharge) occurs in the battery even when it is not connected to an external electrical circuit. A lead-acid battery usually loses from 0.5% to 1% of its charge per day due to self-discharge. To compensate for this process, electrical installations use constant recharging at a fairly stable voltage (depending on the type of battery, at a voltage from 2.15 V to 2.20 V).
To others irreversible process is the electrolysis of water (“boiling” of the battery), which occurs at the end of the charging process. The loss of water can be easily compensated for by topping up, but the released hydrogen, together with air, can lead to the formation of an explosive mixture in the battery room or compartment. Adequate and adequate ventilation must be provided to avoid the risk of explosion.
Other battery types
In the last 20 years, hermetically sealed lead-acid batteries have appeared, which use a jelly-like electrolyte rather than a liquid one. Such batteries can be installed in any position, and in addition, given that they do not emit hydrogen during charging, they can be placed in any room.
In addition to lead batteries, more than 50 types of batteries are produced, based on various electrochemical systems. Alkaline (with an electrolyte in the form of a solution of potassium hydroxide KOH) nickel-iron and nickel-cadmium batteries are quite often used in power plants, the emf of which is in the range from 1.35 V to 1.45 V, and the specific storage capacity is in the range from 15 W h/kg to 45 W h/kg. They are less sensitive to temperature fluctuations environment and are less demanding on operating conditions. They also have a long service life (usually from 1000 to 4000 charge-discharge cycles), but their voltage changes during discharge within a wider range than lead-acid batteries, and their efficiency is slightly lower (from 50% to 70%).
In lithium-ion batteries, the anode consists of carbon containing lithium carbide Li x C 6 in a charged state, and the cathode is made of lithium and cobalt oxide Li 1-x CoO 2. Solid lithium salts (LiPF 6, LiBF 4, LiClO 4 or others) dissolved in a liquid organic solvent (for example, ether) are used as an electrolyte. A thickener (for example, organosilicon compounds) is usually added to the electrolyte, which gives it a jelly-like appearance. Electrochemical reactions during discharge and charge consist of the transition of lithium ions from one electrode to another and proceed according to the formula
Li x C 6 + Li 1-x CoO 2<—>C6 + LiCoO2
The external shape of lithium-ion battery cells can be flat (similar to quadrangular plates) or cylindrical (with rolled electrodes). Batteries are also produced that use other anode and cathode materials. One of important areas development is the development of fast-charging batteries.
There are many other types of batteries (about 100 in total). For example, in aircraft power supply systems, where the weight of the equipment should be as small as possible, silver-zinc batteries with a specific storage capacity of an average of 100 Wh/kg are used. The highest EMF (6.1 V) and the highest specific storage capacity (6270 Wh/kg) are found in lithium fluorine batteries, which, however, are not yet in mass production.
Primary galvanic cells are well suited for long-term operation, and batteries can be used for both long work, and to cover short-term and shock loads. Capacitors and inductors are used primarily to cover pulsed loads and to equalize power during rapid load changes. To equalize the power supplied to the power grid by wind and solar power plants, combinations of batteries with ultracapacitors can be used.
The scope of application of some storage devices in terms of load duration and output power is characterized in Fig. 2.
A chemical current source is a device in which, due to the occurrence of spatially separated redox chemical reactions, their free energy is converted into electrical energy. Based on the nature of their work, these sources are divided into two groups:
Primary chemical current sources or galvanic cells;
Secondary sources or electric batteries.
Primary sources allow only one-time use, since the substances formed during their discharge cannot be converted into the original active materials. A completely discharged galvanic cell, as a rule, further work unsuitable - it is an irreversible source of energy.
Secondary chemical current sources are reversible sources of energy - after an arbitrarily deep discharge, their functionality can be completely restored by charging. To do this, it is enough to pass an electric current through the secondary source in the direction opposite to the one in which it flowed during the discharge. During the charging process, the substances formed during the discharge will turn into the original active materials. This is how the free energy of the chemical current source is repeatedly converted into electrical energy (battery discharge) and the reverse conversion of electrical energy into free energy chemical current source (battery charge).
The passage of current through electrochemical systems is associated with the chemical reactions (transformations) that occur. Therefore, there is a relationship between the amount of a substance that has entered into an electrochemical reaction and undergone transformations, and the amount of electricity expended or released, which was established by Michael Faraday.
The appearance of a potential difference is explained by the fact that the electrode substance dissolves in the electrolyte under the influence of chemical forces (for example, zinc in a sulfuric acid solution) and positive ions it is transferred to the electrolyte. By placing two electrodes of equal metals in an electrolyte, we obtain the difference between them electrode potentials- third-party EMF E = φ1-φ2- Consequently, a device consisting of two dissimilar electrodes placed in an electrolyte is a power source - a galvanic or primary element in which the process of converting (irreversible) chemical energy into electrical energy occurs.
Dry and bulk manganese-zinc elements have become widespread. According to their design, they are divided into cup and biscuit. In the cup design element, the zinc electrode has the shape of a cup, inside of which there is a positive electrode - a carbon rod. The carbon electrode is surrounded by a depolarizer made of manganese dioxide, graphite and carbon black. A zinc glass is filled with an electrolyte - an aqueous solution of ammonium chloride (ammonia) with the addition of starch as a thickener. Electromotive force of the element E = 1.5 V. The rated discharge current of the element is the highest continuous current allowed during its operation. The capacity of an element is the amount of electricity, expressed in ampere-hours (Ah), that can be obtained from the element over the entire period of its operation. Both individual elements and batteries assembled from them are widely used in radio engineering, wired communication equipment, flashlights, hearing aids, etc.
Batteries (secondary elements). Galvanic cells, in which, after being discharged, a reverse charging process with the conversion of electrical energy into chemical energy is possible, are called batteries or secondary cells.
The alkaline battery received its name from its electrolyte - alkali, namely a 21% aqueous solution of caustic potassium CON or sodium hydroxide NaOH. The battery consists of two blocks - plates, located in a steel vessel with electrolyte. The plates are steel frames with steel boxes inserted into them filled with active mass. The active mass of the negative plates of cadmium-nickel elements consists of sponge cadmium, and that of iron-nickel elements consists of sponge iron. The active mass of the positive plates of both batteries consists of nickel oxide hydrate Ni(OH)3.
During discharge, nickel oxide hydrate turns into nickel oxide hydrate, and spongy cadmium (iron) into its oxide hydrate. The chemical reaction during discharge is expressed by the equation:
2Ni(OH)3 + 2KOH + Cd ->- 3Ni(OH)2 + 2KOH + Cd(OH)2.
When charging reaction is underway in the opposite direction and, consequently, the active mass of the electrodes is restored. The electrolyte concentration remains unchanged during discharging and charging. When discharging, the voltage from 1.4 V first quickly decreases to 1.3 V, and then slowly to 1.15 V; At this voltage, the discharge must be stopped. When charging, the voltage quickly increases from 1.15 V to 1.75 V, and then, after a slight decrease, slowly increases to 1.85 V. In addition to alkaline batteries, acid/lead batteries are also widely used.
No matter how you formulate the title of the article, it will still be correct. Chemistry and energy are tied together in the design of a battery.
Lead-acid batteries can operate for several years in charge-discharge modes. They quickly recharge and quickly release stored energy. The secret of these metamorphoses lies in chemistry, because it is it that helps transform electricity, but how?
The “sacrament” of energy conversion in a battery is provided by a set of reagents, including an oxidizing agent and a reducing agent, interacting through an electrolyte. The reducing agent (sponge lead Pb) has a negative charge. During a chemical reaction, it is oxidized and its electrons travel to the oxidizing agent, which has a positive charge. The oxidizing agent (lead dioxide PbO2) is reduced, and the result is an electric current.
The electrolyte is a liquid that conducts current poorly, but is a good conductor for ions. This is an aqueous solution of sulfuric acid (H2S04). In a chemical reaction, a process occurs that is known to everyone from school - electrolytic dissociation.
During the reaction, positively charged ions (H+) are directed to the positive electrode, and negatively charged ions (SO42-) to the negative electrode. When the battery is discharged, ions are sent from the reducing agent (lead sponge), through the electrolyte to the positive electrode. positive charge Pb2+.
Quadrivalent lead ions (Pb4+) are converted into divalent lead ions (Pb4+). However, this is not all chemical reactions. When ions of acid residues with negative charge(SO42-) combine with positively charged lead ions (Pb2+), then lead sulfate (PbSO4) is formed on both electrodes. But this is already bad for the battery. Sulfation shortens the life of the battery and gradually accumulates and can lead to its destruction. Side effect chemical reactions in conventional lead-acid batteries are gases.
What happens when the battery is recharged?
The electrons are directed to an electrode with a negative charge, where they perform their function - neutralize lead ions (Pb2+). The chemical reactions occurring in batteries can be described by the following formula:
The density of the electrolyte and its level in the battery depend on whether the battery is charged or discharged. Changes in electrolyte density can be described by the following formula:
Where is the battery discharge indicator, which is measured as a percentage, - Cp. The density of the electrolyte when fully charged is Rz. Electrolyte density at full discharge - Pr.
The standard temperature at which measurements are made is + 25°C. The density of the electrolyte in accordance with the temperature is + 25°C, g/cm3 - P25.
During a chemical reaction, positive electrodes use 1.6 times more acid than negative electrodes. When the battery is discharged, the volume of electrolyte increases, and when it is charged, on the contrary, it decreases.
In this way, with the help of chemical reactions, the battery receives and then releases electrical energy.
Operating principle. Battery is called a chemical current source that is capable of accumulating (accumulating) electrical energy in itself and, as necessary, releasing it into an external circuit. Electrical energy is accumulated in a battery when current is passed through it from
external source (Fig. 158, a). This process, called battery charge, is accompanied by the conversion of electrical energy into chemical energy, as a result of which the battery itself becomes a source of current. When the battery is discharged (Fig. 158, b), the reverse conversion of chemical energy into electrical energy occurs. The battery has big advantage compared with galvanic cell. If the element is discharged, it becomes completely unusable; the battery is the same. after discharge it can be recharged and will serve as a source of electrical energy. Depending on the type of electrolyte, batteries are divided into acid and alkaline.
On locomotives and electric trains greatest distribution received alkaline batteries, which have a significantly longer service life than acid ones. Acid batteries TN-450 are used only on diesel locomotives; they have a capacity of 450 Ah, rated voltage - 2.2 V. Battery 32 TN-450 consists of 32 batteries connected in series; the letter T means that the battery is installed on the locomotive, the letter H means the type of positive plates (spreadable).
Device. In an acid battery, the electrodes are lead plates coated with so-called active masses, which interact with the electrolyte during electrochemical reactions during the process of charge and discharge. The active mass of the positive electrode (anode) is lead peroxide PbO 2, and the active mass of the negative electrode (cathode) is pure (sponge) lead Pb. The electrolyte is a 25-34% aqueous solution of sulfuric acid.
Battery plates can be of surface or spread type design. Surface type plates are cast from lead; their surface on which electrochemical reactions occur is increased due to the presence of ribs, grooves, etc. They are used in stationary batteries and some batteries in passenger cars.
In the batteries of diesel locomotives, plates of the spread type are used (Fig. 159, a). Such plates have a core made of an alloy of lead and antimony, in which a number of cells are arranged, filled with paste.
After filling the plate cells with paste, they are covered with lead sheets with big amount holes. These sheets prevent the active mass from falling out of the plates and at the same time do not prevent access to the electrolyte.
The starting material for making paste for positive plates is lead powder Pb, and for negative plates - powder, lead peroxide PbO 2, which is mixed on aqueous solution sulfuric acid. The structure of the active masses in such plates is porous; due to this, not only the surface, but also the deep layers of the battery electrodes participate in electrochemical reactions.
To increase porosity and reduce shrinkage of the active mass, graphite, carbon black, silicon, glass powder, barium sulfate and other inert materials called expanders. They do not take part in electrochemical reactions, but make it difficult for particles of lead and its oxides to stick together (sinter) and thereby prevent a decrease in porosity.
The spreadable plates have a large contact surface with the electrolyte and are well saturated with it, which helps reduce the weight and size of the battery and makes it possible to obtain high currents during discharge.
When manufacturing batteries, the plates are subjected to special charge-discharge cycles. This process is called battery molding. As a result of molding, the paste of the positive plates is electrochemically converted into lead peroxide (dioxide) PbO 2 and acquires Brown color. The negative plate paste, when molded, turns into pure Pb lead, which has a porous structure and is therefore called spongy; negative plates turn gray.
Some batteries use shell-type positive plates. In them, each positive plate is enclosed in a special shell (case) made of ebonite or fiberglass. The shell reliably holds the active mass of the plate from shedding during shaking and shocks; to communicate the active mass of the plates with the electrolyte, horizontal slits about 0725 mm wide are made in the shell.
To prevent the plates from being shorted by foreign objects (a probe for measuring the electrolyte level, a device for filling electrolyte, etc.), the plates in some batteries are covered with a polyvinyl chloride mesh.
To increase the capacity, several positive and negative plates are installed in each battery; plates of the same name are connected in parallel into common blocks, to which the output pins are welded. Blocks of positive and negative plates are usually installed in an ebonite battery vessel (Fig. 159,b) so that between each two
plates of one polarity were placed with plates of the other polarity. Negative plates are placed at the edges of the battery, since positive plates are prone to warping when installed at the edges. The plates are separated from one another by separators made of microporous ebonite, polyvinyl chloride, glass felt or other insulating material. Separators prevent the possibility short circuit between the plates when they warp.
The plates are installed in the battery vessel so that there is some free space between their lower part and the bottom of the vessel. Lead sediment (sludge) accumulates in this space, resulting from the falling off of the spent active mass of the plates during operation.
Discharge and charge. When the battery is discharged (Fig. 160, a) positive ions H 2 + and negative ions of the acid residue
S0 4 -, into which molecules of sulfuric acid H 2 S0 4 electrolyte 3 break down, are directed accordingly to the positive
1 and negative 2 electrodes and enter into electrochemical reactions with their active masses. Between the electrodes there is
potential difference of about 2 V, ensuring the passage electric current when the external circuit is closed. As a result
electrochemical reactions that occur during the interaction of hydrogen ions with lead peroxide PbO 2 positive
electrode and ions of sulfate residue S0 4 - with lead Pb of the negative electrode, lead sulfate PbS0 4 (lead sulfate) is formed, into which the surface layers of the active mass of both electrodes are converted. At the same time, during these reactions, a certain amount of water is formed, so the concentration of sulfuric acid decreases, i.e., the density of the electrolyte decreases.
The battery can theoretically be discharged until the active masses of the electrodes are completely converted into lead sulfate and the electrolyte is depleted. However, in practice the discharge is stopped much earlier. The lead sulfate formed during the discharge is a salt white, poorly soluble in electrolyte and having low electrical conductivity. Therefore, the discharge is not carried out until the end, but only until the moment when about 35% of the active mass passes into lead sulfate. In this case, the resulting lead sulfate is evenly distributed in the form tiny crystals in the remaining active mass, which still retains sufficient electrical conductivity to provide a voltage between the electrodes of 1.7-1.8 V.
A discharged battery is charged, i.e., connected to a current source with a voltage greater than the battery voltage. When charging (Fig. 160, b), positive hydrogen ions move to negative electrode 2, and negative ions of the sulfate residue S0 4 - - positive electrode 1 and enter chemical reaction with lead sulfate PbS0 4 covering both electrodes. During the electrochemical reactions that occur, lead sulfate PbS0 4 dissolves and active masses are again formed on the electrodes: lead peroxide PbO 2 on the positive electrode and sponge lead Pb on the negative. At the same time, the concentration of sulfuric acid increases, i.e., the density of the electrolyte increases.
Electrochemical reactions during battery discharge and charging can be expressed by the equation
PbO 2 + Pb + 2H 2 SO 4 ? 2PbSO 4 + 2H 2 O
Reading this equation from left to right, we get the discharge process, from right to left - the charging process.
The rated discharge current is numerically equal to 0.1 C NOM, the maximum when starting a diesel engine (starter mode) is approximately 3 C NOM, the charging current is 0.2 C NOM, where C NOM is the rated capacity.
A fully charged battery has e. d.s. about 2.2 V. The voltage at its terminals is approximately the same, since the internal resistance of the battery is very small. When discharging, the battery voltage drops quite quickly to 2 V, and then slowly decreases to 1.8-1.7 V (Fig. 161), at this voltage the discharge is stopped to avoid damage to the battery. If a discharged battery is left inactive for some time, its voltage is restored to an average value of 2 V. This phenomenon is called “rest” of the battery. When loading such a “rested” battery, the voltage quickly decreases, so Measuring the battery voltage without load does not give a correct judgment about the degree of discharge.
When charging, the battery voltage quickly rises to 2.2 V, and then slowly rises to 2.3 V and, finally, rises quite quickly again to 2.6-2.7 V. At 2.4 V, gas bubbles begin to appear, forming as a result of the decomposition of water into hydrogen and oxygen. At 2.5 V, both electrodes emit a strong stream of gas, and at 2.6-2.7 V, the battery begins to boil, which serves as a sign of the end of the charge. When the battery is disconnected from the charging current source, its voltage quickly drops to 2.2 V.
Battery care. Acid batteries quickly lose capacity or even become completely unusable when
improper use. Self-discharge occurs in them, as a result of which they lose their capacity (approximately 0.5-0.7% per day). To compensate for self-discharge, idle batteries must be periodically recharged. When the electrolyte, as well as battery covers, their terminals and inter-element connections are contaminated, increased self-discharge occurs, quickly depleting the battery.
The battery should always be clean and the terminals covered to prevent oxidation. thin layer technical Vaseline. Periodically you need to check the electrolyte level and the state of charge of the batteries. Batteries must be charged periodically. Storing uncharged batteries is prohibited. If batteries are used incorrectly (discharge below 1.8-1.7 V, systematic undercharging, improper charging, long-term storage of an uncharged battery, decreased electrolyte level, excessive electrolyte density), damage to their plates occurs, called sulfation. This phenomenon consists of the transition of fine-crystalline lead sulfate, which covers the plates during discharge, into insoluble coarse-crystalline lead sulfate. chemical compounds, which, when charged, do not transform into lead peroxide PbO 2 and lead Pb. In this case, the battery becomes unusable.
