Charging with asymmetric current of batteries. Automatic charger with asymmetric mode of operation. For the scheme "Charging and restoring the battery"

Modern automotive batteries are produced maintenance-free or low-maintenance, and their service life directly depends on their proper operation. If used incorrectly, their plates can be sulfated, which is why they fail.

To eliminate sulfation of the plates, a method of charging such batteries with an "asymmetric" current is applicable. In this case, the optimal ratio of charging and discharging current is selected as 10:1. This method allows not only to restore sulfated batteries, but also to carry out preventive treatment of serviceable ones.

A diagram of a simple charger designed to use the above described method is shown in fig. 1

To restore and train widely used batteries with a capacity of 55A / h, we use a pulse charging current of 5 A, while the discharge current will be 0.5 A. The discharge current is determined by the value of the resistor R4.

The circuit is designed so that the battery is charged by current pulses during one half of the period mains voltage when the output voltage exceeds the battery voltage. During the second half-cycle, the diodes VD1, VD2 are closed, and the battery is discharged through the load resistance R4.

The main regulating element is a transistor current stabilizer. Meaning charging current is set by the regulator R2 on the ammeter. Considering that when the battery is charging, part of the current also flows through the resistor R4 (10%), then the readings of the PA1 ammeter should correspond to 1.8 A (for a charging current of 5 A), since the ammeter shows the average current value over a period of time, and the charge is made during half the period.

In the event of a power failure, a battery is provided from an uncontrolled discharge to the resistor R4 using relay K1, which will open the battery connection circuit with its contacts.

As a relay K1, a RPU type with an operating voltage of the winding of 24 V is used. The operation voltage is less, then a limiting resistor is connected in series with the winding.

The charger uses a transformer with a power of at least 150 W with a voltage in the secondary winding of 22 ... 25 V (current 5 ... 7 A). Measuring device RA1 is suitable with a scale of 0 ... 5 A (0 ... 3 A), for example M42100, and its scale will need to be recalibrated (multiplier ≈2.5).

Transistor VT1 is installed on a radiator with an area of ​​at least 200 square meters. cm, which can be used as the metal case of the charger itself.

The circuit uses a transistor with a high gain, which can be replaced by a composite transistor, as shown in Fig. 2.

Types of lead- acid batteries

At the moment, the following types of batteries are most common on the market:

- SLA (Sealed Lead Acid) Sealed lead acid or VRLA (Valve Regulated Lead Acid) valve regulated lead acid. Made according to standard technology. Due to the design and materials used, they do not require checking the electrolyte level and adding water. They have low resistance to cycling, limited opportunities low discharge operation, standard starting current and fast discharge.

- EFB (Enhanced Flooded Battery) The technology was developed by Bosch. It is an intermediate technology between standard and AGM technologies. Such batteries differ from the standard ones in higher resistance to cycling, charge acceptance is improved. They have higher starting current. Like SLA\VRLA, there are limitations to low battery operation.

- AGM (Absorbed Glass Mat) Currently the best technology (in terms of price / performance ratio). Cycling resistance is 3-4 times higher, fast charge. Due to the low internal resistance, it has a high starting current at a low state of charge. Water consumption close to zero, resistant to electrolyte separation due to absorption in the AGM separator.

- GEL (Gel Electrolite) Technology in which the electrolyte is in the form of a gel. Compared to AGM, they have better cycling resistance, greater resistance to electrolyte stratification. The disadvantages include high cost, and high requirements for the charge mode.

There are several other technologies for manufacturing batteries, both related to changing the shape of the plates and specific operating conditions. Despite the difference in technologies, the physical and chemical processes occurring during the charge - discharge of the battery are the same. Therefore, charge algorithms various types batteries are almost identical. The differences are mainly related to the value of the maximum charge current and the voltage of the end of the charge.

For example, when charging a 12-volt battery using the following technology:

Determining the state of charge of the battery

There are two main ways to determine the state of charge of a battery, electrolyte density measurement and open circuit voltage (OCV) measurement.

NRC is the voltage on the battery with no load connected. For sealed (not serviced) batteries, the degree of charge can only be determined by measuring the NRC. It is necessary to measure NRC not earlier than 8 hours after the engine is stopped (disconnected from the charger), using a voltmeter with an accuracy class of at least 1.0. At a battery temperature of 20-25 ° C (as recommended by Bosch). The NRC values ​​are given in the table.

(some manufacturers may have different values) If the battery is less than 80% charged, it is recommended to charge it.

Battery Charging Algorithms

There are several most common battery charging algorithms. At the moment, most battery manufacturers recommend the CC \ CV (Constant Current \ Constant Voltage) charge algorithm.

This algorithm provides a fairly fast and “careful” battery charge mode. To eliminate the long-term stay of the battery at the end of the charging process, most chargers switch to the mode of maintaining (compensating the self-discharge current) the voltage on the battery. Such an algorithm is called a three-stage algorithm. The graph of such a charge algorithm is shown in the figure.

The specified voltage values ​​(14.5V and 13.2V) are valid when charging SLA \ VRLA, AGM batteries. When charging batteries of the GEL type, the voltage values ​​\u200b\u200bshould be set to 14.1V and 13.2V, respectively.

Additional algorithms for battery charging

Precharge A heavily discharged battery (NRC less than 10V) increases internal resistance, which leads to a deterioration in its ability to accept a charge. The precharge algorithm is designed to "build up" such batteries.

Asymmetric charge To reduce the sulfation of the battery plates, it is possible to charge with an asymmetric current. With this algorithm, the charge alternates with the discharge, which leads to the partial dissolution of sulfates and the restoration of the battery capacity.

Equalizing charge During the operation of the batteries, the internal resistance of individual "cans" changes, which leads to uneven charging during the charging process. An equalizing charge is recommended to reduce the dispersion of internal resistance. In this case, the battery is charged with a current of 0.05 ... 0.1C at a voltage of 15.6 ... 16.4V. The charge is carried out within 2 ... 6 hours with constant monitoring of the battery temperature. Sealed batteries cannot be equalized, especially with GEL technology. Some manufacturers allow this charge for VRLA\AGM batteries.

Determination of battery capacity

As the battery is used, its capacity decreases. If the capacity is 80% of the nominal, then such a battery is recommended to be replaced. To determine the capacity, the battery is fully charged. They let it stand for 1 .... 5 hours and then discharge it with a current of 1 \ 20C to a voltage of 10.8V (for a 12-volt battery). The number of ampere-hours delivered by the battery is its actual capacity. Some manufacturers use other values ​​​​of the discharge current to determine the capacity, and the voltage to which the battery is discharged.

Control training cycle

To reduce sulfation of battery plates, one of the methods is to conduct control training cycles (CTCs). CTCs consist of several successive charge cycles followed by discharge with a current of 0.01...0.05C. When carrying out such cycles, the sulfate dissolves, the battery capacity can be partially restored.

An expensive thing is a battery, and its service life is limited. I really want to take some decisive steps to prolong his life. Moreover, there seem to be grounds for this desire. After all, sometimes you hear something like this from motorists: “But one of my acquaintances once said that his neighbor’s battery has been serving for the eighth year, and everything is like new. Maybe he knows some secret, but he doesn’t tell ... ” Of course, more often you have to listen to the lamentations of a loser who curses everything in the world from manufacturers to his evil fate. But still, one gets the impression that the battery has longevity reserves, and considerable ones, you just need to somehow get into the number of those lucky ones ...

In such a situation, reports of various unconventional battery charging methods fall on well-fertilized soil and excite many motorists. In addition, it should be noted that the information that they contain is often very scarce, and the benefits promise very large. True, when we are told about extending the life of a battery by two or three times or about restoring a “sample” that has long been lying in a landfill, this causes a certain mistrust, although, on the other hand, we think, there is no smoke without fire ...

Letters, one way or another concerning the problem of non-traditional methods of battery charging, come to the editor a lot. Different letters: enthusiastic, skeptical, demanding, even indignant. Both with requests and suggestions. In order to answer them, it was first necessary to get a more or less clear idea of ​​the subject ourselves. So to speak, to figure out where the smoke is and where the fire is. We tried to do this by reviewing the available (and inaccessible) literature, but mainly by meeting with employees of many organizations (NIISTA, NIIavtopriborov, NIIAT, etc.).

At first it seemed that this article should look like a collection of clarifications received from different groups specialists. But they are in many respects similar and most often differ in the interpretation of certain theoretical provisions. For us, in the final analysis, the conclusions are important - at least according to the principle of the majority of opinions, or, better, the most convincing. In this regard, what follows is a story about how we understood the essence of the matter.

Speaking of non-traditional methods of charging batteries, they use the most different definitions, and many use them quite freely. Therefore, first of all, let us designate “what is what”.

The control-training cycle (abbreviated as CTC) is as follows. The battery is fully charged with direct current, then discharged with a 10-hour current to a voltage of 10.2 V and again given a full charge. This cycle allows you to evaluate the actual capacity and real capabilities of an "old" battery, and a series of cycles in some cases slightly improves electrical performance if the battery is still suitable for further use. Although some people talk about the charge using CTC as a novelty, it cannot be called unconventional: it has long been described in detail in numerous manuals. The CTC methodology is also set out in the main document for the operation of the battery - the current instruction ZHUITs.563410.001IE (formerly FYa0.355.009IE), which is attached to each battery.

Accelerated, or forced, charging serves the sole purpose of bringing the discharged battery to a working state in the shortest possible time, which is achieved by using unusually large charging currents. This principle itself has also been known for a long time; the modern method of using it is set out in the manual RTM-200-RSFSR-12-0032-77, which was developed by NIIAT. In the future, we will not talk about accelerated charging, since it in no way concerns the problem of increasing the durability of the battery.

Impulse charge means the use of a current that changes its magnitude or voltage periodically, at certain time intervals. According to the nature of these indicators, the pulsed current is divided into two varieties.

A pulsating current is one in which the value varies from zero to the maximum value, while maintaining its polarity unchanged. An example of a ripple current characteristic is shown in fig. 1.

Rice. 1. Charge with pulsating current. Cz is the capacity imparted to the battery during the pulse time t.

Asymmetric, or reversible, current is determined by the presence of a reciprocal amplitude (see the example in Fig. 2); in other words, in each cycle it changes its polarity. However, the amount of electricity flowing with direct polarity is greater than with reverse polarity, which ensures the charge of the battery.

Rice. 2. Charge with asymmetric current. Cz is the capacity imparted to the battery during charging during the time tc; Сз the capacitance removed from it during the time tр.

It is the reverse current that is currently of the greatest interest to enthusiastic researchers. Dozens of copyright certificates have been issued for circuit solutions that make it possible to obtain an asymmetric type charging current with the most different forms graphic characteristics. As for the experimental data on how the reverse current changes the electrochemical processes in the battery, the picture here is much more meager, and even contradictory. Indeed, to develop an original electronic circuit not easy, but for a person who knows this business well, such a task is within his power. However, before creating a structure, you need to know what it will give and what its parameters should be. And here it is not enough to be just a knowledgeable electrochemist: we need subtle laboratory experiments, we need a large amount of correctly set operational tests. Even large specialized organizations do not always have such opportunities. Therefore, developers of pulse chargers, as a rule, proceed from the model of battery operation and aging, which is reflected in the mass technical literature. And here lies the main underwater reef. The point is that the design car batteries does not stand still, the nature of their work is also changing qualitatively, and publicly available data lag behind today's picture, sometimes by a dozen years. What is the technical essence of the changes that have taken place over Lately? Let us consider this important circumstance in more detail.

Some twenty years ago, a battery mass type had an asphalt casing (monoblock) and wooden separators between the electrodes. Cotton linters were used as an expander (porogen) in the negative electrodes. All these materials are not resistant to sulfuric acid. As a result of their dissolution in the electrolyte, organic impurities appeared - "poisoners", which disrupted the normal course of chemical reactions. They were deposited on the surface of the electrodes, shielding the active mass, as a result of which the battery capacity gradually decreased and its voltage decreased when discharged by the starter current. In addition, and more importantly, impurities contributed to the formation and accumulation of large, sparingly soluble crystals of lead sulfate, which not only worsened the performance of the battery, but often led to a complete loss of performance over time. Here are the main reasons for the final failure of the batteries, identified in the early 60s by large-scale surveys in our country and abroad: corrosion of the grids of positive electrodes - about 36%, sulfation of negative electrodes - about 30%, active mass sagging - somewhat more than 20 %, destruction of separators and monoblocks - approximately 16%. We emphasize that almost a third of the batteries were thrown away due to sulfation - a disease that can be treated. And they treated it as much as possible: in many manuals of previous years, you can find tips on eliminating sulfation with different special methods charge, including the use of CTC. That's just about the impulse charge then there was no talk. As for CTCs, especially those with high currents, they had a certain effect also because they removed some of the foreign impurities deposited on the electrodes, transferring them back to the electrolyte.

Now let's move on to the next generation of batteries. The rapid development of the production of synthetic materials made it possible to make all structural elements acid-resistant and chemically neutral. Ebonite and thermoplastics (polyethylene, polypropylene) began to be used for housings, miplast and mipor for separators, BNF and humic acid began to be used as blowing agents. All this not only significantly increased the energy intensity of the batteries, but also increased their average life expectancy by about a third due to getting rid of some defects. This is how the results of a survey of more than a thousand batteries that failed in the late 70s looked like: about 45% were rejected due to corrosion of the grids of the positive plates - about 35%, due to active mass flowing - about 35%, the rest - due to the destruction of the separators , monoblocks and for other reasons. Characteristically, almost no electrode sulfation was detected. Isolated cases were caused by gross errors in maintenance (for example, adding tap water instead of distilled water). Current audits show that this is how things are now. To add to this, one can only add that today a significant part of the fleet of individual cars is already equipped with batteries of a new type - the so-called low-maintenance ones. So far, they are supplied from Yugoslavia, but soon a wide production of a domestic, even more advanced model will begin. Without going into a detailed consideration of batteries of this kind (this is a topic for a separate discussion), let's just say that they finally push the problem of sulfation into the past.

Why are we so insistent on isolating sulfation? It is easy to guess: due to the connection with the charge by reverse currents. Indeed, many serious studies have convincingly shown that the reverse (asymmetrical) current can be good helper in the fight against large crystals of lead sulfate. However, as we have seen, this excellent quality has lost its relevance in our time. But with what thesis begins a typical justification for the next development of a pulse charger (we intentionally do not name the author): “Practice shows that with the most competent and accurate operation of the battery, its service life does not exceed four to five years at best. The main reason lies in the sulfation of the plates. Other causes of battery failure in the individual owner are quite rare.” Like this. The term is named correctly, and the diagnosis is taken from the 50s. We look further: "The cause of sulfation is mainly associated with systematic undercharging and discharge above the permissible limits." The statement is correct. But that's why they are used in modern cars powerful generators alternating current, stable voltage regulators. As a result, if we talk about deviations, then more often you have to deal with overcharging. On average, statistics show the following: about 80% of the time, the degree of battery charge is in the range of 0.75-1.0, about 15% - from 0.5 to 0.75, and only 5% less than 0.5. Moreover, a battery “planted” during a difficult cold start, as a rule, soon restores its charge while driving, without requiring outside help.

Thus, today it is difficult to call quite complex and expensive devices designed to eliminate sulfation. Some may object: excuse me, because even a modern battery can be sulfated, say, if you pour dirty water into it, drive with a constant undercharge, and so on. Of course you can. But one should hardly elevate one's own grossest mistakes to the level of a problem. And if such flaws are considered acceptable, then you need to pay for them in full measure. And it’s completely illogical to keep a special device just “just in case” without using it. Indeed, in case of emergency, you can, as before, try to correct the situation with a series of control and training cycles using a conventional 12-volt rectifier. You should not only carry out this operation unnecessarily, since each CTC takes a piece of battery life. The principle here is as follows: during its life, the battery can give a very certain amount of energy, and each full discharge corresponds to approximately 0.6-1.0% of this amount.

Does the above mean that the charge by pulsed currents has no practical meaning? No, in our opinion, such a conclusion would be completely wrong. It is only necessary to direct this interesting and not yet fully studied method not to fight the ghosts of the past, but to solve today's real problems.

Such an example. Some studies show that under certain conditions, charging with an asymmetric current can increase the battery capacity by 3-5%. As for the conditions, many things jointly influence here: the frequency and nature of current pulses, battery parameters, temperature. It is difficult and the benefits are still small, but it is obviously worth working in this direction.

And further. When charging with direct current, the surface of the electrode is saturated first of all, and this prevents the development of the process in depth. A short discharge in each cycle of the asymmetric current removes the surface polarization and this increases the efficiency of the current drawn from the network. Of course, for homework this is an insignificant factor, and in large fleets this circumstance cannot be neglected.

And, finally, it is impossible not to mention the work of scientists from the Novocherkassk Polytechnic Institute. They developed a theory that reverse current could be used against
the main current enemy is the corrosion of gratings. This theory, as many experts believe, is controversial, the experiments are not yet large enough, and the first conclusions that interpret the need for frequent special recharging of an operated battery (about 10 times a year) are not very consistent with the desire to reduce maintenance volumes. But it's a very tempting goal! Therefore, one can only wish the researchers success and good luck, which will lead to acceptable technical solutions.

In conclusion, the following should be said. Many models and types of chargers for personal use are produced in the country. "Behind the wheel" has repeatedly published messages about new samples. Mention has also been made of the design impulse current(1984, no. 7, p. 29). This information was based on information provided by the manufacturers themselves and reflected their assessment of their product. It was practically impossible to obtain comparative, generalizing data on the entire wide range of products. Now the situation is different. To implement a unified technical policy in the development and production of chargers, a leading organization has been appointed - VNIIpreobrazovatel (Zaporozhye). The Institute conducted a critical examination of manufactured products, based on the results of which it prepares appropriate recommendations for factories. We plan to tell readers about this work.

Sector of tests "Driving"

It has long been known that the charge of electrochemical power sources with an asymmetric current, with a ratio of Icharge: Idis = 10:1, in particular acid batteries, leads to the elimination of sulfation of the plates in the battery, i.e. to restore their capacity, which in turn prolongs battery life. It is not always possible to be near the charger and control the charging process all the time, so often the batteries are either systematically undercharged or recharged, which, of course, does not extend their service life.

From chemistry it is clear that the potential difference between the negative and positive plates in the battery is 2.1 V, which at 6 banks gives 2.1 x 6 \u003d 12.6 V. With a charging current equal to 0.1 of the battery capacity, in At the end of the charge, the voltage rises to 2.4 V per cell, or 2.4 x 6 = 14.4 V. An increase in the charging current leads to an increase in the voltage on the battery and increased heating and boiling of the electrolyte. Charging with a current below 0.1 of the capacitance does not allow the voltage to be increased to 14.4 V, however, a long (up to three weeks) charge with a low current contributes to the dissolution of lead sulfate crystals. Especially dangerous are lead sulfate dendrites, "sprouted" in separators. They cause a rapid self-discharge of the battery (in the evening I charged the battery, and in the morning I could not start the engine). The dendrites can be washed out of the separators only by dissolving them in nitric acid, which is practically unrealistic. Through long-term observations and experiments, a circuit diagram, which, according to the author, allows you to trust the automation. Trial operation for 10 years has shown efficient work devices. The principle of operation is as follows: 1. The charge is made on the positive half-wave of the secondary voltage. 2. On the negative half-wave, a partial discharge of the battery occurs due to the flow of current through the load resistor. 3. Automatic switching on when the voltage drops due to self-discharge up to 12.5 V and automatic disconnection from the 220 V network when the battery voltage reaches 14.4 V. Shutdown - non-contact, by means of a triac and a voltage control circuit on the battery. An important advantage of the method is that while the battery is not connected (automatic mode), the unit cannot turn on, which eliminates short circuit when closing the wires supplying the charging current to the battery. With a heavily discharged battery, the unit can be turned on, perhaps by means of the "AUTOMATIC-PERMANENT" switch. Another very important advantage is the absence of strong "boiling", which, together with automatic shutdown and inclusion, allows you to leave the device turned on unattended for a long hour. The author pro-experimented with a two-week regime of constant inclusion in the "AUTOMATIC" mode. In order to fire safety it is necessary that Charger was in a metal case, the cross section of the lead wires to the battery was at least 2.5 mm 2. Reliable contact at the battery terminals is also required. Mains voltage 220 V is supplied through fuse FU1 and triac VD1 to the primary winding of the power transformer. From the secondary winding AC voltage U2 \u003d 21 V is rectified by the VD3 diode and through the ballast resistor R8 with a resistance of 1.5 Ohm it goes to the "+" terminal of the battery, to which the PA1 15 V voltmeter, the SA2 toggle switch "ON DESULFATION" and the control and management circuit, which is a trigger, are connected Schmitt with a hysteresistor of approximately 1.8 V, determined by the voltage drop across the diodes VD5, VD6 and the base-emitter junction of the transistor VT2. Transistor VT1 turns on at a voltage of 12.6 V on the battery, and through the optocoupler VD4 turns on the triac VD1, which turns on the transformer T1 and energizes the battery being charged. Connecting the resistor R5 with the toggle switch SA2 ensures the asymmetry of the form of the charging current. LEDs VD8 and VD7 indicate the inclusion of the unit in the "DESULFATE" and "ON" modes. respectively. Resistor R7 sets the moment when the unit is turned off at a voltage of 15 V on the voltmeter (= 0.5 V drops on the supply wires). The VD2 bridge ensures that the triac is turned on at both half-waves of the mains voltage and the normal operation of the transformer. Toggle switch SA1 is used to enable the "PERMANENTLY" mode. Details. Power transformer - P=160 W, U2=21 V, wire - PEV-2-2.0. R8 - wire (nichrome) with a diameter of 0.6 mm. R5 - PEVR for 10 ... 15 W. Diode VD3 - any of D242 ... D248 with any letter index on a radiator with an area of ​​\u200b\u200bS = 200 cm2. Other type resistors - MLT, SP; triac - KU208N, without radiator. S1 - any, for example MT1. S2 - TV1-1. HL1 - any 12 V lamp. PA1 - 15 V measuring head.