The lead-acid battery has been widely used due to its low capacity, low capacity and low price. However, if the use is improper, its life will be greatly shortened. There are many factors affecting the life of lead-acid batteries, while using the correct charging method, it can effectively extend the battery life of the battery.The study found that the battery charging process has less impact on battery life and less impact. That is, the vast majority of the battery is not used, but "is" ". It can be seen that a good charger has a pivotable role in the service life of the battery.
1 Battery charging theory foundation
In the middle of the 1960s, American scientist Mas made a large experimental study on the charging process of the opening battery, and proposed a battery-acceptable charging curve with the lowest air rate, as shown in Figure 1. Experiments have shown that if the charging current changes according to this curve, the charging time can be greatly shortened, and the capacity and life of the battery have nothing affected. In principle, this curve is called the optimal charge curve, which has laid the research direction of the fast charging method [1, 2].
As can be seen from Figure 1: The initial charging current is large, but attenuation is very fast. The main reason is that the polarization is produced during the charging process. During the charging of the sealed battery, oxygen and hydrogen are generated inside. When the oxygen cannot be absorbed in time, it is stacked in the positive electrode plate (the positive electrode plate producing oxygen), so that the internal pressure of the battery is increased, the battery temperature rises, and reduces the positive electrode plate The area is manifested as an increase in internal resistance, and the so-called polarization occurred.
The battery is reversible. The chemical reaction formula of its discharge and charging is as follows:
PBO2 + PB + 2H2SO42 → PBSO4 + 2H2O (1)
Obviously, the charging process and discharge process are inversely reactive. The reversible process is a balanced process of thermodynamics. To ensure that the battery can be fully maintained under a balanced state, it is necessary to try to make a small current through the battery. The ideal condition is that the external voltage is equal to the electric potential of the battery itself. However, practice shows that when the battery is charged, the external voltage must be increased to a certain value, and this value is more than the difference in the balanced electric potential value of the battery due to the difference in various factors such as electrode materials, solution concentrations. In the chemical reaction, this electromotive force exceeds the phenomenon of thermodynamics equilibrium value is polarization.
In general, there are three ways to generate polarization.
1) During the ohmic polarization charging, the positive and negative ion migrates to the pole. It is inevitable to be affected by ion migration, referred to as ohmic internal resistance. In order to overcome this internal resistance, the external voltage must additionally apply a certain voltage to overcome the resistance to push ion migration. This voltage is transformed into the environment in a hot manner, and so-called ohmic polarization occurs. As the charging current is sharply increased, ohm polarization will cause high temperatures in the charging process.
2) When the concentration polarization current flows through the battery, in order to maintain a normal reaction, the most ideal case is that the reaction material of the electrode surface can be supplemented in time, and the generated product can be taken in time. In fact, the diffusion speed of the product and the reactant is much longer than the chemical reaction rate, thereby causing the concentration of electrolyte solution in the vicinity of the electrolyte solution. That is, from the surface of the electrode to the central solution, the electrolyte concentration is uneven. This phenomenon is referred to as concentration polarization.
3) Electrochemical polarization This polarization is due to the speed of electrochemical reactions on the electrode, caused by the speed of electron movement on the electrode. For example, before the negative electrode discharge of the battery, the electrode surface is negatively charged, and the solution near the nearby solution is positively charged, both in equilibrium. When discharged, there is an electron release to the external circuit immediately. The negative charge of the electrode is reduced, while the metal dissolved oxidation reaction is slow ME-EME +, and the electrode surface electrons are reduced, and the electrode surface is electrically changed. This surface negative charge is reduced to promote electron exiting electrodes in the metal, metal ion me + transfer to a solution, and accelerate ME-EME + reaction. There is always a moment to achieve new dynamic balance. However, the negative charge of the electrode surface is reduced compared to the discharge, and the electrode potential corresponding to this is corrected. That is, the electrochemical polarization voltage is high, which seriously hinders normal charging current. In the same way, when the battery is positively discharged, the number of positive charges in the electrode surface is reduced, and the electrode potential is gains.
These three polarizations are severe as the charging current is increased.
2 research on charging method
2.1 Conventional charging method
The conventional charging system is designed according to the 1940 internationally recognized experience. The most famous of these is "ampere hour rules": the number of charging current amperage should not exceed the amount of time to charge to be charged. In fact, conventional charging speed is limited by the temperature rise and gas of the battery during charging. This phenomenon is of great significance for the shortest time required for battery charging.
In general, there are three conventional charges.
2.1.1 constant current charging method
The constant current charging method is to maintain a charging method of the charging current intensity as the charging current intensity by adjusting the voltage of the charging device to output a voltage or changing the series resistance of the battery, as shown in FIG. The control method is simple, but since the acceptable current capability of the battery is gradually declined with the charging process, the charging current is mostly used in electrolysis water, generate gas, so that the air is over, and therefore, the common stage charging method.
2.1.2 stage charging method
This method includes two-stage charging method and three-stage charging method.
1) The second-stage method uses constant current and constant voltage combined fast charging method, as shown in FIG. First, charging to a predetermined voltage value with constant current, and then changed to a constant voltage to complete the remaining charging. Generally, the conversion voltage between the two stages is the constant voltage of the second phase.
2) The three-stage charging method is charged with constant current at the beginning and end of charging, and the intermediate is charged with constant voltage. When the current is attenuated to a predetermined value, the second phase is converted to the third stage. This method can minimize the amount of extravasation, but is used as a fast charging method, subject to certain limits.
2.1.3 Constant voltage charging method
The voltage of the charging power supply maintains a constant value in all charging time. As the battery-end voltage is gradually increased, the current gradually decreases. Compared to the constant current charging method, its charging process is closer to the best charging curve. Rapid charging with a constant voltage, as shown in Figure 4. Since the charging initial battery electromotive force is low, the charging current is large, and the current will gradually decrease as charging, therefore, simply control system.
This charging method is very small, and the battery is overchaled. However, in the initial current of the charging, the battery life has a great influence, and the battery polar plate is easily curved, resulting in a battery scrap.
In view of this disadvantage, constant pressure charge is rarely used, and only at a low current voltage is low. For example, during the operation of the car, the battery is charged with constant voltage charging.
2.2 Fast charging technology
In order to maximize the chemical reaction speed of the battery, shorten the time of the battery to achieve a full state, while ensuring that the polarization of the battery positive and negative electrode plate is less as little or light, and the battery usage efficiency is improved. Fast charging technology has been rapidly developed in recent years.
Some of the currently popular faster charging methods are described below. These methods are designed around the optimal charging curve, and the purpose is to make their charging curves into the best charging curve as much as possible.
2.2.1 Pulse Charge Method
This charging method not only follows the intrinsic charge acceptance rate of the battery, but also improves the battery recharge acceptance rate, thereby breaking the restriction of the battery index charging receiving curve, which is also a new development of the battery charging theory.
The pulse charging method is first charged with a pulse current, and then allows the battery to stop for a period of time, which is as shown in Figure 5. The charging pulse makes the battery are filled with electricity, while the battery is chemically reacted, and the hydrogen has time to be absorbed, so that the concentration polarization and ohmic polarization naturally be eliminated, thereby reducing the internal pressure of the battery. Make the next round of constant current charging can be carried out more smoothly, so that the battery can absorb more power. The intermittent pulse makes the battery have a sufficient reaction time, reducing the quantity of the gas, and increases the charging current acceptance rate of the battery [5].
2.2.2 REFLEXTM Fast Charging Method
This technology is a patented technology in the United States, which mainly faces the charging object is a nickel-cadmium battery. Since it uses a new type of charging method, the memory effect of nickel-cadmium batteries is solved, and therefore, the time of fast charging of the battery is greatly reduced. The charging method of the lead-acid battery and the detection method of the charging state are greatly different from the nickel-cadmium battery, but they can learn from each other [3].
As shown in Figure 6, a working cycle of the ReflexTM charging method includes a forward charging pulse, reverse instant discharge pulse, and stops maintaining 3 phases [3].
2.2.3 Change Current Interval Charge Method
This charging method is based on constant current charging and pulse charging, as shown in Figure 7. It is characterized by changing the constant current charging segment.
Break-changing segments for limiting varying current. Each segment of the pre-charging period uses a method of changing electricity, and ensures that the charging current is increased, and most of the charge is obtained. The battery charging segment is used in the late stage, and the amount of charge is obtained, and the battery is restored to the fully charged state. By intermittent parking, the battery has been absorbed by the oxygen and hydrogen produced by the chemical reaction, and the concentration polarization and ohmic polarization naturally be eliminated, thereby reducing the internal pressure of the battery, so that the next round The constant current charging can be carried out more smoothly, so that the battery can absorb more power [4].
2.2.4 changed voltage intermittent charge
On the basis of changed current intermittent charge, some people have proposed a variable voltage intermittent charge, as shown in FIG. Different from the change of the current intermittent charge method in the first stage is not intermittent, but intermittent constant pressure.
Comparison of Figures 7 and 8, it can be seen that Figure 8 is more conforming to the optimal charge. At each constant voltage charging stage, due to constant voltage charging, the charging current is naturally decreased according to the index law, and the battery current acceptance rate is characterized by the charging of charging [4].
2.2.5 variable voltage change current wave-type intermittent positive and negative zero pulse fast charging method
Integrated pulse charge method, ReflexTM fast charging method, variable current intermittent charge method and variable voltage intermittent charging method, the variable voltage variable current wave-shaped positive and negative zero pulse intermittent fast charging method is developed. The control of the charging circuit of the pulse charge is generally two types:
1) The magnitude of the pulse current is variable, and the frequency of the PWM (driving charge and discharge switching tube) signal is fixed;
2) The pulse current value is fixed, and the frequency of the PWM signal is adjustable.
Figure 9 uses a control mode different from the two, the pulse current value, and the frequency of the PWM signal are fixed, and the PWM duty cycle is adjustable. On this basis, the intermittent parking stage is added, which can be shorter Increase in more power, improve the charging acceptance of the battery.
3 conclusion
The lead-acid battery is currently widely used in the world. The product has good reversibility, the voltage characteristics are stable, long service life, wide range of applications, rich raw materials (renewable use) and low cost. Mainly used in various departments of transportation, communication, electricity, railway, mining, port and other national economies, is an indispensable product in social production and operation activities, with broad development prospects.
Article from: http://www.brcpower.com/
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