In order to shorten the charging time, reduce the heat damage to the battery, and increase the power utilization rate of charging, it has proposed a three -level charging method.
The so -called three -level charging is to divide the charging process into three levels as three stages. In the first stage, a large current is charged with a large current, and the battery is charged to 50%to 60%of the total capacity. When the battery end voltage reaches the gasification point, turn to the second stage. The second stage is the constant voltage charging. When the current of the constant voltage charging drops to a certain value, then turn to the third stage. The third stage is charged with small current constant current until it is completely sufficient. The process is shown in Figure 1. This method is advanced compared to simple constant voltage charging and constant current charging. The third -level charging gives people an important tip: as long as the charging energy of the battery can be transformed into a chemical energy, it can be carried out, and it is possible to use a large current to storage the battery.
First analyze the electrification reaction process during charging. During the normal charging process, the charging current flowing through the battery will the PBSO4 → PBO2 on the anode board, PBSO4 → PB on the cathode board. As long as this effective conversion can be performed, the large charging current has no harm to the battery. However, this transformation is limited by many inherent factors, and the conversion rate in the charging process is getting lower and lower. In appearance, the battery temperature rises, the amount of gas is increased, and the electrolytes even show a fierce boiling state. In order to protect the battery, the most fundamental measure is to reduce the charging current, so the charging time is prolonged.
It can be seen that to shorten the charging time, the water decomposition during the charging process must be reduced.
First analyze the vaporization process of water. During the charging, the H+in the electrolyte movement is moved to the negative electrode, and OH- is moved to the positive electrode. At the beginning of the charging, due to the low concentration of sulfuric acid in the electrolyte, the diffusion rate of the new ecological acid was high, and the comprehensive result of the two factors made the acid concentration of the polar plate surface not high. The acid concentration determines the electrode of the electrode, and the voltage on the electrode does not reach the gasification voltage. At this time, the water does not break down and the charging efficiency is high. With the development of charging, the acid content in the electrical hydraulic is increasing, and the acid concentration of the surface of the pole plate has increased. When the concentration rises to a certain value, the charging voltage reaches the gasification voltage value, and the water begins to decompose.
The increase in the acid concentration of the polar plate surface is the key to rapid charging. The control approach is to reduce the rate of acidity and accelerate the spread of acid. The former can only be achieved by reducing the charging current, and the latter is achieved by instant large current discharge. Analysis of the latter’s action process.
As shown in Figure 2, during the charging process, the concentration of the acid surface of the pole plate gradually increased. When the gasification voltage was reached, the relationship between the surface of the pole plate surface was “C” is represented. At this time, the charging circuit monitors this situation according to the voltage value and stop charging. After the charging is stopped, the three acid molecules diffuse into low -concentration solutions. When the “B” “C” moves to the location of the icon, the battery is discharged instantly: “A” is consumed by the vertical discharge, and “C” still moves in the direction of the original direction due to the motion inertia. Before the initial position, a low concentration area was caused on the surface of the polar plate. So when charging again, the polar board has a large characteristics of current receiving rate. From the above analysis, it can be seen that the current of fast charging must be pulsating; there is a discharge wave between the two charging waves. As shown in Figure 2, the working wave shape of a fast charger.
As the charging process is carried out, the charging and discharge cycle of fast charging is becoming shorter and shorter, and the number of charging and releases is almost the same. At this time, the extended charging time is no good. When the monitoring circuit in the device reaches a certain value according to the charging frequency, the power is automatically cut off and the charging process is over. There is only one standard for the advantages and disadvantages of the fast charger; on the premise of not exceeding 40 ° C in the battery temperature, the battery capacity can be charged from 0 to 100%within 1-4H. Since the charging current and pulse charging frequency of the fast charger are determined based on the changes in the battery side voltage, when the voltage value of the battery pack is the total voltage value of the battery pack, when the multi -battery series charging is charged. The voltage. If the balance between the single sections in the battery pack is poor, some batteries will inevitably be charged or insufficient. Leading batteries choose high -capacity single sections, and low -capacity single sections will be over -charged; led the battery to select low -capacity single sections, and high -capacity batteries will not be charged. It is recommended not to charging quickly when the capacity difference between a battery is more than 10%. The difference in capacity can be measured with a battery capacity table. Some units use the fast charger, due to the disorders of the working waveform, the staff cannot adjust it. When charging, the battery temperature rises up to 70 ° C. A large amount of gas emerge from the injection port, and the electrolyte is fiercely boiling. Such a fast charger is actually the width, peak, and phase of the fast -destructive “destroyer” veins, which is the key to determining the performance of the fast charger. If there is no discharge pulse, the charging wave will become pulsating DC.
If the control is improper, it is harmful to the battery’s floating charging with pulse DC. Experiments show that when the charging current contains 5%to 6%pulse value, it is enough to generate overvoltage and corrosion to the pole grille. In the charging operation, the operator is adjusted to the charging current according to the display value of the current meter. In a certain range of the pulse wave, the actual instant charging current value will exceed the current displayed by the meter, as shown in Figure 2-10. When the current is adjusted according to process standards, the actual current value exceeds the battery’s charging resistance, and the excess part of the water will cause water decomposition. As a result, the battery temperature increased, and the grid was corroded, which exacerbated the falling of the active substances.
In Figure 3, A1 is the acceptable current strength that can be acceptable to the battery charging reaction. At the time of A1, the charging current was completely converted into chemistry to be stored in the battery. When the adjustable current is A1, the instrument can only display the average value, but the maximum charging current is in A2, and the shadow part of the A2-A1 shadow part causes the battery damage.
Among the existing chargers, small machines have single -phase half -wave rectification, their current pulse coefficient is 1.57, and the pulse coefficient of single -phase full wave rectification is 0.667. The high -power charger is all three -phase full -wave bridge type type The current pulse coefficient is 0.14, which is far greater than 0.05. Therefore, using a rectifier without filtering device, pay attention to the control of the actual charging voltage.
There is also a silicon charger on the market. The exchange composition of its output waveform is very high, especially in the case where the angle is small (the small current state). The square value of the current value is proportional, so the fever of the battery and wire is intensified, and the battery is very damaged. This charger should not be used for a long time.
When choosing a fast charger, a special problem should be paid attention to. Because the fast charger works in a large -current pulse, if the capacity of the rechargeable battery is large, the pulse value of the charger will affect the grid, which will cause the sine waves of the surrounding cities. If there are electrical appliances with high power supply quality nearby, fast chargers should not be used. Similar technical problems have similar technical problems.