Constant current charging method, which is a charging method to keep the charging current intensity unchanged by adjusting the output voltage of the charging device or changing the series resistance with the battery. The control method is simple, but the acceptable current capacity of the battery decreases gradually with the charging process. In the later stage of charging, the charging current is mostly used to electrolyze water and produce gas, which leads to excessive outgassing. Therefore, the stage charging method is often used.
Stage charging method includes two-stage charging method and three-stage charging method.
The two-stage method adopts a fast charging method combining constant current and constant voltage. First, the constant current is charged to a predetermined voltage value, and then it is changed to a constant voltage to complete the remaining charging. Generally, the switching voltage between two stages is the constant voltage of the second stage.
The three-stage charging method uses constant current charging at the beginning and end of charging, and constant voltage charging in the middle. When the current decays to a predetermined value, switch from the second stage to the third stage. This method can minimize gas output, but it is limited as a fast charging method.
In the constant voltage charging method, the voltage of the charging power supply remains constant during the whole charging time, and the current gradually decreases with the gradual increase of the terminal voltage of the battery. Compared with the constant current charging method, the charging process is closer to the optimal charging curve. Constant voltage fast charging, because the battery electromotive force is low in the initial stage of charging, the charging current is very large, and it will gradually decrease with the charging current, so only a simple control system is needed. This charging method uses little electrolytic water, which avoids overcharging the battery. However, the current is too large at the initial stage of charging, which has a great influence on the battery life, and it is easy to bend the battery plate, leading to battery scrap. In view of this shortcoming, constant voltage charging is rarely used, and it is only used when the charging power supply voltage is low and the current is large. For example, when the car is driving, the battery is charged by the constant voltage charging method.
Fast charging method, specifically divided into the following four:
1. pulse charging method not only follows the inherent charging acceptance rate of battery, but also improves the charging acceptance rate of electric vehicle battery, thus breaking the limit of exponential charging acceptance curve of battery, which is also a new development of battery charging theory. Pulse charging method is to charge the battery with pulse current first, then stop charging the battery for a period of time, and so on. The charging pulse makes the battery fully charged, while the intermittent period gives the oxygen and hydrogen produced by the chemical reaction of the battery time to recombine and be absorbed, so that the concentration polarization and ohmic polarization are naturally eliminated, thereby reducing the internal pressure of the battery, making the next round of constant current charging go on smoothly and making the battery absorb more electricity. Intermittent pulse makes the battery have enough reaction time, reduces gas evolution and improves the charging current acceptance rate of the battery. There are generally two kinds of pulse charging methods to control the charging circuit: the amplitude of the first pulse current is variable, while the frequency of PWM (driving charge-discharge switch tube) signal is fixed. The amplitude of the second pulse current is fixed, while the frequency of the PWM signal is adjustable.
Secondly, the amplitude of pulse current and the frequency of PWM signal are fixed, and the PWM duty cycle is adjustable. On this basis, adding the intermittent charging stop stage can charge more electricity in a short time and improve the charging acceptance of the battery. REFLEXTM fast charging method is a patented technology in the United States, which is mainly used for charging nickel-cadmium batteries. Because of the new charging method, the memory effect of nickel-cadmium battery is solved, so the fast charging time of the battery is greatly reduced. The charging method and detection method of lead-acid battery are quite different from those of nickel-cadmium battery, but they can learn from each other. A working cycle of REFLEXTM charging method includes three stages: forward charging pulse, reverse instantaneous discharge pulse and stop charging maintenance.
3. Variable current intermittent charging method, which is based on constant current charging and pulse charging, as shown in Figure 7. Characterized in that a constant-current charging section is changed into a voltage-limiting variable-current intermittent charging section. At the initial stage of charging, the method of intermittent charging with variable current is adopted to ensure the increase of charging current and obtain most of the charging amount. In the later stage of charging, the constant voltage charging section is used to obtain overcharge, so that the battery can be restored to a fully charged state. By stopping charging intermittently, oxygen and hydrogen produced by the chemical reaction of the battery have time to recombine and be absorbed.
Fourth, the variable pressure intermittent charging method, on the basis of the variable pressure intermittent charging method, someone proposed the variable pressure intermittent charging method. Different from the variable current intermittent charging method, the first stage is not intermittent constant current, but intermittent constant voltage. At each constant-voltage charging stage, the charging current naturally decreases exponentially due to constant-voltage charging, which is in line with the characteristics that the battery current acceptance rate gradually decreases with charging.