Block diagram of high frequency switching charging power supply

In the mid-1960s, American scientist Maas did a lot of experimental research on the gas evolution problem during the charging process of valve-regulated sealed lead-acid batteries, and proposed an acceptable method for valve-regulated sealed lead-acid batteries based on the lowest gas evolution rate. The charging current curve is shown in the figure below. It can be seen from the figure that during the charging process, as long as the charging current does not exceed the acceptable current of the valve-regulated sealed lead-acid battery, a large number of bubbles will not be generated inside it. Conventional charging generally adopts a two-stage charging method of constant current first and then constant voltage. In the early stage of the charging process, the charging current is much smaller than the acceptable charging current of the valve-controlled sealed lead-acid battery, so the charging time is greatly extended; in the later stage of the charging process , the charging current is greater than the acceptable current of the valve-regulated lead-acid battery, so a large number of bubbles will be generated in the valve-regulated lead-acid battery. If the actual charging current can always be equal to or close to the acceptable charging current of the valve-regulated sealed lead-acid battery during the entire charging process, the charging speed can be greatly accelerated, and the gas evolution rate can also be controlled in a very low range. . This is the basic theoretical basis of fast charging. However, during the charging process, the polarization voltage generated in the VRLA battery will hinder its own charging and significantly increase the gas evolution rate and temperature. Therefore, the polarization voltage is an important factor affecting the charging speed. It can be seen that in order to achieve fast charging, we must try to eliminate the impact of polarization voltage on the charging of valve-regulated sealed lead-acid batteries. It can be seen from the formation mechanism of polarization voltage that the magnitude of polarization voltage changes with the change of charging current. When charging is stopped, the resistance polarization disappears, and the concentration polarization and electrochemical polarization gradually weaken. If a discharge channel is provided for the valve-regulated lead-acid battery to allow reverse discharge, the concentration polarization and electrochemical polarization will disappear quickly, and at the same time, the temperature inside the valve-regulated lead-acid battery will also decrease due to discharge. Therefore, by suspending charging in a timely manner during the charging process of valve-controlled sealed lead-acid batteries, and appropriately adding discharge pulses, various polarization voltages can be quickly and effectively eliminated, thereby increasing the charging speed. At present, the more recognized fast charging methods are pulse charging and pulse discharge depolarization methods. The figure below shows the waveforms of pulse charging, pulse discharge, depolarization and fast charging.