li ion 18650 battery pack.Lithium battery fast charge principle

　　Fast charging is called fast charging, and the main purpose is to reduce the charging time of the device and improve the efficiency of use.

　　The charging of lithium batteries is mainly divided into three stages, which are constant current pre-charging, high current constant current charging and constant voltage charging. In the first stage, when the voltage is lower than 3.0V, the charge management line (inside the device or the charger) will use 100mA current to precharge the lithium battery at constant current, in order to slowly restore the overdischarged lithium battery, which is a protective measure. When the lithium battery voltage is higher than 3.0V, it enters the second stage, the high current constant current charging stage (C C Fast charge). Because the lithium battery has gone through the first stage of pre-charging, its state has been relatively stable. So in the second stage, the charging current can be appropriately increased, according to different batteries, the size of this current can range from 0.1C to several C, C refers to the battery capacity, such as 2600mAh lithium battery, 0.1C refers to the size of 260mA current. In this charging stage, the standard charging recommended by the state is charged with 0.1C current, which is the standard charging. However, the standard charging standard was put forward very early, more than a decade ago. At that time, because lithium battery technology is far less stable than now (does not allow high current charging), the advantage of using standard charging is that the charging process is stable, and the probability of explosion is very small; The disadvantage is the longer time! Fast charging refers to charging at this stage with a current greater than 0.1C. If the lithium battery capacity is 3000mAh, then the standard charging current is 300mA, as long as the charging current is greater than 300mA, it can be defined as fast charging. However, from the current level of lithium batteries and the level of charge and discharge management chips, there is no problem with 1C current charging. So fast charging isn't as dangerous as you might think.

　　Generally, the charging current of fast charging is 0.2~0.8C, so fast charging is still safe. Due to the improvement in recent years, the current chargers are basically fast charging types. The last stage of lithium battery charging is the constant voltage charging stage, this stage is detected when the lithium battery voltage is equal to 4.2V, the charger enters the constant voltage charging mode, this stage the charging voltage is constant 4.2V, the charging current is getting smaller and smaller (slowly full, the current must be smaller ~). When the charging current is less than 100mA, it is judged that the battery is full and the charging circuit is cut off. The characteristics of this stage can also explain why after the phone indicates that it is fully charged, pull out the USB cable and plug it in, and the phone shows that it continues to charge. It needs to be said that the above charging is the most ideal charging process for a single lithium battery, and the battery of the battery car generally has two kinds of lead-acid batteries and lithium batteries. These batteries are made up of several batteries (lead-acid battery types consist of 6 or 8 series in parallel; The lithium battery type consists of a number of lithium batteries in series and parallel). When it comes to the charging method of the battery pack, there is another big problem, that is, the battery balance problem. Regarding the battery balance problem, it is the biggest bottleneck to solve the battery group technology at present, and some electric vehicle batteries can be improved from BMS.

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