The principle of fast battery charging

Fast charge is a high current charge ~ can speed up the charging time.

In the above figure, the abscissa is time and the ordinate is the lithium battery voltage. Due to the particularity of the lithium battery, overvoltage or undervoltage will cause the battery to be scrapped. Therefore, the current lithium battery charge and discharge protection circuit principle is to measure the lithium battery voltage, and then judge whether the lithium battery is in a normal state according to the voltage (non-overvoltage, non-under Pressure).

The charging current of the lithium battery is shown in the pink line above. Lithium battery charging is divided into three stages, namely constant current pre-charging, high-current constant current charging and constant voltage charging.

When the voltage is lower than 3.0V, the charger will precharge the lithium battery with 100mA current, which is the CC Pre-charge stage in the above figure. The Chinese name is the constant current pre-charge phase, and the purpose is to slowly recover the over-discharged lithium battery. Is a protective measure. A qualified charger will have this charging phase.

Then the problem is related. When the lithium battery voltage is higher than 3.0V, it enters the second stage, the high current constant current charging phase (CC Fast charge). Since the lithium battery has been precharged in the ** stage, its state has been relatively stable (the role of the precharge stage can be understood as such - but not rigorous). Therefore, in the second stage, the charging current can be appropriately increased. According to different batteries, the current can vary from 0.1C to several C. C refers to the battery capacity, such as 2600mAh lithium battery, 0.1C is Refers to the current of 260mA.

In this charging phase, the standard charging recommended by the state is to charge with 0.1C current, which is the standard charging. However, the standard charging standard was proposed very early, more than a decade ago. At that time, because lithium battery technology is far less stable than current (not allowing high current charging), so there will be such a standard ~~~ The advantage of using standard charging is that the charging process is stable, and the probability of explosion is very small; The downside is that it takes time! ! !

Fast charging means charging at a current of more than 0.1C at this stage. If the lithium battery capacity is 2600mAh, then the standard charging current is 260mA, as long as the charging current is greater than 260mA, it can be defined as fast charging. However, from the current level of lithium battery and the level of charge and discharge management chip, it is no problem to charge with 1C current. So fast charging is not as dangerous as you might think. Generally, the charging current for fast charging is 0.2~0.8C, so fast charging is safe. Due to the improvement in recent years, the current chargers are basically fast charging types.

The last stage of charging the lithium battery is the constant voltage charging phase. When the lithium battery voltage is equal to 4.2V, the charger enters the constant voltage charging mode. At this stage, the charging voltage is constant at 4.2V, and the charging current is coming. The smaller (slowly filled, the current must be smaller ~). When the charging current is less than 100 mA, it is judged that the battery is full and the charging circuit is cut off.

The characteristics of this stage can also explain why the phone is fully charged, pull out the USB cable and plug it in again, and the phone shows to continue charging.

In addition, it needs to be said: the above charging is the most ideal charging process for a single-cell lithium battery, and the current qualified lithium battery charging and discharging protection board works like this.

The battery of a battery car generally has two types of lead-acid batteries and lithium batteries. These batteries are made up of several batteries (the lead-acid battery type consists of 6 or 8 series and parallel; the lithium battery type consists of several lithium batteries connected in series). When it comes to the charging method of the battery pack, there is another big problem here, that is, the battery balancing problem. Regarding the battery balance problem, I will not go into details here, Baidu will be fine. I can only say that most of the current battery car batteries do not have battery balance management, so this leads to the life of the battery pack is far less than the life of a single battery, which explains why the battery of the battery car is not durable, it will be scrapped in a year or so. ~~~ also explains that the current dilemma of electric vehicle development is the limitation of battery group technology.

To put it simply, the conclusion is that fast charging refers to a charging method with a charging current greater than 0.1 C. This charging method has little effect on life and stability for a single lithium battery; but if it is for a battery car battery pack, Fast charging is an act of using time to exchange battery life.

The last thing to say is that charging the battery car with the standard charger is no problem; but for those charging stations that are fully charged for 10 minutes, it is important to note that the use of these charging stations greatly affects battery life.

In addition, for battery packs, battery balancing is more important. Fast charging has an impact on the life of the battery pack because the battery pack equalization problem has not been solved.

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