Lithium Battery Charging Knowledge: Why Do Lithium Batteries Have Constant Voltage And Constant Current Charging?

- Nov 01, 2019-

Lithium battery charging knowledge: Why should lithium batteries be charged with constant voltage and constant current? Lithium-ion batteries have achieved wide success in the fields of consumer electronics, energy storage and power due to their high energy density and excellent cycle life. Lithium-ion batteries are increasingly entering the lives of ordinary consumers. Charging is the most common operation of consumers in the use of lithium batteries, and the charging process has a significant impact on the life characteristics of lithium-ion batteries, then we will discuss today: why lithium batteries should be constant voltage and constant current charging.

Why do lithium batteries have constant voltage and constant current charging?

The first stage of constant current constant voltage charging is charged with a constant current; when the voltage reaches a predetermined value, it is transferred to the second stage for constant voltage charging, at which time the current gradually decreases; when the charging current reaches zero, the battery is completely charged. This is the most common charging method for lithium batteries.

When the battery is constantly charged to a constant voltage, the voltage at this time is not the true voltage of the battery. If the voltage is not limited, the voltage of the battery will continue to rise and internal polarization until the battery structure is destroyed, the battery fails, or even explodes. The above said a bit: just reached a constant voltage, the battery is not fully charged. In order to further fully charge the battery without damaging the performance of the battery, a constant voltage mode is employed. As the charging capacity increases, the actual voltage of the battery will become closer and closer to the set voltage. At this time, in order to maintain the constant voltage, the current value will gradually decrease.

Constant voltage charging is only one of the methods of charging lithium batteries, and there are many other methods, not just constant pressure. The so-called constant voltage is to provide a constant charging voltage. When the battery consumes electricity, the voltage of the battery is relatively low, and the voltage difference between the charging and the charging is large, and the charging current is large. As the charging process continues, the battery continues. Being charged with more and more electricity, the voltage of the battery is getting higher and higher, the pressure difference with the charging voltage is smaller, and the current that can be charged is smaller, until the voltage of the battery and the charging voltage are equal, the current Zero.

The constant voltage constant current power supply is a kind of switching power supply. The difference from the switching power supply is that there are two circuits of constant voltage and constant current inside the constant voltage constant current power supply. The output voltage and current can be continuously adjusted from 0 to the rated value, constant voltage and The constant current mode of operation will automatically switch in actual operation; the lithium battery charger is essentially a constant voltage constant current power supply, the output current is constant, does not change with the grid voltage and load, and most of the circuits have continuous monitoring of the battery voltage. Effectively prevent overcharging.

How does the lithium battery charger achieve constant voltage charging?

Lithium battery constant voltage charging is only one stage in the charging process. When the battery is used up, the voltage of the two terminals of the battery is less than 4.2V. At this time, the charging voltage is less than 4.2V. After the battery rises to 4.2V, the battery is kept constant at 4.2V for a long time. When the battery is fully charged, it automatically switches from constant voltage to constant current charging. The battery voltage rises slowly, about 5V, the battery is fully charged, the charger is turned to trickle charge, the trickle charge will not damage the battery, and it can be charged for a long time. When the battery was just removed, the voltage was 5V. When the battery was used at first, the voltage quickly dropped to 4.2V, and the voltage began to drop until the battery was nearly used up. Description The writing track "The charging indicator is off, you can not take out the battery and keep the charging state." It is common in daily applications, such as emergency lights in public places, cordless, etc., usually in a normal charge state.

Constant current charging and constant voltage charging circuit difference

You can see the output voltage. In the two charging modes, the load is changed, the cross current charging current is constant, and the voltage across the load changes; while the constant voltage charging voltage does not change. The current constant current and constant voltage mode has high charging efficiency and less damage to the battery, and is a common charging method.

In the constant voltage charging mode, the voltage output by the charger should meet the voltage demand value, and the output current cannot exceed the current demand value; in the constant current charging mode, the current output by the charger should meet the current demand value, and the output voltage cannot exceed Voltage demand value.

In summary, it is ok to charge a lithium battery with a constant voltage constant current power supply instead of a lithium battery charger. Its main advantage lies in the centralized charging of lithium batteries, such as series or parallel connection of multiple lithium batteries for uniform charging, convenient and fast, saving time