How to distinguish between constant current charging and constant voltage charging circuits

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How to distinguish between constant current charging and constant voltage charging circuits [Copy link]

Constant current and constant voltage charging is charged with constant current in the first stage; when the voltage reaches the predetermined value, it enters the second stage for constant voltage charging, at which time the current gradually decreases; when the charging current drops to zero, the battery is fully charged. This is the most commonly used charging method for lithium batteries.

As an AC/DC power supply, does the "charging pile core" output constant voltage or constant current? Is this determined by the "charging pile core" itself? In order to answer this question, we need to popularize the "constant voltage" working mode and "constant current" working mode of the switching power supply. Constant voltage (CV, Constant Voltage) mode means that the output voltage of the switching power supply is constant, the control loop of the switching power supply is the voltage loop in effect, and the given voltage of the voltage loop is the "constant voltage" output by the power supply. The output current size in constant voltage mode is determined by the load. 1. For a single-loop control system, in constant voltage mode, the voltage loop is working. 2. For a dual-loop control system, in constant voltage mode, if the voltage loop is the inner loop and the current loop is the outer loop, the inner voltage loop is working, and the outer current loop is not involved in the control, or the outer loop fails; if the voltage loop is the outer loop and the current loop is the inner loop, both loops are working, and the PI output of the outer voltage loop is used as the given current loop of the inner loop. Constant current (CC, Constant Current) mode means that the output current of the switching power supply is constant, the control loop of the switching power supply is the current loop in effect, and the given current of the current loop is the "constant current" output by the power supply. The output current in constant current mode is determined by the load. For single-loop control systems, it is easy to understand. For dual-loop control systems, how the current loop and voltage loop are converted to each other is not easy for beginners to understand. You can look at the output voltage. If the voltage does not change under different loads, it is constant voltage Constant current charging: a method of charging the battery with a constant current; a relatively large current can be used for charging, so the charging efficiency is relatively high. Constant voltage charging: a charging method in which the charging voltage is maintained at a constant value; the charging end is due to the high virtual voltage due to the polarization internal resistance of the battery. Using the constant voltage mode, the charging current is reduced, which can make the battery charge more fully. Take lithium batteries as an example: In the first stage of constant current constant voltage charging (CCCV), the battery is charged with constant current. In this stage, the battery voltage rises linearly with time. When the battery voltage reaches the preset upper limit (generally 4.2V), it enters the second stage and charges the battery with constant voltage at this upper limit voltage. In the constant voltage charging stage, the charging current gradually decreases with time until the current drops to the set minimum value (generally 0.1C-0.02C, C=battery capacity/h). The battery is considered to be fully charged and the charging process ends. The current constant current constant voltage mode has high charging efficiency and less damage to the battery, and is a common charging method. (If you have to say the difference, the load can be changed in both charging modes. The cross-current charging current remains unchanged, and the voltage across the load will change; while the constant voltage charging voltage remains unchanged.) The nature of constant current charging and constant voltage charging during charging During the charging process, the "master brain" BMS of the charging system sends a variety of messages to the "slave brain" charging pile controller (represented by "charger" in the national standard), but there are not many command message information related to whether the charging pile core works in constant current or constant voltage mode. According to the national standard GB/T27930-2015, "Communication protocol between non-on-board conductive chargers and battery management systems for electric vehicles", all relevant information is listed as follows: 1, PGB9984, BMS handshake message, providing BMS "maximum allowable total charging voltage". 2, PGN1536, charging parameter configuration stage, the power battery charging parameters sent by the BMS to the charger, giving the "maximum allowable charging current" and "maximum allowable total charging voltage". 3, PGN4096, battery charging requirement message (BCL), this is the most critical message in the charging process. Excerpt as follows: The CML message mentioned in this article is the charger maximum output capacity message, which is the charger's maximum output voltage, maximum output current, minimum output voltage, minimum output current, etc. sent by the charger to the BMS. This message does not explain how to enter the constant voltage or constant current mode, but only explains the meaning of the constant voltage mode and constant current mode in a different way: In the constant voltage charging mode, the voltage output by the charger should meet the voltage requirement value, and the output current cannot exceed the current requirement value; in the constant current charging mode, the current output by the charger should meet the current requirement value, and the output voltage cannot exceed the voltage requirement value.