The battery should be charged with constant voltage or constant current with low current or medium current immediately after the discharge is terminated (it should not exceed 24 hours in special cases), and the general charging time is 5-8 hours, even as long as 10-20 hours , this charging is called regular charging (normal charging). Although the charging time of conventional charging is long, it can make full use of the low power period for charging, reduce the charging cost, improve the charging efficiency and prolong the service life of the battery.
The main disadvantage of the conventional charging method is that the charging time is too long, which is difficult to meet when there is an emergency operation demand. The conventional charging method is usually suitable for electric cars whose designed driving range is as long as possible to meet the needs of a day’s operation, and can be charged during evening outages. Under the current technical conditions, the cruising range of the battery is about 200km, and the average daily mileage of cars such as private cars, urban sanitation cars, and corporate commercial cars is within the range of the battery’s cruising range, and conventional charging can be used. Way. Conventional charging is divided into two modes: small current charging and medium current charging.
1) Small current charging method
The small current charging method generally uses a small current to charge the battery according to the charging curve of the battery. The charging time is usually 8-10 hours. Because the battery is charged by constant current and constant voltage charging, the whole charging process is closer to the inherent nature of the battery. It can effectively avoid the overcharge and undercharge problems of the battery. In this way, the battery is charged with a relatively low charging current, the related technology is mature and reliable, and the work and installation costs of the charger are also relatively low.
The low-current charging method is mainly used in home charging occasions. The typical charging current is about 15A, and the charging time is 8-10 hours (charged to more than 95%). This charging method has no special requirements for the power grid, and directly draws electricity from the low-voltage lighting circuit, and the charging power is small, generally 1-3kw. The car charger can use the national standard three-port socket, there is basically no interface standard problem, and it is powered by the standard grid power supply of 220V/16A. Since charging at home is usually done at night or during the low electricity consumption period, which is conducive to the effective use of electric energy, the power sector generally takes certain measures to attract electric energy car users to charge during the low electricity consumption period.
Electric car household charging equipment (car chargers) and small charging stations mostly use small current charging methods. The car charger is one of the most basic charging equipment for pure electric cars. The charger is fixed on the car or placed in the trunk as a standard configuration, because it is only necessary to insert the plug of the car charger into the power socket at home. For charging, the operation is simple and the implementation is convenient, so the charging process can generally be completed independently by the user. For batteries and electric cars, low-current charging is the safest and most reliable charging method, but it is difficult to meet users’ urgent or long-distance driving needs.
2) Medium current charging method
The medium-current charging method is mainly used in small charging stations in public places such as shopping centers, hotel entrances, and parking lots. The charging current of the small charging station is 30-60A, and the charging power is generally 5-20kw . It adopts three-phase four-wire 380V power supply or single-phase 220V power supply. The charging method is coin or credit card. At the designated location of the charging station, connect the wire to start charging. The charging time of this method is: 1-2 hours for recharging, 5-8 hours for full charging (to more than 95%), and 1 hour for charging with medium current in a small charging station, the mileage of the electric car can be increased by 40km .
3) Normal charging mode
Different types of electric car batteries have different charging modes. The charging modes used in the conventional charging method are:
(1) Constant current charging mode. The constant current charging mode is the most commonly used charging mode, with simple control and simple equipment. It is only suitable for some batteries (such as Ni/MH), and the battery pack cannot be fully charged, and the charging efficiency is low.
(2) Hierarchical constant current charging mode. The graded constant current charging mode is developed on the basis of the ordinary constant current charging method. In the initial stage, a larger current is used for charging, and a smaller current is used after charging for a certain period of time or when the charging voltage reaches a certain value, and then charging for a certain period of time. Or switch to a smaller current after the charging voltage reaches another higher value. This charging method has higher efficiency, shorter charging time and better charging effect, and is beneficial to prolong the service life of the battery pack, but has higher requirements on the charger system. The graded constant current charging mode is suitable for the early charging of Ni/MH batteries and Li-ion batteries.
(3) Low-voltage constant-voltage floating charge mode. The low-voltage constant-voltage floating charging mode is different from the usual method of fully opening equalizing and floating. The charging power supply always works in the mode of voltage regulation and current limiting, and the battery gradually replenishes the lost energy in the floating state until the charging reaches the termination voltage. . This charging method has the characteristics of simple principle and convenient implementation, but it may cause the battery to be undercharged, and long-term charging will damage the battery pack and accelerate the self-discharge of the battery. It is suitable for lithium-ion batteries.
(4) Gradient constant voltage charging mode. The gradient constant voltage charging mode combines the advantages of the constant current charging mode and the constant voltage charging mode. During charging, the charging voltage is gradually provided according to the current decay, and the current decreases in a stepwise manner. In the early stage of charging (1-3 hours), the battery voltage rises in a straight line; in the middle stage of charging (3-7h), the charging current is close to exponential decay; in the later stage of charging (8-12h), when the charging current is less than the set value, it will be terminated. Charge or transfer to slip current charging stage. The four charging characteristic curves of the battery are shown in Figure 1 . In the figure, 1 is the maximum acceptable charging current curve of the battery, 2 is the continuously decreasing charging current curve, 3 is the multi-stage constant current charging current curve, and 4 is the low-current slow charging c urrent curve.