1. Constant current charging
Constant current charging means that when the battery is charged, the method of segmented constant current is used for charging, and the current is achieved by adjusting the charging device. Its main feature is that the charging method has a large adaptability, and the charging current can be arbitrarily selected and adjusted. Therefore, it can charge batteries in various situations and states (such as initial charging of new batteries, supplementary charging of used batteries, and desulfurization charging, etc.). It is especially suitable for long-time charging mode with small current, charging the battery pack with many batteries connected in series, and is beneficial to the charging of the battery whose capacity recovery is slow.
However, because the charging current in the initial stage of this charging method is too small and the charging current is too large in the later stage of charging, the whole charging process takes a long time, produces a lot of gas, has a large impact on the electrode plate, high energy consumption, and low efficiency (not more than 65%), and the whole charging process must be supervised by a special person. Therefore, it is only used when the battery is initially charged and requires a long period of low current for desulfurization charging.
The following matters should be paid attention to when using the constant current charging method:
① Since the variant of constant current charging is segmented constant current charging, in order to avoid excessive current in the later stage of charging, the charging current should be adjusted in time. In addition, the size of the charging current, the charging time, the timing of the current conversion and the selection of the charging termination voltage must strictly follow the charging specifications;
② The remaining capacity of each charged battery should be similar, otherwise the charging current must be selected according to the battery with the smallest remaining capacity of the series battery pack, and when the small-capacity battery is sufficient, it should be removed immediately, and then continue to charge the large-capacity battery;
③ During the charging process, check the battery cell voltage every 2 to 3 hours. If the voltage has reached 2.4V, it should be transferred to the second stage of charging in time;
④ When the electrolyte temperature rises to 40°C during the charging process, the charging current should be halved. If it continues to rise to 45°C, it should be stopped, and the charging can be continued after the temperature drops below 40°C;
⑤ The density of the electrolyte of the charged battery shall meet the specified requirements, and the density difference of the electrolyte between the cells shall not exceed 0.01g/cm3;
⑥ Maintenance-free batteries should not be charged in this way.
2. Electric vehicle charger - constant voltage charging
Constant voltage charging means that each single battery is charged with a certain constant voltage (generally the number of single cells × 2.5V). Its main characteristics are: the initial charging current is quite large, the battery electromotive force and the relative density of the electrolyte rise rapidly, and the charging current gradually decreases as the charging continues, and only a small current passes at the end of the charging; the charging time is short and the energy consumption is low. Generally speaking, the battery can obtain 90% to 95% of its own capacity after charging for 4 to 5 hours; if the charging voltage is properly selected, the entire charging process can be completed in 8 hours, and the entire charging process does not require human care, so it is widely used in supplementary charging. .
The shortcomings of constant voltage charging are: because the initial charging current is too large, when charging a battery with an excessive depth of discharge, the initial charging current will rise sharply, which is easy to cause overcurrent of the charged battery and damage to the charging equipment; during the charging process, Since the charging current cannot be adjusted, it is not suitable for the initial charging and desulfurization charging of the battery; since it is difficult to compensate for the change of the battery voltage during the charging process, it is difficult to complete the full charging of the battery whose capacity recovery is slow.
When using the constant voltage charging method, the following matters should be paid attention to:
①. Select the charging voltage correctly. If the charging voltage is too high, it will cause the charging current to be too large at the initial stage of charging. If it is too low, the battery will be insufficiently charged, resulting in reduced capacity and shortened life;
②. The terminal voltage of the charged battery must be exactly the same.
3. Balanced charging
For a battery pack composed of many single cells, such as a stationary battery, after a certain period of operation, it is necessary to perform equalization charging on a regular basis. This is because when charging is carried out under the same conditions, the active substances in each part of the plate have different degrees of charging, and as a result, the active substances react in an unbalanced state. In addition, considering that some of the charging and discharging characteristics of the single cells are also different, some single cells may be in an undercharged state. Therefore, after the normal charging is completed, continue to charge for 1 to 3 hours with a current of about 20h. This charging is also known as overcharging. When the battery is usually used under the same conditions, it is beneficial to perform equalization charging on a regular basis for battery maintenance.
Different users have different regulations on the length of time between equalizing charging, and some stipulate that it should be carried out once every three months or half a year. According to the advancement of battery design and manufacturing technology, the characteristics of batteries are not very different, so the interval time for equalization charging tends to be prolonged.
4. Float charging
Batteries that are used intermittently or that are used only when the AC power fails, are charged by float charging. For example, for the stationary type, a voltage of 2.15 to 2.2V is applied to each single cell of the battery, and the battery is charged with a continuous small current. The charger is connected in parallel with the battery, and the charging current can mainly supplement the loss of self-discharge, that is, the range of about 0.3% to 1.0% of the 10h rate, while the usual load is borne by the charger, and the battery is also powered by the battery for short-term heavy loads. At this time, charging is performed automatically due to the drop in the terminal voltage of the battery.
5. Constant voltage current limiting charging
Constant voltage current limiting charging is mainly used to remedy the disadvantage of excessive charging current during constant voltage charging (the method is the same as constant voltage charging). A resistor (current limiting resistor) is connected in series between the charging power supply and the battery to be charged to automatically adjust the charging. current.
When the charging current is too large, the voltage drop on the current limiting resistor is also large, thereby reducing the charging voltage; when the charging current is small, the voltage drop on the current limiting resistor is also small, and the voltage loss output by the charging device is also small. In this way, the charging current is automatically adjusted so that it does not exceed a certain limit. This method is widely used in the initial charging of maintenance-free batteries and the supplementary charging of ordinary batteries.
