When charging batteries, it is essential to select the appropriate method based on different circumstances and to use the charging equipment correctly. This will improve work efficiency and extend the service life of both the battery and the charging equipment.
There are generally two charging methods for batteries: constant current charging and constant voltage charging. In recent years, fast charging (pulse charging) has also been gradually promoted.
(1) Constant current charging
A charging method in which the charging current remains constant during the charging process is called constant current charging, as shown in the figure.
How to charge a lead-acid battery_The charging principle of a lead-acid battery
Constant current charging has great adaptability, allowing the charging current to be selected and adjusted arbitrarily, thus enabling the charging of batteries under various conditions.
This method can be used for initial charging, supplementary charging, and desulfurization charging of new batteries.
However, its disadvantages are that it takes a long time to charge and requires frequent adjustment of the charging current.
(2) Constant voltage charging
A charging method in which the power supply voltage U remains constant throughout the charging process is called constant voltage charging, as shown in the figure.
How to charge a lead-acid battery_The charging principle of a lead-acid battery
When using constant voltage charging, it is important to select the right charging voltage: if the voltage is too high, not only will the charging current be too large in the initial stage of charging, but overcharging will also occur, which may cause the plates to bend, a large amount of active material to fall off, and the battery temperature to rise too high; if the charging voltage is too low, the battery will not be able to be charged.
Constant voltage charging also requires that the battery being charged must be connected in parallel with the charging power source. Since the battery in a car is connected in parallel with the alternator, the battery is always charged under the constant voltage of the alternator (adjusted by the regulator).
The charging methods described above are collectively referred to as "conventional charging." An initial charge takes 60-70 hours, and a supplementary charge takes approximately 20 hours. This excessively long charging time causes significant inconvenience for users.
(3) Pulse fast charging
Pulse fast charging can greatly overcome the polarization phenomenon that occurs during the charging process and effectively improve charging efficiency.
The charging current waveform is shown in the figure:
How to charge a lead-acid battery_The charging principle of a lead-acid battery
The advantages of pulse fast charging are:
① The charging time is greatly shortened. Generally, the initial charge takes no more than 5 hours and the supplementary charge takes no more than 1 hour.
② It can increase the battery capacity. Because pulse fast charging can eliminate polarization, the chemical reaction is more complete during charging, deepening the reaction and increasing the battery capacity. Therefore, a new battery can be used immediately after initial charging without needing to be discharged, which not only saves energy but also makes it more convenient to use.
③ It has a significant desulfurization effect. Due to the above advantages, pulse fast charging is particularly advantageous in sectors with concentrated batteries, frequent charging, or emergency use. However, pulse chargers have complex control circuits, are more expensive than ordinary chargers, and are not yet ideal in practice, requiring further improvement.
④ Identification of the positive and negative polarities of the battery during charging
When charging, the positive and negative terminals of the battery should be connected to the positive and negative terminals of the charger, respectively. Therefore, it is necessary to correctly determine the polarity of the battery.
Battery terminals are usually marked with a "+" or "-" symbol; or the positive terminal is painted red. If the markings are unclear, the following methods can be used for identification:
① Observe the color of the terminals. The positive terminal of a used battery is dark brown, and the negative terminal is light gray.
② Connect a DC voltmeter to the two terminals of the battery and determine the positive and negative terminals by observing the direction of the pointer deflection.
③ Use the electrolyte for identification. Connect the two terminals of the battery to wires and insert them into the electrolyte (do not let the two wires touch). The terminal with more bubbles around the wires is the negative terminal.
Conventional charging methods
There are two common charging methods for lead-acid batteries: float charging (also known as constant voltage charging) and cyclic charging.
When float charging, the charging voltage must be strictly controlled. For example, for a battery with a rated voltage of 12V, the charging voltage should be between 13.5V and 13.8V. If the float charging voltage is too low, the battery will not be fully charged; if it is too high, it will cause overcharging. The voltage should be set so that the initial charging current does not exceed 0.3C (C is the rated capacity of the battery).
For cyclic charging, the initial charging current should not exceed 0.3C, and the charging ampere-hours should be slightly greater than the discharging ampere-hours. Alternatively, you can first charge at a constant current of 0.1C for several hours, and when the charging ampere-hours reach 90% of the discharging ampere-hours, switch to float charging until fully charged.
The above are the commonly used charging methods for lead-acid batteries, but both methods have some drawbacks. During charging, the battery voltage gradually increases, while the charging current gradually decreases. Because constant voltage charging disregards the actual state of the battery voltage, the charging voltage remains constant, and the charging current initially is relatively high, then decreases exponentially. Fast charging may overcharge the battery, easily leading to battery damage. For cyclic charging, using a smaller current yields better charging results. However, for large-capacity batteries, the charging time becomes very long, resulting in low efficiency and numerous inconveniences.
