Charging and discharging of storage batteries

Battery charging

The new battery and the newly repaired battery must be charged initially, and the battery in use must be supplemented; in order to maintain a certain capacity and extend the life of the battery, regular overcharge and exercise charging are required. The accumulator is a DC power source and must be charged with a DC power source. When charging, the positive pole of the charging power source is connected to the positive pole of the battery, and the negative pole of the charging power source is connected to the negative pole of the battery. The characteristics of the initial charging of a new battery or a battery with a replacement plate are that the charging current is small, the charging time is long, and it must be completely sufficient. During the charging process, the charging current is constant (by adjusting the voltage to ensure that the current is constant). When charging, connect batteries of the same capacity in series to connect to the charging power source. Generally, a two-stage charging method is used. In the first stage, use a larger current to charge. When the cell voltage rises to 2.4V and the electrolyte starts to generate bubbles, reduce the charging current by half and perform the second stage constant current charging until the battery is fully charged. The advantages of constant current charging are: the charging current can be arbitrarily selected, which is beneficial to prolong the life of the battery, and can be used for initial charging and desulfurization charging. The disadvantage of constant current charging is that the charging time is long and the charging current needs to be adjusted frequently.

There are mainly the following ways to charge batteries:

① Constant current charging. It is always charging with a constant current, which is realized by controlling the charger. This method of maintaining the current by controlling the charger is simple and convenient to operate, and is particularly suitable for a battery pack in which multiple batteries are connected in series. To make the battery discharge slowly and the capacity easy to recover, it is best to use this low-current and long-term charging mode. weakness is: the constant current value in the initial charging stage is smaller than the rechargeable value, and in the later stage of the charging, the constant current value is larger than the rechargeable value; the whole charging time is long, the gas is released, the impact on the plate is large, the energy consumption is high, and the charging efficiency does not exceed 65%. Generally, maintenance-free batteries should not use this method. There is a variant of constant current charging – segmented constant current charging. It reduces the current in the later stage of charging and avoids excessive current in the later stage of charging. It is usually necessary to determine the size of the charging current, the time, the time of switching the current, and the judgment basis for the termination of charging according to the requirements of the photovoltaic lighting system and the characteristics of the battery.

The charging of the lead-acid battery has just started with constant current charging, and the charging power must be a DC power supply. At the beginning of charging, the terminal voltage rises rapidly, and sulfuric acid is rapidly generated in the pores. In the stable rising stage, the terminal voltage slowly rises to about 2.4V, and the sulfuric acid generated in the pores diffuses out of the pores. When the rate of sulfuric acid generation and diffusion reaches a balance, the terminal voltage rises slowly with the change of the electrolyte density in the entire container. At the end of charging, the voltage quickly rises to about 2.7V and remains stable. The charging current is used to electrolyze water, and the electrolyte is in a boiling state. Avoid prolonged overcharging. The characteristic of a fully charged battery is that the terminal voltage rises to the maximum value of 2.7V, and does not increase within 2 to 3 hours. A large number of bubbles are generated in the battery, that is, the “boiling phenomenon” of the electrolyte.

② Constant voltage charging. It is charged with a certain constant voltage for each single battery. The advantages are: the charging current starts to be large, the charging speed is fast, and the charging time is short. The charging current will gradually decrease to zero with the rise of the electromotive force, so that the charging will stop automatically, without manual adjustment and care, and the amount of gas evolution during the charging process is small, the charging time is short, the energy consumption is low, and the charging efficiency can reach 80%. The disadvantage of constant voltage charging is that the charging current cannot be adjusted, so the battery cannot be fully charged, nor can it be used for initial charging and desulfurization charging. Constant voltage charging is generally used in applications where the battery pack voltage is low.

③ Pulse fast charging. It is a method of fast charging by pulsed high current charging. The specific method is: first charge with high current and constant current until the single cell voltage reaches 2,4V, stop charging for 15~25ms; reverse pulse charging, then stop charging for 25~40ms, and repeat until sufficient.

④Smart charging. That is, the minimum loss charging mode, which can automatically track the acceptable charging current of the battery to make it consistent with the internal polarization current of the battery, while the conventional charging technology cannot dynamically track the actual condition of the battery and the size of the acceptable charging current. The intelligent charging system is composed of a charger and a charged battery to form a binary closed-loop circuit. The charger determines the charging parameters according to the state of the battery, and the charging current is near the acceptable charging current curve from beginning to end, so that the battery is charged almost under the condition of no gas evolution, which saves electricity and does not damage the battery. Smart charging needs to know the current curve of the battery to be charged.

Charging and discharging of storage batteries
Charge and discharge of lithium battery

Battery discharge

When the battery starts to discharge, the terminal voltage drops rapidly from 2.14V to 2.1V; the sulfuric acid in the plate pores is rapidly consumed, the electrolyte density drops rapidly, the concentration polarization increases, and the terminal voltage drops rapidly. Then, entering a relatively stable stage, the terminal voltage slowly drops from 2.1V to 1.85V, the sulfuric acid diffused from the pores of the electrode plate and the sulfuric acid consumed in the pores reach a dynamic balance, and the terminal voltage slowly decreases. Finally, the discharge of the battery enters a rapid decline stage, the terminal voltage drops rapidly from 1.85V to 1.75V; the density of the electrolyte drops linearly.

Although lead-acid batteries are selected under strict control when they leave the factory, after a certain period of use, voltage unevenness will appear and gradually become larger. Charging cannot supplement the undercharged, nor can it limit the overcharged charge. Therefore, in the middle and late stages of the battery pack, the open circuit voltage of each battery is measured regularly and irregularly. If the voltage is lower, charge separately to make the voltage and capacity consistent with other batteries, and try to reduce the gap between them.

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