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In the fields of modern logistics and industrial handling, forklifts have become indispensable equipment due to their high efficiency and flexibility. The performance of the lead-acid battery, the power core of a forklift, directly affects the working efficiency and service life of the forklift. In the maintenance of lead-acid batteries, equalization charging is a key technology, which can effectively solve the performance differences of individual batteries within the battery pack and ensure the stable operation of the battery pack. This article will delve into the principle of equalization charging for lead-acid batteries in forklifts and provide a detailed introduction to its operation methods, offering valuable references for relevant practitioners.

1. Overview of Lead-Acid Batteries for Forklifts

Lead-acid batteries are a type of chemical power source that uses lead and its oxides as electrode materials and sulfuric acid solution as the electrolyte. In forklift applications, lead-acid batteries have advantages such as low cost, mature technology, and good high-current discharge performance, and thus are widely used. A complete lead-acid battery pack for forklifts is usually composed of multiple individual cells connected in series to meet the voltage requirements for forklift operation.

However, in actual use, due to the influence of factors such as manufacturing processes, usage environments, and the number of charge and discharge cycles, even single cells produced in the same batch may have certain differences in performance parameters such as capacity, internal resistance, and self-discharge rate. This difference will gradually widen with the increase of usage time, causing some individual cells in the battery pack to age prematurely, and thereby affecting the performance and lifespan of the entire battery pack.

2. Principle of Equalization Charging

(1) The influence of performance differences of individual cells

During the charging and discharging process of lead-acid battery packs, the performance differences of individual cells can cause many problems. During charging, single-cell batteries with smaller capacity or higher internal resistance will reach the fully charged state first, while those with larger capacity or lower internal resistance have not yet been fully charged. When discharging, the single-cell battery with a smaller capacity will be completely discharged first. If discharging continues at this point, it will cause the single-cell battery to over-discharge, accelerating its aging. If this continues for a long time, it will cause the overall capacity of the battery pack to decline, shorten its driving range, and may even lead to battery pack failure.

(2) The purpose of equalization charging

The main purpose of equalization charging is to eliminate the performance differences among individual cells within a battery pack through a special charging method, so that the voltage, capacity, electrolyte density and other parameters of each individual cell can be kept as consistent as possible, thereby extending the service life of the battery pack and improving its overall performance and reliability.

(3) Implementation methods of equalization charging

Equalization charging usually adopts a constant voltage charging method and is carried out after the regular charging of the battery pack is completed. The specific process is as follows: The battery pack is charged at a relatively high constant voltage. At this point, the charging current of the first fully charged individual cells will gradually decrease as the voltage has reached a relatively high level, while the individual cells that have not yet been fully charged continue to receive a larger charging current until all individual cells reach a balanced state. During the equalization charging process, a series of chemical reactions occur inside the battery, promoting the full utilization of the active substances on the plates and the uniform distribution of the electrolyte concentration, thereby achieving the balanced performance of individual cells.

3. Equalization Charging Operation Method

(1) Preparatory work before operation

Check the battery's appearance: Before performing equalization charging, first carefully inspect the battery's appearance to see if there is any damage, deformation, or leakage on the battery casing. If any problem is found with the battery casing, it should be repaired or replaced in time to avoid safety accidents during the charging process.

Measure the density of the electrolyte: Use a hydrometer to measure the density of the electrolyte in each individual cell. Under normal circumstances, the density of the electrolyte in lead-acid batteries is between 1.28 and 1.30g/cm³ (at 25℃). If the density of the electrolyte is too low, it may be caused by excessive battery discharge or excessive evaporation of water in the electrolyte. If the density of the electrolyte is too high, it might be due to overcharging or an excessively high concentration of sulfuric acid in the electrolyte. For single-cell batteries with abnormal electrolyte density, corresponding adjustments need to be made, such as supplementing distilled water or sulfuric acid solution.

Check the battery connection: Ensure that the connections between each individual battery in the battery pack are firm, without any loosening or oxidation. Loose connections can lead to an increase in contact resistance, generating heat during charging and discharging, which affects battery performance and may even cause a fire. Oxidation can reduce the electrical conductivity of batteries and is also detrimental to their operation. If there is any loose connection or oxidation, the connection part should be sanded with sandpaper and then the connection bolts should be tightened again.

Prepare the charging equipment: Select an appropriate charger. The voltage and current parameters of the charger should match those of the battery pack. At the same time, check whether all the functions of the charger are normal to ensure the safety and stability of the charging process.

(2) Specific steps for equalization charging

Conventional charging: First, perform conventional charging on the battery pack. Follow the normal charging process to charge the battery pack to a state close to full charge. Generally speaking, conventional charging adopts the constant current - constant voltage charging method. It starts with a constant current charge. When the battery voltage reaches a certain value, it switches to constant voltage charging until the charging current drops to the specified terminal current value.

Switch to equalization charging mode: After the regular charging is completed, switch the charger to equalization charging mode and set the appropriate equalization charging voltage and time. The charging time depends on the battery capacity and the degree of aging, usually ranging from 3 to 8 hours.

Charging process monitoring: During the equalization charging process, it is necessary to closely monitor various parameters of the battery, including the voltage of individual cells, the total voltage of the battery pack, the charging current, the temperature of the electrolyte, etc. Record the data every 30 minutes to 1 hour and observe the changing trend of the data. If it is found that the voltage of a certain single battery rises too fast, exceeding that of other single batteries by more than 0.3V, or the temperature of the electrolyte exceeds 45℃, charging should be suspended, and the battery should be checked for any faults. Charging can be resumed only after the faults are eliminated.

Charging completion judgment: When the voltages of all individual batteries stabilize within a certain range, and the charging current drops to a relatively small value and remains unchanged for 1-2 hours, it can be considered that the equalization charging has ended. At this point, first turn off the charger power, then wait for the battery to cool down to room temperature before proceeding with the subsequent operations.

(3) Post-charging handling work

Measure the electrolyte density again: After the equalization charging is completed, use the hydrometer to measure the electrolyte density of each individual battery again. If the density of the electrolyte remains uneven, adjustments can be made according to the actual situation. For single-cell batteries with low density, an appropriate amount of sulfuric acid solution can be added. For single-cell batteries with a relatively high density, distilled water can be added to make the electrolyte density of each single-cell battery as consistent as possible. After adjustment, let it stand for 1 to 2 hours until the electrolyte is fully and evenly mixed. Then measure and confirm again.

Check the battery connection: Recheck the connection between each individual battery in the battery pack to ensure it is firm and there is no loosening. Meanwhile, apply an appropriate amount of Vaseline or conductive paste to prevent oxidation at the connection points.

Record relevant data: Record in detail all the data during the equalization charging process, such as charging time, charging voltage, charging current, changes in the voltage of individual cells, and adjustments to the density of the electrolyte, in the battery maintenance file. These data are helpful for the subsequent analysis and evaluation of battery performance, timely identification of battery problems, and formulation of reasonable maintenance plans.

4. Precautions for Equalization Charging

Safety precautions: When performing equalization charging operations, proper safety precautions must be taken. Operators should wear protective gloves, goggles and other protective equipment to prevent the sulfuric acid solution from splashing onto their skin and eyes. The charging area should be well-ventilated, and smoking and open flames are strictly prohibited to prevent the accumulation of hydrogen gas produced during the charging process from causing an explosion.

Avoid overcharging: Although equalization charging requires a higher voltage and a longer time, it is necessary to strictly control the charging time and voltage to avoid overcharging. Overcharging can cause the battery to heat up severely, accelerate the aging and corrosion of the battery plates, and shorten the battery life.

Regularly perform equalization charging: The frequency of equalization charging should be determined based on the battery's usage frequency and working environment. Generally speaking, for frequently used forklift batteries, it is recommended to perform equalization charging every 10 to 15 charge and discharge cycles. For batteries with lower usage frequency, equalization charging can be carried out once every 1 to 2 months.

The differences among various types of batteries: The performance parameters and charging requirements of lead-acid batteries of different brands and models may vary. Before performing equalization charging, carefully read the battery's user manual and operate according to the parameters and methods recommended by the manufacturer.

5. Summary

Equalization charging of lead-acid batteries in forklifts is an important maintenance measure to ensure the performance and lifespan of battery packs. By deeply understanding the principle of equalization charging, strictly following the operation methods for standardized operation, and paying attention to relevant matters, the performance differences of individual batteries within the battery pack can be effectively eliminated, and the overall performance and reliability of the battery pack can be improved. In practical work, relevant personnel should attach importance to the equalization charging of batteries, establish a complete battery maintenance system, and do a good job in the daily inspection and maintenance of batteries, so as to extend the service life of lead-acid batteries in forklifts, reduce the operating costs of equipment, and improve work efficiency. With the continuous development of technology, more advanced equalization charging technologies and equipment may emerge in the future. We should also keep an eye on industry trends, constantly learn and apply new technologies, and provide better solutions for the maintenance and management of forklift lead-acid batteries.