News

Introduction

In industries such as logistics and warehousing, and manufacturing, forklifts, as important handling equipment, the performance of their power source, lead-acid batteries, is of vital importance. Lead-acid batteries have advantages such as low cost and mature technology, and are widely used in the forklift field. However, as the usage time increases and the number of charge and discharge cycles accumulates, the performance of lead-acid batteries will gradually decline. The cycle life is directly related to the operating efficiency and usage cost of forklifts. Therefore, conducting cycle life tests on forklift lead-acid batteries is of great significance for accurately evaluating their performance, optimizing usage and maintenance strategies, and reducing operating costs.

The basic working principle of lead-acid batteries

Lead-acid batteries achieve the mutual conversion of electrical energy and chemical energy through electrochemical reactions. During the charging process, the external power supply provides electrical energy, which prompts chemical reactions to occur inside the battery. The lead sulfate on the positive plate reacts with water under the action of electric current, is oxidized to lead dioxide, releases sulfate ions, and simultaneously generates hydrogen ions. The lead sulfate on the negative plate is reduced to lead, and sulfate ions combine with lead. At this point, the concentration of sulfuric acid in the electrolyte gradually increases, and electrical energy is converted into chemical energy and stored in the battery.

During discharge, reverse chemical reactions occur inside the battery. The lead dioxide on the positive plate and the lead on the negative plate react with sulfate ions and hydrogen ions respectively with the participation of the electrolyte, and are reconverted into lead sulfate. At the same time, electrons are released to form a current, providing electrical energy for the external load. During this process, the sulfuric acid in the electrolyte is constantly consumed and its concentration gradually decreases.

The plates are the core components of a battery. The active material of the positive plate is lead dioxide, while that of the negative plate is spongy lead. Their quality, structure and manufacturing process have a significant impact on the performance and lifespan of the battery. For instance, the thickness of the plates, porosity, and the firmness of the adhesion of active substances, etc., will all affect the progress of electrochemical reactions and the charging and discharging performance of the battery. As the medium of electrochemical reactions, the concentration, purity and stability of the electrolyte also play a key role in the performance of the battery. An appropriate concentration of sulfuric acid can ensure the smooth progress of electrochemical reactions, while impurities in the electrolyte may trigger side reactions and accelerate battery aging.

The purpose and significance of cycle life testing

Evaluate the actual service life of the battery

By simulating the charge and discharge cycle process of forklifts in actual use and conducting a large number of cycle tests, the number of charge and discharge cycles that lead-acid batteries can withstand under different working conditions can be accurately determined. When the battery capacity drops to a certain extent, it is considered that the battery has reached the end of its service life. This data can provide users with an accurate reference for battery replacement time, avoiding the impact on the normal operation of forklifts due to sudden battery failure, improving work efficiency, and reducing the losses caused by unexpected shutdowns.

Provide a basis for battery maintenance and management

Understanding the cycle life performance of lead-acid batteries under different charging and discharging conditions can help users formulate scientific and reasonable battery maintenance and management strategies. Arrange the usage time and intensity of forklifts reasonably to avoid excessive battery discharge. Meanwhile, by monitoring the number of battery cycles and performance changes during use, potential problems can be identified in a timely manner, and corresponding maintenance measures can be taken to extend the battery's service life and reduce operating costs.

Cycle life testing methods and procedures

Test equipment and tools

Charging and discharging equipment: Professional programmable charging and discharging testers are adopted, which can precisely control parameters such as charging current, voltage, time, discharging current, and terminal voltage, and simulate the charging and discharging processes under various actual working conditions. This device is equipped with high-precision current and voltage measurement functions, and can monitor and record in real time the changes of various parameters of the battery during the charging and discharging process.

Battery monitoring system: Equipped with a battery monitoring system, it can conduct real-time monitoring of parameters such as battery temperature and internal resistance. Temperature sensors are installed on the surface or at key positions inside the battery to accurately measure the temperature changes of the battery during charging and discharging. The internal resistance tester uses the AC injection method or DC pulse method to regularly measure the internal resistance of the battery, so as to timely understand the health status of the battery.

Data acquisition and analysis software: The data acquisition and analysis software that is compatible with charging and discharging equipment and battery monitoring systems can automatically collect, store and analyze a large amount of data generated during the testing process, and generate intuitive charts such as charging and discharging curves, capacity change curves, and internal resistance change curves, facilitating researchers to conduct in-depth analysis of battery performance.

Selection of test samples

Select different representative brands and models of forklift lead-acid batteries from the market as test samples. When making a selection, consider factors such as the rated capacity, voltage, and applicable vehicle type of the battery to ensure that the sample can cover the commonly used lead-acid battery types in the forklift field. Meanwhile, conduct detailed initial performance tests on each sample, including open-circuit voltage, internal resistance, initial capacity, etc., and record the relevant data as the comparison benchmark for subsequent tests.

Test steps and processes

Initial performance test: Conduct a comprehensive initial performance test on the selected lead-acid battery samples. Use a multimeter to measure the open-circuit voltage of the battery and ensure that it conforms to the nominal value. The internal resistance of the battery was measured by using an internal resistance tester, and the initial internal resistance data was recorded. The initial capacity of the battery is measured by the constant current discharge method. The battery is discharged to the terminal voltage at a certain discharge current (usually determined based on the rated capacity and standard discharge rate of the battery), the discharge time is recorded, and the initial capacity is calculated according to the formula.

Cycle charge and discharge test: Connect the battery to the charge and discharge device and conduct a cycle test according to the set charge and discharge system. The charging process usually adopts the constant current - constant voltage charging method. First, the battery is charged with a constant current. When the battery voltage rises to the set charging termination voltage, it switches to constant voltage charging until the charging current drops to the specified cut-off current. The discharge process discharges the battery at a constant current to the set terminal voltage. During each cycle process, the changes in parameters such as voltage, current, temperature and internal resistance of the battery are monitored and recorded in real time.

Capacity monitoring and evaluation: Conduct a capacity test on the battery at regular intervals. Use the same method as the initial capacity test, discharge at a constant current until the terminal voltage is reached, record the discharge time and calculate the current capacity. Compare the capacity obtained from each test with the initial capacity and draw the curve of capacity variation with the number of cycles. When the battery capacity drops to 80% of the initial capacity, stop the cycle test and record the number of cycles at this time. This number of cycles is the cycle life of the battery under this test condition.

Data recording and analysis: Throughout the entire testing process, all monitoring data are recorded and stored in real time using data acquisition and analysis software. Conduct in-depth analysis of the collected data, including plotting charge-discharge curves, capacity change curves, internal resistance change curves, etc., analyze the performance change laws of the battery at different cycle stages, and study the influence of factors such as temperature and charge-discharge current on the battery's cycle life. Meanwhile, observe whether there are any abnormal phenomena such as swelling, leakage, and corrosion of the terminals on the battery's appearance, record and analyze the relationship between these phenomena and the changes in battery performance.

Analysis of Factors Affecting Cycle Life

Charging and discharging mode

The influence of charging methods: Overcharging is one of the important reasons for the shortened lifespan of lead-acid batteries. When the battery charging voltage is too high or the charging time is too long, excessive gas evolution reactions will occur inside the battery, generating a large amount of hydrogen and oxygen, causing the electrolyte to lose water and the active material on the plates to fall off, thereby reducing the battery capacity and cycle life. Undercharging will prevent the lead sulfate on the battery plates from being completely converted into lead dioxide and lead. Long-term accumulation will lead to sulfation of the plates, increased internal resistance, and a decline in battery performance. Adopting the constant current - constant voltage charging method and setting the charging parameters reasonably can effectively avoid overcharging and undercharging phenomena and extend the battery life.

The influence of discharge mode: Deep discharge also has a significant impact on the cycle life of lead-acid batteries. When a battery is over-discharged, the active substances on the plates will be largely converted into lead sulfate, and the lead sulfate crystals will grow larger on the surface of the plates, blocking the pores of the plates and hindering the contact between the electrolyte and the active substances, resulting in an increase in the internal resistance of the battery and a decrease in its capacity. Frequent deep discharges will accelerate the sulfation of the plates and seriously shorten the battery life. Therefore, during the operation of forklifts, it is necessary to avoid excessive battery discharge as much as possible. Generally, it is recommended to charge the battery when its power drops to 30% - 40%. At the same time, the size of the discharge current also affects the battery life. Excessive discharge current will intensify the internal heating of the battery, accelerate the aging of the plates and the shedding of active materials.

Temperature factor

High temperature influence: The optimal operating temperature range for lead-acid batteries is generally between 20℃ and 25℃. When the ambient temperature is too high, the chemical reaction rate inside the battery increases, the gas evolution reaction intensifies during charging, and the rate of water loss in the electrolyte speeds up, causing the battery to dry up. At the same time, high temperatures will also accelerate the dissolution and shedding of the active substances on the plates, reducing the battery capacity and shortening the cycle life. Studies show that for every 10℃ increase in temperature, the cycle life of batteries may be shortened by 20% to 25%. When using forklifts in high-temperature environments, effective heat dissipation measures should be taken, such as enhancing ventilation and installing cooling devices, to lower the battery temperature.

Low-temperature influence: In a low-temperature environment, the viscosity of the electrolyte increases, the diffusion rate of ions slows down, resulting in an increase in the internal resistance of the battery and a decrease in the charging acceptance capacity. At the same time, low temperatures will reduce the discharge capacity of batteries and weaken the driving range of forklifts. If the battery is over-discharged at low temperatures, it may also cause the electrolyte to freeze, damaging the battery casing and plates. To address the impact of low-temperature environments on batteries, the batteries can be preheated to increase the temperature of the electrolyte and improve battery performance. At the same time, in low-temperature environments, the usage intensity of forklifts should be appropriately reduced to decrease the depth of battery discharge.

Maintenance measures: Regular maintenance of lead-acid batteries is the key to extending their cycle life. Maintenance work includes checking the electrolyte level, replenishing distilled water in a timely manner, and keeping the density of the electrolyte within the normal range. Clean the battery surface and terminals to prevent corrosion and leakage. Regularly perform equalization charging on the battery to eliminate voltage and capacity differences among individual cells in the battery pack. In addition, regular performance tests of the battery should be conducted, such as measuring voltage, internal resistance, capacity, etc., to promptly identify potential problems and take corresponding repair measures. Through scientific and reasonable maintenance and care, the battery can be kept in good working condition and its cycle life can be prolonged.

Analysis and evaluation of test results

Analysis of Performance change trends

Capacity change trend: Based on the data of battery capacity changes with the number of cycles recorded during the test process, a capacity change curve is plotted. Analyze the changing trend of the curve and observe the variation characteristics of the battery capacity in the initial stage, the middle stage and the later stage. Generally speaking, in the early stage of the cycle, the battery capacity is relatively stable. As the number of cycles increases, the capacity gradually decreases, and the rate of decline will accelerate in the later stage. By analyzing the trend of capacity changes, the performance of the battery at different usage stages can be evaluated, and the remaining service life of the battery can be predicted.

The trend of internal resistance change: Similarly, analyze the data of the battery's internal resistance change with the number of cycles and draw the curve of internal resistance change. As the number of cycles increases, the internal resistance of the battery usually gradually increases. The increase in internal resistance not only leads to an increase in energy loss during the charging and discharging process of the battery, but also affects the output voltage and charging and discharging efficiency of the battery. By studying the trend of internal resistance changes, aging and fault problems inside the battery can be detected in a timely manner, such as sulfation of the plates and shedding of active substances, providing a basis for battery maintenance and replacement.

Appearance and structural changes: During the testing process, observe whether the battery's appearance shows abnormal phenomena such as swelling, leakage, and terminal post corrosion, and record the number of cycles when these phenomena occur. Disassemble and analyze the batteries with abnormal appearance to observe the changes in their internal structure, such as the deformation of the plates and the shedding of active substances.