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Introduction

In modern logistics and warehousing operations, forklifts, as key handling equipment, their operational efficiency and stability directly affect the smoothness of the entire operation process. As the core power source of forklifts, the performance of lead-acid batteries in forklifts plays a decisive role in the working performance of forklifts. In recent years, with the increase in the frequency of forklift usage and the growing complexity of the usage environment, the problem of increased internal resistance of lead-acid batteries in forklifts has become increasingly prominent, bringing many adverse effects to the normal operation of forklifts. An in-depth study on the influence of the increased internal resistance of lead-acid batteries in forklifts is of great practical significance for improving the operating efficiency of forklifts, extending the service life of batteries, reducing operating costs and ensuring operation safety.

A brief description of the Working Principle of Lead-acid Batteries in Forklifts

The working process of lead-acid batteries is based on complex electrochemical reactions. In the charged state, lead dioxide on the positive plate reacts with sulfuric acid in the electrolyte to form lead sulfate and water, while releasing electrons and making the positive plate positively charged. The lead on the negative plate reacts with sulfuric acid to form lead sulfate as well, and absorbs electrons, making the negative plate negatively charged. During the discharge process, the reaction proceeds in reverse. Lead sulfate is reduced to lead dioxide and lead respectively on the positive and negative plates. Meanwhile, sulfate ions recombine with hydrogen ions to form sulfuric acid. In this process, chemical energy is converted into electrical energy, providing power for the forklift. During this continuous charge-discharge cycle, any factor that interferes with the smooth progress of the electrochemical reaction may cause a change in the internal resistance of the battery.

The reasons for the increased internal resistance of lead-acid batteries in forklifts

Plate vulcanization

Plate sulfation is one of the important reasons for the increase in the internal resistance of forklift lead-acid batteries. When a battery is in a state of undercharging or overdischarging for a long time, the lead on the negative plate will react with sulfuric acid to form coarse lead sulfate crystals. These crystals adhere to the surface of the plate and gradually form a hard white substance, namely sulfide. Unlike the fine crystalline lead sulfate generated during normal discharge, coarse crystalline lead sulfate has poor electrical conductivity and large particles, which can clog the pores of the plates, increase the penetration resistance of the electrolyte, and thereby significantly increase the internal resistance of the battery. According to relevant research, when the degree of sulfation of the plates reaches a certain proportion, the internal resistance of the battery can increase several times, seriously affecting the battery performance. For instance, in some logistics warehouses, due to the frequent use of forklifts, some drivers fail to fully charge the batteries in time, resulting in the batteries remaining undercharged for a long time. After a period of time, the sulfation of the battery plates intensifies significantly, the internal resistance increases, the forklifts become difficult to start, and the working efficiency drops sharply.

The electrolyte dries up.

The electrolyte plays a crucial role in conducting ions in the electrochemical reactions of lead-acid batteries. As the battery usage time increases, especially with frequent charging and discharging in high-temperature environments, the water in the electrolyte will gradually evaporate, causing the electrolyte to dry up. When the electrolyte dries up, the ion conduction inside the battery is blocked, and the electrochemical reaction cannot proceed normally, thereby increasing the internal resistance. In addition, the drying up of the electrolyte may also lead to the exposure of the plates, accelerating their corrosion and damage, and further deteriorating the battery's performance. In practical applications, some forklifts operate for long periods in outdoor high-temperature environments. If the electrolyte is not replenished in time, the battery will soon dry up, the internal resistance will rise rapidly, and the battery capacity will drop sharply, seriously affecting the forklift's endurance.

Battery aging

As the years of use increase, various components inside the lead-acid battery of a forklift will gradually age. The active substances on the plates will gradually fall off, resulting in a reduction of the effective substances involved in the electrochemical reaction. Components such as connection strips and terminal posts may also experience poor contact due to long-term exposure to current impact and environmental corrosion. All these aging phenomena will lead to an increase in the internal resistance of the battery. Generally speaking, the normal service life of lead-acid batteries is about 2 to 3 years. Beyond this period, the aging rate of the battery accelerates and its internal resistance rises at a relatively fast pace. For instance, a batch of forklifts in a certain logistics enterprise that have been in use for over three years have generally seen an increase in the internal resistance of their lead-acid batteries. As a result, the forklifts lack sufficient power during operation, frequently malfunction, and the maintenance costs have risen significantly.

The influence of temperature

The influence of temperature on the internal resistance of lead-acid batteries in forklifts is very significant. In a low-temperature environment, the viscosity of the electrolyte increases, the movement of ions is hindered, and the diffusion capacity decreases, resulting in an increase in the resistance of the electrolyte. Meanwhile, low temperatures will also reduce the activity of electrode materials, slow down the electrochemical reaction rate and increase the polarization internal resistance. Research data shows that when the temperature drops from 25℃ to 0℃, the internal resistance of lead-acid batteries may increase by 50% to 100%. In high-temperature environments, although the resistance of the electrolyte will decrease to some extent, the excessively high temperature will accelerate the chemical reactions inside the battery, leading to problems such as intensified plate corrosion and rapid water loss of the electrolyte, which will also increase the internal resistance.

The influence of increased internal resistance of lead-acid batteries in forklifts

The influence on the power performance of forklifts

Output voltage drop: According to Ohm's Law, when the internal resistance of the battery increases, with the output current remaining unchanged, the voltage drop across the internal resistance will increase, thereby causing the actual voltage output by the battery to the forklift motor to decrease. The output power of a forklift motor is proportional to the square of the voltage. A decrease in voltage will cause a significant drop in the motor's output power, and the forklift's power will be significantly weakened.

Difficulty in starting: When a forklift starts, it needs to provide a large current instantaneously. At this time, the battery with increased internal resistance cannot meet the requirement of high current output. Due to the increase in internal resistance, the starting current generates a significant voltage drop inside the battery, resulting in the voltage output to the starting motor being too low. As a result, the starting motor cannot obtain sufficient torque to start the forklift engine. This will not only prolong the forklift's start-up time and increase the operation waiting time, but also may cause additional damage to the battery and the starting motor due to multiple start-up failures. In some cold storage facilities and other low-temperature environments, due to the increase in battery internal resistance caused by low temperatures, coupled with the demand for large currents during startup, the problem of difficult forklift startup becomes even more prominent.

The impact on battery life

Accelerated plate damage: The increase in internal resistance causes the battery to generate more heat during charging and discharging. Excessively high temperatures will accelerate the corrosion and deformation of the plates. The active substances on the plates are more likely to fall off under the effect of high temperature, further reducing the effective area of the plates and causing the battery capacity to continuously decline. Meanwhile, the corrosion and deformation of the plates may also cause short circuits in the plates, shortening the service life of the battery.

Reduce battery cycle life: Under normal circumstances, lead-acid batteries have a certain charge and discharge cycle life. However, when the internal resistance increases, the energy loss of the battery during each charge and discharge process increases, and the actual energy available for effective operation decreases. To meet the working requirements of forklifts, batteries need to be charged and discharged more frequently, which will accelerate the aging process inside the battery and significantly reduce the number of battery cycles. Studies show that for every 10% increase in internal resistance, the cycle life of a battery may be shortened by 15% to 20%. For some logistics enterprises that frequently use forklifts, the reduction in battery cycle times means that batteries need to be replaced more often, increasing operating costs.

The impact on security

Fire risk caused by overheating: The increase in internal resistance causes the battery to generate excessive heat during charging and discharging. If this heat cannot be dissipated in time, the battery temperature will continue to rise. When the temperature reaches a certain level, it may cause thermal runaway of the battery, leading to the combustion or even explosion of the electrolyte inside the battery, thereby triggering a fire. In some forklift charging areas, if the ventilation is poor, batteries with increased internal resistance are more likely to overheat during the charging process, posing a significant safety hazard. For instance, a certain logistics warehouse once caught fire due to overheating caused by the increased internal resistance of the lead-acid batteries in forklifts, resulting in severe property losses and casualties.

Leakage corrosion risk: As the internal resistance increases, the internal pressure of the battery may change, leading to a decline in the sealing performance of the battery casing and making the electrolyte prone to leakage. The electrolyte is highly corrosive. Once it leaks, it will cause corrosion damage to the metal parts of the forklift, surrounding equipment and the ground, etc. At the same time, the leakage of the electrolyte may also cause harm to the skin and eyes of the operators, posing a significant safety risk. For instance, during the daily inspection of forklifts, it is often found that some batteries with increased internal resistance have bulging casings and electrolyte leakage, which need to be dealt with promptly to prevent the occurrence of safety accidents.

The impact on economic benefits

Increased maintenance costs: Forklift lead-acid batteries with increased internal resistance can cause frequent malfunctions of the forklift and require maintenance. Maintenance work not only involves the inspection, repair or replacement of the battery itself, but may also involve the repair of other components of the forklift that have been damaged due to battery problems. For instance, due to unstable battery output voltage, it may damage key components such as the forklift's electronic control system and motor, and the maintenance or replacement cost of these components is relatively high. In addition, frequent maintenance will also lead to an increase in forklift downtime, affecting operational efficiency and further raising hidden costs. According to statistics, the maintenance cost of forklifts caused by the increase in battery internal resistance may increase by 30% to 50% compared with normal circumstances.

Shorten the battery replacement cycle: Due to the significant impact of increased internal resistance on battery life, forklift lead-acid batteries need to be replaced more frequently. Lead-acid batteries are relatively expensive, and frequent battery replacement will bring considerable financial pressure to enterprises.

Conclusion

The increase in internal resistance of lead-acid batteries in forklifts is a problem that cannot be ignored. It has a serious negative impact on the power performance, battery life, safety and economic benefits of forklifts. Sulfation of the plates, drying up of the electrolyte, aging of the battery and temperature are the main reasons for the increase in internal resistance. To reduce the adverse effects caused by increased internal resistance, forklift user enterprises should strengthen the daily maintenance and management of batteries, including regularly checking the electrolyte level, timely replenishing water, avoiding excessive discharge and undercharging, and controlling the battery usage temperature, etc. Meanwhile, advanced battery detection technologies should be adopted to monitor key parameters such as battery internal resistance in real time, promptly identify problems and take corresponding measures to handle them. In addition, with the continuous advancement of technology, developing new power sources for forklifts or improving the performance of lead-acid batteries is also an important way to solve the problem of increased internal resistance. Only by fully recognizing the impact of the increased internal resistance of lead-acid batteries in forklifts and taking effective preventive and solution measures can we ensure the efficient and safe operation of forklifts, reduce the operating costs of enterprises, and promote the sustainable development of the logistics and warehousing industry.