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Abstract

This article focuses on the lead-acid batteries of forklifts, systematically expounds the multi-faceted influences of internal resistance on their performance, and elaborately introduces various methods for detecting internal resistance. Through analysis, it can be known that the change in internal resistance is directly related to the core performance indicators of the battery such as charging and discharging efficiency, output power and service life. Mastering accurate internal resistance detection technology helps to promptly identify potential problems with the battery, ensuring the efficient and safe operation of forklifts, and providing an important reference basis for the maintenance and management of lead-acid batteries in forklifts.

1. Introduction

In the modern logistics and warehousing industry, forklifts have become indispensable mechanical equipment due to their efficient cargo handling capabilities. As the main power source of electric forklifts, the performance of lead-acid batteries directly determines the working efficiency and operating costs of the forklifts. Internal resistance, as an important parameter of lead-acid batteries, may seem insignificant, but it has a profound impact on the performance of the batteries. Understanding the relationship between internal resistance and battery performance, as well as mastering accurate internal resistance detection methods, is of great significance for ensuring the normal operation of forklifts and extending the service life of batteries.

2. Overview of the Internal Resistance of Forklift Lead-Acid Batteries

2.1 Definition of Internal Resistance

The internal resistance of lead-acid batteries refers to the resistance that current encounters when passing through the battery's interior. It consists of two parts: ohmic internal resistance and polarization internal resistance. The ohmic internal resistance is composed of the resistance of components such as electrode materials, electrolyte, and separators, as well as the contact resistance between these components. Its magnitude is related to factors such as the structure, materials, and temperature of the battery. Polarization internal resistance is the resistance generated by electrode polarization during the charging and discharging process of the battery, including electrochemical polarization resistance and concentration polarization resistance. It is closely related to factors such as the charging and discharging current of the battery and the nature of the active material.

2.2 Formation Mechanism of Internal Resistance

Inside a lead-acid battery, ions in the electrolyte move to conduct current under the influence of an electric field, and electrons in the electrode materials also participate in the conduction process. The resistance inherent in these substances constitutes part of the ohmic internal resistance. At the same time, contact resistance will also be generated at the contact interface between the electrode and the electrolyte, as well as at the contact points between the plate and the connecting piece, jointly constituting the ohmic internal resistance. The generation of polarization internal resistance mainly stems from the chemical reactions during the charging and discharging processes. When the battery is charged and discharged, the active substances on the electrode surface undergo electrochemical reactions with the electrolyte. As the reaction proceeds, the ion concentration near the electrode surface differs from that in the main body of the electrolyte, resulting in concentration polarization. In addition, the rate-limiting nature of the electrochemical reaction itself can also cause the electrode potential to deviate from the equilibrium potential, resulting in electrochemical polarization. The resistances corresponding to these two polarization phenomena are known as the polarization internal resistance.

3. The Influence of Internal Resistance on the Performance of Forklift Lead-Acid Batteries

3.1 Impact on Charging and Discharging Efficiency

During the charging process, the internal resistance of the battery will consume a portion of the electrical energy and convert it into thermal energy, resulting in a decrease in charging efficiency. According to Joule's Law, the greater the internal resistance, the more heat is generated under the same charging current and charging time. This part of the heat not only causes waste of electrical energy but also raises the temperature of the battery, accelerating the aging of the internal substances and performance degradation of the battery. For instance, when the internal resistance of the lead-acid battery in a forklift increases, a battery that originally took 8 hours to fully charge may take 10 hours or even longer to fully charge, which greatly affects the charging efficiency and the operational efficiency of the forklift.

During the discharge process, the internal resistance will also consume electrical energy. As the discharge proceeds, the internal resistance of the battery will gradually increase, causing the terminal voltage of the battery to drop at a faster rate. This leads to a reduction in the actual available electrical energy of the forklift during operation and a shortening of the effective working time. For instance, a battery with normal internal resistance can support a forklift to operate continuously for 6 hours, while a battery with increased internal resistance may only be able to work for 4 hours, seriously affecting the forklift's operational endurance.

3.2 Impact on Output Power

According to the power formula, during the discharge process, the output voltage of the battery will be affected by the internal resistance. When the load current is constant, the greater the internal resistance, the greater the voltage drop inside the battery, resulting in a decrease in the output voltage and thus a reduction in the output power. For forklifts, a reduction in output power will directly affect the performance of their lifting, running and other actions. For instance, when the internal resistance is too high, the forklift may fail to lift the goods of the rated weight normally, or its speed may drop significantly during operation, affecting the operational efficiency and safety.

3.3 Impact on Service Life

Excessive internal resistance will cause the battery to generate a large amount of heat during charging and discharging, resulting in an increase in the internal temperature of the battery. Long-term exposure to high temperatures will accelerate the aging process of the battery, such as sulfation of the internal plates, drying up of the electrolyte, and shedding of active substances, thereby shortening the service life of the battery. In addition, uneven internal resistance can also lead to unbalanced charging and discharging of each individual battery inside the battery, further accelerating the decline of battery performance. For instance, for a forklift lead-acid battery composed of multiple individual cells, if the internal resistance of one of the individual cells is too high, during charging, this individual cell will reach the fully charged state prematurely, while the other individual cells have not yet been fully charged. During discharge, this individual battery will be discharged completely too early. This unbalanced charging and discharging state will cause the performance of the entire battery pack to decline rapidly and significantly shorten its service life.

3.4 Impact on Security

When the internal resistance of the lead-acid battery in a forklift is too high, under conditions of high current charging and discharging, excessive heat and voltage drop will be generated inside the battery. Excessive heat may cause the internal temperature of the battery to rise sharply, leading to serious safety accidents such as battery bulging, leakage and even explosion. Excessive voltage drop will cause unstable battery output voltage, affecting the normal operation of the forklift's electrical system, increasing the probability of electrical faults, and threatening the personal safety and operational safety of forklift operators.

4. Detection Method for Internal Resistance of Lead-Acid Batteries in Forklifts

4.1 DC Discharge method

The DC discharge method is a relatively traditional approach for detecting internal resistance. The principle is that during the discharge process of the battery, by measuring the discharge current and the voltage drop across the battery terminals, the internal resistance of the battery is calculated according to Ohm's Law. When performing the specific operation, connect the battery to a load of known power and let the battery discharge at a certain current. During the discharge process, use a high-precision voltmeter and ammeter to measure the voltage across the battery and the discharge current respectively, and then calculate the internal resistance.

The advantage of this method is that the measurement principle is simple and intuitive, the measurement results are relatively accurate, and it can reflect the internal resistance of the battery under actual discharge conditions. However, its drawbacks are also quite obvious. The direct current discharge method requires deep discharge of the battery, which can cause certain damage to the battery and shorten its service life. Meanwhile, the detection process takes a long time and is not suitable for rapid detection at the forklift operation site. In addition, for some large-capacity batteries, high-power load devices are required, and the operation is rather complicated.

4.2 Communication Injection Method

The AC injection method is currently a commonly used internal resistance detection method. It involves injecting a tiny alternating current signal (usually a sinusoidal wave signal ranging from tens to hundreds of Hertz) into the battery. By measuring the battery's response to this alternating current signal, that is, by measuring the injected alternating current and the generated alternating voltage, the battery's impedance is calculated based on the impedance formula. Since the frequency of the injected alternating current signal is relatively low, the impedance at this time is approximately equal to the battery's internal resistance.

The advantage of the AC injection method lies in that it does not require deep discharge of the battery, will not cause obvious damage to the battery, and the detection process is fast and convenient. It can conduct online detection of the battery at the forklift operation site. Meanwhile, this method has a relatively high measurement accuracy and can accurately reflect the changes in the internal resistance of the battery. However, this method also has certain limitations. Its measurement results are easily affected by external electromagnetic interference. When used in places with complex electromagnetic environments, effective shielding measures need to be taken to ensure measurement accuracy. In addition, the AC injection method has relatively high requirements for detection equipment and the equipment cost is relatively high.

5. Conclusion

The internal resistance of lead-acid batteries in forklifts has a crucial impact on their performance. It not only affects the charging and discharging efficiency, output power and service life of the batteries, but also is closely related to the safety of forklift operations. Through the analysis of different internal resistance detection methods, it can be known that each detection method has its advantages, disadvantages and applicable scenarios. In practical applications, the appropriate internal resistance detection method should be selected based on the specific requirements and conditions of forklift operations. Regular detection of the battery's internal resistance should be carried out to promptly identify any issues with the battery and take corresponding maintenance measures, so as to ensure the good performance of the forklift's lead-acid battery, improve the forklift's working efficiency, and reduce operating costs. Ensure the safe and efficient operation of logistics and warehousing operations. In the future, with the continuous advancement of technology, it is believed that more advanced, accurate and convenient methods and technologies for internal resistance detection will emerge, providing stronger support for the performance monitoring and maintenance of forklift lead-acid batteries.