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Introduction

In modern logistics and industrial production, forklifts, as important material handling equipment, their operational stability and efficiency directly affect production efficiency. As the power source of the forklift, the condition of the forklift battery plays a decisive role in the performance of the forklift. Accurately judging the status of forklift batteries, promptly identifying potential problems and taking corresponding measures are of great significance for ensuring the normal operation of forklifts, extending the service life of batteries and reducing operating costs. This article will deeply explore the key indicators for judging the condition of forklift batteries, providing comprehensive and practical references for relevant personnel.

Voltage index

Open-circuit voltage

Open-circuit voltage refers to the potential difference between the positive and negative terminals of a battery when it is in an open-circuit state. It is an important initial indicator reflecting the state of charge of the battery. For the lead-acid batteries commonly used in forklifts, when fully charged, the open-circuit voltage is generally close to its nominal voltage. If the open-circuit voltage is significantly lower than this range, it may indicate that the battery is undercharged. However, it should be noted that the open-circuit voltage is also affected by the battery temperature. Generally, for every 1℃ decrease in temperature, the open-circuit voltage drops by approximately 0.01V. Therefore, when measuring open-circuit voltage, it is best to record the ambient temperature simultaneously and make appropriate corrections to the measurement results based on the temperature.

Charging voltage

When charging the forklift battery, the change in charging voltage can directly reflect the battery's charging capacity and health condition. Under normal circumstances, as charging proceeds, the battery voltage will gradually rise. Take lead-acid batteries as an example. When constant current charging is adopted, the charging voltage rises relatively slowly at the beginning. As the battery gradually approaches a fully charged state, the voltage rise rate accelerates until the charging terminal voltage is reached. If during the charging process, the voltage rises too fast and far exceeds the normal range, it may indicate that there is a short circuit or the electrolyte has dried up inside the battery, causing the battery to be unable to accept charging normally. On the contrary, if the voltage rises too slowly and fails to reach the charging termination voltage for a long time, it may be due to severe sulfation of the battery plates and a reduction in active substances, which leads to a decline in the battery's charging acceptance capacity.

Discharge voltage

Discharge voltage is a key indicator for judging the performance of forklift batteries under actual working conditions. During the operation of a forklift, the battery continuously discharges, and its voltage will gradually decrease. For a healthy battery, the voltage drop during the discharge process is relatively stable, and before reaching the discharge termination voltage, it can maintain a certain output power to meet the normal operation requirements of the forklift. The discharge termination voltages of forklift batteries of different types and specifications vary. When the battery voltage drops too rapidly during the discharge process and reaches or falls below the discharge termination voltage prematurely, it indicates that the battery capacity has severely declined and is unable to provide sufficient electrical energy to support the normal operation of the forklift. In such cases, battery repair or replacement may be necessary. In addition, by monitoring the voltage consistency of each individual battery during the discharge process, the health status of the battery pack can also be determined. If the discharge voltages of each individual battery differ too much, exceeding a certain range, it indicates that there are individual batteries with significant performance differences in the battery pack, which may affect the performance of the entire battery pack and requires further inspection and handling.

Capacity index

Actual capacity test

The actual capacity of a forklift battery refers to the total amount of electrical energy that the battery can release under certain discharge conditions, and the unit is usually ampere-hours. Accurately measuring the actual capacity is crucial for judging the health condition and remaining service life of the battery. Actual capacity testing usually adopts the standard discharge method, that is, the battery is discharged under specified discharge current, temperature and terminal voltage conditions, the discharge time is recorded, and then the actual capacity of the battery is calculated based on the discharge current and discharge time. Generally speaking, when the actual capacity of the battery drops below 80% of its rated capacity, it is necessary to consider maintaining or replacing the battery, as at this point, the battery's performance has significantly declined and may not be able to meet the normal working requirements of the forklift.

Capacity attenuation rate

Capacity attenuation rate refers to the rate at which a battery's actual capacity gradually decreases as the number of charge and discharge cycles increases during use. It is an important dynamic indicator for measuring battery life and health status. By long-term monitoring of the battery's capacity attenuation rate, the remaining service life of the battery can be predicted, and equipment maintenance and replacement plans can be made in advance. Generally speaking, under normal use and maintenance conditions, the capacity of lead-acid batteries will decline to a certain extent after each charge and discharge cycle, and the capacity decline rate is usually between 0.1% and 0.3%. If during use, it is found that the capacity attenuation rate of the battery is significantly higher than the normal range, it may be due to improper charging methods, excessive discharge, harsh usage environments and other reasons, which cause damage to the internal structure of the battery and accelerate its aging. Therefore, in daily use, these improper operations should be avoided as much as possible to slow down the rate of battery capacity decline and extend the battery's service life.

Internal resistance index

The concept and significance of internal resistance

Internal resistance refers to the resistance that a battery encounters when current passes through its interior during operation. It consists of two parts: ohmic internal resistance and polarization internal resistance. The ohmic internal resistance is mainly composed of the resistances of the positive and negative plates, electrolyte, separator and connecting components of the battery. Polarization internal resistance is the resistance formed due to the electrochemical reaction occurring on the electrode surface during the charging and discharging process of the battery, which causes polarization at the interface between the electrode and the electrolyte. Internal resistance is an important parameter reflecting the internal condition of a battery. It is closely related to the battery's capacity, charging and discharging performance, as well as its lifespan. Generally speaking, the smaller the internal resistance, the higher the charging and discharging efficiency of the battery, and the greater the power it can output. Conversely, the greater the internal resistance, the greater the energy loss inside the battery, and the battery's performance will be seriously affected.

Measurement methods and judgment criteria for internal resistance

At present, the commonly used methods for measuring the internal resistance of forklift batteries include the DC discharge method and the AC injection method. The direct current discharge method involves discharging a battery with a large current instantaneously, measuring the voltage drop during the discharge process, and calculating the internal resistance of the battery based on Ohm's Law. This method provides relatively accurate measurement results, but it can cause certain damage to the battery and is rather complicated to operate, making it unsuitable for frequent measurements. The AC injection rule involves injecting a tiny AC signal into the battery. By measuring the battery's response to the AC signal, the internal resistance of the battery is calculated. This method has a relatively small impact on the battery, a fast measurement speed, and is suitable for online monitoring. For lead-acid batteries, under normal conditions, their internal resistance is generally at the milliohm level. The internal resistance standards vary for batteries of different capacities and types. Generally speaking, the internal resistance of new lead-acid batteries is relatively small. As the usage time increases and the number of charge and discharge cycles grows, the internal plates of the battery gradually become sulfated and the electrolyte dries up, which will lead to a gradual increase in internal resistance. When the internal resistance increases to 1.5 to 2 times the initial value, the performance of the battery will decline significantly, and maintenance or replacement may be required. In addition, by comparing the consistency of the internal resistance of each individual battery in the battery pack, the health condition of the battery pack can also be determined. If the internal resistance of individual batteries varies too much, it will lead to uneven current distribution among each individual battery during the charging and discharging process of the battery pack, accelerate the aging of batteries with poor performance, and thereby affect the service life of the entire battery pack. Generally, the internal resistance difference of each individual battery in a battery pack should not exceed 10% to 15% of the average value.

Electrolyte index

Electrolyte density

The density of the electrolyte is an important parameter for measuring the condition of forklift lead-acid batteries, and it is closely related to the state of charge of the battery. When fully charged, the density of the electrolyte in a lead-acid battery is generally 1.28g/cm³ (at 25℃). As the battery discharges, the sulfuric acid in the electrolyte undergoes a chemical reaction with the active substances on the plates, generating water and causing the density of the electrolyte to gradually decrease. Therefore, by measuring the density of the electrolyte, the degree of battery discharge can be roughly determined. It should be noted that the density of the electrolyte is affected by temperature. For every 1℃ change in temperature, the density of the electrolyte changes by approximately 0.0007g/cm³. Therefore, when measuring the density of the electrolyte, the temperature of the electrolyte should be measured simultaneously, and the measurement result should be corrected to the standard density value at 25℃. In addition, if the density of the electrolyte is found to be abnormally elevated or decreased, it may indicate that there is a problem with the battery. For instance, if the density of the electrolyte is too high, it might be due to overcharging, resulting in excessive evaporation of water. If the density of the electrolyte is too low, it may be due to problems such as short circuits or leakage inside the battery, which prevent it from charging normally, or it could be that impurities have mixed into the electrolyte, reducing the concentration of sulfuric acid.

Electrolyte level

Maintaining an appropriate electrolyte level is crucial for the normal operation of forklift batteries. If the electrolyte level is too low, the plates will be exposed to the air, causing sulfation of the plates and reducing the battery capacity and lifespan. If the liquid level is too high, it may cause the electrolyte to overflow during the charging process, corrode the battery casing and surrounding equipment, and also result in the waste of sulfuric acid. For open-type lead-acid batteries, it is usually possible to determine whether the electrolyte level is normal by observing the liquid level mark inside the battery. Under normal circumstances, the electrolyte level should be 10mm to 15mm higher than the plates. During daily maintenance, the electrolyte level should be checked regularly. When the level is too low, distilled water or special electrolyte replenishment solution should be replenished in time. It should be noted that it is strictly forbidden to add tap water or water containing impurities to avoid affecting the battery performance. For maintenance-free batteries, although they are designed to reduce the maintenance requirements for the electrolyte level, regular inspections are still necessary during use. Some maintenance-free batteries are equipped with liquid level observation Windows. By observing the color or mark inside the window, one can determine whether the electrolyte level is normal. If the observation window shows a low liquid level or an abnormal color, it also needs to be dealt with promptly.

Appearance of electrolyte

In addition to density and liquid level, the appearance of the electrolyte is also an important basis for judging the condition of the battery. The normal electrolyte should be clear, transparent, colorless or slightly light yellow liquid. If the electrolyte becomes cloudy, has sediment or the color darkens abnormally, it may indicate that there is a problem inside the battery. For instance, if black precipitates appear in the electrolyte, it might be due to the shedding of active substances on the plates. If the color of the electrolyte turns dark brown or black, it may be due to excessive battery discharge or internal short circuit, causing severe sulfation of the plates. In addition, if you smell a pungent odor from the electrolyte, it might be due to the decomposition of sulfuric acid in the electrolyte, which produces harmful gases. This also indicates that there is an abnormal condition with the battery, and it needs to be inspected and dealt with promptly.

Appearance and physical condition indicators

Battery casing and connection parts

Checking whether the casing of the forklift battery is damaged, deformed, or leaking is one of the intuitive methods to determine the battery's condition. Damage to the battery casing may lead to electrolyte leakage, which not only corrodes the surrounding equipment but also exposes the internal structure of the battery to the air, accelerating the battery's damage. If obvious cracks or damages are found in the battery casing, the battery should be stopped from use immediately and corresponding protective measures should be taken to prevent electrolyte leakage from causing greater harm. At the same time, check the connection parts of the battery, including the terminals, connection wires and joints, etc., to ensure that the connection is firm and there is no loosening or corrosion. Loosening of the connection parts will lead to an increase in contact resistance, generating a large amount of heat during charging and discharging, accelerating the oxidation and corrosion of the connection wires and terminals. In severe cases, it may even cause a fire. The appearance of white or green corrosion products at the terminals and joints is due to the chemical reaction between sulfuric acid and metals to form sulfates, which will affect the battery's conductivity and reduce the charging and discharging efficiency. For minor corrosion, a dedicated cleaner can be used for cleaning and protective grease can be applied. For severely corroded connection parts, the connection wires or joints should be replaced in time.

Plate state

Although the plates are located inside the battery and cannot be directly observed, the state of the plates can be inferred through some indirect methods. For instance, during the charging process, if the battery experiences abnormal heating or excessive gas emission, it might be due to severe sulfation of the plates or a short circuit issue. Plate sulfation is one of the common faults of lead-acid batteries. It is mainly caused by the battery being in a state of undercharge for a long time or insufficient charging, resulting in the formation of a layer of white and hard lead sulfate crystals on the plates, which hinders the normal progress of electrochemical reactions. In addition, during the battery usage process, if it is found that the power of the forklift has significantly decreased and the driving range has shortened, it may also be related to the poor condition of the plates. For open-type lead-acid batteries, the battery cover can be opened when necessary to observe the appearance of the plates. A normal plate should be flat, free of deformation and cracks. The positive plate is dark brown and the negative plate is bluish-gray. If there are a large number of white crystals on the surface of the plates, the plates are deformed or cracks appear, it indicates that the plates have been damaged, and the battery performance will be seriously affected. Timely repair or replacement is required.

Conclusion

Accurately judging the status of the forklift battery is a key link to ensure the efficient and stable operation of the forklift. Through comprehensive monitoring and analysis of multiple key indicators such as voltage, capacity, internal resistance, electrolyte, as well as appearance and physical condition, potential problems of the battery can be detected in a timely manner, and corresponding maintenance or replacement measures can be taken. In daily use, operators and maintenance personnel should strictly follow the operating procedures to regularly inspect and maintain the forklift battery to ensure that all indicators are within the normal range, thereby extending the service life of the battery, reducing operating costs and improving production efficiency. With the continuous development of technology, more advanced and convenient battery condition monitoring technologies and equipment may emerge in the future, providing more powerful support for the management of forklift batteries. However, no matter how advanced technology becomes, the attention and emphasis on these key indicators will always be the foundation and core for judging the condition of forklift batteries.