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Introduction

In the modern logistics and warehousing field, forklifts, as key handling equipment, the stability and efficiency of their operation are of vital importance. Forklift lead-acid batteries, as the main power source of forklifts, their health condition directly affects the working performance and service life of forklifts. Among the numerous parameters used to assess the health status of lead-acid batteries in forklifts, the density of the electrolyte is a core indicator. Accurately grasping the intrinsic connection between the density of the electrolyte and the health status of the battery, and proficiently mastering the effective method of detecting battery health based on the density of the electrolyte, is of profound significance for ensuring the reliable operation of forklifts and reducing operating costs.

The role of electrolyte in forklift lead-acid batteries

The key role of electrolyte in batteries

Conducting ions: The electrolyte serves as the medium for ion conduction. During the charging and discharging process of the battery, hydrogen ions and sulfate ions in the sulfuric acid solution move directionally between the positive and negative plates, achieving the transfer of charges and thus completing the electrochemical reactions of the battery, ensuring its normal charging and discharging.

Participating in electrochemical reactions: As shown in the above reaction equation, sulfuric acid in the electrolyte directly participates in the electrochemical reactions of the battery and is a key participant in the energy conversion of the battery. The changes in its concentration and composition will significantly affect the rate and extent of electrochemical reactions, and thereby influence the performance of the battery.

The intrinsic connection between electrolyte density and battery health status

The variation law of electrolyte density during charging and discharging

During discharge: As the discharge proceeds, the sulfuric acid inside the battery continuously participates in the reaction, converting into water, which reduces the relative content of sulfuric acid in the electrolyte and subsequently lowers the solution density.

During charging: The charging process promotes the decomposition of lead sulfate, and sulfuric acid is regenerated and dissolved in the electrolyte. The concentration of sulfuric acid in the electrolyte increases, and its density also increases accordingly. When the battery is nearly fully charged, the density of the electrolyte will tend to stabilize and reach the standard density value of this battery type.

The mechanism by which electrolyte density reflects the health status of a battery

Evaluating battery capacity: The density of the electrolyte is closely related to the battery capacity. When the battery is in good health, there is sufficient active material on its internal plates. During the charging and discharging process, the electrolyte can fully react with the active material, causing the density of the electrolyte to change according to the normal rule. Once the battery experiences problems such as aging and sulfation of the plates, the active substances decrease or their activity drops, and the amount of sulfuric acid involved in the electrochemical reaction changes accordingly, resulting in abnormal changes in the density of the electrolyte.

Monitoring internal faults of the battery: If short circuits, open circuits or other faults occur inside the battery, it will affect the normal progress of electrochemical reactions and further disrupt the variation law of the electrolyte density. For instance, when a local short circuit occurs inside a battery, the short-circuited area will continue to discharge, causing the density of the electrolyte near this area to drop rapidly and showing a significant difference from that of the electrolyte in other parts. By measuring the density of the electrolyte at different parts, if the density difference is found to exceed the normal range, it can be initially determined that there is a fault inside the battery.

Factors affecting the density of the electrolyte

Ambient temperature

The direct influence of temperature on density measurement values: Temperature changes can cause thermal expansion and contraction of the electrolyte volume. Generally speaking, when the temperature rises, the volume of the electrolyte expands. For the same mass of electrolyte in a larger volume, the measured density value will be lower. When the temperature drops, the volume of the electrolyte shrinks, and the measured density value will be higher. Therefore, when measuring the density of the electrolyte, the temperature of the electrolyte must be measured simultaneously, and the measured values should be converted to the standard temperature for comparison and analysis

Long-term temperature affects the internal reactions of batteries and the density of the electrolyte: In high-temperature environments, the self-discharge rate of batteries increases, and the sulfuric acid in the electrolyte will accelerate the reaction with components such as the plates, causing abnormal changes in the density of the electrolyte. At the same time, it may also accelerate the corrosion of the plates and shorten the battery life. In a low-temperature environment, the viscosity of the electrolyte increases, the ion conduction rate slows down, the internal resistance of the battery increases, and the electrochemical reaction rate decreases, resulting in a reduction in the actual output capacity of the battery during discharge. This is reflected in the density of the electrolyte, which may lead to a rapid decrease in density during discharge, and even cause the electrolyte to freeze due to the excessively low density, damaging the battery casing and internal structure.

Battery charging and discharging status and depth

Charging and discharging states and density changes: As mentioned earlier, when the battery is in a charging state, the density of the electrolyte increases; When in the discharge state, the density decreases. Different charging and discharging states correspond to different electrolyte density values. By monitoring the density, one can intuitively understand the current charging and discharging stage of the battery.

The influence of discharge depth on density and battery life: Discharge depth refers to the percentage of the amount of discharge discharged by the battery during use to its rated capacity. Deep discharge will cause a large amount of active substances on the plates to be converted into lead sulfate. Moreover, if the battery is not fully charged in time after deep discharge, lead sulfate is prone to crystallization, leading to sulfation of the plates. This, in turn, affects the reaction between the electrolyte and the active substances, causing the density of the electrolyte to deviate from the normal range during subsequent charging and discharging processes, which seriously affects the service life of the battery. For instance, when a lead-acid battery designed for shallow cycle discharge is used in deep cycle discharge applications, the battery may malfunction within a relatively short period of time, and the density changes of the electrolyte will also become disordered.

Purity and impurities of the electrolyte

The influence of purity on electrochemical reactions and density: High-purity electrolyte can ensure the smooth progress of electrochemical reactions and make the density of the electrolyte change according to the normal charging and discharging rules. If the purity of the electrolyte is insufficient, the impurities it contains may undergo side reactions on the surface of the plates, interfering with normal electrochemical reactions, affecting the consumption and generation of sulfuric acid, and thus leading to abnormal density of the electrolyte. For instance, if the electrolyte contains metal impurity ions such as iron and copper, these ions may deposit on the plates, altering their electrochemical performance and causing the density changes of the electrolyte to lose regularity.

Sources and hazards of impurities: Impurities in the electrolyte may come from multiple sources, such as using impure water when replenishing distilled water, or during battery maintenance, impurities from tools and the environment may mix into the electrolyte. The presence of impurities not only affects the density of the electrolyte, but may also cause problems such as increased self-discharge of the battery and accelerated corrosion of the plates, further damaging the health of the battery.

The detection method of electrolyte density

Traditional detection tools and operation methods

Hydrometer

Working principle: The hydrometer operates based on Archimedes' principle. When the hydrometer is inserted into the electrolyte, it will be subjected to an upward buoyancy force, the magnitude of which is equal to the weight of the electrolyte displaced. The density value of the electrolyte can be directly read based on the depth to which the hydrometer is immersed in the electrolyte. The common suction type hydrometer measures by squeezing the rubber ball to draw the electrolyte into the glass tube, causing the hydrometer to float up for measurement.

Operation steps: First, unscrew the battery's liquid filling port cover. Carefully use a hydrometer to draw out an appropriate amount of electrolyte from the liquid filling port, ensuring that the hydrometer can float freely in the electrolyte without touching the glass tube wall. After the hydrometer stabilizes, lift it to the level of your line of sight and read the density scale value. Meanwhile, use a thermometer to measure the temperature of the electrolyte at this time for subsequent temperature correction.

Refractometer

Working principle: The refractometer measures the density of the electrolyte by taking advantage of the principle that light refracts at different angles in media of different densities. When light enters from one medium to another, refraction occurs, and the size of the refraction Angle is related to the densities of the two media. The density of the electrolyte can be obtained by measuring the refraction Angle of light in the electrolyte and comparing it with the known standard value.

Operation steps: After cleaning the prism surface of the refractometer, use a dropper to draw a small amount of electrolyte onto the prism and then cover it with the lid. Align the refractometer with the light source, observe through the eyepiece, adjust the focal length to make the scale lines in the field of view clear, and read the density value displayed at this time. Similarly, the ambient temperature during the measurement should be recorded, and the results should be temperature-corrected if necessary.

Modern detection technology and its advantages

Multi-point optical fiber sensor based on optical principles: This sensor is composed of multiple measurement points and can measure the density of the electrolyte at different depths inside the battery. The principle is to sense the density differences by utilizing the changes in characteristics such as bending loss when light propagates in electrolytes of different densities. Compared with traditional sensors, it can obtain the distribution information of the electrolyte density inside the battery, reflecting the internal state of the battery more comprehensively. This is helpful for more accurately determining the state of charge and health of the battery. It is especially suitable for large forklift battery packs, as it can monitor the density changes of the electrolyte in various parts inside the battery in real time and promptly identify potential problems.

The standard and application for judging the health status of batteries based on the density of electrolyte

The standard range of electrolyte density under different health conditions

New batteries or batteries in good health: For new forklift lead-acid batteries or batteries in good health, when fully charged, the density of the electrolyte is generally within the range of 1.28-1.30g/cm³ at 15℃. Batteries produced by different manufacturers may have slight differences, but generally they fall within this range. During the discharge process, as the discharge degree increases, the density of the electrolyte gradually decreases. When the discharge volume reaches 50% of the rated capacity, the density of the electrolyte approximately drops to 1.23-1.25g/cm³ (at 15℃).

Aging or faulty batteries: When a battery shows signs of aging, such as sulfation of the plates and shedding of active materials, the density of the electrolyte will deviate from the normal range during charging and discharging. Even after charging, the electrolyte density of aged batteries may not reach above the normal 1.28g/cm³ (at 15℃), and in the early stage of discharge, the rate of density decline may be faster than that of normal batteries. For batteries with internal short circuits and other faults, the density of the electrolyte near the faulty part will be significantly lower than that in other parts. The difference in the density of the electrolyte in each cell within the same battery may be greater than 0.01g/cm³.

Practical application cases in the maintenance of lead-acid batteries in forklifts

Regular inspection and preventive maintenance: A certain logistics warehouse has a large number of forklifts. To ensure the normal operation of the forklifts, the staff have formulated a strict battery maintenance plan, among which regular inspection of the density of the electrolyte is a key link. The electrolyte density of the forklift lead-acid battery should be tested once a week, the data recorded and the density change curve plotted. Through long-term monitoring, it was found that the density of the electrolyte in some batteries gradually decreased at an accelerated rate after being used for a period of time. Although it has not yet affected the normal operation of the forklift, based on past experience, these batteries may be about to have problems. So, the staff carried out repair treatment on these batteries in advance, such as using desulfurization charging and other methods, which effectively extended the service life of the batteries, avoided forklift shutdowns caused by sudden battery failures, and improved the efficiency of logistics operations.

Fault diagnosis and Repair: During a forklift fault investigation, it was found that the endurance capacity of a certain forklift had significantly decreased. The staff first inspected the battery. When measuring the density of the electrolyte, they found that the density of the electrolyte in one of the single cells was 0.03g/cm³ lower than that in the other cells. Further inspection revealed that there was a short circuit problem with the plates of this single-cell battery. By replacing the damaged plates and readjust the electrolyte density to the normal range, the forklift's endurance was restored to normal. This case fully demonstrates that battery faults can be diagnosed quickly and accurately through electrolyte density detection, providing a strong basis for timely battery repair and restoring the normal operation of forklifts.

Conclusion

The density of the electrolyte, as a core indicator for detecting the health status of forklift lead-acid batteries, is closely related to the battery's charging and discharging processes, internal chemical reactions, and overall performance. It can not only visually reflect the state of charge of the battery, but also effectively reveal whether there are potential faults such as aging, sulfation of the plates and short circuits inside the battery. By rationally applying traditional detection tools and modern detection technologies, accurately grasping the variation law of electrolyte density, and scientifically applying it in the daily maintenance, fault diagnosis and repair of forklift lead-acid batteries based on the density standard range under different health conditions, the reliability and service life of the battery can be significantly improved, and the operating cost of forklifts can be reduced. Ensure the efficient operation of industries such as logistics and warehousing. In the future, with the continuous advancement of technology, it is believed that battery health detection technology based on electrolyte density will become more accurate and intelligent, bringing greater convenience and benefits to the management and application of forklift lead-acid batteries.