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Introduction

In the industrial field, forklifts, as important material handling equipment, are widely used in various production processes. Among them, lead-acid batteries have become the preferred power source for many forklifts due to their advantages such as mature technology, low cost, and good high-rate discharge performance. However, in actual use, lead-acid batteries often encounter the problem of rapid water loss, which not only affects the battery's performance and service life, but also increases the usage cost and maintenance workload. A thorough understanding of the reasons for the rapid water loss of lead-acid batteries in forklifts and the adoption of effective water replenishment optimization measures are of great significance for ensuring the normal operation of forklifts, improving production efficiency and reducing operating costs.

Analysis of the Reasons for Rapid Water Loss

Charging factor

Excessively high charging voltage: When the charging voltage exceeds the normal tolerance range of lead-acid batteries, it will intensify the electrochemical reactions inside the battery. On the positive plate, water is electrolyzed in large quantities into oxygen and hydrogen, which escape from the battery through the exhaust valve, resulting in an accelerated rate of water loss.

Overcharging: After the battery is fully charged, if the charger fails to stop charging in time or switch to a float charging state and continues to charge at a relatively high current, the battery will be in an overcharged state. At this point, in addition to the normal charging reaction, the electrolytic reaction of water significantly intensifies, generating a large amount of hydrogen and oxygen, resulting in severe water loss. In actual use, some low-quality chargers or charging devices with unreasonable Settings are prone to overcharging.

Excessive charging current: Charging with a large current will cause severe heat generation inside the battery, leading to a rise in temperature. On the one hand, the increase in temperature accelerates the evaporation of water; On the other hand, it will accelerate the rate of water electrolysis reaction, leading to an increased loss of water. Take the 48V, 500Ah lead-acid battery pack commonly used in forklifts as an example. If the output current of the charger used is too large, exceeding the optimal charging current range of the battery pack, it may cause water loss problems.

Battery quality and design factors

Plate materials and manufacturing processes: As the core components of batteries, the materials and manufacturing processes of plates have a significant impact on the performance of batteries. If the purity of the active material on the plates is not high and its structure is unstable, it is prone to shedding and corrosion during charging and discharging, which in turn affects the chemical reactions inside the battery, leading to increased gas evolution and accelerated water loss. Some small manufacturers' plates, due to their limited technological level, cannot guarantee the quality stability of the plates, making the battery more prone to water loss problems.

The design of the safety valve is unreasonable: The safety valve is an important component of lead-acid batteries. Its function is to promptly release gas when the internal pressure of the battery is too high, preventing the battery casing from cracking. However, if the opening pressure of the safety valve is set too low, it will cause the gas inside the battery to be discharged prematurely and excessively, taking away a large amount of water vapor and accelerating water loss. Conversely, if the opening pressure is too high, when the internal pressure of the battery abnormally rises, the safety valve cannot open in time, which may cause more serious problems such as battery swelling or even explosion.

The purity and formula of the electrolyte: The purity and formula of the electrolyte are directly related to the performance and water loss of the battery. If the electrolyte contains impurities such as metal ions, it will trigger side reactions inside the battery, accelerating the corrosion of the plates and the decomposition of water, resulting in rapid water loss. In addition, an unreasonable formula of the electrolyte, such as an excessively high concentration of sulfuric acid, will also increase the self-discharge of the battery, intensify gas evolution, and thereby cause water loss problems.

Use environmental factors

High-temperature environment: In high-temperature conditions, the water loss rate of lead-acid batteries in forklifts will significantly accelerate. On the one hand, the increase in temperature accelerates the evaporation rate of the electrolyte; On the other hand, high temperatures can reduce the gas evolution overpotential of batteries, making the electrolysis of water reaction more likely to occur, generating more hydrogen and oxygen, and thus intensifying water loss. Studies show that for every 10℃ increase in ambient temperature, the rate of water loss in batteries approximately doubles.

High-humidity environment: Although lead-acid batteries have a certain tolerance range for humidity, in a high-humidity environment, condensation is prone to form on the battery surface. If there are tiny cracks or poor sealing in the battery casing, the condensed water may seep into the battery interior, diluting the electrolyte, altering its concentration and composition, and thereby affecting the battery's performance, leading to abnormal gas evolution and water loss. In addition, a high-humidity environment may also accelerate the corrosion of the battery casing and connectors, affecting the normal use of the battery.

Frequent vibration: During the operation of forklifts, vibration is inevitable. Frequent vibration can cause the plates and electrolyte inside the battery to shake, leading to unstable contact between the plates and the electrolyte, accelerating the wear and corrosion of the plates. At the same time, it may also loosen the connection parts inside the battery, causing local overheating, thereby accelerating the decomposition and evaporation of water and resulting in rapid water loss.

Usage habit factor

Deep discharge: If the lead-acid battery of a forklift is frequently in a state of deep discharge, it will cause excessive consumption of the active substances on the plates, resulting in an increase and enlargement of lead sulfate crystals on the surface of the plates, blocking the micro-pores of the plates and hindering the contact between the electrolyte and the active substances, thereby increasing the internal resistance of the battery. To maintain a normal working voltage, the battery requires a higher voltage and current during charging, which intensifies the electrolysis of water and leads to accelerated water loss. Generally speaking, the depth of discharge of lead-acid batteries should not exceed 80%. If they are discharged deeply for a long time, it will seriously shorten the battery's service life and increase the risk of water loss.

Long-term high-current discharge: When forklifts perform heavy-load handling or frequent starts, accelerations and other operations, the battery needs to provide high-current discharge. Long-term high-current discharge will cause the internal temperature of the battery to rise rapidly, and at the same time accelerate the electrochemical reaction, leading to intensified decomposition and evaporation of water, thus resulting in rapid water loss.

Untimely charging: After the forklift is used, if the battery is not charged in time, it will be in a state of low power. When the battery is in a state of low charge, the lead sulfate inside will gradually crystallize, forming an irreversible sulfation phenomenon, which increases the internal resistance of the battery and reduces its charging acceptance capacity. To ensure that the battery can be charged with sufficient power, the charger will increase the charging voltage and current, which will inevitably lead to an intensification of water electrolysis and an increase in water loss. Therefore, timely charging is crucial for maintaining the battery's good performance and reducing water loss.

The harm of water loss to forklift lead-acid batteries

Battery capacity decline

The reduction of water will lead to an increase in the concentration of sulfuric acid in the electrolyte, a decrease in ion activity, a reduction in the contact area between sulfuric acid and lead plates, and an increase in the internal resistance of the battery. This will hinder the electrochemical reactions inside the battery, causing the battery to be unable to fully release and store electrical energy during charging and discharging, thereby reducing the battery's capacity.

Plate vulcanization

Water loss causes uneven concentration of the electrolyte, forming a region with a relatively high concentration of sulfuric acid on the surface of the plates. In this case, the lead sulfate on the plates is more likely to crystallize and form a hard sulfide layer. The sulfide layer will further impede the contact between the electrolyte and the active substances on the plates, intensify the increase in the battery's internal resistance, and further deteriorate the battery's charging and discharging performance. Once the sulfation of the plates is severe, the difficulty of battery repair will increase significantly, and it may even lead to battery scrapping.

The risk of thermal runaway increases

After a battery loses water, its heat capacity decreases and its heat dissipation performance deteriorates. During the charging process, as the heat generated by the electrochemical reaction cannot be dissipated in time, the internal temperature of the battery will rise rapidly. When the temperature rises to a certain extent, it will trigger thermal runaway, that is, the chemical reaction rate inside the battery will increase sharply, generating more heat and further raising the temperature, thus forming a vicious cycle. Thermal runaway may cause the battery casing to deform or crack, and even lead to serious safety accidents such as fires.

Shorten the battery life

Problems such as reduced battery capacity caused by water loss, sulfation of plates and increased risk of thermal runaway will directly or indirectly shorten the service life of forklift lead-acid batteries. Under normal circumstances, the service life of lead-acid batteries in forklifts can reach 2 to 5 years. However, if the water loss problem is severe, its service life may be shortened to 1 to 2 years, or even shorter. This not only increases the cost of battery replacement, but also affects the normal use of forklifts, causing inconvenience to the production of enterprises.

Optimization measures for water replenishment

Judgment of the timing of water replenishment

Observe the appearance of the battery: Regularly check the appearance of the battery. If you find that the battery casing is swollen or deformed, or there is white powder-like substance on the top of the battery, it may indicate that the battery is losing water. Further inspection and consideration of replenishing water are needed.

Measuring the density of the electrolyte: Using a hydrometer to measure the density of the electrolyte is one of the important methods for determining the timing of water replenishment. The density of the electrolyte in lead-acid batteries has corresponding standard values under different charging and discharging states. Generally speaking, when fully charged, the density of the electrolyte is 1.28g/cm³. As the battery discharges, the density will gradually decrease. When the density of the electrolyte is found to be significantly lower than the lower limit of the standard value, it may be due to water loss, which leads to an increase in the concentration of sulfuric acid. At this point, water replenishment is required.

Monitoring battery voltage: During the charging and discharging processes, monitoring the voltage changes of the battery can also assist in determining the timing of water replenishment. Water loss can lead to an increase in the internal resistance of the battery. During charging, the voltage rise rate will be faster than normal, and the charging termination voltage will be reached prematurely. During discharge, the voltage drops at an accelerated rate and the capacity decreases significantly. When abnormal changes in battery voltage are detected, it is necessary to check whether the battery has lost water.

Selection of hydrating materials

Distilled water: Distilled water is pure water obtained through processes such as distillation and condensation, containing almost no impurities. It is the preferred material for replenishing water in forklift lead-acid batteries. It can replenish the water lost by the battery due to water loss, while not introducing new impurities and avoiding adverse effects on the electrochemical reactions inside the battery. In the market, distilled water is relatively common and inexpensive, and is easy to obtain.

Deionized water: Deionized water is pure water obtained by removing various ions from water through methods such as ion exchange resins. Its purity is comparable to that of distilled water and it can also be used to replenish water for lead-acid batteries in forklifts. Deionized water also has the advantage of having fewer impurities and can meet the requirements of battery water replenishment. In some occasions where water quality is highly demanded, deionized water may be a better choice.

Prohibited liquids: It is strictly forbidden to use tap water, mineral water, purified water, battery replenishment liquid or other liquids to replenish water for the lead-acid battery of the forklift. The impurities contained in these liquids, such as metal ions and microorganisms, can trigger side reactions inside the battery, accelerate the corrosion and aging of the plates, and seriously affect the performance and service life of the battery.

Methods and key points of operation for water replenishment

Manual hydration: Manual hydration is a relatively common and simple method of hydration. When operating, it is essential to ensure that the battery is fully charged first. This enables the electrolyte to be evenly distributed within the pores of the plates, facilitating accurate liquid level determination. Open the liquid injection hole cover on the battery, and use a dedicated funnel or syringe to slowly inject distilled water or deionized water into the battery, observing the rise of the liquid level. Generally speaking, after replenishing water, the liquid level should be 10-15mm higher than the plates, or reach the liquid level scale line marked on the battery casing. During the water replenishment process, be careful to avoid water splashing out of the battery to prevent corrosion of the battery casing and surrounding equipment. After replenishing the water, the liquid injection hole cover should be promptly closed and the remaining electrolyte on the battery surface should be wiped clean.

Automatic water replenishment system: To enhance the accuracy and efficiency of water replenishment and reduce the workload of manual operation, an automatic water replenishment system can be installed. An automatic water replenishment system is usually composed of liquid level sensors, controllers and liquid replenishment devices, etc. The liquid level sensor monitors the liquid level of the electrolyte in the battery in real time. When the liquid level is lower than the set lower limit value, the sensor transmits a signal to the controller, which then controls the liquid replenishment device to automatically add an appropriate amount of distilled water or deionized water to the battery. When the liquid level reaches the set upper limit value, the liquid replenishment device will automatically stop working. The automatic water replenishment system can achieve real-time monitoring of battery liquid level and automatic water replenishment, effectively avoiding the problem of insufficient or excessive water replenishment caused by improper manual operation, and also improving the timeliness and reliability of water replenishment.

Whether it is manual water replenishment or using an automatic water replenishment system, the following points should be noted during the water replenishment process: First, the water replenishment tools should be kept clean to avoid introducing impurities; Second, after replenishing water, the battery should be given a equalization charge once to ensure that the electrolyte is thoroughly mixed evenly and restore the battery's performance. Thirdly, for batteries with severe water loss, after replenishing water, multiple charge and discharge cycles may be required to restore the battery's performance to its optimal state. In addition, during the operation, personal protection should be noted to prevent the electrolyte from coming into contact with the skin and eyes. If contact occurs accidentally, rinse immediately with plenty of water and seek medical attention promptly.