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Introduction

In modern logistics and industrial production, forklifts, as important handling equipment, the stability and efficiency of their operation are of vital importance. As a key power source for forklifts, the performance of lead-acid batteries directly affects the working performance of forklifts. However, during long-term use, forklift lead-acid batteries are bound to encounter various faults, which may not only lead to forklift shutdowns and affect production progress, but also cause economic losses. Therefore, accurately diagnosing and promptly eliminating faults in the lead-acid batteries of forklifts is of great significance for ensuring the normal operation of forklifts and extending the service life of the batteries.

Common Fault Diagnosis

Capacity reduction

1. Fail to reach the rated capacity

- ** Cause of failure ** : Insufficient charging after use, resulting in the battery failing to store sufficient electrical energy. This might be caused by factors such as too short charging time, charger malfunction or unreasonable charging system. In addition, a low density of the electrolyte can also affect the capacity of the battery. The density of the electrolyte is closely related to the electromotive force and capacity of the storage battery. When the density is lower than the normal range, the active substances involved in the electrochemical reaction decrease, thereby leading to a decline in capacity. In addition, if the external connection lines are not unobstructed and have a high resistance, the charging current cannot be effectively transmitted to the interior of the battery, resulting in insufficient charging and subsequently affecting the capacity.

- ** Diagnostic Method ** : Check the charging records to see if the charging time meets the requirements and if the output voltage and current of the charger are normal. Measure the density of the electrolyte using a hydrometer and compare it with the standard value. Check the external circuits, including cables, plugs, sockets, etc., to see if there is any loosening, corrosion or open circuit, etc. You can use a multimeter to measure the circuit resistance to determine if it is within the normal range.

2. The capacity gradually decreases

- ** Cause of Failure ** : Sulfation of the plates is one of the common reasons for the gradual decrease in capacity. Long-term insufficient charging, frequent over-discharge or deep discharge at low current, long-term semi-discharge or discharge state, and the electrolyte level being too low, causing the upper part of the plate to be exposed above the liquid surface, etc., may all promote the formation of coarse lead sulfate particles on the plate due to lead sulfate crystals. These particles are difficult to be converted into active substances during the charging process, resulting in a reduction in the effective reaction area of the plate and a gradual decrease in capacity. In addition, when harmful impurities such as iron, copper and other metal ions are mixed into the electrolyte, electrochemical reactions will occur on the plates, consuming active substances and reducing the capacity of the battery. At the same time, local short circuits in the battery, such as the contact of conductive objects between the plates or the contact of positive and negative plates due to the damage of the separator, will also cause some electrical energy to be consumed inside the battery, resulting in a decrease in capacity.

- ** Diagnostic Method ** : Observe the surface of the plates. If there are large white crystalline particles, it may be sulfation of the plates. Conduct component analysis on the electrolyte to detect whether there are any harmful impurities. By measuring parameters such as the open-circuit voltage, discharge voltage and current of the battery, and combining with the charge and discharge curves, it is determined whether there is a local short circuit. Professional battery detectors can also be used to test the internal resistance, capacity and other indicators of the battery to further determine the cause of the fault.

3. ** Capacity suddenly decreases **

- ** Cause of Failure ** : Internal or external short circuits in the battery are the main cause of sudden capacity reduction. An internal short circuit may be caused by excessive shedding of the active material on the plates, with the sediment touching the bottom of the plates, resulting in a short circuit between the positive and negative plates. Lead fluff is produced on the plates and accumulates on both sides of the electrode group or at the upper lugs, causing bridging and short circuits between the positive and negative plates. The partition is damaged, causing direct contact and short circuit between the positive and negative plates, etc. External short circuits may be caused by faults in the forklift's electrical system, such as damage to the insulation layer of the wires, resulting in direct connection of the positive and negative poles. Or during use, conductive objects such as metal tools may accidentally come into contact with the positive and negative terminals of the battery, causing a short circuit.

- ** Diagnostic Method ** : Inspect the appearance of the battery to see if there are any signs of electrolyte leakage, damaged casing, etc. These may be caused by internal short circuits leading to increased pressure. Use a multimeter to measure the resistance between the positive and negative terminals of a battery. If the resistance value is close to zero, there may be a short circuit. Conduct a comprehensive inspection of the forklift's electrical system to check for any damage, short circuits or other issues with the wires. For internal short circuits, it may be necessary to disassemble the battery and check the condition of components such as the plates and separators.

Voltage anomaly

1. The voltage is too high during charging and drops rapidly during discharging

- ** Cause of Failure ** : Sulfation of the plates will increase the surface resistance of the plates. During charging, the resistance of current passing through the plates increases, resulting in a rise in voltage. During discharge, due to the reduction of active material on the plates, there is insufficient substance available to participate in the reaction and provide electrical energy, and the resistance is relatively large, so the voltage drops rapidly. In addition, the drying up or excessively high density of the electrolyte may also cause this abnormal voltage phenomenon. The drying up of the electrolyte will impede ion conduction and increase resistance. If the density is too high, it will accelerate the corrosion of the plates, affect the progress of electrochemical reactions, and subsequently lead to abnormal voltage.

- ** Diagnostic method ** : As mentioned earlier, observe the surface of the plates to determine if there is sulfation. Measure the density of the electrolyte and check if it exceeds the normal range. At the same time, check the electrolyte level. If the level is too low, it might be that the electrolyte has dried up. The cause of the fault can also be further determined by measuring the voltage and current change curves during the charging and discharging processes and comparing them with the normal curves.

2. The open-circuit voltage is significantly reduced during use

- ** Cause of the fault ** : It might be that the terminals of a single cell in the battery pack are connected in reverse, causing a portion of the voltage in the entire battery pack to cancel out, thereby reducing the open-circuit voltage. A similar situation will also occur when the entire battery pack's pole group is connected in reverse. In addition, if the capacity of a single battery is low or there is a short circuit, it will also lower the open-circuit voltage of the entire battery pack. For instance, when a single battery has an internal short circuit, it acts as a resistor, consuming the electrical energy of other normal single batteries and causing the voltage of the entire battery pack to drop.

- ** Diagnostic Method ** : Use a multimeter to measure the voltage of each individual battery cell and check if there is a negative voltage or if it is significantly lower than that of other cells. If so, it may be that the terminals of that cell are connected in reverse or there is a fault. According to the arrangement of the battery pack, check whether the connection between the individual battery terminals and the groups is correct, as well as whether the connection of the battery groups is intact. Also, check if there are any problems such as loosening or oxidation that cause poor contact.

Abnormal gas emission

1. There is no gas leakage or very little gas leakage at the end of charging

- ** Cause of Fault ** : When a short circuit occurs inside the battery, the current is consumed at the short-circuit site and cannot normally participate in the electrochemical reaction to produce gas. Therefore, there is no gas leakage or very little gas leakage at the end of charging. In addition, if the charging current is too small, it may also lead to incomplete electrochemical reactions and a reduction in gas production. For instance, a malfunction of the charger or excessive resistance in the charging circuit may cause the actual charging current to be lower than the normal level.

- ** Diagnostic Method ** : By measuring parameters such as the internal resistance and charging and discharging current of the battery, it is determined whether there is an internal short circuit. Check the output current of the charger and compare it with the specification parameters of the charger to see if it is normal. At the same time, check the charging circuit to ensure a firm connection without any issues such as looseness or corrosion. Measure the circuit resistance to determine if it will affect the charging current.

2. There is no gas leakage after charging

- ** Cause of the fault ** : The main cause is a short circuit inside the battery. The short circuit leads to the inability of the electrochemical reaction to proceed normally and the inability to generate gas. In addition, if the electrolyte dries up and there is not enough water to participate in the electrolytic reaction, no gas will be produced either.

- ** Diagnostic Method ** : As mentioned earlier, use professional equipment to test the internal resistance of the battery and troubleshoot internal short circuit faults. Check the electrolyte level. If the level is extremely low or even dry, distilled water or electrolyte that meets the requirements should be replenished in time.

3. The gas leakage is too early and large during charging

- ** Cause of failure ** : The sulfation of the plates increases the surface resistance of the plates, causing the electrochemical reaction to occur prematurely and resulting in premature gas leakage during charging. Meanwhile, due to the reduction of the active material on the plates and the decrease in the reaction area, in order to maintain the current, the reaction rate increases and a large amount of gas is produced. In addition, excessive charging current can also cause overly intense electrochemical reactions, resulting in large and premature gas extraction. For instance, a mismatched charger was used, and the output current exceeded the capacity of the battery.

- ** Diagnostic Method ** : Observe the surface of the plates to determine if there is sulfation. Check the output current setting of the charger to see if it meets the charging requirements of the battery. During the charging process, monitor the parameters of the battery such as voltage, current and temperature. If the voltage rises too fast, the temperature is too high and there is abnormal gas leakage, it may be caused by excessive charging current or sulfation of the plates.

4. Gas leakage during placement or discharge

- ** Cause of failure ** : Discharging the battery without leaving it idle after charging will cause unstable chemical reactions inside the battery and generate gas. In addition, there are impurities in the electrolyte, and these impurities may trigger additional chemical reactions and produce gases. For instance, if metal impurities are mixed into the electrolyte, displacement reactions may occur on the plates, generating gases such as hydrogen.

- ** Diagnostic method ** : Check the operation records after charging to see if there is any situation of discharging without leaving it idle. Conduct component analysis on the electrolyte to detect whether there are impurities. The problem can be determined by filtering and purifying the electrolyte and observing whether the gas leakage phenomenon improves to see if it is caused by impurities in the electrolyte.

The temperature of the electrolyte is too high

1. During normal charging, the temperature of the electrolyte abnormally rises

- ** Cause of the fault ** : During charging, if the current is too large, it will cause the electrochemical reaction to be overly intense, generating a large amount of heat and leading to an abnormal rise in the temperature of the electrolyte. For instance, a charger with excessive power is used, or the current-limiting function of the charger fails. Internal short circuit in the battery is also an important cause. The resistance at the short-circuited part will convert electrical energy into thermal energy, thereby raising the temperature of the electrolyte. In addition, if the density of the electrolyte is too high, it will increase the resistance of the electrochemical reaction, resulting in more heat generation during the reaction process.

- ** Diagnostic Method ** : Check the output current of the charger and compare it with the charging specification of the battery to determine if it is too large. Use professional equipment to test the internal resistance of the battery and troubleshoot internal short circuit faults. Measure the density of the electrolyte to see if it exceeds the normal range. During the charging process, monitor the temperature of the electrolyte in real time. If the temperature rises too quickly and exceeds the normal range, stop charging immediately and troubleshoot the problem.

2. The temperature of some individual cells in the battery is higher than that of others

- ** Cause of failure ** : The sulfation of the plates will increase the internal resistance of this single-cell battery. During the charging and discharging process, the heat generated by the internal resistance increases, causing the temperature to rise. In addition, some individual battery cells may have local short circuits or poor contact issues, which can also cause excessive heat generation in that cell, resulting in a higher temperature than other cells. For instance, foreign objects between the plates inside a single cell can cause a local short circuit, or the terminal posts connecting the cell to the battery pack can become loose, increasing the contact resistance and generating heat.

- ** Diagnostic Method ** : Observe the surface of the plates of each individual battery to determine if there is sulfation. Use a multimeter to measure the voltage, internal resistance and other parameters of each individual battery cell, compare the differences among the cells, and identify abnormal cells. Check the connection of the terminals of individual battery cells to see if there are any problems such as loosening or oxidation that cause poor contact. For monomers with abnormally high temperatures, devices such as infrared thermometers can be used to measure their temperature distribution more accurately and further analyze the causes of faults.