Common troubleshooting and daily maintenance of automobile batteries

1 Introduction

Lead-acid batteries are one of the most important devices in cars. They provide power for starting the car, turning the car motor, and supplying electricity for starting, ignition and lighting. They are also called SLI[1] (Starting Lighting Ignition). According to the rated voltage, SLI mainly includes 6V and 12V series, but the most widely used is the 12V battery. For battery users, battery maintenance is a very important link[1]. If the maintenance work is done well, the battery life will be long. Otherwise, the life will be short. In the process of using batteries, faults are inevitable. Common battery faults include internal faults and external faults. Internal faults include: plate sulfidation, active material shedding, plate grid corrosion, plate short circuit, self-discharge, plate arching, etc. External faults include: shell cracks, pole corrosion, pole loosening, sealant cracking, etc.

2 Internal fault

2.1 Plate sulfidation

The phenomenon of plate sulfidation failure is manifested as the generation of insoluble white coarse crystalline lead sulfate on the plate, which cannot be converted into active substances during normal charging. When the faulty battery is discharged, the voltage drops sharply and drops to the termination voltage too early, the battery capacity decreases; the electrolyte density is lower than the normal value. When the battery is charged, the single cell voltage rises too fast, the electrolyte temperature rises rapidly, but the density increases slowly, bubbles are generated too early, and there are even bubbles during charging. The following situations can cause plate sulfidation: ① Long-term undercharging or failure to charge in time after discharge causes part of the lead sulfate on the plate to dissolve in the electrolyte. The higher the ambient temperature, the greater the solubility of lead sulfate. When the ambient temperature drops, the solubility decreases, and the dissolved lead sulfate will precipitate. Due to the temperature change when the battery is working, the precipitated lead sulfate will crystallize again on the plate to form sulfidation. 1. Do not leave a half-discharged battery for a long time. In particular, pay attention to regularly recharging the battery to keep it in a fully charged state; 2. The electrolyte level is too low, causing the upper part of the plate to come into contact with the air and be oxidized. During driving, the electrolyte fluctuates up and down and comes into contact with the oxidized part of the plate, which will form a large-grained lead sulfate hardened layer and sulfide the upper part of the plate. Therefore, the electrolyte level and density should be checked regularly. If the liquid level is found to be lower, distilled water should be added in time; 3. Long-term excessive discharge or deep discharge with a small current will cause lead sulfate to form in the pores of the active material deep in the plate. The battery cannot be over-discharged. The starter should not be connected for more than 5s each time to avoid low-temperature and high-current discharge; 4. The new battery is not charged thoroughly at the beginning, and the active material is not fully reduced; 5. The electrolyte density is too high and the composition is impure.

For batteries with slightly sulfided plates, they can be removed by charging with a small current and replacing with distilled water. For batteries with more severe sulfidation, the desulfurization charging method can be used to eliminate the sulfidation. Since the performance of batteries and the degree of plate sulfidation of each company are different, the desulfurization repair process of each battery is different. There are also battery repair equipment such as desulfurization instruments [2]. The process of repairing sulfided batteries by Jiangxi Zhenlong Power Technology Co., Ltd. [3] is as follows: ① For batteries with slightly sulfided plates, the balanced charging method, that is, the method of charging with a small current for a long time can be used to overcome it. That is, the second stage current of the initial charge is used to continuously overcharge until a large number of bubbles are generated in the electrolyte and the electrolyte specific gravity reaches 1.280g/cm3; ② For batteries with severe sulfidation, the "water treatment method" is used for repair. At this time, the electrolyte level drops and becomes semi-dry. First, add pure water to the battery, and then use the second stage current balanced charging method to charge continuously for several days. When the discharge capacity can reach 80% of the rated capacity, it means that the treatment work is basically completed. If the discharge capacity is still very small, continue to repeat the above charging method until the battery returns to normal. Batteries with particularly severe sulfation should be scrapped. However, with the advancement of battery regeneration technology, it has been improved. The main battery regeneration methods include reverse charging and chemical charging method, electrolyte immersion method and battery electrolysis method, and reverse charging method [4].

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The phenomenon of active material shedding is mainly manifested as the shedding of the positive active material lead dioxide. When charging, brown material can be seen from the filling hole, and the electrolyte is turbid, which will cause the battery capacity to decrease. The following situations will cause the active material to fall off: ① The battery charging current is too large and the electrolyte temperature is too high, which makes the active material expand, soft and easy to fall off; ② The battery is often overcharged, and a large amount of gas escapes from the pores of the plate, causing pressure in the pores of the plate, causing the active material to fall off; ③ The battery is often discharged at low temperature and high current, causing the plate to bend and deform, resulting in the shedding of active materials. Therefore, during the use of lead-acid batteries, it is a feasible measure to control the discharge current and electrolyte specific gravity to the minimum value to prevent the active material of the positive plate from falling off; ④ The bumps and vibrations during the driving of the car are inevitable during the driving of the car.

For lead-acid batteries with active material shedding, the troubleshooting method is: if the deposits are small, you can continue to use it after cleaning; if the deposits are large, you should replace new plates and electrolyte. Practice has shown that the shedding of active material on the plates mainly occurs during the discharge process of the battery.

2.3 Plate and grid corrosion

Plate grid corrosion mainly refers to the corrosion of the positive plate grid frame. The plate is in a corroded state, and the active material is accumulated in blocks between the separators. The phenomenon of this failure is manifested as a reduction in the battery output capacity. The following situations can cause plate grid corrosion: ① The battery is often overcharged, and the oxygen generated at the positive plate oxidizes the grid; ② The electrolyte density and temperature are too high, and the charging time is too long, which will accelerate the corrosion of the plate; ③ The electrolyte is impure.

For lead-acid batteries with plate and grid corrosion, the elimination method is as follows: for batteries with lighter corrosion, if there are impurities in the electrolyte, the electrolyte should be poured out and repeatedly washed with distilled water, and then new electrolyte should be added. It can be used after charging; for batteries with more serious corrosion, if the electrolyte density is too high, it can be adjusted to the specified value and continue to be used without charging; for batteries with severe corrosion, such as broken ribs and frames, falling off of active substances, etc., the plates need to be replaced.

2.4 Plate short circuit

The direct contact between the positive and negative plates of the battery or the overlap of other conductive materials is called a plate short circuit. The phenomenon of this fault is that the terminal voltage rises relatively slowly when the battery is charged. If the terminal voltage is tested by discharging the battery, the voltage is very low and will quickly drop to zero. The electrolyte temperature rises rapidly, the relative specific gravity rises very slowly, and there are few bubbles at the end of the charging period. The following situations can cause a plate short circuit: ① The partition is damaged so that the positive and negative plates are in direct contact; ② Excessive deposition of active materials will connect the positive and negative plates; ③ The plate group is bent, the lead-acid battery is over-discharged, or the plate active material falls off a lot, or the battery contains impurities, which will cause the plate to bend; ④ Conductive objects fall into the electrolyte.

For lead-acid batteries with plate short circuit, the troubleshooting method is: when a plate short circuit occurs, the battery must be disassembled and checked to find out the cause of the plate short circuit. Or replace the damaged separator, or eliminate the deposited active material, or correct or replace the bent plate group, etc. For batteries with plate short circuit, the charging and discharging current should not be too large, let alone over-discharging.

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The self-discharge of a battery refers to the phenomenon that the capacity of the battery is naturally lost when it is left in an open circuit state [5]. It is impossible to completely eliminate self-discharge. Generally speaking, if a well-maintained and fully charged battery is left in an environment of 20℃ to 30℃ for 28 days, its capacity loss exceeds 20%, which is called excessive self-discharge. The following situations may cause self-discharge failure: ① The electrolyte is impure, and a potential difference is formed between the impurities and the plates and between the different impurities attached to the plates, which causes partial discharge through the electrolyte. The electrolyte added to the new battery should be prepared as required using pure sulfuric acid and distilled water for batteries. The battery's filling hole must be intact, and the vent on the filling hole cover should be kept unobstructed to ensure that the hydrogen and oxygen generated during charging and discharging can escape in time; ② The battery is stored for a long time, and sulfuric acid sinks, causing a potential difference between the upper and lower parts of the plate to cause self-discharge. For idle batteries, they should be recharged regularly; ③ The electrolyte overflowed from the battery accumulates on the surface of the battery cover, connecting the positive and negative poles. The battery cover should be checked frequently to see if it is clean, whether there is scale or electrolyte, and to ensure that the battery cover is clean; ④ The battery is overheated, the battery is too close to the heat source, and it works in a high temperature environment, which accelerates the dissolution of the negative electrode sea brocade lead, increases the hydrogen evolution, and intensifies the self-discharge of the negative plate. Therefore, the battery should be insulated if it is too close to the heat source.

The method of elimination is: if the electrolyte is mixed with metal impurities, it can be discharged normally, the electrolyte can be poured out, and it can be repeatedly cleaned with distilled water, and then new electrolyte can be added; while charging, the electrolyte density can be adjusted to 1.26g/cm3 with distilled water, and the density can be adjusted to the specified value after it is sufficient. When the self-discharge is more serious, the battery should be completely discharged, the electrolyte should be poured out, the plate group should be taken out, the partition should be pulled out, and it should be cleaned with distilled water to remove the impurities between the plate and the partition, and pure electrolyte should be added to recharge and use. If only a few cells are self-discharged, the partition can be replaced after disassembly and the sediment at the bottom of the tank can be removed.

[page] 3 External Fault

Common external faults of automobile batteries are shown in Table 1[6].

Table 1 Common external faults of automobile batteries

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4.3 Checking the battery electrolyte density

The density of the electrolyte in the battery should be checked regularly. Generally, the relative density of the electrolyte should be checked every (6000-7500) km of driving. The electrolyte density can be checked with a suction density meter (Figure 4).

Since the electrolyte density changes during the charge and discharge process, the battery charge and discharge degree can be determined by measuring the electrolyte density. The charge degree of a 12V battery and the relative density of the electrolyte are shown in Table 2. Battery failure can also be determined by measuring the electrolyte density (see Table 4).

Table 2 Battery charge level and electrolyte relative density

4.4 Battery discharge degree detection

The discharge degree of the battery is tested with a high-rate discharge meter. For a battery in good technical condition, when it is continuously discharged for 15 seconds at the starting current or the specified discharge current, the measured voltage should not be lower than the specified value. The voltage can also be measured to determine battery failure [6], see Table 3.

Table 3 Measuring voltage to judge and handle battery failure

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The national standard stipulates [7] that when a newly charged battery is continuously discharged at a discharge current rate of 20h under the condition of an electrolyte temperature of 255°C until the average voltage of a single cell drops to 1.75V, the output power is the rated capacity. In actual measurement, if the battery is discharged to the end voltage under rated conditions for more than 20 hours, it is qualified. If the discharge time is less than 20h, its capacity is lower than the rated capacity and it is an unqualified product. The capacity measurement method can also be used to judge and deal with battery failures [6], see Table 4.

Table 4 Measuring electrolyte density, capacity judgment and handling battery failure

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The technical performance and service life of automotive lead-acid batteries depend not only on their own structure and quality, but also on the maintenance during use. In short, to extend the life of the battery, the following points must be achieved. ① When using the automotive battery, check whether the battery is firmly installed on the car and whether the connection between the wire connector and the electric pile is tight. Users should often observe whether there is electrolyte leakage on the surface of the battery shell, often remove dust and dirt on the battery cover, and keep the outer surface of the battery clean and dry. Wipe off the electrolyte on the top of the battery, dredge the pores on the filling hole cover, and remove the oxides on the pile and wire connector. ② Regularly check and adjust the relative density and liquid level of the electrolyte. When the liquid level is insufficient, add distilled water. ③ Always keep the normal operation of the car charging system. If the generator and regulator are found to have a fault, it should be eliminated in time. Start the engine correctly. Regularly recharge. ④ Before using a new battery, it is necessary to reasonably select the relative density of the electrolyte. Select according to different use conditions. Use electrolytes with higher relative density in cold areas. ⑤ Regularly check the insulation of the electrical system to eliminate leakage and short circuit. ⑥ Check the terminal voltage regularly, keep the battery fully charged, check the battery discharge level, and charge immediately if it exceeds the specified level. ⑦ Prevent the electrolyte from freezing due to insufficient charging in winter, prevent overcharging and overdischarging due to large current, and prevent overcharging in summer. In short, during the use of the vehicle, the requirements for the battery are high, and regular mandatory maintenance is required. The process specifications must be strictly followed during maintenance.

References

[1] Zhu Songran. Battery Handbook[M]. Tianjin: Tianjin University Press, 1998, 41.

[2] Fuzhou lead-acid battery desulfurization instrument obtained national patent. http://www.ybzhan.cn/News/Detail/4586.html.

[3] Maintenance and troubleshooting knowledge of lead-acid batteries for automobile starting. http://www.zldy.com.cn/china/news_show.asp?id=148.

[4] Chen Hongyu, Xiong Zhenglin, Li Zhongqi. Advanced lead-acid battery manufacturing process[M]. Beijing: Chemical Industry Press, 2010, 318-324.

[5] Yi Xiaobo. Lead-acid battery manufacturing and process control[M]. Beijing: Machinery Industry Press, 2004, 334.

[6] Yang Zhongmin, Xiao Yongqing. Use, maintenance and repair of vehicle batteries[J]. Bus Technology and Research. 2004, 26(2): 35～37.

[7] State Bureau of Technical Supervision. GB5008-1991, Technical requirements for lead-acid batteries for starting [S]. Beijing: China Standards Press, 1991.