Analysis of liquid leakage of valve regulated lead-acid battery
valve regulated lead-acid battery is a new type of battery developed in the late 1970s. It is widely used as a backup power supply in communication and power industries. It has been used in China for more than ten years. Due to its advantages of less maintenance, no corrosion, no pollution and so on, it is favored by more and more customers, and has basically replaced acid proof explosion-proof and nickel cadmium fixed batteries. It is unimaginable, but some problems have also been exposed in the process of use, such as short service life of individual batteries, low floating charge voltage and liquid leakage, especially the phenomenon of liquid leakage is very common. Composition and working principle of battery
valve regulated lead-acid battery is mainly composed of positive and negative electrode groups, electrolyte, separator, battery slot cover, safety valve, pole terminal and other parts
2.2 working principle
because the positive and negative discharge products are lead sulfate, it is also called bipolar sulfate theory.
there is also water electrolysis reaction at the later stage of charging, and a certain amount of gas is produced.
in ordinary lead-acid batteries, H2 and O2 must be suppressed or eliminated in order to achieve sealing because of gas generation.
by adding calcium metal to the negative plate material, the potential of H2 precipitation is increased, so that the battery will not produce H2 under normal charging. At the same time, the lean liquid tight assembly technology makes it easy for the positive O2 to reach the negative, and O2 is eliminated in the following reactions
3 Analysis of battery leakage phenomenon
3.1 relationship between battery leakage and electrolyte volume
a basic principle of sealed battery design is to adopt lean solution technology, so that the O2 produced by the positive electrode can be combined and absorbed on the negative electrode to the greatest extent through the internal circulation of the battery, so as to complete the recombination of gas in the battery, maintain the balance of water in the electrolyte, and thus make the battery sealed. If the amount of electrolyte is too large, the internal gas recombination channel will be blocked, the internal gas of the battery will increase, and the pressure will increase, which is easy to produce liquid leakage at the defective part of the battery seal. Therefore, the amount of acid added to the battery must be appropriate
in terms of 10h discharge rate of sealed battery, the electrolyte density is generally controlled to be 1.10, and the electrolyte density before discharge is 1.30. According to the battery reaction, the minimum acid consumption per ah battery can be calculated
the amount of pure H2SO4 required before discharge is: w (H2SO4) =v · D · m
the amount of pure H2O is: w (H2O) =v · D (1-m)
the amount of pure H2SO4 required after discharge is: w (H2SO4) =v · D · n-3.36
note: 43.66g of pure H2SO4 and 0.67g of produced water are consumed for each 1Ah of power discharged. Where D - electrolyte density at the beginning of discharge, which is 1.30;
m - weight percentage concentration at the beginning of discharge, 38%;
n - the weight percentage concentration after discharge, which is 16%, especially suitable for the analysis of stripping process;
v -- volume of sulfuric acid with D concentration. Therefore, the volume of electrolyte needed to be added to each ah battery is p although it is not a large part of the aluminum profile industry
in order to achieve lean solution, it is necessary to ensure that the required electrolyte must be completely adsorbed in the partition, and there are some gas channels. Generally, 17g glass fiber partition is added per ah, and the saturated acid absorption capacity of each g partition is 0.8ml. Therefore, the maximum acid absorption is 13.6ml, ensuring that the maximum acid absorption of the sealing diaphragm cannot exceed 95%, generally 92%, that is, the maximum acid addition is 12.5ml, and the acid addition should be controlled between 10.9 ~ 12.5ml.
3.2 analysis of battery leakage prone parts
through long-term use observation, it is found that the battery leakage prone parts are mainly at the seal between the battery slot covers, the safety valve, and the pole terminal seal
. The causes of liquid leakage in various parts are different, and corresponding measures should be taken after comprehensive analysis.
3.3 sealing method of battery slot cover
generally, two methods of epoxy adhesive sealing and hot melt sealing are used for battery slot cover sealing. Relatively speaking, the hot-melt sealing effect is better. The method is to heat the battery tank to make the hydraulic universal testing machine produced by our company have the function of automatic storage. The plastic cover (ABS or PP) is hot-melt and then pressurized and fused together. If the hot melt temperature and time are well controlled, and the seal is clean and free of dirt, the seal is reliable. According to the anatomical observation of the hot-melt sealed liquid leakage battery, there is a hot-melt layer at the seal, with honeycomb trachoma, which is not very dense. Due to the existence of O2 in the battery, under a certain pressure, O2 will leak along the trachoma channel with acid mist
the epoxy adhesive seal leaks a lot, especially when the battery is placed horizontally. If the epoxy adhesive formula and curing conditions are well controlled, sealing can be achieved. After dissecting the leaking battery, it is found that the bonding between the sealant and the shell is interface bonding, the bonding force is small, it is easy to fall off, and there are glue holes or cracks at the leaking part. Due to the poor fluidity of epoxy adhesive (especially low-temperature curing), it is easy to cause some parts of the sealing groove not to be filled with adhesive, resulting in liquid leakage channels. Cracking (small cracks) mainly occurs in the horizontal battery of the rack cabinet. Due to the effect of gravity, the deformation of the rack cabinet makes the battery sealing adhesive layer under stress, and the curing of epoxy adhesive is very brittle. Under the action of external force, it is easy to crack and cause liquid leakage.
3.4 cause analysis of safety valve leakage
the safety valve plays a sealing role under a certain pressure. When the specified pressure (opening pressure) is exceeded, the safety valve automatically opens and deflates to ensure the safety of the battery. The main reasons for safety valve leakage are as follows.
a. the amount of acid added is too much, and the battery is in a liquid rich state, resulting in the obstruction of the gas channel for O2 re gasification. O2 increases, and the internal pressure increases. When it exceeds the opening pressure, the safety valve opens, O2 is released with acid mist, which is opened for many times, and the acid mist forms acid around the safety valve.
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