Valve-regulated sealed lead-acid battery technology and maintenance

　　1. The role of valve-regulated sealed lead-acid batteries in communication power systems

　　1. Backup power supply, including DC power supply system and UpS system

　　2. Filtering

　　3. Adjust system voltage

　　4. Power equipment starting power

　　2. Types of stationary lead-acid batteries

　　Acid-proof explosion-proof battery (GF or GFD battery)

　　Stationary lead-acid battery

　　AGM—cathode absorption type (lean liquid type)

　　Valve regulated sealed battery (VRLA battery)

　　GEL—colloidal type

　　1. Compared with GF batteries, VRLA batteries have the following characteristics:

　　(1) During use, there is no need to add water or adjust the acid ratio.

　　(2) No leakage, no acid mist, and no environmental pollution.

　　(3) Small self-discharge.

　　(4) Compact structure, good sealing, earthquake resistance, and high specific energy.

　　(5) There is no memory effect.

　　(6) Wide range of use.

　　2. Comparison between cathode absorption VRLA batteries and gel batteries:

　　(1) There is no gas escaping from the AGM battery in the early stage of use, while the GEL battery needs to be equipped with an exhaust device in the early stage of use.

　　(2) AGM batteries have small internal resistance and have better high-current discharge characteristics than GEL batteries.

　　(3) The consistency and uniformity of AGM batteries are better because the diffusivity and uniformity of the electrolyte are better than those of GEL batteries.

　　(4) GEL batteries (especially tubular electrodes) have a long service life and are not prone to thermal runaway.

　　3. Working principle of VRLA battery

　　1. Battery charging/discharging principle:

　　The basic electrode reaction of lead-acid batteries is the conversion between lead (pb) and divalent lead (pb2+) and tetravalent lead (pb4+).

　　Discharge process: negative electrode: pb→pb2+ positive electrode: pb4+→pb2+ (

　　(+) pbO2+3H++HSO4-+2e put <═══> to charge pbSO4+2H2

　　Electron gain and loss are: negative loss and positive gain, that is, negative oxidation and positive reduction.

　　Charging process: negative electrode: pb2+→pb positive electrode: pb2+→pb4+

　　(-) pb+HSO4-Put <═══> charge pbSO4+H++2e

　　Electron gain and loss are: negative gain and positive loss, that is, negative reduction and positive oxidation.

　　Battery charge and discharge reaction

　　The total reaction of the battery: pb+2H++2HSO4—+pbO2, put <═══> and charge pbSO4+2H2O+pbSO4

　　2. Sealing principle of VRLA battery:

　　(1) Causes of gas generation inside the battery:

　　When the battery is overcharged, the battery decomposes water, producing O2 at the positive electrode and H2 at the negative electrode.

　　H2 is produced when the positive grid corrodes

　　When the battery self-discharges, the positive electrode produces O2 and the negative electrode produces H2

　　(2) Oxygen recombination principle (oxygen cycle principle):

　　During the charging process of the battery, in addition to the transformation of pbSO4 into pbO2 at the positive electrode, there is also an oxygen evolution reaction. Especially in the late charging period of the battery, when the battery capacity reaches 80%, the oxygen evolution reaction is more severe. The gas evolution reactions at the two poles are as follows. :

　　(+)2H2O→O2+4H++4e(--)2H++2e→H2

　　For VRLA batteries used for float charging, even if the float charge current is very small, in the long-term float charge state, except that part of the float charge current is used to convert pbSO4 generated by battery self-discharge into positive and negative active materials, it is unavoidable. The other part of the floating charge current is used for the electrolysis of water, so that oxygen is released from the positive electrode and hydrogen is released from the negative electrode.

　　The generation of oxygen and hydrogen causes water loss inside the battery, changes the density of the electrolyte, and also makes the battery difficult to seal. Since the birth of lead-acid batteries, people have been seeking to seal the batteries to reduce battery maintenance. The emergence of VRLA batteries realizes the sealing of batteries. The key technology of battery sealing is the recombination of oxygen inside the battery to achieve oxygen circulation, and the use of AGM separators to absorb electrolyte so that there is no flowing electrolyte inside the battery and the recombination of oxygen The principle is shown in Figures 3 and 4: During the charging process of the positive electrode, the oxygen released by electrolyzed water quickly diffuses to the negative electrode through the pores of the AGM separator, reacts with the sponge-like lead, the negative electrode active material, to form lead oxide (pbO), and the surface of the negative electrode When the pbO meets the electrolyte H2SO4, a chemical reaction occurs to generate pbSO4 and H2O. The pbSO4 is recharged and transformed into sponge-like pb. The generated H2O returns to the electrolyte. Due to the recombination of oxygen, the loss of water is avoided, thus achieving Battery sealing.

　　Measures to achieve sealing of lead-acid batteries:

　　1) Choose high-porosity AGM separators with a porosity of more than 93% to provide channels for oxygen recombination.

　　2) Adopt quantitative acid filling so that after the glass wool separator absorbs the electrolyte, there is still 5-10% porosity that has not been filled with electrolyte. Therefore, VRLA batteries are also called liquid-poor batteries.

　　3) Excessive negative active material. The capacity ratio of positive and negative plates is generally 1:1.1~1:1.2. In this way, after the positive electrode is fully charged, the negative electrode is not fully charged to prevent hydrogen from being precipitated at the negative electrode. If a large amount of hydrogen is precipitated, it is Cannot be compounded.

　　4) For the tight assembly of the battery cluster, cluster pre-compression technology is adopted to press the assembly between 40-60Kpa to ensure good contact between the AGM separator and the surface of the positive and negative plates, because the electrolyte of the VRLA battery mainly relies on the AGM separator. supply.

　　5) High-purity pb-Ca-Sn-Al antimony-free grid alloy, because pb-Ca alloy has a higher hydrogen evolution overpotential than pb-Sb alloy, which can reduce the possibility of hydrogen evolution due to grid corrosion.

　　6) A safety valve with stable and reliable opening and closing valve pressure. The standard for VRLA batteries for communication requires the opening pressure to be 10-35Kpa and the closing pressure to be 3-15Kpa. The opening and closing valve pressures are relatively close, which can reduce gas emissions and water loss.

　　7) Using constant voltage and current limiting charging method, VRLA batteries are more sensitive to overcharging, which will accelerate current damage. Constant voltage and current limiting charging can prevent overcharging and thermal runaway.

　　3. Self-discharge principle of VRLA battery:

　　Reasons for battery self-discharge:

　　1) The reaction between the positive active material and the electrolyte;

　　2) The reaction between the positive active material and the grid alloy;

　　3) The reaction between the positive electrode active material and the negative electrode to release hydrogen gas.

　　Four. Two major categories of VRLA battery technologies

　　Applying the same oxygen recombination principle, but using different fixed electrolyte technology and different oxygen recombination channel technology, it can be divided into two major types of VRLA batteries, namely AGM technology and GEL technology (colloid), so it is also called AGM Batteries and gel batteries. Both types of batteries have their own advantages and disadvantages. Currently, AGM batteries are still mainly used in telecommunications, power and other markets.

　　1. AGM technology

　　For VRLA batteries using AGM technology, the AGM separator adopts U-shaped coating method (S-shaped coating method can also be used). The characteristics of VRLA batteries using AGM technology: small internal resistance, using ultra-fine glass wool separators to absorb the electrolyte, so that there is no electrolyte in the battery. The AGM separators have a porosity of more than 93%, and about 10% of the pores are used as The O2 precipitated from the positive electrode is recombined with the negative electrode to realize the circulation of oxygen and achieve the purpose of battery sealing.

　　2. Gel technology (colloid technology)

　　The OpZV gel battery produced by German Sunshine Company using Gel technology is a typical representative.

　　The characteristics of the gel battery: the internal resistance is large, and the thixotropic SiO2 colloid is used to absorb the electrolyte so that the electrolyte does not flow.

　　Composite channel of O2 with colloid microcracks. In the early stages of use of the gel battery, the colloid failed to form a large number of microcracks, and the recombination efficiency of oxygen was low.

　　5. Failure modes of VRLA batteries

　　Despite its many advantages, VRLA batteries, like all batteries, have reliability and longevity issues. VRL battery literature reports: its service life is about 15 years (floating charge at 25°C). However, VRLA batteries at home and abroad have experienced premature failure during actual use. The current failure modes of VRLA batteries mainly include corrosion and growth of the grid, drying up of the electrolyte, sulfation of the negative electrode, early capacity loss (pCL), thermal runaway, etc.

　　6. Use and maintenance of VLRA batteries

　　1. Selection of VLRA batteries

　　The VLRA battery model must be correctly selected before use to ensure that the battery has sufficient discharge capacity so that communication equipment can operate normally; in addition, choosing a reasonable capacity can avoid waste caused by selecting too large a capacity.

　　There are two selection methods: 1) calculation method 2) and curve search method.

　　2. Installation, use and precautions of VLRA batteries

　　Before installing and using the battery, you should first read the product manual carefully and install and use it as required. When installing, special attention should be paid to the following aspects:

　　1) The installation plan should be formulated according to the location and conditions, such as ground load, ventilation environment, sunlight exposure, corrosion and organic solvents, machine room layout, convenience for maintenance, etc.

　　2) New and old batteries generally cannot be mixed during installation, and batteries of different types or batteries with different capacities must not be mixed.

　　3) Batteries are all 100% charged before leaving the factory. They must be handled with care to avoid short circuits. Insulated tools and insulating gloves should be used during installation to prevent electric shock.

　　4) Before installation and use, the battery should be stored in an environment of 0 to 35°C. The storage period is 3 months. If it exceeds 3 months, the battery should be recharged according to the standards given in the instruction manual.

　　5) According to the specified series and parallel lines, connect the batteries between columns, between layers, and panel terminals. Before installing the terminal connector and connecting the entire power system, you should carefully check the positive and negative polarity and measure the system voltage. And note: on the premise of complying with the design cross-sectional area, the lead wire should be as short as possible to reduce the voltage drop during large current discharge; when more than two groups of batteries are connected in parallel, the cables from each group of batteries to the load should be of equal length to ensure It is beneficial to balance the current of each group of batteries when charging and discharging the battery.

　　6) When connecting the battery, the screws must be tightened, but excessive tightening force must also be prevented from damaging the copper-embedded poles.

　　7) After installation, the system voltage and the positive and negative polarity directions of the battery should be checked again to ensure that the battery is installed correctly.

　　8) Use a soft cloth soaked in soapy water to clean the battery case, cover, panel and connecting wires. Do not use organic solvents to avoid corrosion of the battery cover and other components.

　　3. Maintenance of VRLA batteries

　　1) Installation of valve-regulated sealed lead-acid batteries

　　Valve-regulated sealed lead-acid batteries do not need to have a dedicated battery room and can be installed in the same room as communication equipment. Can be stacked or mounted on a rack.

　　2) Items to be checked frequently

　　a. Float voltage, ambient temperature;

　　b. Is there any looseness or corrosion at the connection?

　　c. Whether the battery case is leaking or deformed;

　　d. Whether there is acid mist overflowing around the pole and safety valve;

　　3), supplementary electricity

　　a. After the battery system is installed, recharge the battery pack;

　　b. The battery has been left unused for more than three months;

　　battery discharge

　　a. A verification discharge test should be conducted every year based on the actual load, and 30%-40% of the rated capacity should be discharged;

　　b. Do a capacity test every three years, and once a year after six years of use;

　　4) Measurement of battery capacity

　　Method 1: Offline measurement method

　　a. After fully charging the battery pack separated from the power supply system, let it stand for 1-24 hours, and then start discharging when the ambient temperature is 25℃±5℃;

　　b. The terminal voltage of the battery should be measured before the start of discharge. During the discharge period, the discharge current, time and ambient temperature of the battery should be measured. The fluctuation of the discharge current should not exceed 1% of the specified value;

　　c. During discharge, the battery terminal voltage and room temperature should be measured. The measurement time intervals are: 10h rate discharge for 1 hour, 3h rate discharge for 0.5h, 1h rate discharge for 10 minutes. Measurements should be made at any time at the end of discharge to accurately determine the time to reach the discharge end voltage. ;

　　d. The discharge current multiplied by the discharge time is the capacity of the battery pack. When the battery is not discharged at a 10-hour rate or the environment

　　When the temperature is not 25℃, the actual measured capacity should be converted into the capacity at 25℃;

　　e. After the discharge is completed, the battery pack must be charged. The charged capacity should be 1.2 times the discharged capacity.

　　Method 2: Online measurement method

　　a. In the power supply system, turn off the rectifier and let the battery pack discharge to supply the communication equipment. When the battery pack is discharging, find the battery with the lowest voltage and the worst capacity in the battery pack as the object of the capacity test;

　　b. Turn on the rectifier to charge the battery pack, and wait for the battery pack to be stable for more than 1 hour after it is fully charged;

　　c. Conduct a 10-hour rate discharge test on the worst battery found during discharge in a. Measure the terminal voltage, temperature, discharge time and room temperature of the battery before and after discharge. In the future, the test will be performed every 1 hour. When the discharge is approaching the termination voltage, the test should be performed at any time in order to accurately record the discharge time:

　　d. The discharge time multiplied by the discharge current is the capacity of the battery. When the room temperature is not 25°C, it should be converted into the capacity at 25°C according to formula (1);

　　e. After the discharge test, use a charger to charge the battery to restore its capacity;

　　f. Draw the discharge curve based on the measured data;

　　Method 3: Verification capacity test method

　　In order to know the approximate capacity of the battery pack at any time, it is necessary to conduct a verification discharge test. The method is:

　　a. In the DC power supply system, turn off the switching power supply and let the battery power the communication equipment. Test the terminal voltage, temperature, specific gravity, room temperature and discharge time of each battery before and after the battery pack is discharged, and discharge 30%-40% of the rated capacity. until;

　　b. After discharging, recharge the battery;

　　c. Make a discharge curve based on the test data and keep it for comparison when testing again;

　　Precautions:

　　The above three battery capacity test methods are commonly used in daily maintenance, but no matter which method is used, communication security will be threatened to a certain extent during the capacity test. Therefore, when doing the capacity test, it is necessary to prevent the mains power from being interrupted, and the backup power generation unit should be in good condition.

　　5) Periodic maintenance projects

　　monthly maintenance

　　Complete the following inspections monthly:

　　1. Keep the battery room clean and hygienic;

　　2. Measure and record the ambient temperature in the battery room;

　　3. Check the cleanliness of the batteries one by one, the damage and heating marks of the terminals, and the damage or overheating marks of the casing and cover:

　　4. Measure and record the total voltage and float current of the battery system;

　　Quarterly maintenance

　　1. Repeat various monthly inspections;

　　2. Measure and record the float voltage of each online battery. If the voltage of more than two batteries is lower than 2.18V after temperature correction, please contact the manufacturer.

　　Annual maintenance

　　1. Repeat all quarterly maintenance and inspections;

　　2. Check the connection parts every year for looseness;

　　3. Every year, the battery pack undergoes a verification discharge test with actual load, and discharges 30%-40% of the rated capacity;

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