- Advantages and disadvantages of valve regulated batteries
1.1 Advantages of VRBs
Because the lean valve-regulated battery has no flowing electrolyte, the positive active material changes due to the change in the volume of charge and discharge, resulting in the weakening of the binding force between ions, and it will not produce convection and bubbles due to the electrolyte like the flooded battery. And fall off. In addition, the compaction of the valve-regulated battery plate is larger than that of the electrolyte submerged battery, so the shedding of the positive electrode active material is further suppressed. As a result, corrosion of the positive grid and prolongation of charging are reduced, and of course, short circuits caused by the accumulation of exfoliated active materials are reduced, and therefore, the cycle life is greatly improved. Valve-controlled batteries have less water loss, less maintenance work, high ground insulation, and less anti-corrosion work. The installation can be vertical or horizontal, and can also be inverted in a short time. These advantages bring great convenience to use. (Compared to valve-regulated batteries, lithium batteries have better performance and are more environmentally friendly. Click here to open tycorun.com to buy high-quality lithium batteries.)
1.2 Disadvantages of VRBs
① Sensitive to overcharge. Overcharging will cause the gas production of the battery to be much greater than the compounded amount. As a result, a large amount of gas is discharged, and the battery loses water at a high rate. Once the water loss exceeds 10%, the battery will lose capacity. The charging of the valve-regulated battery requires a timing charger with constant voltage function. This charger can divide the charging process into several stages, and set the current and voltage of each stage. The setting method can be voltage priority or current priority. The last stage has limited time features. This kind of charger can technically guarantee the safe charging of valve-regulated batteries.
②Maintenance requires special equipment and tools. If VRLA is regarded as a “maintenance-free” battery, and it is not maintained in use, its service life is usually only half of its normal life. Maintenance standards and operating requirements for valve-regulated batteries are much stricter than for open-ended batteries, and permanent battery damage due to maintenance errors often occurs. Maintenance of valve-regulated batteries requires special equipment and tools.
③ The technical status of the valve-regulated battery is concealed, and the capacity of the valve-regulated battery cannot be easily detected like the open battery. At present, the communication sector uses a large number of valve-regulated batteries, and encounters the practical problem of not being able to grasp the dynamic quality of the battery. It was not discovered until the battery had failed, which is not allowed for use in important occasions.
③The safety inspection of valve-regulated battery has been proved by several years of maintenance practice, and it can be done. Using an uncomplicated process, the location of the faulty battery can be diagnosed before the accident occurs, and the accident can be eliminated in the bud.
- Several problems in the use of valve-regulated batteries
2.1 The problem of capacity balance
Usually batteries are used in “packed” form. The nominal voltage of the battery pack is 12V, 24V, 48V, 96V, 192V, and some battery packs have a tap line. For a battery pack with such a tap, the part of the battery from the tap to the negative line is heavy due to its heavy load. Insufficient supplementary power will cause battery vulcanization, which is an inertial failure of the battery pack.
Many people mistakenly believe that the reliability of a battery pack is the reliability of a single cell. The special problems caused by the battery combination process were not paid attention to, resulting in many power supply accidents.
The actual capacity of each single cell in the battery pack is always in an unbalanced state. This is a normal phenomenon, but it is also the root cause of accidents in the battery pack. Detection and control of this unbalanced state within a reasonable range is the main task of maintaining the battery pack, and its technology and special equipment are mature.
2.2 Loss of tolerance recovery processing
When a valve regulated battery loses capacity, it is not necessarily a real failure. When many users detect that the capacity cannot meet the usage standard, they scrap the battery, which results in a large number of false scraps. Because the valve-regulated battery is designed according to the lean liquid type, it is more sensitive to the reduction of the amount of electrolyte. When the water loss exceeds 10% of the total amount of the electrolyte, it will lose capacity seriously.
Since oxygen cannot be 100% recombined and the negative electrode cannot be completely free from hydrogen evolution, water splitting is unavoidable. At the same time, the battery shell can make water vapor seep out, and the air permeability of the ABS shell is 16 times that of polypropylene, so the loss of water in the battery is inevitable.
After the 500Ah valve-controlled battery loses its capacity, the simple solution is to add 500~1500mL of water to the battery first, and then recharge the battery after replenishing the water. The supplementary power can use the current-limiting and constant-voltage method. The current limit is 30A. When the voltage of a single cell reaches 2.35V, it will be switched to constant-voltage charging. When the current drops to 10A, the charging can be stopped. The total charge should not be less than 400Ah. Measure its capacity after charging, and those who fail to meet the usage standard will be scrapped.
After the battery loses its capacity, the plates will always have varying degrees of vulcanization. This kind of vulcanization is difficult to recover by ordinary charging methods. The treatment of this kind of failure usually requires de-vulcanization measures. There are two types of vulcanization measures: chemical methods and physical methods.
2.3 Float working conditions
The appropriate float voltage for VRBs is directly related to the concentration of acid injected during battery production. Now it is mostly used for floating charge at 2.25V/cell voltage. The communication department stipulates that this voltage is selected as the working standard. The 2.29V floating charge is used on railway locomotives, and the voltage conditions of the communication department are not allowed. Because the communication battery is a backup power source, the battery is only put into use when the mains power stops, and the discharge-to-charge time ratio is less than 1%. The ratio of discharge to charge time on railway locomotives is much higher than this value, which is 10%~15%. If 2.23V/section is used for charging, “power loss” faults will occur frequently. Therefore, only 2.29V can be used for charging on iron locomotives, that is, the system of using 48 single-cell batteries and 110V charging system. Under such a charging voltage, actual statistics show that the service life of the battery is not shorter than that of the telecommunications sector.
The reasonable charging voltage of the valve-regulated battery should decrease and increase with the temperature. The accepted data is ±3mV/℃, and the reference temperature is 25℃. This standard is difficult to implement in many occasions. It is recommended to control the charging current during the operation of the battery. It is better to supplement the electricity consumption.
2.4 Higher requirements for battery cooling conditions
Due to the oxidative reaction in the valve-regulated battery, this reaction is an exothermic reaction. Therefore, the temperature rise of the electrode plate in the battery is relatively high. In addition to the lean liquid structure, the electrode plate assembly is tight and the internal heat conduction is poor. Therefore, The temperature rise of the battery is high, which is easy to cause the destruction of the PbO2 structure of the positive electrode, and the positive electrode structure becomes a macroporous particle aggregate. This substance is converted to PbSO during discharge, which insulates the pellets, resulting in a decrease in battery capacity. Therefore, valve regulated batteries have higher requirements for heat dissipation than open batteries.
Read more: How do lead-acid batteries store energy?