What factors influence the service life of lead-acid battery and the points of attention

1 Preface

Battery is an important part of the UPS system, and its advantages and disadvantages are directly related to the reliability of the entire UPS system. No matter how advanced and functional the UPS design is, once the battery fails, even a good UPS can not provide uninterrupted power supply. Do not choose low-quality lead-acid batteries because of the desire to be cheap. This will affect the reliability of the entire UPS system and will cause greater losses.

The battery is the shortest part of the average failure time(MTBF) in the entire UPS system. If it can be used and maintained correctly, its service life can be extended, and otherwise its service life will be greatly shortened. Therefore, we need to understand the basic principles of the battery and the use of precautions.

2 Lead acid batteries

The types of batteries can generally be divided into lead-acid batteries, lead-acid-free maintenance batteries, and nickel-cadmium batteries. Taking into account factors such as load conditions, use environment, service life, and cost, UPS generally chooses a valve-controlled lead-acid-free maintenance battery. Its main feature is the production of oxygen on the positive plate at the time of charging, which is reduced to water on the negative plate by chemical reaction. It does not need to be maintained with water during the specified floating life period. Therefore, it is also called maintenance-free lead-acid battery. The maintenance exemption is only compared with ordinary batteries. The use process eliminates the addition of pure water or distilled water and the adjustment of the electrolyte liquid surface. It does not eliminate all maintenance work. On the contrary, in order to achieve UPS uninterrupted power supply, we need to maintain and maintain the lead-acid free maintenance battery more carefully.

3 Main factors and considerations affecting useful life

The following are the main factors that affect the service life of the battery and the matters that should be noted during use:

(1) The ambient temperature has a greater impact on the battery. High ambient temperature will cause the battery to overcharge to produce gas, and low ambient temperature will make the battery under-charged, which will affect the service life of the battery. Therefore, the ambient temperature is generally required to be around 25 °C, and the UPS floating charging pressure value is also set at this temperature. In practical applications, batteries are generally charged within a range of 5 °C to 35 °C, and below 5 °C or above 35 °C will greatly reduce the battery capacity and shorten the service life of the battery.

(2) The impact of discharge depth on battery life is also very large. The deeper the battery discharge, the fewer times it is recycled, so deep discharge should be avoided when it is used. Although UPS has a battery low potential protection function, UPS will automatically shut down when a single battery discharges to about 10.5 V. However, if UPS is in the case of light discharge or empty discharge, it will also cause deep discharge of the battery.

(3) Batteries will lose part of their capacity due to self-discharge during storage, transportation, and installation. Therefore, before the battery is installed and put into use, the remaining capacity of the battery should be judged according to the open circuit voltage of the battery, and then the battery should be recharged by different methods. For standby storage batteries, should be recharged once every 3 months. The battery can be judged by measuring the open voltage of the battery. Take a 12V battery as an example. If the open circuit voltage is higher than 12.5 V, it means that the battery storage energy is more than 80. If the open circuit voltage is lower than 12.5 V, it should be recharged immediately. If the open circuit voltage is less than 12V, it means that the battery stores less than 20 <UNK> and the battery is unusable.

(4) Battery charge and discharge currents are generally expressed as C, and the actual value of C is related to the battery capacity. For example, 100AH battery, C = 100A. The optimal charging current of Panasonic lead-acid maintainance-free batteries is about 0.1 C, and the charging current can not be greater than 0.3 C. Too much or too little charging current will affect the battery's service life. The discharge current generally requires between 0.05 C and 3C. UPS can meet this requirement in normal use, but it must also prevent accidents, such as battery short circuits.

(5) Charge voltage. Since the UPS battery is a standby mode of operation, the market is normally in a charging state and will only discharge when the power is out. In order to extend the service life of the battery, UPS chargers are generally controlled by constant voltage limits. After the battery is full, it turns into a floating state, and each flotation voltage is set to 13.6 V. If the charging voltage is too high, the battery will overcharge, and otherwise the battery will not be charged enough. The charging voltage anomaly may be caused by a battery configuration error or a failure of the charger. Therefore, when installing batteries, it is necessary to pay attention to the correctness of the battery specifications and quantities, and batteries of different specifications and batch numbers should not be mixed. Do not use poor charger, and installation should consider the problem of heat dissipation. At present, in order to further improve the battery life, advanced UPS adopts an ABM(Advanced BatteryManagement) three-phase intelligent battery management program, that is, the charging is divided into three stages: initial charging, floating charging, and rest. The first stage is constant current balanced charging. Charge the battery capacity to 90 <UNK>; The second stage is floating charging, charging the battery capacity to 100, and then stopping charging; The third stage is natural discharge. In this stage, the battery uses its own leakage current discharge until the specified lower voltage limit, and then repeats the above three stages. This method changed the previous type of battery that was full of electricity and still kept the battery in a state of 24 H a day, thus extending the battery's life.

(6) Maintenance-free batteries will not produce any gas during normal use due to the use of absorption electrolyte systems, but if the user uses it improperly, causing the battery to overcharge, it will generate gas, and the internal pressure of the battery will increase. Overhead the pressure valve on the battery, which will seriously burst the battery.

(7) During the operation of the UPS, attention is paid to monitoring the end voltage value of the battery, the floating charge current value, the voltage value of each battery, the ground resistance and the insulation state of the battery and the DC bus.

(8) Do not increase or reduce the load of several individual cells in the battery alone, which will result in imbalance in the capacity of the individual cells and uneven charging, and reduce the useful life of the cells.

(9) Batteries should be installed in clean, cool, ventilated and dry places as far as possible, and should be free from the effects of sunlight, heaters or other sources of radiation. Battery should be placed upright, not inclined angle. The terminal connection between each battery should be strong.

(10) Regular maintenance. Batteries should be regularly checked after a certain period of time, such as to observe whether their appearance is abnormal, and to measure whether the voltage of each battery is equal. If there is no power outage for a long time, the battery will remain in charge, which will degrade the battery's activity. Therefore, even if there is no power outage, UPS needs to perform periodic discharge tests to keep the battery active. The discharge test can generally be conducted once every three months by means of UPS carrying-preferably more than 50 %, and then disconnecting the market power so that UPS is in a battery discharge state. The discharge duration is generally several MS to several tens of MS depending on the battery capacity. After discharge, restore the power supply to the market, Keep charging the battery.

4 Conclusion

Understanding and clarifying the main factors that affect the service life of lead-acid batteries and the matters that should be paid attention to during use will greatly help us to correctly use and maintain lead-acid batteries in the UPS system. We hope that we can use and maintain lead-acid batteries correctly in our daily work so that they can be used more rationally.

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