UPS is called an uninterruptible power supply because it can quickly transition to the "inverte

UPS is called an uninterruptible power supply because it can quickly transition to the "inverter" state during a power outage

So as not to cause the computer in use to lose important files due to sudden power outages and access to storage in the future; The UPS power supply system plays an important role in ensuring power supply in various industry data centers. To provide uninterrupted power supply for loads, it is necessary to have the function of energy storage,



Most of the UPS uses valve regulated maintenance free Lead–acid battery (referred to as VRLA battery in English), which can be roughly divided into three categories according to capacity, namely large, neutral and small. Monomers of 200Ah and above are considered large, 20-200Ah are considered medium, and those below 20Ah are considered small. Most of the UPS power supply is designed with medium-sized Lead–acid battery, while the power system is generally designed with large Lead–acid battery



As an important component of the UPS system, the quality of the battery directly affects the performance of the UPS; Even if the same production technology is used, the battery life of different manufacturers is not the same. Once the battery fails, it not only reduces the reliability of the system but also increases the cost of replacing the battery. Many UPS failures are caused by batteries, so it is necessary to strengthen the understanding of battery characteristics, correctly select and use batteries, and carry out daily maintenance to extend the service life of batteries as much as possible.



Selection of UPS battery



For ordinary users, technical performance, Service guarantee and product price must be considered when purchasing UPS. The three factors need to be comprehensively balanced and balanced. In the UPS power supply system, it can be said that the battery is the pillar of the system. A UPS without a battery can only be called a stable voltage and frequency power supply. The reason why UPS can achieve uninterrupted power supply is because of the presence of a battery. When designing UPS, first of all, consider which type of battery to choose, namely, the rated voltage, Nameplate capacity of the battery and how many batteries should be combined.



1. Selection of Nameplate capacity of storage battery



Due to the fact that the actual usable capacity of a battery is closely related to factors such as discharge current, system voltage, discharge time, working environment temperature of the battery, storage time of the battery, load type and characteristics. The capacity of the battery generally refers to the Power number (W) output by the battery when it is discharged to 1.75V/cell at 20h discharge rate at 20 ° C.



The selection of UPS batteries can be calculated based on the known UPS power size and backup time, such as:



One UPS300KVA with a delay of 30 minutes;



The maximum discharge current of the battery is 846A=nominal power 300000VA × 0.8 ÷ (0.9 efficiency * 30 cells * 10.5V discharge voltage per cell);



The nominal capacity of the battery pack=846 ÷ 0.92C=919AH;



Total capacity of battery pack=919AH × 30 sections × 12V=330840AH;



Requires 6 battery cabinets with 150 AH30 batteries and 6 battery packs.



2. Selection of battery indicators



Internal resistance: A battery with low internal resistance should be selected in order to continuously discharge high current. If the internal resistance is large, the power consumption increases during the charging and discharging process, causing the battery to overheat.



Float charging voltage: At the same temperature, a high float charging voltage value means a large amount of energy storage, while batteries with poor quality generally have a smaller float charging voltage value. The float charging voltage value of the battery should be corrected at different temperatures.



Use 2V single series batteries in large and medium-sized (several kVA to several thousand kVA) UPS to avoid using small capacity combination batteries for hybrid connection.



II. Installation, Use, and Maintenance of Storage Batteries



1. Operating environment and installation of batteries



As a backup battery, the battery is usually in a floating charge state, and at this time, there is still complex energy conversion inside the battery. The electrical energy used in the float charging process is basically converted into thermal energy. Therefore, it is required that the environment where the battery is located should have good ventilation and heat dissipation capacity or have air conditioning equipment.



Install the battery in a clean, cool, ventilated, and dry place as much as possible, and avoid the influence of sunlight, heating, or radiation heat sources to ensure a good working and storage environment for the battery.



Batteries should generally be charged within the range of 5 ℃ to 35 ℃. Any temperature below 5 ℃ or above 35 ℃ will reduce their lifespan. The set voltage for charging should be within the specified range. If it exceeds the specified range, it will cause damage, reduced capacity, and shortened lifespan of the battery.



(1) Initial charging: The first charging of a battery after installation or major repair is called initial charging. Whether the initial charging is good or not will seriously affect the lifespan of the battery.



(2) Float charging: In order to ensure uninterrupted DC power supply and extend the service life of the battery, a float charging power supply method is usually used in parallel with the charging power supply and battery pack.



(3) Balanced charging: A battery pack that is in normal operation and usually does not require balanced charging. But if it is found that the voltage between individual batteries in the battery pack is unbalanced, the battery pack should be charged evenly.



(4) Supplementary charging: During storage, transportation, and installation, batteries may lose some capacity due to self discharge. Therefore, before being put into use after installation, the remaining capacity of the battery should be determined based on its open circuit voltage, and different methods should be used to supplement and charge the battery. For standby storage batteries, supplementary charging should be carried out every 3 months.



2. Daily use and maintenance of batteries



With the continuous development of domestic technology and the continuous maturity of production technology, the performance of UPS is getting better, the average time between failures is getting longer, and the reliability of the entire machine is getting higher. It is particularly important to do a good job in the use and maintenance of batteries in UPS.



(1) Charging of new batteries



After the installation of a new battery, it is generally necessary to charge it for a longer period of time according to the instructions in the manual. After the battery pack is fully charged, it is discharged and then recharged to extend the battery's service life, improve the battery's activity and charging and discharging characteristics.



(2) Regular charging and discharging



If the UPS battery is not used for a long time or the battery is in a floating charge state for a long time without discharge, a large amount of Lead(II) sulfate in the battery will be adsorbed on the cathode surface of the battery, resulting in an increase in internal resistance and a decrease in activity, which will greatly shorten the service life of the battery. For units with good mains power supply, it is necessary to conduct a "therapeutic" charging and discharging process every three months, that is, to discharge and recharge the battery on load, and record relevant data. Compare and analyze the battery performance with previous discharge records, and maintain and inspect the overall battery pack. Only in the event of a mains power outage can load safety be effectively protected.



(3) Deep discharge is strictly prohibited



The service life of a battery is closely related to its discharge depth. Deep discharge can cause sulfation on the surface of the internal electrode plate of the battery, leading to an increase in internal resistance. In severe cases, it can cause individual batteries to experience "reverse polarization" and permanent damage to the battery. The depth of battery discharge seriously affects the service life of the battery. It is necessary not to leave the battery in a deep discharge state.



(4) Regularly measure the float charging voltage and internal resistance of the battery



With the extension of UPS usage time, the charging and discharging characteristics of some batteries will gradually deteriorate, with an increase in internal resistance and a significant decrease in terminal voltage. It is necessary to detect and replace them in a timely manner, otherwise it will affect the use of the entire set of batteries. The performance of this type of battery cannot be solved by relying on the charging circuit inside the UPS. Continuing to use it may pose hidden dangers, and maintenance personnel need to regularly measure and check the voltage and internal resistance of each individual battery. If any batteries exceed the range, they should be confirmed and replaced in a timely manner.



(5) Other precautions



① The battery pack should be charged promptly after each discharge;



② Do not charge the battery pack with overcurrent or overvoltage;



③ Batteries should be avoided from being left unused for a long time, and should not be floating charged without discharge for a long time.