UPS power supply selection and battery capacity calculation
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Foreword: How to choose UPS power supply in weak current system? There are so many brands on the market, which one should we choose? How to match the battery? Text: 1. Determine the power range first In short, the first thing is to confirm the power of the equipment we want the UPS to carry, and then we can confirm the power of the UPS. Generally speaking, we recommend that the load power accounts for 30%~80% of the UPS power. If the load is too large, it may cause the UPS power supply to be overloaded when starting at the same time. If the load is too small, it will not only cause waste, but also be bad for the performance of the battery. 2. UPS working mode The most common working modes in the market are backup type, online interactive type, and online double conversion (pure online), as follows: (1) Backup type UPS, without voltage stabilization, has conversion time when switching between AC power and battery, generally used for personal computer protection, or used in situations where UPS power performance is not required. The power range of this type of UPS is generally small; (2) Online interactive type, without voltage stabilization, has conversion time when switching between AC power and battery, but has voltage regulation function, generally used in wiring rooms or micro computer rooms, protecting servers and network equipment, etc. The power range of this type of UPS is generally below 5KVA. (3) Online double conversion UPS, has no conversion time when switching between AC power and battery, and has no switching time. It is generally used to protect servers or network equipment and other equipment in the computer room. The power range of this type of UPS ranges from small to large, with a relatively large span of 1KVA~1000KVA, and is currently more common in the market. The performance of the above UPS power supplies is ranked from high to low: online double conversion, online interactive, and backup. The price is generally proportional to the performance. Do we have to choose an expensive UPS? The answer is no. As our title says, we have to choose a UPS that suits us. If it is for a personal computer, then you can choose a backup UPS. If it is for a server, you should choose between online interactive and online double conversion. The selection should be made according to the following conditions: 1. Equipment requirements To see if your equipment requires high-precision power supply, you can check the logo on the nameplate of the load equipment or ask the equipment manufacturer. If high-precision power supply is required, you need to choose an online double conversion UPS. The second is to look at the load type. Some loads are not allowed to have power supply interruptions, such as relay-type equipment or switch signal equipment. If you equip this type of equipment with an online interactive UPS, then it is possible that the load will be powered off or malfunction when the UPS switches between the mains and the battery. Therefore, an online double conversion UPS should be selected for this type of equipment. If your equipment does not have the above two requirements, you can continue with the following steps. 2. Local power grid If the quality of the local power grid is relatively good, that is, the voltage fluctuation is small at ordinary times, then you can consider choosing an online interactive UPS. However, if the quality of the local power grid is poor and the voltage fluctuation is large, then we recommend using an online double-conversion UPS, because this type of UPS has better adaptability to the mains than the online interactive type. 3. Battery life after UPS conversion to battery If you require a longer delay, you can consider choosing a standard dual-purpose machine or buying a UPS without a built-in battery. Both UPS power supplies can be equipped with original batteries or third-party batteries to achieve a longer delay. 4. Installation method Generally speaking, there are two installation methods for UPS power supplies, one is tower installation and the other is rack installation. You can choose according to your computer room environment or on-site environment. It should also be noted that not all UPS power supplies support both installation methods at the same time. In most cases, rack-mounted UPS can also be tower-mounted, but tower-mounted UPS may not be rack-mounted because tower-mounted UPS may not be able to install rails. Therefore, after confirming the UPS power range and working mode, you must confirm whether the UPS power supply can meet your installation requirements. III. Advantages and disadvantages of different types of UPS batteries I: Types of commonly used UPS batteries, factors affecting battery life, advantages and disadvantages of different types of batteries: There are three types of batteries in UPS applications: including open liquid lead-acid batteries, maintenance-free batteries, and nickel-chromium batteries. The batteries currently equipped by UPS manufacturers are generally maintenance-free batteries. The following is an introduction to the characteristics of the three types of batteries based on maintenance-free batteries: 1: Open liquid lead-acid batteries: This type of battery can be divided into two types according to its structure: 8-10 years and 15-20 years of life. Since the electrolysis of sulfuric acid in this battery will produce corrosive gas, this type of battery must be installed in a ventilated room away from precision electronic equipment, and the battery room should be paved with anti-corrosion tiles. Due to evaporation, the open battery needs to measure the specific gravity regularly, add acid and water. This battery can withstand high temperature, high pressure and deep discharge. The battery room should be non-smoking and use an open battery rack. This battery cannot be transported after charging, so it must be charged after installation on site. The initial charging generally takes 55-90 hours. Normally, the voltage of each battery is 2V, and the initial charging voltage is 2.6-2.7V. 2: Maintenance-free battery: also known as valve-regulated sealed lead-acid battery, the following principles should be followed in use and maintenance: a: The allowable operating range of sealed batteries is 15 degrees to 50 degrees, but using within 5 degrees to 35 degrees can extend the battery life. Below minus 15 degrees, the battery chemical composition will change and cannot be charged. Using within the range of 20 degrees to 25 degrees will achieve the highest life. The battery will have a long life but lower capacity when running at low temperatures, and a higher capacity but short life when running at high temperatures. b: The relationship between battery life and temperature can refer to the following rules. After the temperature exceeds 25 degrees Celsius, the battery life will be reduced by half for every 8.3 degrees higher. c: The design floating charge voltage of maintenance-free batteries is 2.3V/cell. The 12V battery is 13.8V. CSB recommends 2.25-2.3V per cell. In the case of 120 batteries in series, after the temperature is higher than 25 degrees Celsius, the floating charge voltage should be adjusted down by 3MV for every degree of temperature increase. Similarly, the voltage should be adjusted up by 3MV for every degree of temperature increase to avoid undercharging. The discharge termination voltage is 1.67V per battery under full load (<30 minutes). Under low discharge rate conditions (low current long-term discharge), it should be increased to 1.7V-1.8V per battery. APCSYMMETRA can adjust the charging voltage according to the load. d: If the battery is not recharged within 72 hours after the discharge is completed, sulfate will adhere to the plate and insulate the charge, thus damaging the battery. e: When the battery is floating or equalizing, the gas generated inside the battery is electrolyzed into water on the negative plate, thereby maintaining the battery capacity without adding water. However, the corrosion of the battery plate will reduce the battery capacity. f: The battery separator life is only 5-6 months when the ambient temperature is 30-40 degrees. Batteries stored for a long time must be charged once every 6 months. The battery must be stored in a dry and cool environment. The self-discharge rate of maintenance-free batteries at 20 degrees is 3-4% per month and changes with temperature. g: Maintenance-free batteries are equipped with safety valves. When the internal gas pressure of the battery rises to a certain level, the safety valve can automatically discharge excess gas. When the internal gas pressure is restored, the safety valve will automatically recover. h: The cycle life (charge and discharge times) of the battery depends on the discharge rate, discharge depth, and the way of restorative charging. The most important factor is the discharge depth. When the discharge rate and time are constant, the shallower the discharge depth, the longer the battery cycle life. The cycle life of maintenance-free batteries at 25 degrees 100% deep discharge is about 200 times. i: When the battery reaches the end of its life, it will show capacity attenuation, internal short circuit, shell deformation, plate corrosion, and open circuit voltage reduction. j: IEEE defines the end of battery life as a capacity less than 80% of the nominal capacity AH. The nominal capacity and actual backup time have a nonlinear relationship. If the capacity decreases by 20%, the backup time will decrease significantly. Some UPS manufacturers define the end of battery life as when the capacity drops to 50-60% of the nominal capacity. 4. How to calculate the number of batteries for a UPS 4.1. Battery calculation method: For example, for a 40KVA UPS,The DC voltage is 384V, and each group consists of 32 12V batteries. If the backup time is required to be 2 hours, the battery capacity is calculated as: 40000VA*2H/(0.7*384V)=297AH. So choose 3 groups of 100AH batteries, a total of 96. The current of the battery group is 40KVA/384V=104A, so choose a 50mm2 cable for the battery connection. Total number of batteries = (power/DC voltage*hour)/Ah per battery*Number of batteries per group. The power is the power of the UPS, the DC voltage is the voltage required by the UPS battery for power supply, and the DC voltage of UPSs with different powers is different. The number of batteries per group is the minimum number of batteries required. Generally, when configuring batteries, it must be an integer multiple of the number of batteries per group. The common UPS DC voltage and number of batteries per group are as follows (each battery is calculated based on 12V): For example, a 5K8-hour delay UPS is configured with a power of 5000, a DC voltage of 96V, 8 batteries per group, and 100AH batteries. The total number of batteries required is: (5000/96*8)/100*8=32 batteries. UPS is the abbreviation of uninterruptible power supply system. Its function is to provide uninterrupted, stable and reliable AC power supply. The reason why UPS can provide uninterrupted power supply when the city power is interrupted (power outage) is the result of battery energy storage. The length of time that can be powered is determined by the capacity of the battery. 4.2. The calculation method of UPS battery configuration is introduced as follows: A. The following factors affect the backup time: 1. The total load power Ptotal (W). Considering the power factor of UPS, the volt-ampere (VA) of Ptotal can be directly used in the calculation. 2. Vlow is the termination voltage of the battery after discharge (V). 2V battery Vlow = 1.7V; 12V battery Vlow = 10.2V 3. Vfloat is the floating charge voltage of the battery (V). 2V battery Vfloat = 2.3V; 12V battery Vfloat = 13.8V 4. Kh is the battery capacity conversion factor (Ct/C10). The discharge rate of 10Hr is 1, the discharge rate of 5Hr is 0.9, the discharge rate of 3Hr is 0.75, and the discharge rate of 1Hr is 0.6 5. I is the battery operating current (A), T is the continuous discharge time (H), and V is the DC power supply voltage of the UPS external battery (V) B. Calculation method 1. The number of 12V single cells N: N = V ÷ 122V The number of single cells is 6N 2. Battery operating current I: I = P total ÷ V 3. Actual battery capacity C: C = I × T ÷ Kh For example: The power backup time of 1KVA is 4 hours. The model of the UPS selected is HP9101H, V = 36V, then ① N = 36V ÷ 12V = 3 cells ② I = 1000VA ÷ 36V = 28A ③ C = 24A × 4H ÷ 0.9 = 124AH ④ The battery allocation can be selected as 100AH in a group of 3 cells, or 65AH in two groups of 6 cells. The selection result is biased, which depends on the user's needs and cost considerations. Note: The common capacity specifications of 12V batteries are 7Ah, 17Ah, 24Ah, 38Ah, 65Ah, 100Ah, 200Ah, etc. ![]() [Disclaimer] The content of this article comes from the Internet, and the copyright belongs to the original author. cn/mmbiz/wyice8kFQhf5geQK3gu2FUugjB8iaSGpjO38zXqdgwMx0oC9BCs08koDu1N0thHuib7TjD5SdkYZalvkm0cAClI9Q/6 40?wx_fmt=gif&tp=webp&wxfrom=5&wx_lazy=1[/img][Disclaimer] The content of the article comes from the Internet, and the copyright belongs to the original author. cn/mmbiz/wyice8kFQhf5geQK3gu2FUugjB8iaSGpjO38zXqdgwMx0oC9BCs08koDu1N0thHuib7TjD5SdkYZalvkm0cAClI9Q/6 40?wx_fmt=gif&tp=webp&wxfrom=5&wx_lazy=1[/img][Disclaimer] The content of the article comes from the Internet, and the copyright belongs to the original author.
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