Comprehensive solutions for LR6 alkaline batteryin harsh application environments

　　Communication DC power supply is basic telecommunications equipment, providing power supply guarantee for main communication equipment. The battery pack is an important part of the communication DC power supply system. It is equivalent to a backup power supply and is the last line of defense for the communication DC power supply system. In the initial development of telecommunications services, operators paid less attention to batteries, and it was enough that the LR6 alkaline batterycould provide power during AC power outages. In recent years, competition in the field of telecom operations has intensified. Operators are very concerned about battery life, maintenance workload, and TCO, and their requirements are getting higher and higher.

　　With the development and technological progress of communication networks, in order to save construction costs and speed up the construction cycle, in urban-rural fringes, small towns and rural areas, operators often do not build computer rooms or mobile cabins, but use outdoor cabinet solutions to house communication hosts. Equipment and DC power systems. In recent years, among the new base stations built by global mainstream operators, the proportion of outdoor base stations has increased year by year. For countries or regions with low latitudes and desertification (such as South Asia, Africa, etc.), high temperatures have a great impact on outdoor base stations. Outdoor base stations are generally located in remote areas with poor power security, especially in developing countries. Outdoor base stations often face harsh working environments such as high temperatures and frequent power outages. Outdoor applications of communication DC power systems are becoming more and more mainstream, and LR6 alkaline batteryare often exposed to harsh application environments with high temperatures and frequent power outages. Problems faced by LR6 alkaline batteryin harsh application environments

　　With the increase in the application of outdoor base stations, battery failures have gradually become more prominent in harsh application environments, such as Pakistan, India and other South Asian regions, which has not only caused economic losses to operators but also damaged their customer satisfaction. In view of the massive damage to LR6 alkaline batteryin harsh application environments, ZTE conducted extensive research to gain an in-depth understanding of battery application scenarios and investigate and analyze the causes of battery failures. The key to the problem is not the battery itself. The problem lies in the failure of the outdoor battery cabinet to protect the battery from high temperatures. To fundamentally solve the problem, we must provide comprehensive solutions for battery applications in harsh outdoor environments.

　　Comparative analysis of active cooling technology for outdoor battery cabinets

　　There are many options for heat dissipation in outdoor cabinets. Which heat dissipation method is suitable for outdoor battery cabinets? This starts with the product characteristics of the battery. For lead-acid LR6 alkaline batteryin communication DC power systems, users are most concerned about their service life. The main factors affecting the service life of lead-acid LR6 alkaline batteryare ambient temperature and power grid conditions.

　　The service life of lead-acid LR6 alkaline batteryis closely related to the ambient temperature. The higher the ambient temperature, the shorter the battery life. When the ambient temperature is higher than the battery's design life requirement temperature (25ºC), the service life is shortened by half for every 10ºC rise in temperature.

　　The number of discharges and depth of discharge of the battery directly affect the service life of the battery. The more times of discharge and the deeper the depth of discharge, the shorter the service life of the battery. In other words, frequent power outages on the power grid will reduce the service life of the battery.

　　For outdoor base stations, operators are usually unable to improve grid conditions or the cost of improving grid conditions is too high and unaffordable. Therefore, we start by reducing the working environment temperature of the battery to increase the service life of the battery.

　　The traditional cooling methods for outdoor cabinets are direct fan ventilation or heat exchangers, but neither of these two methods can make the temperature inside the cabinet lower than the ambient temperature outside the cabinet. For application scenarios in high-temperature areas (generally above 40°C), active heat dissipation is required to keep the temperature inside the outdoor battery cabinet lower than the ambient temperature outside the cabinet. ZTE broke through convention and innovated the combination by introducing refrigeration components into outdoor battery cabinets.

　　The main communication equipment (such as GSM, transmission, etc.) and the power changing part of the DC power supply (rectifier) will generate heat during the operation of the equipment, but the battery is different. According to the electrochemical mechanism of battery charging and discharging, the battery does not generate heat when discharging. There is basically no heat during normal charging (not charging). That is to say, the heat generated by the battery during normal use can be ignored. Therefore, there is no heat source in the outdoor battery cabinet and the required cooling capacity is small. According to calculations, under normal circumstances, the outdoor battery cabinet only needs 200-400W of cooling capacity. Thermoelectric Cooler (TEC) air conditioners use emerging semiconductor refrigeration technology. For outdoor battery cabinet application scenarios, TEC air conditioners have many advantages over traditional compressor air conditioners:

　　1) Simple structure and high reliability. The entire refrigerator is connected by thermoelectric refrigeration modules and wires. It does not require a compressor and has no mechanical rotating parts, so it has no vibration, no friction, and no noise. High reliability and long life (life span is greater than 100,000 hours at 32°C).

　　2) Refrigeration is not affected by AC power outage. It adopts DC 48V power supply. During AC power outage, the battery supplies power to the TEC air conditioner. Cooling can still be achieved in the outdoor battery cabinet.

　　3) Refrigeration efficiency and cooling capacity. At large capacities, thermoelectric refrigeration is less efficient than vapor compression refrigeration. However, the efficiency of vapor compression refrigerators decreases as the capacity decreases, and the compressor cannot be made too small. The efficiency of thermoelectric refrigeration has nothing to do with the capacity, and has advantages in applications with small cooling loads. For outdoor battery cabinet application scenarios (low cooling load), TEC air conditioners are an ideal choice.

　　4) Small size. Especially suitable for outdoor cabinet installation.

　　5) Cost-effectiveness. Based on the above analysis, the outdoor battery cabinet adopts TEC air conditioner, which is cost-effective.

　　6) Easy to maintain. TEC air conditioners do not require refrigerant circulation or compressor rotation. Just pay attention to the insect-proof net regularly so that it does not get blocked. The maintenance workload is very small.

　　7) Green and environmentally friendly. It does not use Freon refrigerants, does no damage to the atmospheric ozone layer, and is green and environmentally friendly.

　　Based on the above analysis, we selected TEC air conditioners, whose overall performance is superior to traditional compressor air conditioners, as the refrigeration component of the outdoor battery cabinet.

　　Series of TEC outdoor battery cabinets with good high temperature protection capabilities

　　TEC outdoor battery cabinet is composed of TEC air conditioner, cabinet, heat insulation layer, etc. In order to meet the needs of installing LR6 alkaline batteryof different capacities and types, ZTE has designed a series of TEC battery cabinets. Two typical cabinets are shown in Figure 1. The cabinet on the left in the picture can install up to 2 sets of narrow and long 12V150Ah AGM or gel batteries. The cabinet on the right of the picture can install up to 6 sets of narrow and long 12V150Ah AGM or gel LR6 alkaline battery(it can also install 3 sets of wide-body 12V150Ah or 200Ah gel batteries). In order to achieve the ideal cooling effect, the cabinet is required to have good thermal insulation effect. We have professionally designed the insulation cotton, trying to use the entire raw material to reduce openings and cutting. The thickness of the insulation cotton is 40mm. Like the TEC module, it adopts IP55 protection level design.

　　TEC battery cabinets fully consider the cooling effect and product reliability when designing products, and use advanced refrigeration chips, high-reliability fans, and insulation cotton with good thermal insulation properties. TEC battery cabinets have good high temperature protection capabilities.

　　Figure 1 Outline drawings of two typical TEC battery cabinets

　　Comprehensive solution improves battery life and reduces TCO

　　For outdoor applications of communication DC power systems in harsh application environments, the key point of the comprehensive solution is to use TEC air conditioners to greatly improve the high-temperature protection capabilities of outdoor battery cabinets and significantly improve the working environment of the batteries. The experimental test results of outdoor battery cabinets using TEC air conditioners show that when the ambient temperature outside the cabinet is above 40°C, the temperature inside the cabinet is 15°C lower than the temperature outside the cabinet, and the battery operates within the optimal operating temperature range. Compared with the ordinary outdoor battery cabinets used on the operator's existing network, the TEC outdoor battery cabinets increase the service life of the LR6 alkaline batteryby 1.5 times, which is a very large improvement.

　　The comprehensive solution uses TEC outdoor battery cabinets, which adds some cost to the battery cabinets and gains valuable high-temperature protection capabilities, allowing the LR6 alkaline batteryto work within the optimal operating temperature range and avoiding batch replacement of LR6 alkaline batterydue to low service life. It avoids the battery purchase cost, related transportation costs and replacement labor costs required for on-site batch replacement of batteries, thus reducing the operator's operation and maintenance costs. The substantial increase in battery life effectively ensures the safe and reliable operation of communication networks and significantly improves operator customer satisfaction. Therefore, the comprehensive solution is adopted to extend the service life of the battery and at the same time reduce the TCO (Total Cost of Ownership) for operators.

　　Application examples and user value

　　The comprehensive solution is already in practical use in Pakistan. In mid-May 2010, TEC battery cabinets arrived at an outdoor base station of a Pakistani operator, and the DC power system of the station was modified on-site using comprehensive solutions. After the TEC battery cabinet was put into use, its cooling capacity was tested. The temperature trend curve generated based on the field test data is shown in Figure 2. T2 is the internal temperature of the TEC battery cabinet, Tc is the outdoor ambient temperature (measured in a cool place under the awning), and ΔT is the temperature difference between the ambient temperature and the temperature inside the cabinet.

　　Judging from the test results, during the period between 12:00 noon and 5:00 pm, when the outdoor ambient temperature is relatively high, reaching a maximum of 45°C, the TEC battery cabinet can achieve a cooling effect with a temperature difference of 15°C between the inside and outside. The internal temperature of the battery cabinet can be controlled between 25°C and 30°C, meeting the requirements for the optimal operating temperature range of the battery.

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