Four major reasons affecting the battery life of base stations

From the perspective of the quality of batteries produced by several large domestic valve-controlled sealed battery manufacturers, they can basically meet the requirements of various operators, but there are differences in the quality and performance of batteries produced by various manufacturers. From the survey and use, the quality of batteries produced by some manufacturers has certain problems due to high costs and too low bidding prices. However, when the battery quality is not a problem, the capacity of some base station batteries still decreases too quickly and the service life is greatly shortened. From the comprehensive factors such as the product structure, product performance, and on-site survey of the use of base station batteries, combined with the use of exchange stations, the capacity of valve-controlled sealed batteries should not decrease so quickly after 1 to 4 years of use under normal circumstances. Therefore, the main reason for the rapid decrease in the capacity of base station batteries and the shortened service life should be related to the battery usage characteristics of the base station itself and the base station usage environment. From the survey, when there is no problem with the battery quality, the main reasons for the rapid decrease in the capacity of base station batteries and the shortened service life are as follows.

First, frequent power outages at base stations, long power outages, and irregular power outages cause the batteries to charge and discharge frequently, which is one of the main reasons for the rapid decrease in battery capacity and shortened service life.

According to the dissection of scrapped batteries in base stations, the reason for the end of battery life is the sulfation of the negative plate of the battery, which is a typical phenomenon of early capacity failure (PCL) of the battery. The author believes that the reasons for the sulfation of the negative plate of the battery may be the following two aspects:

(1) The frequency of power outages at the base station is too high. There are power outages several times a day, or even for several consecutive days. This causes the base station battery to discharge again before it is fully charged after discharge, resulting in undercharge of the battery. If undercharge occurs repeatedly, it will cause cumulative loss of battery capacity, and the battery capacity of the base station will decrease in a short period of time, and its service life will end quickly. The rate of battery capacity decrease is proportional to the number of consecutive undercharges of the base station battery. The internal reason for the decrease in battery capacity is that the battery is discharged again before it is fully charged after discharge, and the lead sulfate generated by the positive and negative electrodes after discharge cannot be completely restored to lead dioxide and metallic lead respectively. The positive and negative plates are discharged again, causing the battery to be undercharged. Continuous undercharges cause the negative plates to gradually sulfate, producing irreversible crystalline lead sulfate. Especially when the battery is in a deep over-discharge, the sulfation of the negative plates of the battery will be more serious and the sulfation rate will be faster, causing the surface of the negative plates to be shielded, and its function will gradually decrease until it fails, resulting in a decrease in the battery service life until it ends. Based on the actual use of batteries in existing base stations, it is possible that the batteries are undercharged cumulatively. In addition, although the batteries have been undercharged multiple times, the secondary undercharges or multiple undercharges do not occur regularly and continuously. The possibility and probability of the battery being undercharged cumulatively need to be further determined.

(2) Another point of view is that the main reason for the decrease in base station battery capacity and shortened service life is the sulfation of the battery negative plate. In addition to the cumulative undercharging of the battery will lead to the sulfation of the negative plate, the increase in the number of battery charge and discharge cycles or the excessively frequent charge and discharge cycles within a certain period of time will also lead to the sulfation of the negative plate, or it may be an important factor leading to the sulfation of the negative plate.

Of course, there are many other reasons for the sulfation of the negative plate of the battery, such as excessive impurities in the electrolyte or glass fiber wool, which accelerates the self-discharge rate of the battery. The floating charge or equalization voltage is too low, so that some lead sulfate crystals cannot be dissolved. Frequent excessive discharge or frequent low-current deep discharge reduces the initial charging efficiency of the battery. The working environment temperature of the battery is too high, and the impurity ions are more active, which accelerates the self-discharge of the battery.

According to the current scale, production process and technical level of battery manufacturers, the main reason for the sulfation of the negative plates of base station batteries is not the product quality. Under normal use of the battery, the sulfation time of the negative plates of the battery is relatively long, which makes it difficult to restore the battery capacity. In addition, from the analysis of usage, different manufacturers, whether imported or domestic batteries, have this problem. Therefore, the main reason for the sulfation of the negative plates of base station batteries is the frequent power outages in the base station, frequent over-discharge and deep over-discharge with small current, which causes the battery to be undercharged. The continuous occurrence of under-charging results in the cumulative under-charging of the battery, and the excessively frequent charge and discharge cycles of the base station, which causes the irreversible sulfation of the negative plates. The sulfation of the negative plates is currently the main reason for the decrease in capacity and shortened service life of base station batteries.

Second, the parameters of the switching power supply are unreasonable. The base station battery undervoltage protection setting voltage is too low, and the reset voltage is too low, causing the battery to over-discharge or even deep over-discharge. On the other hand, it aggravates the sulfation of the battery negative plate, which is another major reason for the reduction of battery capacity and shortened service life.

At present, the combined switching power supply of base stations is equipped with low voltage isolation protection function or secondary power-off function. When the battery is discharged to a certain set voltage value, the switching power supply system will automatically cut off the power supply to some heavy loads or all loads to protect the battery from over-discharge and ensure the service life of the battery. If the minimum undervoltage protection value of the battery is set too low, the battery will be over-discharged. Multiple over-discharges and failure to replenish power in time after over-discharge or insufficient charging will seriously affect the battery life; in addition, if the reset voltage of the switching power supply is set too low, the battery will be repeatedly discharged during the discharge process; the specific minimum undervoltage protection value of the battery should be set according to the load current size, and the current minimum undervoltage protection value of the base station battery is generally set at about 1.8V per single cell voltage, and some are even set to 1.75V per cell. According to the discharge performance of the valve-controlled sealed battery combined with the actual load current of the base station (currently most of the actual load current of the base station is less than 0.1C10A), the minimum undervoltage protection value of the base station battery should be set at about 1.8V per battery cell voltage. Therefore, the reference voltage of the current base station battery undervoltage protection setting is too low. If the base station is out of power for a long time, the battery will be over-discharged, or even deeply over-discharged with a small current. It takes a long time to fully charge the over-discharged battery and restore its capacity. It is generally difficult for a deeply over-discharged battery to fully restore its rated capacity under the only constant voltage charging condition currently available in the base station. Therefore, the unreasonable setting of the switching power supply parameters will aggravate the sulfation of the battery negative plate, thereby causing the battery capacity to decrease and the service life to be shortened.

Third, the base station environment is bad. After the base station is powered off, the base station environment temperature gradually rises due to the lack of air conditioning. Or due to air conditioning failure, the indoor temperature of the base station is too high, which reduces the battery life.

All indoor base stations are equipped with air conditioners, which are general cabinet or split air conditioners. Long-term uninterrupted use causes some base station air conditioners to malfunction and shut down. The air conditioners are sometimes not repaired in time after being damaged. The indoor base station is a closed machine room. After the air conditioner is shut down, the indoor temperature of the base station rises sharply. The indoor temperature of the color steel plate machine room can even reach above 70℃. On the other hand, even if the air conditioner is normal, the base station has no AC power after the power outage, and the air conditioner cannot be cooled. Especially in summer, the indoor temperature of the base station will rise sharply, thus affecting the normal operation of the battery. On the one hand, the high indoor temperature will increase the water loss inside the valve-controlled sealed battery, reduce the electrolyte saturation (reduced electrolyte in the glass fiber cotton diaphragm), reduce the battery capacity and shorten the battery life. On the other hand, due to the high indoor temperature, the thermal runaway effect of the battery will be aggravated, resulting in the corrosion rate of the positive plate of the battery, deformation and expansion of the plate, bulging and even cracking of the battery shell, etc., which will eventually lead to a rapid decrease in battery capacity and shortened battery life. According to relevant data, when the ambient temperature exceeds 25℃, the battery life will be shortened by 1/2 for every 10℃ increase.

Fourth, after the base station loses power, the battery is discharged to the termination voltage. If it is not recharged in time, the battery capacity will decrease and the service life will be shortened.

Since some base stations are located in suburbs or remote mountain villages, the city power supply is poor, the city power outages occur frequently and for long periods of time. Once the city power outage occurs, the battery is discharged to the termination voltage and the city power has not yet been restored. This may cause over-discharge of the battery on the one hand, and the battery cannot be replenished in time after discharge on the other hand. According to relevant information, if the battery cannot be replenished in time after discharge, the battery capacity will gradually decrease. After several cycles, the battery life will be significantly shortened.

The above four reasons are the main reasons for the early failure of the current base station battery capacity and shortened service life. Of course, there are many factors that affect the battery capacity and service life. Under normal use, the main factors affecting the battery life are the corrosion rate of the positive plate and the saturation of the electrolyte in the glass fiber diaphragm (AGM). However, due to the special environment of the base station itself (mains power supply, ambient temperature, etc.), the main reason that really affects the battery life is the sulfation of the negative plate. The main reason for the sulfation of the negative plate is that the base station frequently has power outages, resulting in the cumulative undercharging of the battery and increasing the number of battery cycles; in addition, the improper setting of the battery undervoltage protection value, the excessively high indoor temperature of the base station, and the failure to replenish the battery in time after discharge further aggravate the sulfation of the negative plate. This can also explain from another side why the battery life of urban base stations or base stations with good power supply conditions is longer than that of other types of base stations, and the service life of early batteries is longer than that of recent batteries.