Monitor the battery to improve the reliability of

Monitor the battery and improve the reliability of UPS

in our work and life, we have relied on electronic equipment in many aspects. From mobile communication to data center, many kinds of equipment must realize the shortest downtime, which makes the reliability of power supply become a key problem. Uninterruptible power supply (UPS) can provide backup power in case of power failure, so it is widely used to ensure the normal operation of key electronic equipment in case of power failure

although other science and Technology (such as flywheel energy storage) can be applied, most UPS still use various batteries to store energy. The battery can provide a considerable amount of energy, which can provide electricity almost in an instant. If UPS needs to operate reliably, the most important thing is that the battery should not only be fully charged, but also in good condition

the service life of the battery is limited. If the environmental conditions (especially the temperature) exceed the optimal range, the service life of the battery will be greatly shortened. The batteries in most equipment will be replaced regularly according to the fixed interval specified in the warranty (usually every 5 years). However, this method also has defects, that is, the battery will run out of power soon when used outside the expected environmental conditions, and the battery with good maintenance will have a longer service life

modern UPS requires higher power output, so many batteries are needed. In large battery packs, the failure of a single battery will lead to the failure of the whole battery pack. Large and medium ups will be redundant to ensure that the failure of the battery pack will not lead to the failure of the entire ups. At the same time, ups will continue to operate, the output peak current will be reduced, and the operation time of the system using UPS will be shortened. Moreover, the failed battery will also affect other battery packs in the battery pack, thereby shortening the service life of these battery packs

battery monitoring and maintenance represent an important cost associated with running ups. Generally speaking, engineers will visit the site regularly (possibly every month) to measure the electrical characteristics of the battery in the device. Engineers usually measure the voltage of the battery to identify whether the battery is out of range. If it is out of range, replace it. The output voltage may not be a good indicator of battery failure, so the battery may fail between two routine inspections, and the engineer needs to conduct additional inspections

on the one hand, monitoring the battery reduces the time for engineers to actually check the status of each battery on site, improves the efficiency of on-site inspection, and therefore reduces the cost; On the other hand, monitoring also realizes preventive maintenance. By identifying possible faults, engineers can replace the faulty battery in the routine inspection process, so as to ensure that the device operates more reliably, and engineers do not need to conduct emergency inspection

lime uses sentinel battery monitoring system to measure the battery in broadcast equipment equipped with 800 KVA ups. Figure 1 shows the output voltage of several batteries in a battery pack. In this example, each battery pack has 200 single cells, which can provide a voltage of about 440 v. The voltage changes greatly, mainly due to the incorrect configuration of battery conditions, which will be discussed later

Figure 1 battery output voltage

the figure clearly shows that a battery outputs 2 V voltage instead of the conventional 2.2 V voltage. Although the voltage produced by a battery is lower than expected, the difference is quite small and stable. This kind of performance is very common, which makes it no longer reliable to use the output voltage as an indicator to predict failure. This is because the voltage value can be maintained within the threshold range, so the alarm will not be triggered

in this example, sentinel battery monitoring system is used to evaluate the effectiveness of the scheduled maintenance plan, not to prompt potential problems. Since no measures have been taken and authorization has been obtained from different companies of Alcoa that decided to use the sensors, figure 2 shows the complete failure of the battery on October 9. Please note that before the battery voltage drops to 0.7 V, the voltage of the faulty battery remains unchanged, and there is no sign of possible failure. After replacing the battery on November 19, the battery voltage returned to normal

Figure 2 battery failure

since the output voltage did not change before the battery failure, the output voltage is not a good indicator of possible failure. Another characteristic parameter of the battery impedance is a better indicator, as shown in Figure 3. The figure illustrates that the impedance rising in June increased by more than 20% in early July. The change trend is easy to detect: the problem can be found three months before the battery failure by measuring the impedance. If the customer uses impedance data, the battery can be replaced during routine preventive maintenance before the battery deteriorates and becomes invalid

Figure 3 battery impedance prediction failure

long term monitoring of the battery provides more useful information to improve the reliability of ups. For example, in Figure 1, we can clearly see a large number of charge/discharge processes (shown by multiple spikes on the voltage trajectory). Although all batteries need to be conditioned, the battery discharges too frequently, 4 to 5 times a month. While some battery conditioning can prolong the service life, too many discharge processes will shorten the service life: a normal configuration will only cycle two to three times a year. Generally, the battery warranty service life is adjusted first, and the scope range is 20 to 50 cycles. In this case, we are considering that the battery may exceed the warranty process in just a few months, and the scheme of replacing the battery every five years may mean that the battery needs to experience several times more discharge process than the designed one

the frequent charging/discharging process at the site is caused by the installer leaving the ups in the trial operation mode, which enables the battery to be continuously recharged for testing. This unexpected common error may greatly shorten the battery life. During the engineer's inspection of the continuous automatic monitoring site, the wrong configuration may not be obvious, but the problems are obvious

another reason for shortened battery life is high temperature. Even if the temperature rises only a little, it will increase the probability of unnecessary chemical reactions in the battery and eventually lead to battery failure. Generally speaking, the battery manufacturer will prompt that the service temperature of the battery is 20 ° C. Figure 4 shows the ambient temperature of the system over time, at which the temperature reaches 22 ° C. The air conditioning system fails to keep the temperature within an acceptable range, which will lead to the shortening of battery life. Moreover, the temperature rise may invalidate the battery manufacturer's warranty

Figure 4 temperature monitoring

we found that long-term monitoring of the battery by using the full Chinese menu operation of sentinel devices produced by lime, for example, has many advantages in addition to reducing costs by making engineers' on-site inspection more effective. In this example, automatic monitoring of battery impedance can identify the battery that is about to fail three months before the battery becomes invalid

continuous monitoring also makes it easy to identify UPS configuration problems: in particular, incorrect charge/discharge frequencies that may greatly shorten battery life. The monitoring also measures the environmental conditions, so as to ensure that the battery life will not be shortened due to the influence of high temperature

Figure 5 LEM sentinel on-site

long-term monitoring of the battery can maximize the service life of the battery, ensure that there is no need to replace the battery pack too early and ensure early detection of the deteriorated battery, so as to replace the battery pack before it runs out of power, and other measures reduce the risk of battery failure and save money. Although key devices such as ups are usually not the first goal of cost savings, it is very important for users to change the device to long-term monitoring, because this can not only reduce costs, but also increase the reliability of the device