1. The necessity of battery monitoring
With the rapid development of my country’s communications, electric power, UPS and other industries, the consumption of batteries is also increasing rapidly. As far as our battery usage conditions are concerned, some unexpected situations often occur, such as a seemingly normal battery that cannot be discharged when it is discharged. The main reason for this situation is that the operating state of the battery has not been effectively monitored. Once a battery fails in a battery pack composed of multiple batteries connected in series, the entire battery pack cannot be discharged normally.
As the last guarantee for safe uninterrupted power supply, the battery is also the most unsafe factor in the uninterruptible power supply system. From system theory, we know that the degree of security of a system depends ON the most insecure factor in the system, which is the “cask theory” that we often refer to.
Second, the status quo of battery monitoring
1.planned maintenance
The current most common practice in terms of battery maintenance is to perform a check discharge test on the battery pack at least once a year. Because if the battery pack is not charged/discharged once for 3-4 years, the electrolyte of the battery pack will be delaminated, that is, the electrolyte will be decomposed into liquid layers with different concentrations of acid solutions, which will affect the battery during power failure. power supply capacity.This phenomenon can eventually lead to
The plate is corroded.
However, with this planned maintenance, the status of the battery cannot be continuously monitored due to the long interval between the two maintenances; at the same time, the user does not dare to say whether the battery pack will continue to operate normally the day after the discharge test. ; Plus, discharge testing can often take hours or even days, a costly, destructive, and unsafe process for the battery (including recharging).
2.Monitor the battery by monitoring the battery voltage
For the operation mechanism and failure mode of the battery, relevant standards have been issued in China, and the necessary devices for battery monitoring, such as Voltage inspection instruments, are installed in the DC power supply occasion. However, according to the working conditions of the backup battery, it may not be discharged for a long time, and it may also fail during the two regular check discharge tests, and the terminal voltage of the battery is completely normal. As shown below (excerpted from IEEE):
It can be seen from this that only detecting the voltage is not enough, and it is easy to mislead the user to use a bad battery as a good battery, which is quite harmful.
So is there a better way to monitor the status of the battery more effectively, and to give an early warning signal when the performance of the battery drops to a certain level, so that we can replace the battery or maintain it before the battery fails, so as to avoid catastrophic What about a power outage? The answer is yes. By measuring the state of the internal resistance of the battery, the deterioration degree of the battery can be effectively predicted, that is, the SOH (Status Of Health) of the battery can be accurately monitored. As shown below:
The yellow trend line shows that the internal resistance of the battery rises sharply from October to November due to various reasons, so it can be judged that the state of the battery has seriously deteriorated, and it is confirmed that the battery has indeed failed after the battery is discharged.
3. Introduction of LEM battery monitoring module
From the above analysis, we can summarize several necessary conditions for monitoring the battery:
1) Continuous monitoring is required
2) Need to monitor a single battery
3) Need to monitor the internal resistance of the battery
LEM has developed Sentinel, the world’s smallest intelligent battery sensor with highly integrated functions, aiming at the operation mechanism and failure mode of the battery. It operates, enabling continuous monitoring of the battery. As shown in the figure:
The general parameters of the device are as follows:
1. Measuring voltage 1.5V-15V, accuracy +/- 0.5%
2. Temperature error, +/- 2℃
3. Measurement repeatability of internal resistance +/- 2%
4. All connectors are used, and the installation is extremely fast
5. <3mA in power saving mode
6. 5 years quality assurance
Compared with similar battery monitoring products in the market, there are mainly the following four advantages:
1) Distributed installation, one-to-one correspondence between modules and batteries, simple on-site wiring and low engineering costs
2) The independent modules make monitoring very flexible, and compared with centralized monitoring products, the advantages are more prominent in places where the number of batteries is small.
3) The module adopts the pulse current discharge method to measure the internal resistance (see the figure below), and the discharge current is small (the discharge current of the 12v battery is less than 2A), which is not only safe but also not easy to cause damage to the battery.
4) The measurement algorithm developed by the Swiss headquarters and RWTH Aachen University has been researched for many years. The measured resistance value is reliable (see the figure below), the anti-interference ability is strong, and the warranty period is 5 years.
Note: The Swiss LEM headquarters has conducted a long-term test at the AACHEN University of Technology in Germany. The internal resistance measured by the LEM module in the figure is basically the same as the resistance measured by the laboratory equipment EISmeter analyzer.
4. Introduction of LEM battery monitoring system
LEM’s battery monitoring solution is a complete solution that includes a range of components for quick and easy installation, including the following components:
• Sentinel: It can measure the voltage, temperature and internal resistance of a single VRLA battery or flooded battery, and transmit it to the data logger S-BOX through the dedicated bus S-BUS.
• Current sensor: The current sensor detects the state of the battery pack (charging, discharging or floating state).
•S-BUS converter: This module converts the S-BUS protocol into a standard serial output protocol.
• S-BOX: A data logging device with an Ethernet interface to record trends and alarms for each Sentinel.
• Cellview Net: Visualization software used in conjunction with S-BOX to graphically Display various data, alarm and generate various reports.
As shown below:
Of course, OEM manufacturers can also only use Sentinel modules provided by LEM, and cooperate with their own systems to form battery monitoring systems with their own characteristics. These manufacturers can be either UPS manufacturers or integrators specializing in the development of battery monitoring systems.
The sentinel module of LEM has been well applied in China, especially in the power industry, as shown in the figure below:
In a word, this set of solutions is very suitable for the current monitoring of communication, power and UPS backup batteries; I believe that LEM’s battery monitoring products will definitely make due contributions to my country’s safe electricity system.