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A Telecommunication company in Cambodia is having difficulty in testing their sets of batteries which are in parallel connection. These batteries are being used in a data centre application called Energy Storage Module (ESM). The total number of modules they need to test is 10 sets.
Each individual set is composed of 10 cells. They are looking for a test set which can do online battery impedance test, cells in parallel connection and can test a 53 V DC system voltage.
Description
This ESM plays an important role in a Telecommunication system. They supply power to critical systems such as computers, meters, servers and as backup power source during power failure.
The ESM is an energy storage unit composed of lithium batteries. It features better charge and discharge performance, longer service life and less self-discharge loss than ordinary batteries.
The ESM consists of electrochemical cells, an energy storage management unit (ESMU), a fire control module, power and signal terminals, and mechanical parts. It can be used as an independent 48 V unit, supporting the mixed use of old and new batteries as well as lithium and lead-acid batteries, and can collaborate with third-party power systems.
Background: The lithium-ion battery
Lithium-ion (or Li-ion) batteries are a family of batteries that consist of different types of chemistries, each with their own unique characteristics and configurations.
Aging of lithium-based batteries is due to both calendar aging and battery cycling. The overall rate of aging will be a combination of both the battery cycling and the calendar aging.
As lithium-ion batteries age, there will be a reduction of available capacity (fading) and an increase in internal battery impedance. For many Li-ion technologies, the aging will proceed at a relatively linear rate up to a certain point, typically 60 or 70 of rated capacity. At this point the rate of aging will accelerate.
Figure 1 shows one set of ESM to test.
Lithium-ion Battery Maintenance
In stationary applications, the battery is backing up the key asset. In these applications, it is preferable to lose the battery instead of the asset. Therefore, the battery needs to be configured to open only in the case of potential battery failure.
NOTE: This can still lead to an open battery string and a loss of backup. In critical applications that utilise lithium-ion batteries, a parallel string configuration is needed to provide redundancy.
In stationary applications, the batteries are not being discharged and charged on a regular basis. The batteries remain on float for extended periods of time.
In these applications, periodic testing is recommended along with visual inspection.
The battery voltage and impedance should be measured on a periodic basis. Trending test results over time will identify SEI build up.
For some materials, the internal resistance increase that occurs with age can be relatively small, and for others, a doubling or tripling of internal resistance is not unusual. Check with the manufacturer for your particular battery.
The BITE5 can perform the voltage and impedance measurements on all lithium-ion batteries. It will store the results and allow you to trend them over time for each cell. You can also transfer the data to the Power DB PC-based software. This will allow for automated analysis and customised report generation.
To learn more about the Li-Ion battery, please download and read the application from Megger entitled “Lithium-Ion battery maintenance”.
Problem
The telecommunication company needs to check and do a regular maintenance of their ESM. However, they are having some challenges:
How can they check the status of the individual cells within the ESM?
Can they do online test of these batteries as they cannot afford to have unscheduled downtime?
Can any test set measure the impedance of a battery string in parallel connection with 53 V DC system voltage?
Furthermore, the EMS systems was just delivered less than a year ago and they are mindful that they need
to have baseline for impedance measurement of individual cell. The existing tester they have can only handle up to 48 V DC and cannot do parallel string without the current clamp for escape current.
