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Why aren't alarms clearing in the BMS (Battery Management System) AP9921X after replacing batteries?


Issue

My Battery Management System alarms aren't clearing after I replaced the batteries attached to it.


Product Line
  • Battery Management System
    • AP9921X


Environment
  • All serial numbers
  • All firmware revisions
  • New batteries installed



Cause

After changing a battery in a string which is monitored by the APC Battery Management System, it is imperative to clear the old baseline measurements.  If you do not clear the baseline, the unit is comparing a new battery (with different internal characteristic set) to an old baseline number which was established for the old batteries. This can lead to alarms that may not be warranted.


Resolution

In BMS firmware 3.X.X, you can reset the baseline by browsing to the System tab on the top of the interface.  On the left side of this screen, there is a Reset option to choose. When this is opened, there is a check box where resetting the Charge Current Deviation Benchmark can be selected (see image below).  Once this is reset, the unit will initiate the process of establishing a new baseline.

To establish the baseline the system will perform the same test on an hourly basis, repeated until the overall string Delta is less than 3%. Once the string delta is less than 3%, the BMS considers that to be a stable reading, and that data is stored as the baseline for comparison.
 



 

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