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BMS AP9921X-AP9922; alarms "Battery Thermal Runaway"

Issue:

Product line:

Battery Management System (BMS) AP9921X & AP9922

Environment:

All models, all serial numbers

Cause:

The response current is higher than the configured value. Default: 20% higher than the benchmark, or greater than 95°F. A thermal runaway occurs when oxygen and hydrogen fail to recombine at the positive plates in the cells of a VRLA battery. Without recombination, the battery cannot maintain the electrolyte level and the cell voltage decreases, causing the charge current to increase.

This alarm indicates that there is potential for a thermal runaway. It does not indicate that a thermal runaway is occurring. Inspect the battery. Closely monitor the battery to ensure that thermal runaway does not occur. If random batteries occasionally generate Battery Thermal Runaway alarms, the Charge Current Deviation from Benchmark setting (default 30%) may be too close to the normal deviation range of the battery string. To reconfigure this value, see Charge Current Deviation from Benchmark.

If a specific battery causes repeated alarms (especially if the alarms have increasing deviation percentages), the battery is failing. Replace the battery.

Note: Any time a battery is replaced FSE must reset the battery base-line or benchmark. System>Reset> Reset Charge Current Deviation Benchmark; check this off and apply when replacing batteries.

Note: a setting tighter than default 30% could cause false alarms.

Resolution:

Test the battery, replace battery.
If battery has been replaced and above procedure not done you could get false positives for battery thermal runaway. If the battery meters ok with cell recorder then have FSE reset its Charge Current Deviation Benchmark in the BMS GUI/ web interface. You can also check the setting or adjust it to a higher value maybe 35-40% sees is false alarms clear. Charge Current Deviation from Benchmark alarm threshold setting can be found in the Web GUI under the System>Configuration>Alarms tab.