Issue:
Battery Management System; high battery voltages on 40 Jar battery applications
 
 
Product line:
AP9921X-AP9922 Battery Management System installed on a 40 Jar battery applications
 

Environment:
All models, all serial numbers
 

Cause:
In applications where you have AP9921X-AP9922 Battery Management System (BMS) installed on a 40 Jar battery solution; such as we see on MGE UPS battery systems, it’s possible to see high voltages on one or more B side batteries. The voltages will typically be found higher than 13.5vdc and the BMS unit may be in alarm, Battery High User Defined Voltage, Battery High Chemistry Voltage alarm may exist.
 
Connector 35 is the negative side of the battery string voltage to the BMS power supply.
 

Resolution:
First check the BMS “A” side harness wiring for incorrectly terminated #35 wire to battery 32 negative post instead of the last battery 40 negative terminal. This miss wire may result in some batteries with high voltages on the “B” side connector. If this is a 40 jar battery string, please be sure that you have BMS “A” side #35 wire terminated at Battery jar 40 negative terminal.
 
Please find wiring example below for 40 Jar battery string:
 
Connector A - Wire 1 = Positive Terminal Battery 1
Connector A - Wire 34 = Positive Terminal Battery 1
Connector A - Wire 2 = Positive Terminal Battery 2
Connector A - Wire 3 = Positive Terminal Battery 3
...continues…
Connector A - Wire 32 = Positive Terminal Battery 32
Connector A - Wire 33 = Negative Terminal Battery 32
 
Connector B - Wire 1 = Positive Terminal Battery 33
Connector B - Wire 2 = Positive Terminal Battery 34
Connector B - Wire 3 = Positive Terminal Battery 35
...continues…
Connector B - Wire 8 = Positive Terminal Battery 40
Connector B - Wire 9 = Negative Terminal Battery 40
Connector A - Wire 35 = Negative Terminal Battery 40
 
If the BMS harness is not miss wired then proceed with testing of the battery (s) and wiring, replace any battery that doesn’t pass the cell recorder test. If a specific battery causes repeated alarms (especially if the voltage continues to increase), the battery is failing.