Why is the Battery Management System AP9921X-AP9922 reading negative ohmic values?

Issue
My AP9921X-AP9922 is displaying negative ohmic values.

Product Line

Environment

• All serial numbers
• All firmware versions

Cause
The battery management system will not display a valid ohmic value until it has seen a discharge event long enough to scan the entire battery string.


Resolution
It takes a discharge of five seconds at a minimum of 10amps to trigger the discharge test.  Once that is triggered, the system begins scanning at four monitoring points per second until:

1. a positive current flow indicates that the discharge has ended, or
   
2. the user defined low voltage is reached. At that point, the BMS goes to a "hibernate" mode, simply checking for a positive current flow on a regular timed cycle, and shuts everything else off. When a positive current flow is detected, the system wakes up and begins monitoring again.

Publié pour:APC Switzerland (French)