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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:
- a positive current flow indicates that the discharge has ended, or
- 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.