AP9921X Battery Monitoring System

[BillP]

I have recently installed an AP9921X Battery Monitoring unit in an existing system. I am able to get the battery voltage readings, but I am getting "Ohmic Data Not Available" when trying to look that data up. When programming this unit is there a line or box I may have missed to allow the unit to take the ohmic readings?

I appreciate all the help.

[B-DoubleE_apc]

Hi James,

Ohmic values are only generated when the BMS considers all batteries on a particular string fully charged, and has been placed under a discharge with at least a 50 amp load

[BillP]

Just checking for understanding, I will not be able to see ohmic values until there has been a discharge of least a 50 amp load? Is there only time the ohmic values available after a discharge? Maybe I should change ohmic with resistance readings. As this system is right now my network personnel can see the voltages, but not the resistance of the batteries in this system. I am sure I probably missed something while programming in the battery string information on this BMS.

Thank you.

[B-DoubleE_apc]

Technically it requires a discharge of "20% of battery percentage after battery voltages were polled" - the complete list of what the BMS requires to generate ohmic values can be found here: https://www.apc.com/us/en/faqs/FA156171/

[BillP]

This is information useful. Is this the same situation when batteries are replaced? Will, they need to be discharged after the batteries are fully charged to be able to see the resistance values of the new batteries? 

[B-DoubleE_apc]

That's correct - the ohmic values are timestamped with the date of the discharge event. If the batteries are replaced, a new discharge event would need to occur before new values are shown.

[BillP]

I will need to pass this information on. How does the BMS update the resistance values we are able to see as the batteries age? I would not think it would have to wait until another discharge. I would believe the BMS is set up to do a "battery check" at a predetermined time frame and will give the updated resistance so that a battery can be replaced before it goes bad and if a discharge is needed not having battery availability.

I do appreciate the time you are giving me as I know how busy we all are.

[B-DoubleE_apc]

When the BMS senses a battery string is good, it runs a "benchmark" test (the nature of the test is considered proprietary) to get most values. Every 6.5-7 hours the benchmark test is repeated

[BillP · Accepted solution]

I understand the proprietary aspect of the system. The discharge and the full charge of the batteries after is the signal to the BMS that the battery string is good?