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How to Fix Premature UPS Shutdowns.  

Takeaway:  

How to calibrate UPS units.  How to achieve the best runtime.  How to prevent early shutdowns.   Smart-UPS units use Battery Constant to calculate runtime.  Inaccurate battery constant leads to inaccurate runtime calculations (i.e., drifting).

Problem:  

UPS reports inaccurate battery runtimes.  Poorly calculated runtime cause premature shutdowns during power outages.  Misconfigured external battery counts or old firmware can also trigger early shutdowns.

Drifting:

Batteries become less efficient as they age.  The UPS changes its battery constant value to reflect these inefficiencies over time.  The UPS unit is supposed to reset its battery constant after installing new batteries.

Unwelcome drifting occurs if the UPS does not detect new batteries nor reset its battery constant value.  As such, it miscalculates available runtime that leads to premature shutdowns.  According to APC, drifting may occur when factory batteries are replaced with generic brands.  Drifting may also occur during a hot-swap replacement.  Self-tests may also introduce drifting.

Soft Runtime Calibration: 

Initiate a runtime calibration from the management card.  This process recalculates runtime capacity based on its current load.  Run "Soft" Runtime Calibration from the network management card (NMC).

Calibration Tips:  

  • Do not run calibration on new UPS units. 
  • Re-calibrate after replacing old batteries with generic batteries. 
  • Schedule an annual calibration.  
  • Discharge and recharge old batteries -before calibration.   
  • Calibrate with a 40% load. 
  • Completely discharge and completely recharge UPS.
  • Change/ reset the number of external batteries from the management card.

Manually configure the battery constant if the soft runtime calibration fails.

Hard-set the Battery Constant:

Change the battery constant value from the serial console -otherwise known as the nuclear option!  Use caution because incorrect commands can brick the UPS.
  1.  Shut down UPS.
  2.  Remove NMC.
  3.  Use an APC serial cable to console to the UPS:
         2400 baud,
         8-N-1,
         Xon/Xoff,
         uncheck FIFO.
  4.  Enter Smart mode:  Shift+Y (i.e., CAP "Y").
       Prompt changes to SM#.
  5.  Enter Program mode: Y, 1, 1
      N.B., each comma represents a pause. 
  6.  Enter "0" to display the battery constant.  The battery constant value (e.g., B2) is located under column 0 and is in HEX format:

    UPS Model  4   5   6   0   Hex   Firmware
    750XL          EE  F8  B2
  7.  Change the battery constant value to FF.
         Use "+" or "-" keys to change the value.  
  8. Type "R" to save and exit.
  The FF value is the highest possible battery constant value.  It is entirely inaccurate -don't panic.  Our goal is to maximize runtime and eliminate premature shutdowns.  The UPS will still initiate a shutdown when battery voltage is less than 10.5V per battery.

Use manual calibration method after the battery constant is rest.

Manual/ Hard Calibration

   Hard calibration provides the most accurate runtime estimates.  This method generally corrects inaccurate soft calibration estimates:
  1. Move production servers to an alternate power source.
  2. This test requires at least 30% load.  Attach old servers, workstations, etc to simulate production load.
  3. Ensure batteries hold a full charge.  
  4. Pull the plug so that the UPS operates on battery power.  
  5. Allow the UPS to operate until it shuts down.
  6. Plug the UPS back in and allow it to recharge.
The UPS now provides an accurate runtime estimate.  It is ready to protect production equipment.

That's It!

About Steven M. Jordan

Steven Jordan is an infrastructure and process management specialist. Steven holds a Master of Science degree in ICT from the University of Wisconsin Stout. Steven is also a Cisco Certified Network Professional (CCNP) and Master Gardener.
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