How can I perform a runtime calibration when the load on the UPS is only 21%?

[BillP]

This question was originally posted by Michael on APC forums on 4/23/2014

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I just replaced the battery pack in a rack mount Smart-UPS 3000.

The batteries have charged up to 100% but the runtime only shows 6 minutes.

It's been recommended that I perform a calibration but the guidelines indicate that the load should be at least 30%.

The load on the UPS is at 21%. Can I run the calibration anyway?

[Battman_apc]

This was originally posted on APC forums on 4/24/2014

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HI, while APC recommends at least 25 % load, I would not be concerned about being low by 5%. This is especially true given your runtime is reporting as way too low; which means the UPS's internal "battery constant" ( a hexadecimal variable that the UPS's cpu constantly updates in its internal flash memory as it goes on and off battery over time) is out of whack....  the lower load will allow the UPS a better chance to do a calibration accurately...in my experience if the battery constant is seriously out of whack and the load on the UPS is high the calibration doesn't always give the expected results:   at 20% load on a 3000 VA ups (and no external batteries) the runtime should be around 40 to 50 minutes.

Try the calibration and if you are still seeing 6 minutes afterwards you will either need to brain dead the UPS to try re-setting the constant ( which means run it on battery under load until the UPS dies and shuts off, then pull the battery, press and hold the on button for a bit to discharge the UPS internally (capacitors), then connect the battery and power up again). Or, you can try to get one of APC's "CalKey" dongles (only works on older smart-ups), or there is a way of changing the constant using hyperterminal to the serial port on the UPS.

[BillP]

This reply was originally posted by Angela on APC forums on 4/24/2014

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Another important thing for doing a calibration is making sure the load does not fluctuate a lot. I also suggest giving it a try and let me know if it does not work and we can explore different options.

[BillP]

This reply was originally posted by Michael on APC forums on 4/24/2014

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Thank you. I will try the calibration as it is and report back with the results.

[BillP · Accepted solution]

This reply was originally posted by Angela on APC forums on 4/24/2014

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Another option is a manual calibration, outlined here for something similar -> Why are the battery charge LEDs flashing on a Smart-UPS? | FAQs | Schneider Electric US