Low Battery Duration

[AndrewJ_apc]

I have a question about the shutdown configuration settings in UNMC.  Low Battery Duration, according to the APC help file "Defines how long the UPS can continue to run on battery power after a low-battery condition occurs."  If I set it for the shortest duration possible (2 minutes) is it going to initiate UPS shutdown 2 minutes after Low Battery is detected (minimum runtime, maximum battery preservation), or is it going to initiate shutdown when only 2 minutes of runtime remain (maximum runtime, minimum battery preservation)?  I'm assuming the former is correct, but I have seen several posts in the forum indicating the later.   Which one is correct? 

[mitsmith_apc]

Hi Andrew,

The key here is that we are focusing on UPS shutdown and not the shutdown of your severs. If we are just looking at the UPS, the UPS will shutdown with 2 minutes remaining (the second option). This low battery setting we are looking at is what will signal our graceful shutdown software, powerchute, to start turning off your servers. The UPS will stay running during this time until only 2 minutes remain to make sure everything was able to shutdown. 

To turn the UPS off earlier, you would have to have powerchute network shutdown and make sure you select the setting turn UPS off when configuring it. The way this will work is when the low battery condition exists the UPS will send a signal to powerchute. Powerchute will then start turning off your servers. Once enough time has passed to shut down your servers, powerchute will then send a signal back to the UPS to turn off.  

[AndrewJ_apc]

Michael,

Thank you for the quick reply.  Our UPS units (approximately 150 of them) are powering network equipment, not servers, so my only concern is the UPS shutdown, not servers or PowerChute.  While I understand what you explained, it seems to contradict the documentation.  The documentation describes Low Battery Duration shutdown in terms of the number of minutes AFTER Low Battery Condition is detected.  Your explanation describes shutdown in terms of the number of minutes BEFORE the complete depletion of the battery.  If the calculation is based solely on remaining minutes of battery function, why is the setting described as Low Battery Duration?  And why does it make reference to the onset of Low Battery Condition, when Low Battery Condition appears to have nothing to do with the time interval?   

[voidstar_apc]

The "low battery condition" just means the available runtime is below the "low battery duration." So when the "low battery condition" is reached, then by definition, the "low battery duration" is how long the UPS can continue to run on battery power. It's two different ways of looking at the same concept, although I find the NMC help's approach rather unnatural.

ASCII diagram illustrating the two views:

Time BEFORE complete depletion of the battery:

         |<-- Low Battery Duration -->|
         |                            |
Runtime: | =========================> | ----------------------- | --------------------- |
         ^                            ^                         ^                       ^
     Battery Depleted          Low Battery Condition     Current Runtime      Runtime at Full Charge

Time remaining AFTER low battery condition is reached:

         |<-- Low Battery Duration -->|
         |                            |
Runtime: | <========================= | ----------------------- | --------------------- |
         ^                            ^                         ^                       ^
     Battery Depleted          Low Battery Condition     Current Runtime      Runtime at Full Charge

[AndrewJ_apc]

Thank you, this is helpful.  I will treat the Low Battery Duration field as "number of minutes before complete battery depletion."

Follow up question:  If I understand it correctly, Maximum Required Delay is a time interval set by the UPS (ours is 2 minutes) that functions as a shutdown buffer.  In other words, if we set the Low Battery Duration to 5 minutes, the system will add an additional 2 minutes of Maximum Required Delay automatically.  So shutdown will actually begin 7 minutes before complete battery depletion.  Is this correct?

[mitsmith_apc]

Hi Andrew,

You are a little off. The maximum required delay is used for the use with powerchute network shutdown. It essentially will look at all the PCNS installs and determines what the longest shutdown delay is out of those installs. If not using PCNS it will match the low battery setting by default. It is calculated whenever the management interface of the UPS turns on or is reset, or when the Force Negotiation option is selected and you click Apply. In your case you will not need to worry about this setting since it only applies to PCNS. 

There is a un-configurable setting of a 2 minute buffer for shutdown of the UPS. So if you set the low battery duration at 5 minutes it will signal low battery at 7 minutes. 

[AndrewJ_apc · Accepted solution]

Thank you all for your assistance.  I appreciate it.