NMC Low Battery Duration vs NMC Basic Low Battery Duration

[pgpc_apc]

This was originally posted on APC forums on 6/21/2015

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There are countless confusing and contradictory posts about the meaning and effect of the Low Battery Duration setting in the NMC interface, but despite hours of searching I have not found any that explain the effect of the Basic Low Battery Duration setting.  Unfortunately, our UPS already is installed in a production system, so I do not have the luxury of running tests to figure out the effect of the Basic Low Battery Duration setting and how it relates to the Low Battery Duration setting.

We have an AP9631 NMC with firmware 6.2 installed in a SMX2200RMLV2U.  The NMC manual and NMC help file both state that Basic Low Battery Duration "defines the amount of available battery runtime at which the UPS signals a low battery condition."  This explanation seems straghtforward until one compares it to the explanation in the NMC help file for Low Battery Duration, which states that Low Battery Duration "defines how long the UPS can continue to run on battery power after a low battery condition occurs."  If I want the NMC to give a low battery signal with 10 minutes of UPS runtime left, which of Basic Low Battery Duration or Low Battery Duration do I set to 10 minutes? 

If the answer is Low Battery Duration and not Basic Low Battery Duration, what is the purpose of the Basic Low Battery Duration setting?

If the answer is Basic Low Battery Duration, then is it correct to expect the UPS to shutdown X + 2 minutes after the shutdown signal triggered by the Basic Low Battery Duration setting, where X is the number of minutes specified in Low Battery Duration?

[BillP]

This reply was originally posted by Bill on APC forums on 6/22/2015

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Hi,

Sorry for the confusion. Basic Signaling Shutdown and Basic Low Battery Duration work together. If you enable basic signaling shutdown and have a basic signaling cable connected to the UPS the attached system will receive a shutdown command when the UPS hits the threshold set in Basic Low Battery Duration.

Low Battery Duration works with PowerChute Network Shutdown. When the UPS meets the low battery duration threshold the NMC sends a shutdown signal to any configured PowerChute Network Shutdown agents.

The difference is, Lower Battery Duration threshold is used by PowerChute Network Shutdown agents over the local network and Basic Low Battery Duration is used by a system or systems attached to the UPS via basic signaling cable.

[pgpc_apc]

This was originally posted on APC forums on 6/23/2015

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Thanks for the clarification, Bill.  Your answer spurred some follow-up questions.  

We have two devices protected by the SMX UPS.  One is a server running PCNS that communicates with the NMC via the network and the other is a Netgear ReadyNAS running a built-in version of NUT that communicates with the SMX UPS via USB cable.  I do not understand the NMC manual's definition of basic signaling, so I cannot tell you whether the USB cable is a basic signaling cable, but I can confirm that NAS does communicate with the SMX UPS via the cable because the NAS' status page reports the model of the UPS, and the same percentage charge and runtime that the SMX UPS itself reports on its own front panel.  Do we need to enable Basic Signaling Shutdown for the SMX UPS to be able to shut down the NAS?  

We have PCNS configured to shut down the server after the SMX UPS has been On Battery for 15 minutes.  When PCNS reaches the end of the 15-minute period, it begins the OS shutdown process (we have no command files) and signals the NMC to begin the SMX UPS shutdown process. When the NMC receives this signal and the SMX UPS begins shutting down, will it signal the NAS to shut down?  Or, is the SMX UPS limited to signaling the NAS to shutdown only when the SMX UPS runtime drops below the time specified in Basic Low Battery Duration?

If the SMX UPS will send the NAS a shutdown signal as a result of the NMC receiving a shutdown signal from PCNS, when does it send the signal?  Does it send it immediately on receiving the shutdown signal from PCNS, at the end of the Low Battery Duration period or at some other time?

[voidstar_apc]

This was originally posted on APC forums on 6/23/2015

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A USB cable is not a basic signaling cable. Since your system doesn't have one, the basic low battery duration does nothing and can safely be ignored.

So there are two main pieces of information both PCNS and the NAS have access to:

- Is the UPS battery low? ie, is the UPS runtime below the low battery duration?

- Is the UPS shutting down?

Either of these conditions will cause PCNS to start a shutdown and your NAS should presumably do the same. So if PCNS tells the UPS to start a shutdown after 15 minutes on battery, the UPS will start the shut down process and your NAS should respond by shutting itself down. Make sure:

- The off delay for the NAS' outlet group is long enough for it to safely turn off.

- The return runtime duration for the NAS' outlet group is long enough for it to start up then safely turn off.

- Either low battery duration or load shedding set up to trigger when runtime is less than the off delay.

[pgpc_apc]

This was originally posted on APC forums on 6/23/2015

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I appreciate voidstar taking a shot at answering my question, but voidstar made an incorrect assumption that led to an incorrect conclusion.  The USB cable I mentioned is the USB cable provided by APC with the SMX UPS that the manual says is for connecting the SMX UPS to computer power management software. Indeed, as I mentiond in my earlier post, the NAS is receiving correct data from the SMX UPS through the cable regarding the SMX UPS' model, percentage charge and available runtime.  Thus, we do have a signaling cable, I just was not clear whether it was of the "basic" variety.  Per a call I just had with APC tech support, it is. 

My key question was whether the SMX UPS would send a shutdown signal to the NAS when it receives a shutdown signal from PCNS or whether it will only send a shutdown signal when the runtime drops below the Basic Low Battery Duration.  I wish voidstar had been right to presume the SMX UPS would shut down the NAS when it receives a PCNS shutdown signal.  According to APC tech support, however, the SMX UPS will send a shutdown signal to the NAS only if the SMX UPS runtime is less than the Basic Low Battery Duration. If PCNS triggers an SMX UPS shutdown, the SMX UPS will not send a shutdown signal to the NAS and the NAS will experience a hard shutdown unless the SMX UPS runtime happens to drop below the Basic Low Battery Duration before the SMX UPS shuts itself off.  

This is not the answer I wanted to receive, but perhaps publishing it here will help someone else avoid the configuration mistake I made.

[voidstar_apc · Accepted solution]

This was originally posted on APC forums on 6/24/2015

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 Does the "SMX UPS ... send a shutdown signal to the NAS when it receives a shutdown signal from PCNS"?

The problem with this question is it pre-supposes the UPS sends a shutdown signal [via USB], which it doesn't resulting in answers based on what people consider "sending a shutdown signal" but doesn't necessarily answer your question. It's more accurate to think of the UPS as providing data about it's operation which PCNS and the NAS consume. As you've noted, you can see this information. It's the NAS' responsibility to respond appropriately by shutting down when the UPS shuts down. PCNS itself will do this.

If you're really curious, the USB spec is open and you can see it here:

http://www.usb.org/developers/hidpage/pdcv10.pdf

Particularly page 26 / Power Generic Status lists the ShutdownRequested, ShutdownImminent and Used status bits.