PCNS Multiple Configuration -- When does the stand-by unit kick in?

[Anonymous user]

About the setup:
We have two identical UPS each connected to one of the redundant power supplies on our server.

What we want:
In the event of a power outage, we want one UPS to power our server until it's battery is low, then switch to the other UPS until it's battery is low, then gracefully shutdown.

My understanding:
In a Multiple Configuration with two UPS, one UPS is designated as "primary" and one as "stand-by".

The question:
Under what circumstances does the "stand-by" UPS begin supplying power?

[Techie_apc]

hmm...You will need to install the PCNS software through a Custom Installation in order to achieve your goal.

Custom:
PCNS is installed and listens for UPS events from two or more Network Management Cards.
Designed for graceful, unattended shutdown with redundant UPS systems.
PCNS treats all UPS units as one, meaning shutdown will not occur unless both UPS units switch to battery or report an event that requires shutdown.

A custom installation requires:
Two UPS units of the same product family (ie. Smart UPS)
Matching firmware on all Network Management Cards being monitored.

Regarding your question, the Server which has got dural power supplies will pull power from the standby UPS after the primary UPS stops providing power to it.

[Anonymous user]

Thanks for the reply.

Does this mean the stand-by unit will not supply power until the primary unit signals low battery?

[Techie_apc]

In this situation, the second UPS power will not be utilized until the first UPS stops power to its outlets due to low battery condition. Have you tried installing the PCNS through the custom installation?

[voidstar_apc]

In addition to what other people have said, it's your redundant power supplies that determine how they want to utilize the UPSes. If they draw power from both equally, then your UPSes will drain at the same time. If only one power supply is utilized at a time, then it will drain one UPS, then when the UPS shuts off, switch to the other power supply and UPS.

From the perspective of the UPS, it doesn't matter which of those scenarios occur. Your runtime should be about the same, and by following the advice of the other posters, you'll have PCNS set up so that it only shuts down your server when the amount of time left on the batteries of both of your UPSes is too low.

[BillP · Accepted solution]

PCNS will not shutdown your system until it receives an on battery signal (or other specific event you have configured) from both UPSs.

The only three events that could happen to only one UPS, that will cause the server to shutdown, are mentioned [in this article|http://nam-en.apc.com/cgi-bin/nam_en.cfg/php/enduser/std_adp.php?p_faqid=3143].