DOCUMENT:Q105241  25-OCT-1993  [W_NT]
TITLE   :Windows NT May Shut Down Immediately if Power Fails with UPS
PRODUCT :Windows NT
PROD/VER:3.10
OPER/SYS:WINDOWS
KEYWORDS:

----------------------------------------------------------------------
The information in this article applies to:
 
 - Microsoft Windows NT operating system version 3.1
 - Microsoft Windows NT Advanced Server version 3.1
----------------------------------------------------------------------
 
SUMMARY
=======
 
If you use an uninterruptible power supply (UPS) that does not have
the ability to send a low battery signal to the computer, Windows NT
may shut down immediately if a power failure occurs.
 
MORE INFORMATION
================
 
If a UPS is used that is not capable of sending a signal to the
computer to inform it of a low battery condition, Windows NT instead
relies on information provided by the user to determine the length of
time that the system can be run on battery power. When the battery
power reaches two minutes of life remaining, Windows NT begins a
shutdown of the system.
 
When you boot Windows NT, it starts under the assumption that the
battery is completely drained. This is a safety feature which assumes
that a computer has just been turned on and that the UPS battery is
not charged yet.
 
Windows NT then computes the amount of life it expects the battery to
have based on the "Expected battery life" and "Battery recharge time
per minute of run time" settings in the UPS Service setup screen. If,
for example, the battery recharge time is set to 100 minutes, then the
system must run 100 minutes for Windows NT to believe that the battery
has a one minute charge. It must run 200 minutes for Windows NT to
calculate a two minute charge.
 
Because Windows NT will begin a shutdown immediately if the power
fails when the battery life is calculated to be 2 minutes or less,
Windows NT may shut down immediately if the power fails and the
calculated battery life is two minutes or less.
 
Thus, Windows NT may shut down sooner than expected after a power
failure if the computer was rebooted recently, even though the UPS may
be fully charged.
 
This behavior is expected because Windows NT assumes worst-case
conditions for unattended UPS monitoring.
 
Additional reference words: 3.10 
KBCategory:
KBSubcategory: fautol hrdwr

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1993.