524 lines
15 KiB
HTML
524 lines
15 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
|
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>UPS Basics</TITLE
|
|
><META
|
|
NAME="GENERATOR"
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
|
|
REL="HOME"
|
|
TITLE="UPS HOWTO"
|
|
HREF="index.html"><LINK
|
|
REL="PREVIOUS"
|
|
TITLE="An Overview of Power Protection"
|
|
HREF="x71.html"><LINK
|
|
REL="NEXT"
|
|
TITLE="Testing Your UPS"
|
|
HREF="testing.html"></HEAD
|
|
><BODY
|
|
CLASS="sect1"
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#840084"
|
|
ALINK="#0000FF"
|
|
><DIV
|
|
CLASS="NAVHEADER"
|
|
><TABLE
|
|
SUMMARY="Header navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TH
|
|
COLSPAN="3"
|
|
ALIGN="center"
|
|
>UPS HOWTO</TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="left"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="x71.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="80%"
|
|
ALIGN="center"
|
|
VALIGN="bottom"
|
|
></TD
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="right"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="testing.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="sect1"
|
|
><H1
|
|
CLASS="sect1"
|
|
><A
|
|
NAME="AEN142"
|
|
></A
|
|
>3. UPS Basics</H1
|
|
><DIV
|
|
CLASS="sect2"
|
|
><H2
|
|
CLASS="sect2"
|
|
><A
|
|
NAME="AEN144"
|
|
></A
|
|
>3.1. How To Select A UPS</H2
|
|
><P
|
|
>UPSes are nowadays very inexpensive. In the U.S. in 2006, quite
|
|
capable ones are available for less than $100, and prices are heading
|
|
down. In fact prices are so low now that we're not going to walk you through
|
|
the elaborate optimization step that would have been important
|
|
even two or three years ago, of estiming the watt dissipation of your
|
|
computer and matching it to a UPS rating. Instead we'll explain
|
|
why this would be a waste of effort and how to buy in a simpler
|
|
and more effective way.</P
|
|
><DIV
|
|
CLASS="warning"
|
|
><P
|
|
></P
|
|
><TABLE
|
|
CLASS="warning"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="25"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
><IMG
|
|
SRC="../images/warning.gif"
|
|
HSPACE="5"
|
|
ALT="Warning"></TD
|
|
><TD
|
|
ALIGN="LEFT"
|
|
VALIGN="TOP"
|
|
><P
|
|
>Bear in mind that the UPS systems that you're likely to buy in a
|
|
store or computer catalog are <EM
|
|
>not</EM
|
|
> intended for safety
|
|
or life-critical equipment. These devices should be considered to be pieces
|
|
of consumer electronics. As such, the number-one basis on which most of these
|
|
devices compete with each other is on price, not quality.</P
|
|
><P
|
|
>Cost-effectiveness is more important to UPS vendors (because it
|
|
appears to be more important to their customers) than ultimate
|
|
reliability. If your life depends on computer uptime, you need a special
|
|
purpose, online, big, redundant, expensive system. These systems are beyond
|
|
the scope of this document. When you buy a UPS at your local computer
|
|
store, you are <EM
|
|
>not</EM
|
|
> buying this sort of system.</P
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
><P
|
|
>UPSes are rated by the watts a full battery can put out before
|
|
it drains. However, they are marketed using a VA (voltage-amps)
|
|
figure; often, consumer-grade UPSes don't even specify a wattage on
|
|
the box where you can see it. This is because the VA figure is larger
|
|
and looks sexier. As a rule of thumb. assume the wattage is half of
|
|
the VA rating; for an explanation of the complexities involved (if you
|
|
care) see the white paper <A
|
|
HREF="http://sturgeon.apcc.com/whitepapers.nsf/URL/WP-17/$FILE/WP17.pdf"
|
|
TARGET="_top"
|
|
>Understanding
|
|
Power Factor, Crest Factor, and Surge Factor</A
|
|
> on the APC
|
|
website.</P
|
|
><P
|
|
>But even if you know the watt rating of the UPS, it is the ratio of
|
|
that figure with the wattage dissipation of your computer that
|
|
controls the dwell time. Your dissipation is hard to predict; it can
|
|
even be effected by things like the size of monitor you use (big ones
|
|
can be quite power-hungry).</P
|
|
><P
|
|
>Manufacturers try to get around this technical thicket by
|
|
putting an expected dwell time on the box. But they exaggerate and
|
|
even lie about their dwell times a lot (this is called
|
|
<SPAN
|
|
CLASS="QUOTE"
|
|
>"marketing"</SPAN
|
|
>). What they'll do is quote you the dwell
|
|
time you would get driving a bare minimum system with the disk drives
|
|
shut off and a tiny monitor, in much the same way laptop manufacturers
|
|
lie about their battery dwell times. The more honest UPS
|
|
manufacturers give you a little table showing expected dwell times for
|
|
different system configurations (<SPAN
|
|
CLASS="QUOTE"
|
|
>"desktop"</SPAN
|
|
>,
|
|
<SPAN
|
|
CLASS="QUOTE"
|
|
>"tower"</SPAN
|
|
>, etc.). As a rule of thumb, assume you will get
|
|
about 50% of the dwell time listed on the box for your configuration
|
|
type.</P
|
|
><P
|
|
>My advice is to forget the numbers game. Just go online or to
|
|
your local computer store and buy one of the higher-end consumer or
|
|
home-office models from APC, Best, Tripp-Lite, Belkin, or some other
|
|
reputable manufacturer. Go ahead and grab the model with the longest
|
|
dwell time, highest watt rating, or biggest VA number you can find;
|
|
the premium for it is not likely to be more than $75 over the
|
|
bargain-basement model. I guarantee you will feel very good about
|
|
your decision not to pinch pennies come your first extended power
|
|
outage.</P
|
|
><P
|
|
>Perhaps a more compelling reason it is better to over-buy
|
|
capacity rather than ending up with a UPS that is too weak for your
|
|
power drain is that overstrained UPSes can fail in ugly ways,
|
|
including catching fire and exploding.</P
|
|
><P
|
|
>Be sure you get a <I
|
|
CLASS="firstterm"
|
|
>line interactive</I
|
|
> UPS
|
|
rather than the older <I
|
|
CLASS="firstterm"
|
|
>standby</I
|
|
> or
|
|
<I
|
|
CLASS="firstterm"
|
|
>SPS</I
|
|
> type. The older technology doesn't
|
|
actually filter your power through the battery, so you're not assured
|
|
of good voltage conditioning. The main advantage of an SPS (low cost)
|
|
has been eroded now that line-interactive UPSes are so inexpensive.
|
|
There are other UPS types, but they are either obsolescent or targeted
|
|
at large data-center installations. For a detailed discussion of the
|
|
different UPS types, see <A
|
|
HREF="http://sturgeon.apcc.com/whitepapers.nsf/URL/WP-1/$FILE/WP1.pdf"
|
|
TARGET="_top"
|
|
>The
|
|
different types of UPS systems</A
|
|
>, a white paper on the APC
|
|
site.</P
|
|
><P
|
|
>Another important consideration is how your UPS will communicate
|
|
with your computer. Do not buy a serial line UPS (one that
|
|
communicates via an RS-232C cable). These are passing out of use in
|
|
favor of UPS designs that use USB or Ethernet, for the very excellent
|
|
reason that RS-232C interfaces are flaky, difficult to configure,
|
|
and difficult to debug. Ethernet is overkill for this application;
|
|
UPSes simply don't need that kind of bandwidth. We recommend sticking
|
|
with USB, which is well-matched in price/performance to this job
|
|
and relatively easy to troubleshoot.</P
|
|
><P
|
|
>Until recently there was an important distinction between
|
|
<I
|
|
CLASS="firstterm"
|
|
>smart</I
|
|
> and <I
|
|
CLASS="firstterm"
|
|
>dumb</I
|
|
> UPSes.
|
|
Dumb UPSes did voltage-level signaling through individual pins; smart
|
|
ones used the link as a primitive character channel and could pass
|
|
more status information over it. But if you avoid RS232C UPSes you
|
|
will never see a dumb one; indeed, it is likely that by the time you
|
|
read this no dumb UPses will be in production any longer.</P
|
|
><P
|
|
>Some UPSes advertise that they deliver a sinusoidal waveform. Those
|
|
that don't may be delivering something more like a square wave or a very
|
|
noisy sine wave. There are differing schools of thought about how
|
|
important this is. One school of thought holds that one should always run
|
|
equipment on the best approximation of sinusoidal input that one can, and
|
|
that deviations produce harmonics which may either be interpreted as signal
|
|
if they get through a power supply, or may actually damage the
|
|
equipment. Another school holds that since almost all computers use
|
|
switching-type power supplies, which only draw power at or near the peaks
|
|
of the waveforms, the shape of the input power waveform is not
|
|
important.</P
|
|
><P
|
|
>Who's right? We don't know. Nick's opinion is that sinusoidal output
|
|
is worth the extra money, especially for on-line UPS systems that
|
|
continually provide their waveform to the computer; Eric is inclined to
|
|
doubt it matters much with modern power supplies. If you don't know that
|
|
your equipment has a switching-type power supply, you certainly might want
|
|
to think twice before buying a low quality UPS.</P
|
|
><P
|
|
>Personally, I (Eric) like APC UPSes (nether Eric nor Nick has any
|
|
connection with the company). But this is not the kind of widget for which
|
|
manufacturer makes a whole lot of difference as long as you stick with one
|
|
of the reputable brands.</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="sect2"
|
|
><H2
|
|
CLASS="sect2"
|
|
><A
|
|
NAME="AEN173"
|
|
></A
|
|
>3.2. Deploying your UPS and other devices: the total picture</H2
|
|
><P
|
|
>Our recommendation for a production Unix environment is a
|
|
configuration like the following:</P
|
|
><P
|
|
></P
|
|
><OL
|
|
TYPE="1"
|
|
><LI
|
|
><P
|
|
>An UPS for the computer system. </P
|
|
></LI
|
|
><LI
|
|
><P
|
|
>Surge suppression on all phone lines, and also on
|
|
serial/parallel lines that leave the room.</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
>Line conditioners on any devices not connected to the UPS. If
|
|
you do take a power hit, it's cheaper to replace a $50 line
|
|
conditioner than a $1500 laser printer.</P
|
|
></LI
|
|
></OL
|
|
><P
|
|
>If this is too expensive for you, then downgrade the UPS to
|
|
a line conditioner like the TrippLite. But don't go without at least
|
|
that. Running unprotected is false economy, because you
|
|
<EM
|
|
>will</EM
|
|
> lose equipment to electrical storms —
|
|
and, Murphy's Law being what it is, you will always get hit at the
|
|
worst possible time.</P
|
|
><P
|
|
>One thing to note is that you typically shouldn't put a laser printer
|
|
on the brownout-protected sockets in a UPS — toner heaters draw
|
|
enough current to overload a UPS and cause a shutdown within
|
|
seconds. Modern UPSes generally have some plugs that are marked
|
|
surge-suppressed but not filtered through the battery; plug your
|
|
printer into one of those.</P
|
|
><P
|
|
>A UPS should be wired directly to (or plugged directly into) the
|
|
AC supply (i.e. a surge suppressor is neither required nor suggested
|
|
between the wall and the UPS). In addition, a surge suppressor
|
|
between the UPS and the equipment connected to it is redundant.</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="sect2"
|
|
><H2
|
|
CLASS="sect2"
|
|
><A
|
|
NAME="AEN187"
|
|
></A
|
|
>3.3. Software Assistance</H2
|
|
><P
|
|
>Your UPS communicates with your computer so it can gracefully
|
|
shut the computer down when an outage has lasted too long for the
|
|
battery to cope. In order for graceful shutdown to actually happen,
|
|
your computer needs to have a background process — a daemon, in
|
|
Unix terms — watching whatever messages come over the UPS cable
|
|
for the one that says <I
|
|
CLASS="firstterm"
|
|
>terminate</I
|
|
>. Then it
|
|
needs to tell the operating system to shut down.</P
|
|
><P
|
|
>Your UPS probably comes with a CD full of such software. Throw
|
|
it away, as (a) most of it will be useless bits written for Windows
|
|
systems, and (b) in the unlikely event you get Linux software it will
|
|
almost certainly be stale binaries for a version you don't run.</P
|
|
><P
|
|
>Back in the days of dumb serial-line UPses, there used to be
|
|
about half a dozen different open-source UPS monitor daemons:
|
|
<SPAN
|
|
CLASS="application"
|
|
>apcd</SPAN
|
|
>, <SPAN
|
|
CLASS="application"
|
|
>dumbupsd</SPAN
|
|
>,
|
|
<SPAN
|
|
CLASS="application"
|
|
>genpowerd</SPAN
|
|
>.
|
|
<SPAN
|
|
CLASS="application"
|
|
>powerd</SPAN
|
|
>, <SPAN
|
|
CLASS="application"
|
|
>smupsd</SPAN
|
|
>,
|
|
<SPAN
|
|
CLASS="application"
|
|
>usvd</SPAN
|
|
> and more. These were fairly stupid
|
|
programs for a simple job. Many required you to hand-wire a custom
|
|
RS232C cable to get around various evil things that UPS manufacturers
|
|
did to their ports in order to lock in customers.</P
|
|
><P
|
|
>Those days are gone. USB UPSes get rid of the cable-hacking and
|
|
hardware klugery, but require a bit more smarts from a monitor daemon.
|
|
Accordingly the field has narrowed considerably. There appear
|
|
to be only two such projects left standing.</P
|
|
><P
|
|
>The <A
|
|
HREF="http://www.networkupstools.org/"
|
|
TARGET="_top"
|
|
>Network UPS
|
|
Tools</A
|
|
> project is a generic UPS monitor daemon that aims to
|
|
communicate intelligently with all current UPS designs.</P
|
|
><P
|
|
><A
|
|
HREF="http://www.apcupsd.org/"
|
|
TARGET="_top"
|
|
>apcupsd</A
|
|
> is a daemon
|
|
specifically designed for communicating with UPSes made by APC, the
|
|
American Power Corporation.</P
|
|
><P
|
|
>Both are solid, well-run projects. Their development groups are
|
|
mutually friendly, and there has been occasional talk of a merger.
|
|
Awkwardly, the <SPAN
|
|
CLASS="application"
|
|
>apcupsd</SPAN
|
|
> project is in many ways
|
|
the more featureful of the two, with, among other things, better USB
|
|
support and better documentation — but the NUT tools have a cleaner
|
|
architecture, more developers, and acceptance in Red Hat and other major
|
|
distributions.</P
|
|
><P
|
|
>My advice is simple; run <SPAN
|
|
CLASS="application"
|
|
>apcupsd</SPAN
|
|
> if
|
|
you buy an APC UPS, and the NUT tools if you buy anything else. RPMs
|
|
and Debian packages (which will modify your system's boot sequence
|
|
appropriately as well as installing the daemon binaries) are available
|
|
for both, so installation should be easy either way.</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="sect2"
|
|
><H2
|
|
CLASS="sect2"
|
|
><A
|
|
NAME="AEN208"
|
|
></A
|
|
>3.4. Preparing Your System For Auto-Reboot</H2
|
|
><P
|
|
>If you are using your UPS to try to keep a DNS/Web/mailserver up
|
|
24/7, you will want to make sure the machine can be configured to
|
|
boot automatically when it is powered up.</P
|
|
><P
|
|
>This is not the normal behavior of most computers as shipped
|
|
from the factory. Normally after the power is cut and restored, you
|
|
must explicitly press a button for the power to actually be turned
|
|
on. You can test your computer by powering it down; shutting off the
|
|
power (pull the plug); then plugging the cord back in. If your
|
|
computer immediately starts up, good. There is nothing more to
|
|
do.</P
|
|
><P
|
|
>If your computer does not start up, manually turn on the
|
|
power (by pressing the power on button) and enter your computer's
|
|
SETUP program (often by pressing DEL during the power up sequence;
|
|
sometimes by pressing F10). You must then find and change the
|
|
appropriate configuration parameter to permit instant power
|
|
on.</P
|
|
><P
|
|
>Normally, this is located under the <EM
|
|
>BOOT</EM
|
|
> menu item, and will be called something
|
|
such as <EM
|
|
>Restore on AC/Power Loss</EM
|
|
> or
|
|
<EM
|
|
>Full-On</EM
|
|
>. The exact words will vary
|
|
according to the ROM BIOS provider. Generally you will have three
|
|
options: <EM
|
|
>Last State</EM
|
|
>, <EM
|
|
>Power On</EM
|
|
>, and <EM
|
|
>Power
|
|
Off</EM
|
|
>.</P
|
|
><P
|
|
>Some BIOSes do not support such an option. This is idiotically
|
|
bad design, but it does happen. If so, your only practical remedy is
|
|
to get a new motherboard.</P
|
|
></DIV
|
|
></DIV
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
SUMMARY="Footer navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="x71.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="index.html"
|
|
ACCESSKEY="H"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="testing.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>An Overview of Power Protection</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
> </TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>Testing Your UPS</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |