UPS-HOWTO(1).pdf

UPS HOWTO

Eric Steven Raymond

Thyrsus Enterprises

Revision History

Revision 1.1

2004−02−21

Revised by: esr

Add a little deployment advice, and stuff on other technologies.

Revision 1.0

2003−10−07

Revised by: esr

Initial release.

An Uninterruptible Power Supply (UPS) is an important thing to have if you live in an area where power

outages are at all common, especially if you run a mail/DNS/Web server that must be up 24/7. This HOWTO

will teach you things you need to know to select a UPS intelligently and make it work with your open−source

operating system.

UPS HOWTO

Table of Contents

1. Introduction. ....................................................................................................................................................1

1.1. Why this document? .........................................................................................................................1

1.2. New versions of this documen. ........................................................................................................1

1.3. License and Copyright. .....................................................................................................................1

2. An Overview of Power Protection. ................................................................................................................2

2.1. Surge suppressors. .............................................................................................................................2

2.2. Line Conditioners .............................................................................................................................2

2.3. Uninterruptible Power Supplies. .......................................................................................................3

3. UPS Basics. ......................................................................................................................................................4

3.1. How To Select A UPS. .....................................................................................................................4

3.2. Deploying your UPS and other devices: the total picture. ................................................................5

3.3. Software Assistance. .........................................................................................................................5

3.4. Preparing Your System For Auto−Reboo. .......................................................................................6

4. Maintaining Your UPS. ..................................................................................................................................7

4.1. Extending battery life. .......................................................................................................................7

4.2. Recalibrating Your UPS. ..................................................................................................................7

4.3. Replacing Your Batteries. .................................................................................................................7

4.4. Buying Batteries. ..............................................................................................................................8

5. Acknowledgements and Related Resources. ...............................................................................................10

1. Introduction

1.1. Why this document?

An Uninterruptible Power Supply (UPS) is an important thing to have if you live in an area where power

outages are at all common, especially if you run a mail/DNS/Web server that must be up 24/7. The aging

power grid in the U.S. has made this a more urgent issue than it used to be even for American hackers, but

everyone is vulnerable to outages caused by storms and other natural phenoena. This document covers both

the software and hardware aspects of protecting yourself.

The advice in this document is aimed primarily at small installations one computer and one UPS. Thus we'll

focus on consumer−grade UPes, especially those designed for home and small−business use. If you are a data

center administrator running a big server farm, there is a whole different (and much more expensive) range of

technologies we'll do no more than hint at here.

1.2. New versions of this document

You can also view the latest version of this HOWTO on the World Wide Web via the URL

http://www.tldp.org/HOWTO/UPS−HOWTO.html.

1.3. License and Copyright

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free

Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no

Invariant Sections, no Front−Cover Texts, and no Back−Cover Texts. A copy of the license is located at

www.gnu.org/copyleft/fdl.html.

Feel free to mail any questions or comments about this HOWTO to Eric S. Raymond,

< esr@snark.thyrsus.com> . But please don't ask me to troubleshoot your general UPS problems; if you

do, I'll just ignore you.

1. Introduction

2. An Overview of Power Protection

There are three levels of power protection available to the home computer user. The levels are:

Surge Suppressor

Line Conditioners

Uninterruptible Power Supplies

While this HOWTO mainly focuses on UPSs, we'll start with some basics about the other two kinds of power

filtering to help you understand where UPSes fit in. This is useful even though plummeting UPS prices have

made the low−end alternatives less interesting than they used to be.

2.1. Surge suppressors

These are basically a fancy fuse between the source and your hardware; they clamp down spikes, but can't fill

in a low voltage level or dropout.

This is a bare minimum level of protection that any piece of expensive electronics should have. Note that this

applies to more than just AC power; surge suppressors are available for (and should be used on) phone lines,

and RS−232 and parallel connections (for use on long lines; generally not needed if the devices are colocated

with the computer and all devices are protected from outside sources). Note also that all devices connected to

your computer need to be protected; if you put a surge suppressor on your computer but not your printer, then

a zap on the printer may take out the computer, too.

An important fact about surge suppressors is that they need to be replaced if they absorb a large surge .

Besides fuses, most suppressors rely on on components called Metal−Oxide Varistors (or MOVs) for spike

suppression, which degrade when they take a voltage hit. The problem with cheap suppressors is that they

don't tell you when the MOV is cooked, so you can end up with no spike protection and a false sense of

security. Better ones have an indicator.

You can buy surge suppressors at any Radio Shack; for better prices, go mail−order through Computer

Shopper or some similar magazine. All of these are low−cost devices ($10−50).

2.2. Line Conditioners

These devices filter noise out of AC lines. Noise can degrade your power supply and cause it to fail

prematurely. They also protect against short voltage dropouts and include surge suppression.

The Tripp−Lite 1200 I used to have was typical of the better class of line conditioners; a box with a good big

soft−iron transformer and a couple of moby capacitors in it and no conductive path between the in and out

sides. With one of these, you can laugh at brownouts and electrical storms. A fringe benefit is that if you

accidentally pull your plug out of the wall you may find you actually have time to re−connect it before the

machine notices (I did this once). But a true UPS is better.

Netter Trey McLendon has good things to say about Zero Surge conditioners. He says: "Our systems at work

[...] have been protected for 2.5 years now through many a violent storm...one strike knocked [out] the

MOV−type suppressors on a Mac dealer's training setup across the street from us. The Zero Surge just sort of

buzzed when the surge came in, with no interruption whatsoever. The basic principle is this: ZS units slow

2. An Overview of Power Protection

UPS HOWTO

down the surge with a network of passive elements and then sends it back out the neutral line, which is tied to

ground outside at the box by code. MOV units shunt the surge to ground at the computer , where it leaps

across serial ports, network connections, etc. doing its deadly work."

Price vary widely, from $40−400, depending on the power rating and capabilities of the device. Mail−order

from a reputable supply house is your best bet. Line conditioners typically don't need to be replaced after a

surge; check to see if yours includes MOVs.

2.3. Uninterruptible Power Supplies

The remainder of this document will focus on UPes. A UPS does three things for you. First, it filters the

power your machine sees, smoothing out spikes and voltage fluctuations that can stress or even damage your

electronics. Secondly, it provides a certain amount of dwell time in the event your power goes out entirely

this can often get you through brownouts and short blackouts. Third, when the UPS is about to run out of

power it can arrange a graceful shutdown of your computer so that no unpleasant things happen to your disk

filesystems. While the risks of unexpected shutdown are much lessened in these days of journalling

filesystems like Linux's EXT3 or JFS from what they once were, ensuring a clean shutdown is still a valuable

contribution to any system administrator's peace of mind.

2. An Overview of Power Protection

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