Hardware Reference
In-Depth Information
Some surge suppressors also include a pass-through for a telephone line, adding surge
protection to it as well. This is valuable if you're using a DSL modem, because a lightning
strike can come through a phone line and destroy a modem. Modems are one of the
components most often damaged by power surges, because phone lines are frequently left
unprotected.
Uninterruptible Power Supplies
A surge suppressor does nothing to help with power sags or outages. For that you need an
uninterruptible power supply (UPS)
: a combination of a surge suppressor and a battery
backup. It handles power surges in the same way as a surge suppressor, but it has the
added bonus of being able to power the PC for a few minutes when a power outage occurs.
This is very useful because it helps avoid problems that crop up when a PC is shut down
incorrectly, such as disk errors.
In some cases, a UPS also includes
power conditioning
, so it protects against under-
voltage situations (brownouts) as well as complete power failures. (Not every UPS has this
feature.)
Most UPS devices have a cable that connects to a PC that allows the operating
system to interact with the UPS. With this feature enabled, the UPS can signal the OS
when the battery is being used, and Windows can shut itself down automatically. This
is useful for people who leave a PC running when away from home or overnight at
the offi ce.
There are two types of UPS devices. An
online UPS
runs the PC off the battery at all
times. The power comes into the battery and charges it continuously, and the PC draws
its power from the battery. If power stops coming from the wall outlet, the PC continues
running on the battery as long as it can. This type of UPS is rather expensive. Some call it a
“true UPS.”
The other type is a standby UPS. It works as a surge suppressor most of the time,
passing the wall outlet current straight through to the devices plugged into it. The battery
stays charged but isn't in the main loop. If the wall outlet stops providing power, the UPS
quickly switches the devices over to the battery. There is a momentary skip when the power
changes over, but it's so brief that most devices will continue working without interruption.
This type of UPS is the model that local computer stores typically carry for sale and is
much more affordable. However, some people argue that it isn't a real UPS, but rather a
standby power source
(or
standby power
supply) (SPS)
.
A UPS is much larger and heavier than a surge suppressor, mainly because of its
big battery. The battery will last for many years, but it's replaceable if it ever goes bad.
The UPS has self-testing routines and lights that show the battery's status, and it will let
you know when it's time to replace the battery. Figure 5.6 shows the back of a typical
consumer-level UPS. Notice that there are outlets for surge protection only for both
power and modems, and also three outlets that provide both battery backup and surge
protection.
