BOOT CAMP 317 (16/03/04)
Despite the remarkable
variability of our weather and ongoing climate changes Spring still seems to be
the season for thunderstorms, if the number of emails and letters we get from
readers with frazzled modems and computers is anything to go by.
Several thousand PCs are
destroyed by lightning every year, usually as a result of a strike on a nearby
telephone pole or power line. This sends a ‘spike’ or surge of several thousand
volts down the cables into the back of the PC. Fortunately such calamities tend
to be fairly localised, usually to within a few hundred metres of the strike as
both the telephone network and power grid are well protected against lightning.
Nevertheless, the risk remains, more so in rural areas with long stretches of
exposed overhead power and telephone lines.
It’s not only PCs that
are affected, a growing number of devices, including digital set-top boxes, are
also connected to the telephone network; in fact any mains power equipment that
uses microchips, including home entertainment systems and TVs are vulnerable,
not just to lightning strikes but to any disruption in the mains
In recent years those of
us living in cities and large towns have become dangerously complacent about the
stability and reliability of the UK’s mains supply. Power cuts and ‘brown outs’
are comparatively rare and even when they do occur the worst that usually
happens is the lights flicker, the TV or stereo system may go into standby mode
and no damage is done. However, if you also happen to be booting up your PC or
saving data to your hard disc drive when the interruption occurs you could loose
all of your work, or worse, end up with a dead PC. It is wise to take
precautions against power fluctuations particularly if you live in a rural area
or use your PC for any sort of business or record keeping.
There are two main
concerns: ‘transients’, which are momentary spikes or surges in mains supply
voltage, and interruptions to the supply.
During a severe
thunderstorm the only absolutely certain way to protect your PC and any other
electronic gizmos you might have is to switch them off, unplug them from the
mains and where appropriate, disconnect the telephone cables as well and wait
for the storm to pass.
Clearly you cannot
always be around to unplug your equipment during a storm but you can greatly
reduce the chance of damage with surge and spike suppressors. These come in many
different forms but the most convenient types look like regular multi-way mains
adaptors. Some have built in phone line protection circuits as well and the more
sophisticated models bleep or flash a warning lamp, to let you know that a
transient has been intercepted and safely dealt with. Multi-way adaptors with 4,
6, 8 and 10 outlets are readily available from most PC suppliers and prices
start at around £15 for basic no-frills designs. Some come with several thousand
pounds worth of insurance, covering the cost of damage to any connected
equipment should the suppressor fail in its duty.
Power cuts are a lot
harder to deal with, though most electronic devices can handle very short
interruptions lasting no more than half a second or so. However, the only
solution to a complete break in the supply is an uninterruptible power supply or
UPS. These are devices that connect between the mains outlet and the PC. Inside
the box there is a rechargeable battery, battery charger and an ‘inverter’,
which is an electronic circuit that converts low voltage DC, from the battery,
into 230 volts AC.
Many UPS operate in
‘online’ mode, where the battery is constantly charged, supplying power to the
inverter and generating a continuous 230 volt AC output so in the event of power
cut there will be no break at all in the mains supply going to the computer.
This method has the added advantage of isolating the mains from the computer,
eliminating spikes and surges. Most other type of UPS operates in ‘standby’, or
a hybrid online/standby mode and kick in automatically when there’s a power cut,
restoring the supply to the computer, usually with a few milliseconds, which is
too brief a period to do any damage.
The cheapest domestic
models, which are about the size of a shoebox and are designed to power a single
desktop PC and monitor; these cost from around £50 upwards. Low cost UPS are
normally capable of providing between 10 and 20 minutes of power, which is more
than enough time to save data and safely shut the machine down. Many models are
supplied with software to do the job automatically though some very basic types
only sound an alarm or generate an on-screen warning display. When shopping
around for a UPS it is important to ensure that it has sufficient power for your
PC and its peripherals (see Tip of the Week). Incidentally, if your main PC is a
laptop then you don’t need a UPS or spike suppressor, the facility is built in,
courtesy of the computer’s battery and battery charger.
Next week – Linux, what’s it all about?
large reduction in the mains supply voltage, causing lights to dim and
electronic devices like PCs to stop working
television decoder, for BSKYB Satellite and FreeView television
increases in mains voltage, varying from a few volts to several thousand
TIP OF THE WEEK
Considering the cost of a PC and the value of the data most
of them contain it is a false economy not to install a UPS. But the wrong type
can be almost as bad as having no protection at all. UPS devices are normally
rated by capacity, stated in volt-amperes or ‘VA’. Heavy duty models, for
network servers and systems may be rated at upwards of 2000VA but for a single
desktop PC and monitor a UPS rated between 300 to 500VA will normally be able to
provide between 10 and 15 minutes worth of power.