Chapter 14: Power Supply and Electrical Issues^331
The power stored in the UPS’ battery is passed through an inverter that creates an AC
supply for the PC to convert to DC power. Figure 14-12 shows an example of the type of
UPS commonly found in an office setting. Better UPS devices supply AC power to a PC
that is usually better than the AC power from the wall. A less expensive UPS may not
provide a smooth power wave and may actually damage equipment plugged into it.
UPS Device Types
There are two general types of UPS devices, which are differentiated by how they store
and supply power to a PC. The two categories are:
Standby This type of UPS is nothing more than a battery backup that acts as
a safeguard against a blackout or brownout. As long as the UPS is in standby
mode, it uses a small amount of power to charge its battery but passes the
remaining unfiltered AC power to the PC. Should there be a need for power,
the UPS continues to provide the PC with AC power. One of the downsides to
standby type UPS units is that it will typically pass any large surges or spikes
through to the PC.
Online An online (a.k.a. inline) UPS provides AC power from its battery and
a power inverter that converts the battery’s DC power to AC power. The UPS’
battery is constantly being recharged from an AC power source through an
input inverter. The UPS absorbs all high and low-voltage events, such as
spikes, blackouts, and brownouts, on the AC power line. Extended brownouts
and blackouts are restored from the UPS’ battery, which begins discharging
immediately and will eventually fail without the AC power being restored.
With this type of UPS, the PC gets its power from the UPS’ battery with the
battery constantly being from the AC power source. Figure 14-13 shows a large
online UPS that would be used to protect one or more servers on a network.Figure 14-11. A plug strip that includes a surge suppressor