UPS (uninterruptible power supply)
is a device that allows your computer to
keep running for at least a short time
when the primary power source is lost.
It also provides protection from power sur-
ges. A UPS contains a battery that "kicks
in" when the device senses a loss of pow-
er from the primary source. If you are using
the computer when the UPS notifies you of
the power loss, you have time to save any
data you are working on and exit gracefully
before the secondary power source (the
battery) runs out. When all power runs out,
any data in your computer's random acc-
ess memory (RAM) is erased. When power
surges occur, a UPS intercepts the surge
so that it doesn't damage your computer.

     A system that provides protection
against commercial power failure and va-
riations in voltage and frequency.
Uninterruptible power systems (UPS) have
a wide variety of applications where unpre-
dictable changes in commercial power
will adversely affect equipment. This equip-
ment may include computer installations,
telephone exchanges, communications
networks, motor and sequencing controls,
electronic cash registers, hospital intensive
care units, and a host of others. The uninte-
rruptible power system may be used on-
line between the commercial power and
the sensitive load to provide transient free
well-regulated power, or off-line and
switched in only when commercial power
fails.

     VRLA stands for valve regulated lead
acid and is the designation for low main-
tenance lead-acid batteries, also called
recombinant batteries.

     VRLA batteries are commonly further
classified as:

• Absorbent glass mat battery
• Gel battery

    These batteries are often colloquially
called sealed lead-acid batteries, but
this term is misleading: a sealed battery
would be a safety hazard due to overpre-
ssure risks when overcharging, and
there is always a safety valve present,
hence the name valve-regulated. Sealed
is opposed to vented (also called flooded).
Because VRLA batteries use much less
electrolyte (battery acid) than traditional
lead-acid batteries, they are also occasi-
onally referred to as an "acid-starved"
design. 

     The name "valve regulated" does not
wholly describe the technology; these
are really "recombinant" batteries, which
means that the oxygen evolved at the po-
sitive plates will largely recombine with
the hydrogen ready to evolve on the neg-
ative plates, creating water--thus preven-
ting water loss. The valve is strictly a
safety feature in case the rate of hydrog-
en evolution becomes dangerously high.

     One result of this design is a much
higher ratio of power to "floorspace" than
large, flooded type battery systems;
another is a high-rate power capacity,
though of relatively short duration. As a
result, VRLA batteries are frequently
employed in UPS (uninterruptible
power supply) or other high-rate applic-
ations. Long duration applications such
as telecommunications are not as well-
suited to VRLA batteries, as there are
other, more applicable battery designs
available.