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UPS
SYSTEMS
Maximising UPS
battery efficiency
By Alan Luscombe, director
at Uninterruptible Power
Supplies Ltd., a Kohler
company
Proactive battery management: critical for a
dependable UPS service.
The deployment of uninterruptible power supplies
(UPSs) and the benefits that they can offer is
generally well understood. However, the reliable and
correct functioning of the UPS is highly dependent
upon the batteries within and this is an operational
vulnerability.
If left in service long enough batteries will need to
be replaced and their performance and even life span
can be compromised by a range of fault conditions.
Batteries are fundamental to the effectiveness
of this important power backup resource and
understanding the possible fault conditions, their
causes and how to mitigate their impact, is critical to
reliable operation.
All UPSs depend on a reliable energy storage
mechanism for accumulating electrical energy during
normal mains power availability and then dispensing
its critical load when the supply fails or exceeds critical
limits. Currently, this is most frequently achieved
using valve-regulated lead-acid (VRLA) batteries and
operators should understand what can be done to
optimise performance and maximise battery life.
Sealed VRLA batteries are environmentally friendly
in operation, safe, and highly suited for office
deployment. UPS manufacturers usually design their
cabinets to accommodate batteries, even offering
matching battery cabinets or racks should extra
battery autonomy be required.
A battery system for a UPS application comprises a
number of blocks that can be built up and configured
to meet the specific needs of individual applications.
Firstly, a single series string can be assembled to meet
UPS float voltage settings, as the voltage across the
string’s terminals equals the sum of the individual
block voltages. Then, a number of series strings can be
connected in parallel, either to increase the battery Ah
rating and autonomy, or to build in redundancy. If one
series string fails, any others connected in parallel will
continue to operate.
Once the battery blocks have been configured and
installed into the UPS system, a regular monitoring
and maintenance programme can be initiated. This
is essential for maximum battery performance and
the longest operational life. To understand such a
programme, an understanding of the problems that
can afflict batteries will help.
Common battery problems
A lot of problems arise from poor equalisation
meaning that some battery blocks overcharge while
others undercharge.
During overcharging excessive charge voltages
force a high overcharge current into the battery which
dissipates as heat. In a VRLA battery it can cause gas
emission through the safety valve which will in turn
corrode the positive plate material, reducing battery
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