Page 223 - Uninterruptible Power Supplies

Batteries
Batteries 221

The above figures are at best a rough guide, and economics may vary
with the power rating being considered
One should also bear in mind the life-cycle of the various cells. VRLA
cells are normally available with a design life varying from 5 to 10
years, and there is the possibility of increasing these figures. At least
one manufacturer claims a design life of 20 years, but under a strict
regime of operation. In the writer’s knowledge most 10-year design life
cells afford in practice a life of approximately 7 to 8 years.
There is little doubt that an installation with a long forecast life (say
20 years) may find nickel-cadmium or Plante cells more attractive, but
site conditions such as available space will have a significant impact on
final choice.
One should also bear in mind that cost of battery replacement is high
and attention should be given to labor costs, the disposal costs of the
old cells, and downtime for the system, as well as to cost of new cells.
It should be remembered that all the figures and diagrams relate to
manufacturers’ accredited information. There will be slight variations
between manufacturers’ figures.

Future Trends
Future trends will show an increasing emphasis on relating battery
design to UPS application.
A problem facing battery manufacturers is the ever-increasing desire
to reduce the use of such elements as cadmium and lead, both of which
are considered environmentally unfriendly. However, well-established
and effective recycling mechanisms exist for all batteries using these
elements.
Possibly, future UPS units may use lithium-ion cells which continue
to be developed. Certainly, changes in design of batteries will result
from the very active research program in progress at present.

Bibliography
IEEE 1184-1994—Guide and sizing of batteries for UPS
IEC 62060 Battery Monitors
UL 1778—Flame retardancy of battery cases
UL 94V-O or 94V-2—Flame retardancy
UL 924—Battery vents
BS 6290 EN-28601
BS 6290 EN60068-2-6
BS 6290 EN 60068-2-20
BS 6290 EN 60068-2-32
BS - EN 60623

Books
Berndt, D., Maintenance-Free Batteries: Lead-Acid, Nickel/Cadmium, Nickel/Metal
Hydride: A Handbook of Battery Technology, New York, Wiley, 1997.

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