standards and guidelines for communication sites - Radio And ...

STANDARDS AND GUIDELINES FOR COMMUNICATION SITES BATTERY SYSTEMS
Floor loading, growth, and system load are a few of the factors that determine the number of strings of
batteries required. All battery backup systems require maintenance. Some of the maintenance
operations require the batteries to be off-line. Because there is no way to predict a short duration power
interruption, a minimum of two strings of batteries is strongly recommended. This will ensure some
amount of battery backup should an interruption occur during battery maintenance.
Too many strings of batteries also presents a problem. Should a fault occur in one cell in one string of
batteries, diagnosing and locating the fault becomes more difficult as the number of strings increases.
To protect the battery plant from a catastrophic failure of a single string of batteries, overcurrent
protection is necessary for each individual string in the plant. The sizing of this protection should be as
follows:
System amp capacity/Number of battery strings -1 = Required protection
Manufacturer recommendations for the maximum number of strings varies widely. Motorola
recommends that the power system be initially designed for a minimum of two strings and a maximum
of six strings of batteries when the system is fully implemented. This will allow some margin for excess
growth should the system exceed the anticipated load of a fully implemented system.
6.7.7 BATTERY CHARGING
Batteries that have been discharged to a state below full charge must be fully recharged within 24 hours.
During this process considerable charging current may flow and flooded cell batteries will give off a
higher level of gas than during normal float charge. A float charge must be maintained to keep the
battery in a fully charged state. Over or under charging of batteries will cause an increased need for
battery maintenance and may greatly shorten the service life of the battery. It is important that the
charging system is properly adjusted per the manufacturer's specifications. Overcharging and
undercharging alarms shall be installed to ensure that battery charging problems are detected quickly.
6.7.8 BATTERY TEMPERATURE REQUIREMENTS
Battery performance and service life are significantly affected by operating temperature. For full-rated
performance and maximum service life, the battery temperature should be maintained close to 24° C
(75° F). The battery operating time is reduced as the temperature falls; conversely, the operating time is
increased as the temperature rises. However, when batteries are subjected to elevated temperatures the
service life of the battery is reduced.
Reference temperature is often overlooked in rating batteries. Battery manufacturers typically use
22.2° C (72° F) as the reference temperature. A battery operated at 0° C (32° F) produces 30% capacity,
but lasts for 130% or more of the rated life. Conversely, a battery operated at 38° C (100° F) produces
130% battery capacity, but may last less than 1 year.
NOTE: If building codes do not allow batteries within the same compartment as the climatized radio equipment
enclosure, outdoor battery pedestals may have to be protected from direct sunlight or elevated to
prevent their burial in snow during winter (where applicable).
68P81089E50-B 9/1/05 6-33