Lucent Technologies Lineage
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2000 ECS/GPS Battery Plant J85500G-2
3 - 10 Engineering, Planning and Ordering
Issue 6 May 1999
dc distribution are then selected so that the drop in each is
roughly the same as that for the most distant string.
Some using systems, such as electronic switching systems or
transmission systems, dictate maximum allowable voltage
drops. A common rule-of-thumb is a maximum drop of 0.25
volts in the leads from battery string terminals to the dc
distribution. Voltage drop calculation methods are described
below under Calculating voltage drop. For the calculation, use
the plant List 2 drain divided by the number of parallel battery
strings.
For extraordinarily long runs between batteries and dc
distribution, wire gauges may be called for that cannot be
conveniently terminated at the equipment at either end. In such
cases, the necessary larger cables may usually be tapped down to
smaller ones to make the actual connections to the bus bars and
battery terminals.
Battery size
versus voltage
drop
The critical requirement for a battery plant is that the input
voltage to the load equipment remain within the proper
operating range for the prescribed reserve time. Constants
imposed by the typical 48-volt battery system are the normal
battery float voltage and the minimum battery end voltage.
Note: Engineering of plants with end cell or counter-emf cell
battery arrangements is not included in this discussion.
The variables that may be adjusted to ensure service for the
specified time period are battery capacity and voltage drop from
batteries to the load. If the system is engineered with a relatively
small voltage drop, large gauge cabling is required, but battery
capacity can be minimized. If a large voltage drop exists
between batteries and load, the minimum load voltage may be
reached before the batteries reach their end voltage so that their
rated capacity is only partially used. In this second case,
additional battery capacity would be required.
The trade-off between battery size and wire size is an economic
one. For systems with long cabling runs, the cost of large
quantities of heavy wire should be balanced against the cost of
additional batteries. Finding the exact optimum combination of
cabling and batteries involves complex iterative calculations
which are beyond the scope of this discussion. Some using
systems, such as electronic switching systems or transmission
