Lucent Technologies Lineage
®
2000 ECS Battery Plant J85500D-3
Issue 5 January 1999
Engineering, Planning and Ordering 3 - 11
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
systems, dictate maximum allowable voltage drops, thus
simplifying the calculations. Lucent Technologies offers a
computerized service to optimize the selection of cable sizes and
battery capacity for any application. Contact your Lucent
Technologies Energy Systems Account Executive for details on
this service.
Alternatively, various rules-of-thumb are used to specify
maximum voltage drops. During discharge, the critical voltage
drop is the total drop from the battery terminals to the load
equipment. Increasing the voltage drop from dc distribution to
load can potentially be compensated by decreasing the voltage
drop from batteries to dc distribution.
The voltage drop from the batteries to the distribution (0.25
volts) has been covered above, under Battery string voltage
drop and balancing. One rule-of-thumb specifies a maximum
voltage drop of 0.75 volts in the feeder loop from the dc
distribution to the load and back again, using the List 2 drain for
that circuit as listed in Table 3-B. Voltage drop calculation
methods are described in thenext section, Calculating voltage
drop.
Fill in the selected or calculated system voltage drops below.
19. Maximum drop (batteries to dc distribution): ____ volts
20. Maximum drop (dc distribution to load): ____ volts
21. Maximum drop (batteries to load): (19) + (20) = ____
volts
