Lucent Technologies Lineage
®
2000 ECS/GPS Battery Plant J85500G-2
Issue 6 May 1999
Engineering, Planning and Ordering 3 - 9
At least one on-line spare rectifier must be included in the plant
for increased reliability.
Any on-line spares must be the same size as the largest rectifier
in the plant.
At least 20 percent additional capacity must be included in the
plant to provide recharge capacity and spares.
See below, Lineage
®
2000 Engineering Specifics, Rectifier
Sizing, for specifics on sizes and quantities of rectifiers for the
ECS Battery Plant.
Battery string
voltage drop and
balancing
The rectifiers, while recharging or floating the batteries,
maintain a constant voltage at the battery plant bus bars. When
batteries are accepting recharge current after a discharge, there
is a finite voltage drop from the charge bus bars inside the ECS
bay to the battery string terminals. This voltage drop is, of
course, proportional to the magnitude of the recharge current.
Any voltage drop from the battery plant bus bars to the terminals
of each battery string will tend to slow the rate of battery
recharge and delay their readiness for future discharges. The
same cable resistance responsible for voltage during recharge
creates a voltage drop during discharge as well. Voltage drop
during discharge can limit the effectiveness of the batteries in
supplying the necessary reserve.
For these reasons, the engineer should minimize the voltage drop
between bus bars and batteries by interconnecting them with the
largest practical wire size.
In battery plants with multiple, parallel strings of batteries, the
cable lengths from the dc distribution subsystem to each string
will be different. It is as important to “balance” the strings as it
is to minimize voltage drop. Multiple strings are balanced by
sizing cables for equal resistance (and therefore equal voltage
drop) between terminals and bus bars. If battery strings are
unbalanced, the string with the least voltage drop to the dc
distribution provides more than its share of current during each
discharge. A battery string that undergoes excessive discharges
may fail unexpectedly before its predicted end of life.
To both minimize and equalize voltage drops to parallel strings,
the largest practical wire size should be selected for the most
distant battery string. The cable sizes for the strings nearer to the
