Rockwell Automation 1757-BEM ProcessLogix Battery Extension Module Installation Instructions - Manual (Page 9)

ProcessLogix Battery Extension Module 9
Publication 1757-IN093B-EN-P - April 2004
A settable, positive temperature coefficient (PTC) overcurrent protection device in series with
the load safeguards the battery pack against excessive current drain.
Test Control
Two tests are routinely performed on the battery: battery present and battery load. The
battery present test is a simple (unloaded) check that a battery is present. It is run at relatively
frequent intervals of once every 8.5 seconds. At less frequent intervals, the battery load test
presents a load to the battery sufficient to provide a level of confidence that the battery is
healthy. A load of 350mA is applied to the battery for a short period of 8.5 seconds at
intervals of once every 73 minutes. Precautions are taken such that the test load is removed
from the battery circuit if main power fails while the test is in progress.
During the battery tests, charger voltage must be removed temporarily from the battery
circuit. A 'window' voltage comparator then detects the actual battery voltage below a
minimum level of 3.0 volts, as well as above a maximum level of 4.6 volts.
Display and Alarm
One LED, visible through the front cover of the 1757-BEM, provides you status information.
The LED is labeled OK and indicates the health of the internal battery pack. This BATTERY
OK LED is a dual color red/green LED driven from the output of the battery window
voltage comparator.
• When the LED is green the battery voltage is within the acceptable level.
• When the LED is red the battery voltage falls outside the acceptable range.
Attach the external and/or remote alarm(s) through screw terminals accessible through the
front door of the 1757-BEM. These terminals are connected to the normally-opened and
normally-closed contacts of a relay that is driven from the output of the battery window
voltage comparator.
• The relay NO contacts are closed if the battery voltage is within the acceptable level
(3.0-3.6 vdc).
• The relay NO contacts are open if the battery voltage falls outside the acceptable
range.