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Magnum VS –48 Vdc User’s Manual Page 24
Battery Low Voltage Disconnect
In order to prevent damage to the battery due to deep discharge, the dc power system has
hardware and software support for a battery Low Voltage Disconnect (LVD). When the battery
voltage reaches the threshold set by the LVD 1 Trip Voltage setting during discharge, the dc
power system will activate the LVD contactor to disconnect the battery from the system. The
LVD will remain open until ac power is restored to the system and the bus voltage reaches the
level defined by the LVD 1 Reset Voltage variable. The LVD control can be disabled on the
LVD parameters screen in the controller.
NOTE: The LVD is normally energized and must be commanded to open. This assures that
the LVD will remain closed even if the controller fails or is removed.
The LVD will not be energized until a battery string is installed with the correct polarity and the
battery disconnect switch is turned on. This will prevent the battery from being hooked up
backwards and damaging the rectifiers and/or the loads. Once the battery is connected
correctly and the LVD is closed, the LVD will open only in low voltage situations. The battery
connections are to be used for the battery only.
Battery Functional Test
The controller is able to functionally test the battery. This is a short duration test intended to
confirm that the battery can deliver current to the load without an unusual drop in system
voltage. Excessive voltage drop may be an indication of high resistance electrical connections,
high battery internal impedance or impending battery failure. For the test the controller lowers
the system voltage sufficiently that the batteries will deliver the current required by the load
equipment and thereby start to discharge. The controller monitors the voltage drop to determine
if the battery is good or bad. A collapse of voltage will not cause an interruption in power to the
load, as the rectifiers remain operational and will continue to support the load if this occurs.
Functional test defaults are a 10 second duration and -48 V pass/fail voltage threshold. Very
high or low equipment loads relative to the size of the battery may invalidate the results of this
test. Presently this test may only be initiated manually via the controller with display keypad. A
future upgrade will add this capability to the network management card for remote access.
Counter Electro-Motive Force Module Connections
A connection is provided to connect a Counter Electro-Motive Force (CEMF) Module. A CEMF
is a semiconductor device connected in series with a battery and used to reduce the voltage to
loads that cannot tolerate the “normal” main cell voltage. The CEMF cells are automatically
switched out of the circuit when the discharge voltage drops to a predetermined level and are
automatically switched back into the circuit when the battery approaches its normal float value.