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4
4.0 – THEORY of OPERATION
The EP is built around a switching power supply with
a wide range AC / DC power-factor-corrected input.
The output of the supply is rectangular-current-
limited ideal for battery charging; and the charging
voltage is temperature compensated.
The EP has isolated form C alarm contacts for
remote signaling that indicate line power status.
Magnetic circuit breakers are provided on both the
line input and load output. Indicators for Input,
Alarm, and Load show visual system status. A
replaceable fuse and voltage clamp protect the EP
and the load equipment against reverse battery
hook-up.
The EP has 2 modes of operation: "LINE-UP", when
line power is present, and "LINE-DOWN", when line
power is missing.
4.1 – LINE-UP Mode
Please see Fig. 4.1.1. In LINE-UP mode, the power
supply delivers 13.8 Volts nominal for 12 Volt
systems, or 27.6 Volts nominal for 24 Volt systems,
to the battery and load. Power is divided between
the battery and load based on which requires the
most current (lowest impedance). Under light load
conditions, the full 150 Watts produced by the power
supply is available for battery charging.
In the LINE-UP mode, the alarm contacts are closed
in the N.C. position. Fig. 4.1.1 shows the current
path for the alarm circuit. The AC indicator is lit and
the ALARM indicator is dark.
LINE
POWER
POWER
SUPPLY
ALARM
N.C.
N.O.
COM
Figure 4.1.1 – Operation in LINE-UP Mode.
4.2 – LINE-DOWN Mode
POWER
TO LOAD
STORAGE
BATTERY
See Fig. 4.2.1. In LINE-DOWN mode, the power
supply delivers no power. All load power is supplied
by the battery.
In the LINE-DOWN mode, the alarm contacts are
closed in the N.O. position. Fig. 4.2.1 shows the
current path for the alarm circuit. The AC indicator is
dark and the ALARM indicator is lit.
Figure 4.2.1 – Operation in LINE-DOWN Mode.
4.3 – Temperature Compensation
Batteries are damaged by prolonged under-charging
or over-charging. The correct voltage for battery
charging depends on temperature. Low
temperatures require a higher voltage to avoid
under-charging. High temperatures require a lower
voltage to avoid over-charging. Outdoor systems
have the widest temperature extremes. To extend
the life of the battery, the EP is temperature
compensated. It adjusts the maximum charge
voltage according to the temperature of the
battery.
4.4 – Load Voltage
At all times, the load voltage is essentially equal to
the battery voltage. All variations due to state-of-
charge and temperature compensation are passed
directly to the load. Some sensitive electronic
equipment cannot tolerate the wide voltage range
over which batteries operate. The load equipment
input must be designed for the normal range of
battery voltage, 11 – 15 Volts for 12 volt systems,
22-30 Volts for 24 Volt systems.
Applications requiring precise input voltage should
use a DC-DC converter with a regulated output.
These converters provide a stable voltage to the
load regardless of battery voltage. Contact Newmar
for more information.
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