Nautel NAB05E, Технические инструкции

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48 VOLT BATTERY CHARGER
NAB05E
Page 2-1
01 September 2004
SECTION 2
THEORY OF OPERATION
GENERAL
2.1
The theory of operation for the battery
charger is presented in this section. The information
is presented in detail using figure SD-2 - electrical
schematic as a reference.
BATTERY CHARGER OVERVIEW
2.2
The 48 volt dc battery charger operates on
the principle that the terminal voltage of batteries
being charged will eventually stabilize at a voltage
that can be predetermined when they are fully
charged, under no load conditions. Prior to reaching
the full-charge condition, the battery terminal voltage
will approach or reach this full charge voltage when a
charging current is being applied and then decay to a
lesser voltage when the charging current is removed.
If the battery terminal voltage is compared to a
reference voltage that is slightly less than the
full-charge, no load, terminal voltage, it will take
progressively longer for the battery terminal voltage
to decay to a level that is less than the reference
voltage as the battery approaches the full charge
condition. This feature is utilized in the battery
charger and is used to control the application of eight
second bursts of current to the batteries being charged.
When the batteries are in a discharged condition, the
eight second current bursts will occur at frequent
intervals. As the batteries approach the fully charged
condition, the eight second current bursts will occur
less frequently until the interval time is nearly infinite.
The following provides an overview of the subject
battery charger, using the block diagram shown in
figure SD-1.
2.2.1 AC POWER SUPPLY OVERVIEW:
The ac power supply consists of an EMI filter, an on/
off switch, a fuse and a power transformer. The EMI
filter, removes unwanted transients from the ac power
source. The power transformer has two identical 115
volt primary windings and two sets of secondary
windings. When the ac power source voltage is 115
vac, 60 Hz, the primary windings of the power
transformer are connected in parallel. When the ac
power source voltage is 230 V ac, 50 Hz, the primary
windings are connected in series. One set of
secondary windings provides 17.5 V ac, RMS for the
low voltage power supplies. The second set of
secondary windings provides a centre tapped 150
(75-0-75) V ac RMS for the battery charging dc
voltage source.
2.2.2 23 V DC POWER SUPPLY OVERVIEW:
The 17.5 volt ac, RMS voltage from the power
transformer is applied to a full-wave bridge rectifier.
The output of the bridge rectifier will be an
unregulated, ripple, dc voltage with a nominal level of
23 V dc. The ripple frequency will be twice the
frequency of the ac power source. Their are two
outputs from the 23 V dc power supply, one is the
unsmoothed, ripple, dc voltage and the other is a
smoothed, unregulated, 23 V dc. The dc return path
for the 23 V dc power supply is not connected to
chassis ground but is connected to the positive
terminal of the battery voltage. This point is the dc
reference level for all of the logic circuits. A light
emitting diode is connected across the 23 V dc output
and will indicate the battery charger is functioning by
turning on when 23 V dc is present.
2.2.3 15 V DC POWER SUPPLY OVER-
VIEW: The regulated 15 V dc power supply consists
of an integrated circuit device that acts as a voltage
regulator. The output of the regulator is maintained at
+15 V dc with respect to the same dc reference level
as the 23 V dc power supply, regardless of the
fluctuations in the output of the 23 V dc power supply
output.
2.2.4 DIGITIZER OVERVIEW: A logic
circuit compares the ripple dc voltage from the
unregulated 23 V dc power supply to a fixed, dc refer-
ence voltage and produces a rectangular waveform at
the ripple frequency. The frequency of the ripple and
therefore the repetition frequency of the rectangular
waveform is twice the frequency of the ac power
source. The rectangular waveform will be high (+23
V dc) when the reference voltage is more positive
than the ripple voltage. It will remain in this state for
a relatively short duration. It will switch low (dc
reference level) when the reference voltage is less
positive than the ripple voltage and will remain in this
state until the ripple voltage falls below the reference
voltage.