Nautel NAB05E, Технические инструкции

Страница: 15 / 45

48 VOLT BATTERY CHARGER
NAB05E
Page 2-2
01 September 2004
2.2.5 RAMP GENERATOR OVERVIEW:
The ramp generator consists of a switching transistor
and an integrating circuit. When a 'ramp inhibit'
signal is not applied to the ramp generator from the 8-
second timer; a 'high' output from the digitizer will
turn on the transistor. When the transistor is turned
on, the voltage across the capacitor in the integrating
circuit, which is the output of the ramp generator, will
discharge to the dc reference level. When the output
of the digitizer, switches to 'low', the transistor will
turn off. The capacitor in the integrating circuit will
charge t23 V dc. The ramp generator's
output will be a relatively linear ramp voltage (the
R/C time constant of the integrating circuit is long at
the switching repetition rate), that increases from the
dc reference level to a positive dc voltage. A linear
ramp waveform will be generated for each half cycle
of the ac power supply voltage applied to the 23 V dc
power supply. When a 'ramp inhibit' signal is applied
to the ramp generator, the charging voltage for the
capacitor in the integrating circuit is removed and the
ramp generator's output will be maintained at the dc
reference level.
2.2.6 VOLTS COMPARATOR OVERVIEW:
The battery voltage comparator circuit utilizes a logic
circuit that compares the battery terminal voltage to a
temperature compensated, adjustable, reference
voltage. The reference voltage is preset to a level that
is slightly below the fully charged, no load, terminal
voltage of the battery. The fully charged, no load
terminal voltage of batteries with different electrolyte
will differ. The precise no load, voltage; of the
batteries to be charged must be obtained from the
battery manufacturer. When the battery terminal
voltage decays to a level that is below the reference
voltage, the output of the logic circuit generates a
'master reset' signal for an eight second timer. If the
battery terminal voltage does not decay to a level that
is below the reference voltage, the 'master reset' signal
is not generated. A temperature sensor, that is
monitoring the ambient air in the vicinity of the
batteries, automatically changes the reference voltage
with changes in temperature. This feature reduces
boiling off of battery electrolyte, when the ambient
temperature is high, by lowering the reference voltage
as the sensed temperature increases and effectively
increasing the time required to generate a 'master
reset' signal as the batteries approach their fully
charged condition.
2.2.7 EIGHT SECOND TIMER
OVERVIEW: An oscillator/timer integrated circuit
device is used as the eight second timer. In the
absence of a 'master reset' signal, the output of the
eight second timer will apply a 'ramp inhibit' signal to
the ramp generator. When a 'master reset' is applied,
the timer will remove the 'ramp inhibit' signal for
eight seconds and then reapply it until the next 'master
reset' signal is generated.
2.2.8 CHARGING CURRENT CONTROL
OVERVIEW: The charging current control circuit
consists of an operational amplifier that produces an
adjustable dc voltage as its 'control voltage'. The
control voltage is proportional to the differ-ence
between a dc reference and a dc voltage (charging
current voltage) that is representative of the battery
charging current. The 'charging current voltage' is
developed across a resistor in the battery charging
circuit. The dc reference voltage is adjusted, during
calibration, to a level that represents the maximum
charge current to be applied to the batteries. When
current is being applied to the batteries at the desired
magnitude, the 'charging current voltage' will be equal
to the dc reference voltage. The resultant 'control
voltage' output will stabilize to a level that will cause
the 'thyristor control' pulse to be generated during the
portion of each ac power supply voltage half cycle
that will result in the average dc voltage output, of the
switched full-wave rectifier, maintaining the charging
current at the desired level. If the charging current
attempts to change, as the result of the internal
resistance of the battery changing, the 'control voltage'
output will change in the appropriate direction
(increase if less current is required or decrease if more
current is required) and cause the 'thyristor control'
pulse to be generated later or earlier in each ac power
supply voltage half cycle and maintain the charging
current at the desired level.
2.2.9 THYRISTOR TURN-ON OVERVIEW:
The thyristor turn-on control consists of a comparator
and a switching transistor. The comparator compares
the voltage level of the ramp generator's output to the
'control voltage' output of the charging current control
circuit. When the ramp generator's output is less
positive than the 'control voltage', the comparator's
output will be a high (+23 V dc) level and the switch-
ing transistor will be turned off. An output will not be
produced by the thyristor turn-on control circuit.
When the ramp voltage goes more positive than the