Hitachi RAF-25FX8 Service Manual page 116

R003,R004,R608,R613, detect the DC voltage at the power circuit. The microcomputer receives a DC
voltage and applies correction to the overload set value so the DC current will be low when the DC
voltage is high.
(Since the load level is indicated by the DC voltage multiplied by DC current, R247, R248, R249 are
provided to perform the same overload judgement even when the voltage varies.)
0
0
(3). Start current control
It is required to maintain the start current (DC current) constant to smooth the start of the DC motor of
the compressor.
RAC-25FX8 and RAC-35FX8 use software to control the start current.
The start current varies when the supply voltage varies. This control method copes with variations in the
voltages as follows.
(1) Turns on the power module's U + and V - transistors so the current flows to the motor windings as
shown in Fig. 6-6.
(2) Varies the turn-ON time of the U + transistor according to the DC voltage level and the start is
controlled so the start current is approx. 10A .
P
DC
Voltage
N
Rotation speed
Fig. 6-5
IPM
DC current
+
U
-
U
Detection
resistor
Fig. 6-6
DC voltage : low
DC current : high
DC voltage : 260V
DC voltage : high
DC current : low
Compressor motor
+ +
V W
U
V
W
-
-
V
W
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