Hitachi RAS-25JX4 Service Manual page 69

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.)
(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-25JX4, RAC-35JX4 uses 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 moduleÕs U
as shown in Fig. 6-6.
(2) Varies the turn-ON time of the W
is controlled so the start current is approx. 10A .
DC
Voltage
0
0
and V - transistors so the current flows to the motor windings
+
+
DC current
P
Detection
N
resistor
Rotation speed
Fig. 6-5
transistor according to the DC voltage level and the start
IPM
U + V + W +
U V W
− − −
Fig. 6-6
74
DC voltage : Low
DC current : High
DC voltage : 260V
DC voltage : High
DC current : Low
Compressor motor
U
V
W