Start Current Control - Hitachi RAS-18YH5 Service Manual

R003,R004,R608,R613, detect the C voltage at the power circuit. The microcomputer receives a
C voltage and applies correction to the overload set value so the C current will be low when the
C voltage is high.
(Since the load level is indicated by the C voltage multiplied by C current, R247, R248 and 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 ( C current) constant to smooth the start of the C motor
of the compressor.
RAC -18YH5 uses software to control the start current.
The start current varies when 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 U
is controlled so the start current is approx. 10A .
Voltage
0 0
C current
P
C
etection
N
resistor
Rotation speed
Fig. 6-5
and V - transistors so the current flows to the motor windings
+
+
transistor according to the C voltage level and the start
IPM
U + V +
U V
Fig. 6-6
– 58 –
C voltage : Low
C current : High
C voltage : 260V
C voltage : High
C current : Low
Compressor motor
W +
U
V
W
W