Hitachi RAS-25CNH2 Service Manual page 58

(2) Overload control circuit (OVL control circuit)
Overload control is to decrease the speed of the compressor and reduce the load when the load on the
G
air conditioner increases to an overload state, in order to protect the compressor, electronic components
and power breaker.
Overloads are judgement by comparing the DC current level and set value.
G
Fig. 8-4 shows the overload control system configuration and Fig. 8-5 is a characteristic diagram of
G
overload judgement values. There are two judgement methods-external judgement which compares the
externally set value with the DC current value regardless of the rotation speed and internal judgement
which compares the set value that varies according to the rotation speed programmed in the micro
computer software with the DC current value.
To power module
–
negative terminal
(R24)
Detection
resistor
1
. Overload external judgement circuit
The filter consisting of R2 and C515 removes high harmonic components from the voltage generated by
G
the current flowing to Detection resistor; R2 and C501A average the voltage. This voltage is then input
to OP1 pin 5 and amplified and is supplied to micro computer pin
input with the internally set value, and if the input exceeds the set value, it enters overload control status.
Fig. 8-7 shows the rotation speed control. When the voltage at pin
G
set value, the micro computer decreases the rotation speed of the compressor and reduces the load
regardless of the rotation speed commanded by the indoor micro computer.
Voltage amp
circuit
(Internal judgement)
DC voltage
Fig. 8-4 Overload Control System Configuration
Judgement value according to the rotation speed
(internal judgement value)
Rotation speed
– 61 –
AX-8J01 micro computer
Judgement OVL
with respect to
externally set
value
Judgement OVL
A/D
according to the rotation
converter
speed
Selects data according
A/D
to the rotation speed and
converter
DC voltage
OVL start current data
Fig. 8-5
:
. The micro computer compares this
:
Motor control
process
of the micro computer exceeds the