Hitachi RAM-18QH5E, Service Manual

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8. Overload control circuit (OVL control)
●
Overload control decelerates speed of compressor reducing load when the load to protect compressor,
electronics parts and power breaker, when operation enters overload status due to increase of load for
room temperature adjustment.
●
To judge overload, DC current and set value are compared.
●
Fig. 8-1 shows the overload control system configuration and Fig. 8-2 shows characteristic diagram of
overload judgement values. There are two judgements. One is external judgment: External set value and
DC current value are compared for judgment regardless of rotation speed. The other is internal judgment:
set value varying according to rotation speed programmed in microcomputer is compared with DC current
value for judgment.
DC current
Voltage amplifier
circuit
(Internal judgement)
DC voltage
Judgement value according to the rotation speed
(internal judgement value)
OVL judgment
to external set
value
A/D
converter
(E2PROM built-in)
A/D
converter
OVL judgment
according to
rotation speed
Data selection
according to rotation
speed/DC voltage
OVL start current data
Rotation speed data
Motor control
process
AX-6M01 micro computer
Detection
resistor
Fig. 8-1 Overload Control System Configuration
Fig. 8-2
DC current
Rotation speed
(1) Overload external judgement circuit
●
Voltage generated from current flowing in shunt R is balanced by R245 and C220 and input to pin 5 of
IC4. Then voltage-amplified value is input to pin
:
of microcomputer to compare with internal data of
EEPROM. When values correspond, microcomputer enters overload control.
●
Fig. 8-4 shows the rotation speed control. When value at pin
:
of microcomputer exceeds set value,
rotation speed of compressor decelerates to reduce load regardless of rotation speed commanded from
indoor unit.