Hitachi ZW180, Technical Manual

Page: 166 / 374

SYSTEM / Electrical System
T2-4-16
SURGE VOLTAGE PREVENTION CIRCUIT
•
When the engine is stopped (key switch: OFF),
current from terminal M of the key switch is
stopped and the battery relay is turned OFF.
•
Although the key switch is turned OFF, the engine
does not stop immediately due to inertia force so
that the alternator continues to generate
electricity.
•
As the generating current cannot flow to the
battery, surge voltage arises in the circuit and
failures of the electronic components, such as the
controller, possibly cause. In order to prevent the
occurrence of surge voltage, the surge voltage
prevention circuit is provided.
•
When the alternator is generating electricity,
generating current from terminal L of the
alternator flows to terminal 2-2 of the monitor unit.
The monitor unit connects terminal 2-10 to the
ground.
•
Current flows through the load dump relay
exciting circuit and the load dump relay is turned
ON.
•
Accordingly, although the key switch is turned
OFF while the engine is rotating, battery current
continues to excite the battery relay through the
load dump relay. In addition, the battery relay is
turned OFF in ten seconds after the alternator
stops generating of electricity.