Fiat Kobelco EX355 Tier2, Technical Manual

Page: 57 / 968

T2-3-10 EX355
ELECTRICAL SYSTEM
STARTING CIRCUIT
(Key Switch: START)
When the key switch is turned to the START position,
terminal B on the key switch is connected to terminals,
M, and ST. The current from terminal M magnetizes
the battery relay, leading the battery current to termi-
nals B on the starter and starter relay via the battery
relay.
Terminal ST of the key switch is connected to terminal
S on the starter relay so that the battery current flows
through the coil in the starter relay, allowing the relay
to close the circuit. Then, the battery current can flow
to terminal C on the starter, closing the inner starter
relay.
Thereby, the starter begins to rotate.
The current from terminal M flows to the MC,
instructing that the key switch is positioned at ON or
START. When this signal arrives at the MC, the MC
actuates the EC motor which moves the governor
lever. Starter Relay Operation
• When the key switch is turned to the START
position, key switch terminal B and ST have conti-
nuity in the key switch. Then, the current flows to the
base of transistor (Q2) via resistance R4 in the
starter relay, switching transistor (Q2) ON.
Thereby, the current flows through coil (L) of relay,
closing the circuit between starter terminals B and
C. Then, the starter begins to rotate.
• Once the engine is started, the alternator begins
to charge the batteries so that the voltage at
starter relay terminal R rises. When the voltage at
terminal R reaches 21 to 22 V, zener diode (Z)
comes ON. Accordingly, transistor (Q1) is switched
ON so that the base current to transistor (Q2) is cut,
switching transistor (Q2) OFF. At this time, continu-
ity between starter terminal B and C is opened.
Then, the starter is switched OFF.
Capacitor C1 shown in the figure is used to stabilize
the operating voltage. Diode D4 protects the circuit
from damage when the batteries are inversely
connected.
Key Switch
To Alternator
Terminal L
Starter Relay
Batteries
Starter
S B
C
B M
C
12V
12V
E
R
R
2
Z
R
3
D
2
D
3
R
4
(1)
(2)
B
ST
D
4
L
C
1
C
(2)
Q
2
Q
1
(1)
SM4015A