Utility Voltage Failure And Engine Cranking - Generac Power Systems 7 kW NG Repair Manual

Section 4.3
Operational Analysis
• After the controller's 10-second timer has timed out, if Utility voltage is still below 65% of nominal, the controllers logic will
energize the internal crank relay followed by the internal run relay.
• When the internal crank relay energizes 12 VDC is delivered to the starter contactor relay (SCR) via Wire 56. When the SCR
energizes its contacts close and battery voltage is delivered to a starter contactor (SC). When the SC energizes its contacts close
and battery voltage is delivered to the starter motor (SM); the engine is now cranking.
• With the engine cranking a speed reference signal is generated by the magnetos and is delivered to the controller through Wire
18. If a valid signal is received, the controller will energize the internal run relay and deliver 12VDC on Wire 14. The fuel solenoid
energizes (opens) and fuel is available to the engine. The choke solenoid (CS) begins to operate and the controller grounds Wire
90, energizing the choke solenoid cyclically curing cranking, and continuously while running.
• During Cranking 3-5VDC is supplied to the rotor for field flash via a field boost diode connected in parallel with Wire 56.
• With ignition and fuel flow available the engine will start.
4
0
FIELD BOOST
DIODE
56
56
A
SCR
B
0
0
BATTERY
12V
Page 100

UTILITY VOLTAGE FAILURE AND ENGINE CRANKING

GOVERNOR
ACTUATOR
56
85
HTO
86
14
0
14
FS
LOP
0
0
13 13
SCR
0 16
SC
SM
PART 4
1 2 3 4 5 6 7 8 9
J5
PRINTED CIRCUIT BOARD
F1
J3
1 2 3 4 5 6 7 8 9
90 0 13
818 85 14
817 819 820 210
CS
14
0
SP1
IM1
13
SP2
IM2
Figure 97.
ENGINE/DC CONTROL
10 11 12 13 14
Crank Atempt # 1
CONTROLLER
J4
10 11 12 13 14 15 16 17 18 19
86 18 56 194
209
56
820
817
818
819
0
18
18
20 21 22 23
23