Generac Power Systems 53187 - Manual (Page 17)

Thermal Protector !
A Therm al Protector is physically im bedded in the
w ire w indings of the Stator and electrically connected In
series w ith the excitation w inding output leads to the
Regulator. The device is a norm ally-closed (N.C.),
tem perature sensitive sw itch. The sw itch contacts w ill
open w hen stator tem peratures exceed a safe level. The
sw itch is self resetting. That Is, it w ill re-dose w hen
stator tem peratures decrease to a safe level.
If the sw itch contacts should op>en, excitation w inding
AC output to the Voltage Regulator w ill be term inated
and the Regulator’s green EXCITATION lam p w ill go
out. Since the Regulator cannot op>erate w ithout excita­
tion w inding output, the red REGULATOR lam p w ill also
go out. Generator AC output voltage w ill then drop to a
value com m ensurate w ith the Rotor’s residual m ag­
netism .
If the Therm al Protector contacts open during opera­
tion due to a stator overtem perature condition, the
cause of the overtem perature condition m ust be found
and corrected. High Internal stator tem peratures can be
caused by any one of the follow ing:
D
Insufficient cooling air flow into the generator
interior. Look for blockage of cooling air inlet/out-
let openings, air openings that are too sm all,
am bient tem peratures that are too high, etc.
□ Exceeding the w attage/am perage capacity of the
generator. If the unit is overloaded for a period of
tim e, internal stator tem peratures can rise quickly
and cause the Therm al Protector contacts to
open.
D A shorted condition in the generator stator w ind­
ings or in an electrical load connected to the
generator’s AC output.
The Thennal Protector is not accessible and cannot
be rem oved and replaced. If the device has failed open,
it can be bypassed by connecting excitation lead No. 2
to a bypass lead (W ire No. 5). Once the device has been
bypassed, stator overtem perature protection Is no
longer available.
PART 1
THE REVOLVING FIELD AC GENERATOR
Field Boost
W hen the generator engine Is cranked, direct current
(DC) Is delivered to the Rotor w indings. The cunent flow
is provided by the action of an Engine Control circuit
board housed In the control panel and Is delivered to the
Rotor via W ire No. 9, a Field Boost Resistor (R2), a Field
Boost Diode (D2), W ire No. 4, and the brushes and slip
1
SECTION 1.3- MAJOR COMPONENTS
(UNITS WITH 15 INCH STATOR
rings. The direct current (approxim ately 9-10 volts DC)
flow s through the Rotor w indings, the negative (-) slip
ring and brush, and to ground.
Field boost current creates a m agnetic field strength
that is additive to the Rotor’s residual m agnetism . The
Increased m agnetic field strength during engine crank­
ing provides an early "pickup* voltage In the stator. The
Regulator is turned on m ore quickly and AC output
occurs sooner. In effect, field boost current "flashes the
field" on every startup.
Failure of the field boost system nr^y or m ay not result
In a reduction of AC output to that produced by residual
Rotor m agnetism . If residual m agnetism Is adequate to
turn the Regulator on and provide the required pickup
voltage, the generator w ill operate norm ally w ith or
w ithout field boost. How ever, if residual m agnetism Is
not adequate, generator AC output w ill not build and w ill
be com rr^nsurate w ith Rotor residual m agnetism .
PART OF CONTROL PANEL
WIRING HARNESS
rrSM DESCRIPTION
1 HEAT SHRINK
• 2 BARREL LUG
3 DIODE-600V., 6 AMP
4 RESISTOR-5 W ATT. 10 OHMS
Figure 9. The Field Boost Circuit
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