Generac Power Systems 53187 - Manual (Page 36)

SECTION 1.6- TROUBLESHOOTING
(UNITS WITH 15 INCH STATOR)
1 PARTI
THE REVOLVING FIELD AC GENERATOR
Detailed Instructions (Continued)
Results:
1. Replace the Rotor if it fails test.
2. If Rotor checks good, go to Test 12.
Figure 7. Rotor Assem bly Test Points
TEST 12- CHECK BRUSHES AND SLIP RINGS:
Discussion: The brushes and slip rings are de­
signed for long life and dependability. Problem s w ith
therse com ponents are very infrequent. It is possible
that, after a prolonged non-operating period, the slip
rings can develop a corrossive film around their outer
periphery. This film can separate the brushes from the
slip rings and open the excitation circuit.
Procedure: Rem ove w ires from the brushes. Re­
m ove the brush holders from the rear bearing carrier.
Carefully inspect brushes, brush holders, w ires and slip
rings. Replace brushes that are chipped, cracked, or
w orn excessively. Replace brushes as com plete sets.
Replace any dam aged brush holders. If the slip rings
have a dull or tarnished appearance, they m ay be
cleaned w ith fine sandpaper. DO NOT USE ANY ME­
TALLIC GRIT TO CLEAN SLIP RINGS. Polish the slip
rings until shiny.
Results:
1. Replace any dam aged brushes or brush holders.
Clean and polish slip rings, if necessary.
2. If brushes and slip rings are good, go to Test 13.
TEST 13- CHECK W IRES NO. 1 AND 4:
Discussion: W ire No. 1 is routed from the nega­
tive (-) brush to the unit grounding lug; and from the
grounding lug to Pin 1 of the Voltage Regulator. W ire
No. 4 is routed from the positive (+) brush (nearest the
Rotor bearing) to Pin 4 of the Voltage Regulator. Reg
ulated excitation current (DC) is delivered from the
Regulator to the Rotor via these w ires.
' Procedure: Inspect W ires No. 1 and 4 along their
entire length. Use a VOM to check the w ires for an open
or shorted condition. M ake sure w ires are properly
connected.
Results:
1. Reconnect, repair or replace any dam aged or defec­
tive w ire(s).
2. If W ires are good, go to Test 14.
TEST 14- TEST FIELD BOOST:
Discussion; During engine cranking, the action of
an engine control circuit board delivers battery voltage
(12 volts DC) to the Rotor w indings via W ire No. 9, a
field boost resistor (R^, a field boost diode (D2) and
W ire No. 4. Resistor (R2) reduces this voltage to ap­
proxim ately 7-10 volts DC. As soon as engine cranking
stops, circuit board action term inates field boost cur­
rent. Field boost current flow to the Rotor w indings
w hile cranking turns the Voltage Regulator on earlier
and ensures m at a ’pickup* voltage is available to start
the generation of electricity. Loss of field boost current
m ay or m ay not affect generator AC output voltage. If
Rotor residual m agnetism is sufficient to provide the
required ’pickup" voltage in the stator, loss of field
boost w ill have no affect. How ever, if Rotor residual
m agnetism is not adequate to produce the required
’pickup’ voltage, generator AC output voltage w ill build
only to a value com m ensurate w ith Rotor residual m ag­
netism (about 2-7% of rated voltage).
The field boost, in effect, flashes the field eveiy
tim e the engine is cranked and started. This test w ill
check the field boost circuit to determ ine if it is function­
ing properly w hile the engine is cranking.
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