103149GS Generator Troubleshooting.pdf

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For Briggs & Stratton Discount Parts Call 606-678-9623 or 606-561-4983
INDEX
Section
Page Number
Remarks
Synchronous Alternators
2 – 4
General Fault Finding
Capacitors
5 – 6
Fault Finding & Testing
Diodes,Varistors, EMC capacitors & Recifiers
7 – 10
Fault Finding & Testing
Rotors
11 – 12
Fault Finding & Testing
Stators
13 – 14
Fault Finding & Testing
DC Welders
15 – 20
Fault Finding & Testing
3 Phase Alternators
21 – 26
Fault Finding & Testing
AVR (ERR) Alternators
27 – 31
Fault Finding & Testing
Asynchronous Alternators
32 – 34
Fault Finding & Testing
AC Welders
35 – 38
Fault Finding & Testing
Page 1 of 38
Technical Support Document: 103149GS Rev0
www.mymowerparts.com
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SYNCHRONOUS ALTERNATORS.
Fault Finding Guide Capacitor Excited Alternators
Alternators used on the majority of Briggs and Stratton Power Products generators are capacitor exited, self-regulating.
The alternator consists of a rotor and a stator. The rotor is connected to the engine crankshaft power take off and rotates within the stationary
stator, which is bolted to the engine crankcase.
The stator generally has two windings; these are the excitation winding and the power winding. Some alternators have an additional battery
charge winding.
Excitation (the function that turns the rotor into a magnet) is produced by the excitation winding. The outlet sockets are connected to the power
winding. It is the action of the magnet (rotor) revolving within the stator power windings that produces the voltage output.
To create a magnetic field on the rotor, a direct current (DC) is produced in the rotor winding.
The output from the stator excitation winding is alternating current (AC) and it is the action of the diode(s) on the rotor that converts the
alternating current (AC) to direct current (DC). When the alternator is at rest, the rotor retains a small amount of magnetism; this is termed as
residual magnetism.
A capacitor is connected across the stator excitation winding. The current flowing through the capacitor induces a current in the rotor windings,
and so regulates the strength of the rotor magnetic field.
Fault Finding
Follow these basic procedures to fault find:
Start engine and check engine speed, reset the governor if the engine is not running at the correct RPM
Check output voltage directly from the output sockets.
( Use an accurate sensitive voltmeter because you are looking for zero or extremely low voltage)
Note: Zero voltage indicates either an open circuit or total loss of residual magnetism on the rotor.
Page 2 of 38
Technical Support Document: 103149GS Rev0
SYNCHRONOUS ALTERNATORS.
Voltage at
Outlet Socket
Possible Fault
Test
Possible Cause and Action
0V
No Connection from Outlet to Main
Winding.
Measure resistance at
outlet socket.
Cable connection - Repair
Faulty circuit breaker – Replace circuit Breaker
Alternator to panel Connector. Repair/Replace
Main Winding Fault
Measure resistance at
connector.
Connector and/or cable – Repair connection/replace stator.
Faulty main winding – Replace stator
Rotor Not Rotating
Check rotation
Rotor bolt loose – Check crankshaft and refit/replace rotor
bolt.
Alternator has been overloaded or shorted – Attempt to
restore residual magnetism
Rotor Demagnetized (No Residual)
No Test
Low Output
9 to 27V
Excitation circuit failure
Test Capacitor
Overload/ Short/RPM High –Check RPM and replace
capacitor.
Overload/ Short/RPM High – Replace Stator
Test Excitation
Winding.
Test Diode Set
As above – Replace Diode Set
Test Rotor Winding
As Above – Replace Rotor
130 – 180V
Dual rotor winding – One Diode set
failed
Test Diode Set
As above – Replace Diode Set
Test Rotor Winding
As Above – Replace Rotor
Page 3 of 38
Technical Support Document: 103149GS Rev0
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SYNCHRONOUS ALTERNATORS.
Restoring Residual Magnetism:
Should only be carried out when test results show zero voltage and no open circuits are found on the alternator, panel and
associated wiring.
To restore residual magnetism we pass 12V DC through the power windings by connecting a battery directly to the outlet
sockets.
It is important to immobilize the engine by removing the spark plug lead from the spark plug.
1.
Immobilize the engine.
2.
Connect a 12 Volt battery directly to the outlet sockets (polarity is not important)
3.
Turn the engine over. Note: 4 complete pulls of the recoil or approximately 3-4 seconds on the starter motor.
4.
Remove the battery and connections.
5.
Replace the spark plug lead.
6.
Start the engine and measure output.
7.
If the fault is loss of residual magnetism, output should be restored.
Restoring Residual Magnetism: Alternative Method
If a small amount of magnetism has been retained in the rotor it may be possible to restore out put by increasing the engine RPM slightly.
It is extremely important not to over rev the engine.
1.
Start and run engine for a few minutes to warm.
2.
Locate the throttle linkage at the carburetor and slowly increase RPM to a maximum of 3600RPM over a period of 5 seconds.
3.
Allow engine to stabilize and recheck output at the outlet sockets.
Page 4 of 38
Technical Support Document: 103149GS Rev0
CAPACITORS.
Capacitors are used in the excitation circuit of self-regulating alternators.
The capacitor is connected across the excitation winding (figure 1B). The current that flows through the capacitor produces a current in the rotor
windings; this regulates the strength of the rotor magnetic field. It is the rotor magnetic field that generates the voltage in the power windings.
The capacitor value is chosen to give the correct generator output voltage therefore it is important to always replace the capacitor with one of the
same rating.
A: Capacitor
B: Circuit
C: Capacitor Rating
Figure 1
If the excitation capacitor fails, the alternator will loose it’s regulating effect and the output voltage will drop. The output voltage will drop to
between 9 and 27volts and will be due only to residual magnetism in the rotor.
If output tests indicate a failed capacitor, replace the capacitor with a known serviceable capacitor of the same voltage range. This “test”
capacitor need not be of the same Farad rating. A significant change in output (160V – 250V) will confirm diagnosis.
Page 5 of 38
Technical Support Document: 103149GS Rev0
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