Briggs & Stratton 86262GS Familiarization & Troubleshooting Manual page 79

Portable Generator Familiarization & Troubleshooting Guide
Section 3 • Generator Diagnostics and Adjustments
Troubleshooting "Two Board"
Regulation Generators (Brush
Type)
Refer to Figure 3.31.
Test 1:
— Check (AC) Frequency and Voltage
Connect an accurate (AC) frequency meter across the two
parallel blades of one of the panel 120VAC receptacles.
• Start the engine and let it stabilize.
Read the (AC) frequency. A frequency reading of
61-63 Hertz should be obtained.
If frequency is not within specifications:
• Consult the appropriate engine service manual for
adjustment.
With the generator engine running, connect the VOM test
probes across the parallel blades of the panel
120VAC receptacles. A reading of approximately
130-140VAC should be indicated.
If voltage checks as specified:
• Discontinue test.
If voltage reading is zero:
• Go to Test 2: "Flash The Field."
If voltage reading is low:
• Go to Test 7: "Check The Rotor."
Test 2:
— Flash The Field
In normal generator operation, upon startup there is some
"residual" magnetism in the rotor to get the generating
process started. Residual magnetism is the magnetism left in
the rotor after the unit is shut down. When residual
magnetism is lost, the unit will have an output voltage that
will remain at zero. If residual magnetism is lost, it can
usually be restored by "flashing the field" with a simple
process involving a (DC) battery. This usually occurs if the
unit is out of use for a long period of time.
NOTE:
Some units are equipped with "FIELD
BOOST" and should never lose residual magnetism
unless a field boost failure has occurred. Field boost
current flashes the field on every startup (see "Field
Boost" on page 45). Refer to the appropriate electric
schematic and/or wiring diagram to determine if a
unit has field boost.
If the unit is equipped with a voltage regulator or a bridge
rectifier, flash the field as follows:
• Obtain a 12VDC battery.
• Get two jumper leads that can go from the battery to
the brushes. (Wires with alligator clips work well.)
• Find the brushes inside the alternator portion of the
unit.
• Start the engine and get it up to running speed.
• Connect the battery positive (+), to the positive brush,
which will be the brush closest to the rotor bearing.
• Connect the battery negative (-), to the negative brush,
which is the brush farthest away from the rotor bearing
(Refer to Figure 3.32).
Figure 3.32 — Restoring Residual Magnetism
• After about five seconds, disconnect the battery wires
from the brushes and check for proper (AC) output
voltage.
• Shut the engine down. Restart the unit and check once
again for proper (AC) output voltage.
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