Briggs & Stratton 86262GS, Familiarization & Troubleshooting Manual

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Section 2 • Generator Components & Systems
Portable Generator Familiarization & Troubleshooting Guide
Engine Assembly
As a general rule, the engine must deliver approximately 2
horsepower for each 1000 watts (1.0 kW) of generator
output power.With this in mind, the following horsepower
to output ratios are common:
• 2400 watt unit / 5 horsepower
• 3500 watt unit / 7 horsepower
• 4000 watt unit / 8 horsepower
• 5000 watt unit / 10 horsepower
• 8000 watt unit / 16 horsepower
The engine “power takeoff shaft” (PTO), on most portable
generators, is directly connected to the rotor assembly.
Usually, the engine’s PTO shaft is tapered and doesn’t have a
keyway.The rotor assembly is tightened to the shaft by
means of a long rotor bolt.
A mechanical, fixed speed, engine governor maintains actual
engine speed at approximately 3720 RPM for
60 Hertz units or 3100 RPM for 50 Hertz units with no
electrical loads connected to the generator (“no-load”
condition). Rated operating speed is 3600 RPM, at which the
2-pole rotor will supply a rated frequency of 60 Hertz or
3000 RPM for a rated (AC) frequency of
50 Hertz.The slightly high “no-load” speed (3720 RPM) for
60 Hertz units will provide a frequency of about
62 Hertz. Setting the no-load speed slightly high helps
prevent excessive RPM and frequency “droop,” when heavy
electrical loads are applied.
Several different engine manufacturers may be found on the
various
Generac Portable Products®
generator models.They include:
• Briggs & Stratton®
• Tecumseh®
• Kawasaki®
• Honda®
• Robin®
• Generac Power Systems®
Rotor Assembly
A pre-lubricated and sealed ball bearing is pressed onto the
rotor shaft. No additional lubrication is required for the life
of the bearing.The bearing supports the rotor at the “rear
bearing carrier.” Slip rings on the rotor shaft permit
excitation current to be delivered to the rotor windings.
Although residual magnetism is always present in the rotor,
this excitation current flow through the rotor produces a
magnetic field strength that is additive (in addition) to
residual magnetism.
A typical rotor (Figure 2.2) can be a rotating permanent
magnet having no electrical current flow.
In practice, most rotors are a rotating electromagnet with a
direct current flowing through its coiled wires.
Concerning electromagnetism in regards to rotors, these
general statements can be made:
• The strength of the magnetic field is directly
proportional to the number of turns of wire in the
rotor.
• The strength of the magnetic field is directly
proportional to the current (in amperes) flowing
through the rotor windings.
From these statements, we can deduce that the field
strength of the rotor’s magnetic field may be increased by:
• Increasing the number turns of wire in the rotor.
• Increasing he current flow (in amperes) through the
rotor windings.
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Figure 2.2 — A Typical Rotor Schematic Symbol