35
CHAPTER 6 ELECTRICAL SYSTEMS
END CAP
BRUSH SPRINGS
BRUSH CARD
HOUSING
ENGAGING NUT
GEAR
1
2
OPERATION
STARTING CIRCUIT AND ELECTRIC STARTERS
GENERAL INFORMATION
The electrical system consists of three main elements: a battery, a starting circuit, and a charging circuit. The
battery is part of both the starting and charging circuit. The battery should be checked before going into any
extensive starter or charging system checks. If a battery has a shorted cell, overcharging can result, and the
regulator or rectifier may appear to be at fault. If a cell has an open or high resistance connection, the electric
starter operation will be affected.
The power source used to provide the energy to turn an electric starter motor on Tecumseh engines is either
120 volt A.C. current or 12 volt D.C. A 120 volt A.C. starter circuit utilizes a 120 volt power source instead of a
battery. The 12 volt battery models require a charging system to maintain proper battery charge.
The starting circuit includes the battery, battery cables, starter or ignition switch, safety switches, starter solenoid,
and an electric starter motor.
The charging system consists of alternator charge coils, rectifiers or diodes, regulator, ignition switch, flywheel
magnets, and a battery. All engines that have a charging system will use a combination of some or all of these
features.
After all of the safety interlock switches have been
activated, the starter switch closes the starting circuit.
A strong magnetic force is produced by the electrical
current running through the armature windings. The
armature magnetism repels the magnetism produced
by the permanent field magnets of the electric starter.
The repelling magnetic forces cause the armature to
rotate, moving the drive pinion laterally on the splined
armature shaft, meshing the starter pinion gear with
the flywheel ring gear. When the drive pinion contacts
the stop at the end of the armature shaft, the pinion
rotates along with the armature shaft to crank the
engine. The armature and pinion remain positively
engaged until the engine fires and the flywheel rotates
faster than the armature. The greater momentum of
the flywheel throws the starter pinion gear out of mesh
and forces the starter pinion back to the disengaged
position. After the switch is released, the starting
circuit is opened and the armature coasts to a stop.
A small anti-drift spring holds the pinion in the
disengaged position (diag. 1).
CHARGING CIRCUIT
The charging system works independently of any
manual controls. The engine needs to be running to
produce an electric current flow. When a conductor
(alternating coils) cuts the magnetic field generated
by the magnets in the flywheel, a current is induced
in the alternator coil. The permanent magnets in the
flywheel have a magnetic field in which the lines of
magnetic force run from the North Pole to the South
Pole. As the flywheel rotates and the position of the
magnets change, the direction of the magnetic field
changes or alternates. The alternating coils are wound
in different directions to allow current to flow as an
A.C. waveform (diag. 2).
ROTATION OF FLYWHEEL
DUST COVER
RETAINER
SPRING
RETAINER
SPRING
END CAP
THRUST
WASHER
ARMATURE
LOCK NUT
BOLT
NUTS
WASHER
BRUSHES
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