When a regulator bypass test is being performed,
what type of voltage is used to excite the rotor
Learning Objective: Identify starting-circuit
components, their function, operation, and maintenance
The internal combustion engine is not capable of
self-starting. Automotive engines (both spark-ignition
and diesel) are cranked by a small but powerful electric
motor. This motor is called a cranking motor, starting
motor, or starter.
The battery sends current to the starter when the
operator turns the ignition switch to start. This causes a
pinion gear in the starter to mesh with the teeth of the
ring gear, thereby rotating the engine crankshaft for
The typical starting circuit consists of the battery,
the starter motor and drive mechanism, the ignition
switch, the starter relay or solenoid, a neutral safety
switch (automatic transmissions), and the wiring to
connect these components.
The starting motor (fig. 2-37) converts electrical
energy from the battery into mechanical or rotating
energy to crank the engine. The main difference
between an electric starting motor and an electric
generator is that in a generator, rotation of the armature
in a magnetic field produces voltage. In a motor,
current is sent through the armature and the field; the
attraction and repulsion between the magnetic poles of
the field and armature coil alternately push and pull the
armature around. This rotation (mechanical energy),
when properly connected to the flywheel of an engine,
causes the engine crankshaft to turn.
Starting Motor Construction
The construction of the all starting motors is very
similar. There are, however, slight design variations.
The main parts of a starting motor are as follows:
ARMATURE ASSEMBLYThe windings,
core, starter shaft, and commutator assembly
that spin inside a stationary field.
COMMUTATOR END FRAMEThe end
housing for the brushes, brush springs, and shaft
Figure 2-37.Typical starting motor.