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2. Starter and Solenoid
Automotive – Electrical Systems
Starter and Solenoid
Topics covered in this presentation:
 Electromagnetic principles
 Starter motor construction and operation
 Starter solenoid construction and operation
2. Starter and Solenoid
Automotive – Electrical Systems
Starting
Crankshaft must rotate
for vehicle to start.
Modern vehicles use
battery power to
operate starter motors.
Starter motors and solenoids operate
using electromagnetic principles.
Hand crank
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2. Starter and Solenoid
Automotive – Electrical Systems
Electromagnetic Principles
Magnetic field is formed
when current passes
through a wire (conductor).
Flux has direction that is
current direction dependant.
‘X’ indicates current
flowing away from you.
‘Dot’ indicates current
flowing towards you.
Magnetic
field
Conductor
Current flow
away from you
Flux direction
Current flow
towards you
Magnetic poles
Conductors repel when
magnetic fields oppose.
Therefore, conductor will move if
placed between magnetic poles.
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2. Starter and Solenoid
Automotive – Electrical Systems
Electromagnetic Principles
A wire looped several times will
form a coil.
Magnetic
fields
Current will flow in opposite
directions on each side of the coil.
Magnetic forces on each side of the
coil will act in opposite directions.
Produces a twisting (torque) force
on the coil.
Loop
Direction of
current flow
Force will turn the coil until it is at right angles to the magnetic field.
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2. Starter and Solenoid
Automotive – Electrical Systems
The Simple DC Motor
Electric motor converts electrical energy into rotational kinetic energy.
When a voltage is applied to a coil in a magnetic field, the two magnetic
fields react to cause rotational movement.
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2. Starter and Solenoid
Automotive – Electrical Systems
Motor Principle - Commutator
Coil is kept turning by reversing the direction of the current when the
coil is at right angles to the magnetic field.
Using a commutator ensures
that the current is always
flowing in the same direction
around the coil (relative to the
fixed magnetic field).
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2. Starter and Solenoid
Automotive – Electrical Systems
Motor Principle - Commutator
Commutator is a conductive
cylinder split into two halves.
Each coil terminal is
connected to its respective
half of the commutator.
Electrical connection is
made to the commutator
with carbon brushes held
in place by springs.
The commutator and coil
spin freely about a
central pivot point while
the brushes do not move.
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2. Starter and Solenoid
Automotive – Electrical Systems
Motor Principle - Commutator Action
Positive voltage applied to side A of
the coil - current flows from A to B.
Creates a magnetic field around
the coil that reacts with the main
magnetic field, causing the coil to
turn counter-clockwise.
When the coil gets to the vertical
position the carbon brushes reach
the gap in the commutator - current
stops flowing in the coil.
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2. Starter and Solenoid
Automotive – Electrical Systems
Motor Principle - Commutator Action
Momentum of the coil causes the
coil to continue rotating.
Positive voltage is now applied to
side B of the coil - current flows
from B to A.
Magnetic fields react again to
cause counter-clockwise direction.
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2. Starter and Solenoid
Automotive – Electrical Systems
Commutator in Real Motor
With this design the motor will
not be able to start when the
brushes are in contact with the
insulation between the two
halves of the commutator.
In reality a motor will
contain more than one coil.
The commutator is made so
that at least one coil is
energized at any one time.
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2. Starter and Solenoid
Automotive – Electrical Systems
Typical Starter Motor Construction
Solenoid Operated Starter
Solenoid
Armature
Metal housing
Shift lever
Field coils
Drive pinion
Brushes
Commutator
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2. Starter and Solenoid
Automotive – Electrical Systems
The Armature
Central rotating part of a starter motor.
Many loops (coils) are required.
Coils are wound in slots, in
a laminated soft metal core.
Ends of coils are
soldered to the
commutator.
Bearings
Each segment is insulated.
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2. Starter and Solenoid
Automotive – Electrical Systems
Field Coils
Carbon brush
Coils produce magnetic field.
Made from insulated wires,
wrapped around iron cores.
Connected in pairs to provide
North and South poles.
One end of each pair is
connected to supply terminal,
the other end of each pair is
connected to a carbon brush.
Powerful magnetic field is set
up, when current flows.
Coils
Supply terminal
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2. Starter and Solenoid
Automotive – Electrical Systems
Starter Motor Electrical Configurations
Windings can be configured to
provide different torques.
Common arrangement
uses four field coils.
Two pairs of field coils are
wired in series.
Armature in series
with field coils
Coils
in series
Field
coils
Field coil series pairs
are wired in parallel.
The parallel field coils
are wired in series with
the armature windings.
Coils in
parallel
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2. Starter and Solenoid
Automotive – Electrical Systems
Typical Solenoid Construction
Solenoid connects battery to starter motor.
Mounted separately on early vehicles.
Field Windings.
Solenoid plunger.
Moving contacts.
Heavy duty terminals.
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2. Starter and Solenoid
Automotive – Electrical Systems
Typical Solenoid Construction
Mounted on starter motor
on modern vehicles.
Winding 1
Fitted with shift lever to
‘pre-engage’ starter
motor pinion gear with
flywheel ring gear.
Shift level
Winding 2
Usually contains
two field windings.
Low winding
connects to ground.
High winding connects
to the starter motor.
Low
winding
Starter
motor
High
winding
From ignition
switch
From battery
Heavy duty contacts
To starter
motor
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2. Starter and Solenoid
Automotive – Electrical Systems
Typical Starter Motor Operation
Low winding
Plunger
Ignition switch set to
start, current flows
through both windings.
High winding
12V from
ignition
switch
Shift lever
As starter motor is
connected to high
winding, it slowly
begins to turn.
Current flow produces
magnetic field, which
moves plunger, shift
lever and pinion.
Pinion
Armature
Field coils
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2. Starter and Solenoid
Automotive – Electrical Systems
Typical Starter Motor Operation
Lever movement causes slow
moving pinion gear to engage
with flywheel ring gear.
Low winding
Ignition switch set to run
Battery
voltage
Heavy
duty
terminals
Plunger
At full lever
travel, heavy duty
Shift lever
contacts close,
Pinion
battery voltage is
applied to starter
motor, which
turns at full
speed.
Once gears are
meshed, low winding keeps
solenoid plunger in position.
Armature
Shift lever and solenoid plunger return to rest
position when ignition switch is set to run.
Field coils
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2. Starter and Solenoid
Automotive – Electrical Systems
Inertia Starter Motor