Toro VACU-POWER Service Manual page 68

SECTION 6 ELECTRICAL SYSTEMS
IGNITION CIRCUIT
Ignition Circuit operation
While the ignition circuit is described in each of the
applicable engine manuals, the subject will also be
briefly described here since the wire harness is part of
the chassis. See Figure 109.
unit Ignition coil
I
E : :
Ground
Spark plug
I
Figure 109
A magneto style ignition as shown in the figure above
is based on the principle that a magnet passing by a
coil of wire produces an electrical current flow in the
wire. (Note: the coil of wire must form a complete
circuit.)
The flywheels on Vacu-Power engines house a magnet
on one side. Because the coil is mounted close to the
flywheel, current flows through the primary side of the
coil and through the electronic ignition module when
the magnet passes by. However, the amount of current
present in the primary is very small, so something must
be done to 'step
it
up'.
To increase voltage, a second coil is used. This coil is
called the secondary.
It
is different from the primary in
that it is constructed of finer wire and has many more
windings. The magnetic field produced by the primary
tries to force current to flow in the secondary, but
cannot because of the open circuit at the spark plug
electrodes. While current will not flow, something
important does happen. A voltage difference is
produced across the electrodes. When the voltage
gets high enough, an arc occurs, thereby producing
spark at the plug.
Unfortunately, the components we have described so
far cannot produce a voltage high enough at the plug
to produce spark. To create an arc we must add one
more component: the electronic ignition module.
The electronic ignition module opens the primary
circuit while the magnet is passing by, thereby causing
a rapid decrease in primary current flow. Opening the
primary circuit is important because any change in
primary current (whether an increase or a decrease)
boosts the voltage in the secondary. The faster the
change in primary current, the greater the increase in
secondary voltage. When the electronic ignition
module is functioning properly, the voltage at the spark
plug electrodes becomes high enough to overcome
the resistance of air, thus producing spark.
While producing spark may be somewhat difficult to
understand, stopping spark is not. All Vacu-Power
engines use a' kill wire' that runs to a switch. When the
switch is closed, the primary coil is grounded.
Grounding does not prevent current flow in the
primary. Current still flows each time the magnet
passes by the coil. However, as you can see in Figure
1 10, the current flow bypasses the electronic ignition
module which eliminates the 'momentary open" in the
primary circuit. With no 'momentary open', high
voltage car-mot be produced and spark cannot occur.
Ignition cod
Figure 1 10
Ignition Circuit Troubleshooting
For ignition system troubleshooting information, see
the appropriate engine service manual for your engin
KEY-LECTRlC@ STARTING SYSTEM
Key-Lectrlc Starting System Operation
The Key-Lectric starting system used on Vacu-Power
Mowers consists of a battery, starter switch, starter
motor, the alternator and the wire harness. See Figure
111.
Vacu-Power wer
63
Electrical Systems