Ignition Systems Ignition Systems

Page 3 in handoutPage 3 in handout

Quick recap on the coilQuick recap on the coil

• In pairs, write a short sentence on what you know about the ignition coil.

The coils secondary voltage builds The coils secondary voltage builds up until it creates a spark at the up until it creates a spark at the plugs. When these are in good plugs. When these are in good condition the voltage needed to condition the voltage needed to

jump the spark plug gap may be as jump the spark plug gap may be as low as ………….. Volts, but with low as ………….. Volts, but with

constant use and possible engine constant use and possible engine faults this voltage can rise to faults this voltage can rise to

…………. volts…………. volts

7000

15000

The coil usually has an output The coil usually has an output capacity of ………………. volts. capacity of ………………. volts.

But with transistorized coils But with transistorized coils output can be as high as output can be as high as

…………….. volts. …………….. volts.

25000

40000

A number of things can influence a A number of things can influence a coils output voltage capacity, state coils output voltage capacity, state

three possible factorsthree possible factors

• Primary voltage

• Condition of contact breaker points and condenser (capacitor)

• Speed of operation

• Number of coils in each winding (primary and secondary)

Primary voltage can be affected Primary voltage can be affected when ………………. the engine when ………………. the engine due to the drain on the battery due to the drain on the battery

imposed by the imposed by the ………………………….. …………………………..

Starting

Starter motor

Manufacturers recognised this Manufacturers recognised this problem and altered the problem and altered the

ignition system to incorporate a ignition system to incorporate a ………………… resistor………………… resistor Ballast

Basically the coil used is a low Basically the coil used is a low voltage coil, which is designed voltage coil, which is designed to work on a ………………… to work on a …………………

voltage, approximately voltage, approximately …………. V. …………. V.

Reduced

6 - 7

On start up, the resistor is by On start up, the resistor is by passed and the primary voltage passed and the primary voltage

is ……………. to battery voltage is ……………. to battery voltage Closer

Label the diagram of the ignition Label the diagram of the ignition system incorporating a ballast resistor.system incorporating a ballast resistor.

Battery

Earth connection Low voltage

coil

Ignition switch

Secondary (HT)

Capacitor Ballast resistor

Questions Questions

1. What is the function of the primary windings in the coil?

2. What is the function of the secondary windings in the coil?

3. State three factors that influence a coil’s output voltage.

4. Why is a ballast resistor used in some systems?

5. What can cause the voltage drop at the coil on starting?.

Answers 1 – 3 Answers 1 – 3

• Primary windings are in the coil to initiate the magnetic field.

• The secondary windings are where the high voltage is induced when the magnetic field collapses.

• Three factors of a coils output; number of windings in the secondary circuit, voltage of primary circuit, condition of contact breaker points, and speed of collapse of magnetic field.

Answers 4 and 5Answers 4 and 5

• The ballast resistor is used to increase the voltage output of the coil secondary circuit to give a more powerful spark, and to offset the power drain of the starter motor. This improves starting.

• The starter motor drains the battery of power, this can cause the primary voltage to drop too low, and cause a weak spark at the plugs.