Ignition systems, Contact Breaker Points

1. Ignition Systems Page 4Ignition Systems Page 4
Contact breaker pointsContact breaker points

2. Contact breaker points are noContact breaker points are no
longer used in production withlonger used in production with
modern vehicles, but can still bemodern vehicles, but can still be
found in some road vehiclesfound in some road vehicles
today.today.

3. The contact breaker points areThe contact breaker points are
used to switch the primaryused to switch the primary
circuit of the coil off and on, thuscircuit of the coil off and on, thus
causing the collapse of thecausing the collapse of the
magnetic field.magnetic field.

4. This rapid collapse of theThis rapid collapse of the
magnetic field is what causesmagnetic field is what causes
the high voltage to be inducedthe high voltage to be induced
into the secondary circuit.into the secondary circuit.

5. Label the picture of the contactLabel the picture of the contact
breaker points below.breaker points below.
Capacitor
Adjusting screw
Heel
Contacts
Wire connection
to earth side of
coil
Look at the cam
in the middle of
the distributor,
how many
cylinders has this
engine?
Spring

6. The picture below shows theThe picture below shows the
operation of the contacts and whenoperation of the contacts and when
the high tension circuit is flowing.the high tension circuit is flowing.

7. In the picture opposite there is aIn the picture opposite there is a
component called a condenser,component called a condenser,
what is its purpose?what is its purpose?
• It stops arcing across the contacts as they
open
• It allows a quicker charge of the primary
circuit as the points close
• The condenser acts as a battery that gets
charged and drained very quickly.

8. Why do modern vehicles not useWhy do modern vehicles not use
this system anymore?this system anymore?
• The contact breaker points are not used
today as the mechanical system has been
taken over by firstly electronic ignition,
then by ECU’s and programmed ignition.
• Contact breakers have a limited lifespan.
• Secondary voltage is limited.

9. QuestionsQuestions
1. What is the function of the contact
breaker points?
2. What is the function of the capacitor?
3. Why are contact breaker systems no
longer in use today?
4. What condition is known as ‘point
bounce’
5. What would happen to an engine that’s
contact air gap had shut completely?

10. AnswersAnswers
1. To switch the primary circuit on and off, this
then operates the secondary circuit.
2. To stop the points arcing when they open, to
help the primary circuit to charge when the
points close.
3. The points wear quickly, the secondary voltage
output is low.
4. Point bounce is when the points bounce due to
being opened and closed too quickly.
5. The spark plugs couldn’t spark, so the engine
can’t run.