1. Small Engines/ Ag. 221
Ignition theory

2. Objectives
Identify basic terms and definitions associated with magneto ignition systems
List and identify parts related to a magneto ignition system
Describe the principles of magneto ignition systems
Identify the function of individual parts related to ignition systems

3. Terms and Definitions Amperage Voltage
A unit for measuring the rate of current flow through wires.
Similar to the flow of water in pipes
Voltage
A unit of electrical force or pressure
Comparable to water pressure

4. Circuit
The complete path of electric current

5. Magneto
An alternator with permanent magnets used to generate current for the ignition of an internal combustion engines

6. Ohm
Measure of the resistance to current flow through a wire or other current carrying material

7. Primary circuit Secondary circuit
Current generated from flywheel magnet and armature, carried through the breaker points and condenser (points closed)
Secondary circuit
current generated from the primary circuit, carried through the coil and spark plug wire (secondary wire) to the spark plug (points open)

8. Ignition Parts
armature

9. Breaker points (older engines)

10. crankshaft

11. coil

12. Condenser (older engines)

13. Electronic ignition module (conversion)

14. flywheel

15. Flywheel key

16. Point plunger (older, points and ignition systems)

17. Spark plug

18. Magneto Ignition

19. Ohm’s Law
Ohm’s law – a pressure of one volt (E) will force a current (I) of one amp through a resistance of one ohm (R).
E=I * R
Amperage (I) and resistance (R) are directly proportional to voltage (E).
If amperage or resistance increases then voltage will also increase

20. An ignition system of an engine requires 10,000 to 12,000 volts to create a sufficient arc across the spark plug
To obtain that high of voltage a coil wire is used to increase resistance which directly increases voltage

21. How Electricity is Produced
If a wire is passed through a magnetic field and electrical current will flow on the wire.
A larger wire or a larger number of wires that are passed through a magnetic field will increase the amount of the current
If a current flows on a wire a magnetic field is produced around the outside of the wire

22. Resistance (R) can be used to reduce the current (I) and increase the voltage (E).
In a small engine
Magnet is located on the outer edge of the flywheel
Coil of wires is in a stationary position outside of the flywheel
The magnet passes by the coil with each revolution of the flywheel, creating electricity on every revolution

23. Magneto Ignition Consists of two circuits Primary circuit
Secondary circuit
Condenser
Breaker Points
Kill Switch
Spark Plug

24. Primary Circuit Primary coil winding; larger gauge wire Points
Condensor
Or an electronic
ignition module

25. Secondary Circuit Secondary coil winding; smaller gauge wire
Spark plug
Condenser
Breaker Points
Kill Switch
Spark Plug