Small Engines/ Ag. 221 Ignition theory

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

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

Circuit The complete path of electric current

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

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

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)

Ignition Parts armature

Breaker points (older engines)

crankshaft

coil

Condenser (older engines)

Electronic ignition module (conversion)

flywheel

Flywheel key

Point plunger (older, points and ignition systems)

Spark plug

Magneto Ignition

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

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

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

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

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

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

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