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Chapter 9 Ignition Systems page 147
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Basic Ignition System Operation
charge builds up in coil (12 volts in) creates a magnetic field (windings of wire) voltage is stepped up (secondary windings) switch open (magnetic field collapses) high voltage discharged (to plug)
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Fundamental Electrical Principles
Electricity is lazy Electricity wants to go to ground electron theory (-) to (+) conventional theory (+) to (-) Conductors Insulators
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The Electron Theory Electricity moves from – to +
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Electrical Units of Measurement
Volts---- Push V Current ---Quantity A Resistance ----Resistance to flow
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Ohm’s Law E = I x R E / I = R E / R = I E I R
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Magnetism Alike charges repel (-) (-)
Dissimilar charges attract (-) (+)
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Magnets & Electricity Magnets can be used to for electricity
Electricity can be used to form magnets Electricity when applied to magnets make stronger magnets
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Ignition Coils Coils of wire wrapped around an iron core
Step up transformer
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Spark Plugs Spark plugs contain an air gap for electricity to create a spark and make a seal
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Heat Ranges The difference between a "hot" and a "cold" spark plug is in the shape of the ceramic tip. The manufacturers will select the right-temperature plug for each engine. Some engines with high-performance naturally generate more heat, so they need colder plugs. If the spark plug gets too hot, it could ignite the fuel before the spark fires It is important to stick with the right type of plug Engine that burn oil may need hot plugs
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Measuring Spark Plug Temperature
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Types of Electrodes Center electrode Side electrode
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Switching Devices Breaker points Electronic
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Breaker Points Ran by cam shaft
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Electronic Switching Devices
NO breaker points to burn or wear out
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The MBI Magneto System Mechanical Breaker Point Ignition
produce power without an outside power source Condenser-prevents arching
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The MBI Magneto Cycle Magnets pass legs
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Coil 150 turns of large wire 20,000 turns of fine wire Iron core
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The Stop Switch Plug only fires when points open Switch grounds points
Fasten metal to head bold
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Ignition Advance Systems
Cause spark earlier BTDC As engine warms up Speeds up Centrifugal Vacuum Mechanical
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Dwell & Cam Angles Time points stay closed Lobes size = dwell time
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Electronic Ignition Solid state No maintenance No points-burning
Spark plug life Easy starting Higher output Starts flooded engine Higher spark output
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Electronic Ignition Hermetically sealed Uniform performance
Good under adversity Improved idling Smoother power under load
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Operation of Capacitive Discharge Ignition ( CDI)
Solid State Newest NO Breaker points Magnets only moving parts
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Operation of Transistor Controlled Ignition (TCI) Systems
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Magneto Ignition Systems Compared
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Battery Ignition Systems
Low voltage primary circuit High voltage secondary circuit ignition switch builds field field collapses spark to plug
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High Voltage Secondary Circuits
Uses a step up transformer Several winding of wire / iron core
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Auto-Transformer Type Ignition Coils
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The Lead Acid Battery
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Vehicle batteries
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