The document discusses automobile electrical systems, focusing on ignition systems. It describes the major components of ignition systems including spark plugs, distributor, ignition coil, and switch. There are three main types of ignition systems - battery ignition, magneto ignition, and electronic ignition. Battery ignition provides better spark at low speeds but requires battery maintenance. Magneto ignition is more reliable with no battery but not as good at low speeds. Electronic ignition solves problems with mechanical systems like inconsistent spark timing. Ignition timing and advance/retard mechanisms are also covered.

1. Electrical systems
Anoop P
Asst. Professor
Department of Mechanical Engineering

2. Introduction
• Automobile electrical system includes starting system, charging system,
ignition system and lighting system and some accessories.
• The accessories include cigarette lighter, horn and mobile charging system,
etc.
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3. Major Components
• Ignition System
– Spark plugs (for petrol vehicle)
– Distributor
– Ignition coil
– Ignition switch, etc.
• Charging System
– Alternator
– Regulator, etc.
• Starting System
– Battery
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4. Ignition System
• In spark ignition engines, a device is required to ignite the compressed air-
fuel mixture at the end of compression stroke. Ignition system fulfills this
requirement.
• It is a part of electrical system which carries the electric current at
required voltage to the spark plug which generates spark at correct time.
• It consists of a battery, switch, distributor ignition coil, spark plugs and
necessary wiring.
• A compression ignition engine, i.e. a diesel engine does not require any
ignition system.
• Because, self ignition of fuel air mixture takes place when diesel is injected
in the compressed air at high temperature at the end of compression
stroke.
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5. Requirements
• The ignition system should be capable of producing high voltage current,
as high as 25000 volts, so that spark plug can produce spark across its
electrode gap.
• It should produce spark for sufficient duration so that mixture can be
ignited at all operating speeds of automobile.
• Ignition system should function satisfactory at all engine speeds.
• Longer life of contact points and spark plug.
• Spark must generate at correct time at the end of compression stroke in
every cycle of engine operation.
• The system must be easy to maintain, light in weight and compact in size.
• There should be provision of spark advance with speed and load.
• It should be able to function smoothly even when the spark plug
electrodes are deposited with carbon lead or oil.
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6. Types of Ignition Systems
There are three types of ignition systems which are used in petrol engines.
• Battery ignition system or coil ignition system.
• Magneto ignition system.
• Electronic ignition system.
• In battery ignition system, the current in the primary winding is supplied by
a battery whereas it is supplied by a magneto in magneto ignition system.
• Battery ignition system is used in cars and light truck.
• Magneto ignition system is used in some scooters.
• Both the systems work on the principle of mutual electromagnetic
induction.
• Electronic ignition systems use solid state devices such as transistors and
capacitors.
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7. Battery ignition system
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8. Advantages
• Low initial cost.
• Better spark at low speeds and better starting than magneto system.
• Reliable system.
• No problems due to adjustment of spark timings.
• Simpler than magneto system.
Disadvantages
• Battery requires periodical maintenance.
• In case of battery malfunction, engine cannot be started.
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9. Magneto Ignition System
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10. Advantages
• Better reliability due to absence of battery and low maintenance.
• Better suited for medium and high speed engines.
• Modern magneto systems are more compact, therefore require less space.
Disadvantages
• Adjustment of spark timings adversely affects the voltage.
• Burning of electrodes is possible at high engine speeds due to high voltage.
• Cost is more than that of magneto ignition systems.
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11. COMPARISON
Battery ignition
1. It offers better spark at low
speeds, starting and for
cranking purpose
2. Initial cost is high
3. Reliable system, need periodic
maintenance
4. High sped engine drive is
usually simpler
5. With increasing speed, sparking
voltage drops
6. Because of battery bulk of the
system is high
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Magneto ignition
1. More reliable as there is no
battery and cable connections
2. More suitable for medium and
very high speed engines
3. Less space is required
4. At low speed voltage is low. So
not good in slow speed case.
5. The power sparks at high
engine speeds cause burning of
the electrodes

12. Electronic Ignition System
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13. Why Electronic Ignition?
• The disadvantage of the mechanical ignition system is that it requires
regular adjustment to compensate for wear and the opening of the
contact breakers, which is responsible for spark timing, is subject to
mechanical variations.
• In addition the spark voltage is also dependent on contact effectiveness
and poor sparking may lower the engine efficiency.
• Electronic ignition has solved these problems
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14. Ignition Timing
• Ignition timing is the correct instant of generating spark just before the
completion of compression stroke.
• Correct ignition timing is necessary to maximize power output of an
engine.
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15. Ignition Advance
• Ignition advance is the condition when ignition of fuel occurs earlier than the
correct ignition timing.
• Ignition of mixture takes place near the end of compression stroke.
• If the ignition is advanced it means fuel-air mixture will burn too early before
the end of compression stroke.
• In this case, the crank and connecting rod will have to push the piston in order to
compress the gases (for completing the compression stroke).
• In this situation, the force applied on piston by the connecting rod in upward
direction may not be able to overcome the downward force acting on piston.
• This downward force acting on the piston is due to enormous pressure
generated by the combustion of fuel.
• Under this condition, the engine may stop or stall.
• Spark advance may also cause the fuel to explode suddenly under certain
operating conditions.
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16. Ignition Retard
• Ignition retard means the condition when ignition occurs after the correct
ignition timing.
• It is known that after ignition burning (combustion) of fuel takes place.
• If ignition is retarded too much then the combustion of fuel-air mixture
(charge) will continue during power stroke (expansion stroke).
• Therefore, peak pressures will not be developed.
• Consequently work output of the engine will decrease.
• In this case, burnt gases will leave the engine cylinder at higher
temperature which will overheat the exhaust valve.
• It results in loss of power, overheating and sometimes burning of exhaust
valve, and excessive carbon deposits.
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17. Need of Spark Advance/Retard Mechanism
• Correct/Proper ignition timing is necessary to maximize the performance
of the engine.
• Correct ignition timing depends upon several factors.
• These are compression ratio, diameter (bore) of cylinder, composition of
mixture, engine speed and load, engine temperature and quality of fuel
used.
• Except first two factors other factors keep on changing.
• Therefore, there must be an automatic mechanism of adjust the ignition
timing of engine.
• Sometimes the spark is to be advanced and sometimes it is required to be
retarded.
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18. Centrifugal Spark Advance Mechanism
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19. • This mechanism consists of two fly weights, a base plate, cam and a spring.
• Fly weights are also called advance weights.
• The base plate is fixed to the drive shaft.
• The fly weights are rotated by distributor drive shaft through the base
plate.
• The weights are pivoted on the base plate and also attached to the cam
with the help of springs.
• The cam is also joined with the distributor shaft through springs, flywheel
and plate.
• If engine speed increases, the fly weights are displaced out radially due to
centrifugal force acting on it.
• Movement of weights causes the ignition advance (spark advance).
• At low speeds there is no advance while it is full advance of very high
speeds
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20. Vacuum Advance Mechanism
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21. • Vacuum advance mechanism consists of a diaphragm whose movement
automatically advances and retards the ignition depending upon engine
speed and other operating conditions.
• One side of diaphragm is connected to the induction manifold and other
side is connected to atmosphere. (Induction manifold is at lower pressure
than atmospheric and this pressure depends upon engine speed).
• The diaphragm is connected to the distributor through a linkage.
• As engine speed increases the pressure on one side of diaphragm decreases.
• This change in pressure controls the movement of diaphragm which
ultimately controls the ignition timings.
• At normal position of diaphragm the ignition timing is set at fully retarded
position.
• As engine speed increases the ignition timings are advanced.
• Vacuum advance mechanism takes more care of engine load and less of
speed where as centrifugal advance mechanism takes more care of engine
speed and less of load.
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22. Standard Bendix Drive
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23. Bendix Drive with Compression Spring
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24. Folo-thru Starting Drive
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25. Over Running Clutch Drive
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26. Wiring Circuit for Cutout Relay
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27. Wiring Circuit for 3 Unit Regulator
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28. Spark Plug
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29. Hot and Cold Spark Plugs
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30. Capacitive Discharge Ignition
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31. Head Lamp
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32. Horn Circuit
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33. Horn Circuit with Relay
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34. Wind Screen Wiper
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35. Fuel Gauge
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36. Temperature Gauge
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37. Automotive Air Conditioning System
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38. Battery
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39. Functions
The battery performs the following functions:
• To supply the heavy current required by the starter motor for starting the
engine.
• To supply the current to lamps, radio and other accessories when the
engine is not running.
• To act as a stabilizer to the voltage in the electrical system.
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40. Battery Types
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41. Dry Cell
• Uses an electrolytic paste.
• The electrolytic paste reacts with the electrodes to produce a negative
charge on one electrode and a positive charge on the other.
• The difference of potential between the two electrodes is the output
voltage.
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42. Lead Acid Cell
• Anode: Lead-dioxide
• Cathode: Porous lead
• Electrolyte: Sulfuric acid
• During Discharging
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43. Effect of charging
• When the battery is charged by passing an electric current in the opposite
direction from an external source, the electrical energy is absorbed in the
form of chemical energy.
• The following reactions occur during charging.
At Anode (+ve plate):
• PbSO4 + 2H2O+SO4 → PbO2 + 2H2SO4
At Cathode (-ve plate) :
• PbSO4 + H2 → Pb + H2SO4
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44. • Advantages:
– Batteries of all shapes and sizes, available in
– Maintenance-free products and mass-produced
– Best value for power and energy per kilowatt-hour
– Have the longest life cycle and a large environmental advantage
– Ninety-seven percent of the lead is recycled and reused in new
batteries
• Disadvantages:
– Lead is heavier compared to alternative elements
– Certain efficiencies in current conductors and other advances continue
to improve on the power density of a lead-acid battery's design
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45. Battery capacity
• The amount of electricity of battery will deliver within a certain time limit is
known as its capacity or ampere-hour capacity.
• The amount of current furnished by the battery depends upon the following
factors:
• Number of plates of battery.
• Area of plate surface in contact with the electrolyte (sulphuric acid)
• Quality of electrolyte
• Temperature.
• The battery capacity is greatly reduced by low temperature which retard the
electro-chemical action in the cells.
• Hence capacity will decrease with the decrease in temperature
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46. Battery Ratings
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47. Checking of Batteries for Voltage and
Specific gravity
• Specific gravity test (Hydrometer Test)
• High rate discharge test.
• Open circuit voltage test
• Cadmium test.
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48. Causes of Battery Failure
• Electrolyte level
• Under charging
• Over charging
• Temperature
• Corrosion
• Cycling
• Vibration
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