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Battery powered ignition
• A typical battery powered ignition uses a transformer, a several switching devices, and a power source.
• The power source is the battery.
Battery powered ignition
• The first switch allows battery voltage to the primary coil.
• Voltage from the primary coil then goes to a second switch in the engine, then to ground.
• This switch is “timed” to open when spark is desired.
Battery powered ignition
• The opening, causes the current to stop in the primary.
• This collapses the magnetic field around both coils.
• For every one primary turn there are 2,000 secondary turns in this coil pack.
Battery powered ignition
• The resultant exchange causes 12 volts to become a 24,000 volt surge.
• The 2 amps becomes 1 milliamp
Battery powered ignition
• This high voltage is enough to break down the dielectric air gap between the spark plug electrodes and produce a spark.
Battery powered ignition
• Once the spark starts it will continue conducting current at a lower voltage value
• This will happen until the magnetic field is “drained” from the coil.
Battery powered ignition
• Shortly after this the switch will need to close to give the magnetic field time to rebuild in the coil, for the next spark event.
• The points are often mounted on a moveable(rotating) plate to provide variable timing options
• This allows good engine operation at all RPM ranges.
Battery powered ignition
• The secondary voltage is carried to the spark plug via a rotary switch called the distributor.
• Then it travels through “high tension” wires to the plugs.
• They are sequenced to the firing order needs of the engine.
Battery powered ignition
• These extremely high surges in the coils cause rapid oscillations of voltage and current.
• This can damage the “engine switch” (points or contact points)
• A condenser is installed as a parallel path to ground.
Battery powered ignition
• This drains the A/C oscillations to ground preventing high current arcing of the points.
• A condenser is a large capacitor.• It is imperative that the capacitor be
balanced with the inductor(coil) and the supply voltage.
Battery powered ignition
• Summary:• The off/on switch is between the
battery and the coil.• The engine switch is between the coil
and ground.• Current is supplied from a battery,
which is charged by an engine driven generator.
Battery powered ignition
• To defeat the system the circuit is broken stopping voltage to the coil.
• If the battery fails the systems fails.• But the battery can produce great
spark at any engine speed, including cold or hot starts.
Magneto powered ignition
• Magneto operation differs primarily because it does not use battery current.
• It incorporates its own rotating permanent magnet generator.
Magneto powered ignition
• The rest of the components are similar, but the theory of operation is somewhat different.
• Its primary advantage is that it can be completely self contained in a small engine driven package.
Magneto powered ignition
• Multiple units can be installed for redundancy and improved flame propagation.
Magneto powered ignition
• Two main disadvantages are that they need moderate engine RPM to function.
• They do not provide a means to vary the timing during operations other than start.
Theory of Mag Operation
• Internal circuits include:• Magnetic• Primary-electrical• Secondary-electrical
Theory of Mag Operation
• Magnetic circuit includes:• Rotating four (or more) pole
magnet• Pole shoes w/extentions• Coil core
Theory of Mag Operation
• Primary circuit includes:• Primary coil winding• Points• Condenser• Connecting wire• Grounding “P” lead and switch
Theory of Mag Operation
• Secondary circuit includes:• Secondary coil winding• Distributor• High tension leads• Spark plugs
Theory of Mag Operation
• The magnetic circuit allows the lines of flux in the rotor to oscillate.
• At neutral the poles are not lined up with the shoes.
• There is no flux concentrating in the poles and coil core.
Theory of Mag Operation
• At all other times flux is varying in the coil core and poles.
• The flux reverses each cycle, or one time for each rotor pole.
• Due to hysterisis the plot of this is a flattened circular shape.
Lenz’ Law
• States that current inducted in a circuit will produce counter magnetic lines of flux that oppose the original induction flux.
Lenz’ Law
• This means if the flux in the pole shoes and coil core is allowed to pass through a complete circuit, the resultant current will create flux that opposes the rotor flux.
Lenz’ Law
• No coil the flux will concentrate on the core.
Lenz’ Law
• As the core moves close the lines bend to fit it.
Lenz’ Law
• They finally concentrate in it.
Lenz’ Law
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• With a coil as the core moves close counter current will cause
Lenz’ Law
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• opposite polarity magnetism, resisting a build up of flux.
Lenz’ Law
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Lenz’ Law
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• As the core moves away the current and resultant field switches
Lenz’ Law
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• The magnetic polarity is the same and the fields
Lenz’ Law
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• resist any decreases
Lenz’ Law
• Thus the addition of a coil circuit to the core will create an inductive lag in the magnetic flux.
Lenz’ Law
• This lag allows us to maximize the field buildup and minimize the collapse time when the current is cut off.
Theory of Mag Operation
• So as a result of Lenz’ law the flux lags and stays “built” around the coil until something after the rotor gets back to neutral.
Theory of Mag Operation
• At this time the points open, the current disappears
• the time between when the rotor passes neutral and when the points open is called E-gap, or efficiency gap.
Theory of Mag Operation
• At this point if there had been no coil the magnetic circuit would already have been reversed.
• So rate of field collapse when the points open is enhanced some by the reversed field.
Theory of Mag Operation
• Enhancing too much (E-Gap) then interferes with the buildup of the next field cycle.
• In a sense the primary circuit and the magnetic circuit are constantly working against each other, and the secondary is auxiliary to them.
Theory of Mag Operation
• But what we desire from this system is the field collapse around the secondary.
• The secondary is identical to a battery operated system.
• A distributor switches each spark to the next cylinder inline for firing.
Theory of Mag Operation
• The magnetos is disabled by adding another circuit parallel to the primary points.
• This causes the primary circuit to stay active causing constant magnetic flux lag, that never rapidly collapses around the secondary.
Theory of Mag Operation
• These devices have no means to alter when the spark fires for each cylinder like other timing devices do.
• Primarily because the most of the power of a propellered engine is produced between 300-400 RPM.