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 With a coil as the core moves close counter current will cause N S
Lenz Law opposite polarity magnetism, resisting a build up of flux. N S S N
Lenz Law N S S N
Lenz Law As the core moves away the current and resultant field switches N N S S
Lenz Law The magnetic polarity is the same and the fields N N S S
Lenz Law resist any decreases N N S S
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.