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 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 . • Then it travels through “high tension” wires to the plugs. • They are sequenced to the 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. 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 inline for firing. Theory of Mag Operation

• The 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.