We want a very high voltage, so we use a conductor with a great number of windings-more than 50 times the number of windings in the lt circuit. These are the secondary or ht windings. They are connected by ht lead to one or more spark plugs. If there is more than one plug, the ht lead runs to a distributor, which distributes the ht spark to whatever cylinder is firing.
Inside the coil, if we connect the primary windings to the secondary windings (secondary winding to the negative side of the primary winding), then, whenever the contact breakers are open, the two windings are wired in series with one another. When the contacts open, the magnetic field, as well as inducing a current in the secondary ht winding, will also induce an EMF in the primary lt windings-approximately 300 volts. This self induced EMF in the primary winding is added to the induced EMF in the secondary windings to give a much higher output to the spark plug.
1. IGNITION COIL SELF-INDUCTION EFFECT
A magnetic field is generated when a current flows through a coil. As a result, an EMF (electromotive force) is generated which creates a magnetic flux in a direction which impedes the generation of magnetic flux in the coil. Therefore, current does not flow immediately when it is first introduced in the coil, but a certain period of time is required for the current to rise.
For the more, when current is flowing in a coil and that current is cut off suddenly, an EMF is generated in the coil in the direction in which the current is tending to flow (in a direction which hinders the decay of the magnetic flux.)In this way, when current starts to flow in a coil, or when current is cut off, the coil generates EMF which acts to impede changes in the coil's magnetic flux. This is called the "THE SELF-INDUCTION EFFECT".
|Self-induction diaphragm inside the Primary Coil|
|Breaker Points Closed Formation|
2. IGNITION COIL MUTUAL INDUCTION EFFECT
When two coils are arranged in a line, and the amount of current flowing in one of the coils (the primary coil) is changed, an EMF is generated in the other coil (the secondary coil) in a direction which impedes the change in the primary coil's magnetic flux. This is called the "MUTUAL INDUCTION EFFECT".
|Mutual Induction Effect inside the Secondary Winding|
BREAKER POINTS OPEN WHEN MUTUAL INDUCTION EFFECT
As the crankshaft rotates the camshafts, the distributor cam opens the breaker points, causing the current flowing through the primary coil to be suddenly interrupted.
|Breaker Points Open Formation|
IGNITION COIL W/ RESISTOR
1. AUTOMOTIVE CONSTRUCTION OF IGNITION COIL WITH RESISTORThe ignition coil with resistor has a resistor connected in series to the primary coil. Unlike the ignition coil without resistor type, the secondary voltage drop in the high speed range can be reduced. In almost all production automobiles that are fitted with the conventional ignition system, the ignition coil is of this type. Two types of coil are available: one in which the resistor is an external resistor type, and one in which it is an integrated resistor type.
|Ignition Coil w/ Resistor Type|
Since the integrated resistor coil has three external terminals, do not confuse the B and (+) terminals when making connections.
2. FUNCTION OF IGNITION COIL WITH RESISTOR
When the flow of current through a coil is started, there is a tendency for the current's flow to be impeded by the self-induction effect (during the time it takes from the point when the breaker points close for the current saturation value to be reached). Therefore, when current flow is started in the primary coil of the ignition coil, the primary current rises gradually, with the current rise delayed as the number of windings in the coil increases.In an ignition coil without resistor type, since the length of time the breaker points are closed is long when the engine speed is low, enough current flows so that a secondary voltage which is sufficiently high can be obtained.However, when the engine speed is high, the time the breaker points are in contact is shortened and not enough primary current flows, resulting in the secondary voltage becoming low.In an ignition coil with resistor type, the number of windings in primary coil is reduced, thus be impeded by self-induction. Therefore the primary current rise time is faster. In this way, sufficient primary current flows even at high speeds and drops in the secondary voltage can be prevented.
|Ignition Coil w/ Resistor Type and Capacitor|