The Lenz effect
The German Heinrich Friedrich Emil Lenz (12 February 1804 - 10 February 1865) is known for formulating the law that bears his name, Lenz's law, according to which:

The current induced in a circuit due to a change or a motion in a magnetic field is so directed as to oppose the change in flux and to exert a mechanical force opposing the motion.

However, he is less known for his discovery, which also bears his name, called the Lenz effect, on which all ignition systems are based. It is also called magnetic disruption or magnetic collapse.

Lenz noted that when a magnetic field induced by the electric current on a winding around a core and this current is cancelled abruptly, the coil self-induces voltage in the opposite direction of a very high value. What happens is that, when the cause that maintained the magnetic field suddenly ceases to exist, it decays at an infinite speed, and the flow variation is so fast that the winding produces an extremely high tension, which is utilized.

The magnetic collapse is generated at the time of the contacts opening, as shown in the image. A condenser is used to make current cut-offs slower, which prevents all of the energy being lost between the contacts and reduces the resulting voltage to about 20 kilovolts —nothing to look down on— on the secondary, but with minimal current intensity necessary to ignite.

The coil consists of a single step-up transformer with a primary low voltage circuit and a secondary high voltage circuit. The coil is usually identified as HT coil. The difference in this regard to a current transformer is that its secondary circuit has a strong insulation, without which the high voltages required are not generated.

Electronic ignitions
In today's modern engines, the collapse is generated in reverse: instead of cutting off the current, its discharges voltage of about 200 volts, stored in a capacitor, with the same voltage that is generated at the time of opening the contacts of a breaker. This system is called capacitive discharge ignition, CDI being its acronym, and uses a thyristor to produce discharge on the HT coil.

In the first electronic ignitions to hit the market, the electronic part went along with the HT coil all in one piece, called an electronic CDI coil. Subsequently, designs were made in which the electronic part was separated, known as CDI module. Currently, two ignition systems coexist —separate and joint electronics— whose use depends on each specific need.

Spark advance
The gases taken in by the cylinder present an approximate ratio of 15 parts of air to 1 petrol, a relation called stoichiometric ratio. The mixture has a combustion time, and the speed of the pistons forces the time of ignition to occur slightly before the piston reaches top dead center (TDC). This time is called ignition timing and is measured in degrees. With the explosion occurring just above, the mixture continues the combustion while the piston goes down, losing all power. Maximum performance is obtained when, once it has reached the TDC and the fuel is completely burned, maximum pressure and force for pushing the piston is reached.

Using trigonometry, the degrees of progress can be transformed into millimetres, whose unity is very extended to make the timing of engines using a micrometer dial gauge.

Note angle α, which indicates progress in degrees:

  • The higher α is, the igntion timing is advanced.
  • The lower α is, the ignition timing is retarded.

It is important to note that, by manipulating the carburettor, we can modify the air/mixture ratio and thus modify the burning time in such a way that the motor acts like we are changing the timing setup.

Electronik Kontacktloser module RP-5
In order to respond to the needs that arise in the restoration of outdated motorcycles, Levistronic has gone a step further in the innovation of ignition system designs. Thus, we have developed a module capable of adapting to all classical 2T engines and some 4T, with the main new feature being that it provides the specific spark advance of each motor so that it avoids the tedious process of ignition timing setup up.

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