EXPERIMENT – ENERGY FROM NOTHING
An AA battery delivering 1.5 V is tested to light an LED. It won’t glow at first. More pressure is required. Then the primary windings of each coil are connected in parallel with the LED. It doesn’t burn out again. A drum roll follows — the battery is removed and the LED starts blinking. The energy comes from the coil’s inductance, not from the battery.
Where do those kilovolts come from under the hood that ignite the fuel mixture in cylinders when the battery voltage barely tops 12 V? They are generated by the same inductance.
Does the power come from the horn?
One can safely grab the battery terminals with both hands: 12 V rarely causes trouble. Yet touching the energized ignition signal wiring with a finger can hurt badly. Automobiles use relays that sometimes whistle when switched off.
The effect described here is parasitic, but in an ignition system it is put to practical use.
In signals, relays, and ignition coils there is a wire wound around a core. In electrical engineering this design is called an inductor. In relays and horns it is the main electromagnet, and in an ignition coil it forms the core element of a two winding transformer.
Ignition modules rely on this principle. If one winding fails, the whole assembly can become expensive to replace. Regular maintenance like timely candle replacement helps avoid defects.
How does current flow? It happens slowly
When direct current flows through an inductor, its behavior resembles a warm bulb or a filament. When the load disappears, the current falls to zero but changes gradually. A few centuries ago scientists noted that current in an inductor cannot change instantly — it must shift smoothly. When the circuit closes, current rises with a delay; when it opens, it does not stop immediately — it mirrors inertia in a moving body.
The device of an individual ignition coil with a switch includes a path to the spark plug, a primary winding, contacts, an electronic unit, a secondary winding, and a magnetic core.
The phenomenon is known as self induction. Any change in a magnetic field generates current — that is how generators work. This rule applies to the coil and relay fields as well. When the power source is disconnected from such loads, the magnetic field collapsing creates a voltage surge, much higher than the original supply, which helps the current fade away smoothly.
On the primary winding of ignition coils, the surge can reach hundreds of volts. The secondary winding, with many more turns, responds to the changing field by producing tens of thousands of volts. This effect remains central to how ignition systems operate.
Block diagram of a typical ignition coil: control input, designer, overheating protection, current protection, control cascade, voltage protection, power, primary winding, secondary winding, exit to the spark plug, feedback driver, feedback output, and a ground reference.
Jules Verne, Ruhmkorff and the bicycle
The ignition coil is reminiscent of a bicycle in that the basic design has stood the test of time. The first practical version appeared in the workshop of the German mechanic Ruhmkorff in the middle of the 19th century. Jules Verne even mentions the so called Ruhmkorff device in his novels.
Owners of Muscovite and Zhiguli vehicles know the cylindrical coil with a center high voltage wire leading to the distributor. The original design used oil filled insulation as a transformer with two windings. Power interruptions in the primary were controlled by a mechanical breaker, and every time it opened, a high voltage pulse appeared in the secondary that traveled to a spark plug in one cylinder. The oil improved insulation and cooled the coil.
Oscilloscope traces show voltage in the primary and secondary: when the current in the primary is interrupted, high voltage pulses appear in the secondary.
Transistor Offensive
The early electronic ignition systems in the USSR on the VAZ-2108 and GAZ-24-10 replaced the mechanical breaker with sensors — Hall or magnetoelectric — while an electronic switch sits between sensor and coil. The coil’s core design remains substantially the same, though later models used dry type coils in plastic housings.
For the microprocessor G8 — VAZ-21083-02 — a coil was developed that could fire two cylinders from one spark event, technically a four terminal coil. In a four cylinder engine, one high voltage discharge would reach two cylinders at once: one cylinder was under pressure and ignited, the other simply cleaned the candle on the exhaust stroke. This avoided the need for extra power, and reduced the number of high voltage wires from five to four.
Ignition coils with feedback for Toyota and Lexus engines show a large cylindrical winding assembly and a compact head housing the electronics with four wires.
To each on its own spool
Later, ignition modules emerged that integrated the coil and switch into a single unit. The ideal solution remained individual ignition coils mounted directly on each spark plug.
Coils with built in switches became widely adopted. A standard coil requires two wires for power, but the advanced four terminal coil carries an electronic switch on top and a long core winding. It still needs plus and minus, but one terminal provides the control signal that tells the spark when to occur, and another gives feedback on whether the spark happened.
Most car owners rarely notice the presence of spark plugs, coils, and other incendiary components under the hood. The idea of laser plasma candles triggering the mixture with a powerful beam is common talk, even now.
- Behind the wheel can be read in Odnoklassniki.