How does the 12 volts of battery steps up to 25000 volts?

Answer 1

Here is how the ignition system in a car works. In older cars, the battery supplies electricity to the ignition coil and ignition points. The ignition coil is actually a device known as a transformer. Transformers have at least 2 windings, and electricity from one winding is "induced" into the other winding when the field in the first winding collapes. In transformers, the thicker and shorter the wire, the more current is involved, and the thinner and longer a wire is, the more voltage is involved. Anyway, the primary coil is magnetized by the battery. When the ignition points open, that field collapses and the fading magnetism creates electricity in the secondary winding. The primary winding is made for current, while the secondary winding is made for voltage. Since there are many more windings (maybe over 2000 times the number used in the primary winding), the voltage is much higher. From there, the distributor cap determines which spark plug gets the high voltage. Everything is timed to where each spark plug gets a jolt of high voltage each time a piston reaches the top (and yes, this even happens on the exhaust stroke, though it does no good, at least in a traditional, non-computer engine).

In modern engines, the principles are the same, though the methods are different. Instead of points, there is an ignition timing sensor, and it tells the ignition module when to fire or even where each piston is. That causes transistors or other semiconductors to build and collapse the magnetic field on the primary coil winding.