How do ignition coils work in cars?

Answer 1

The ignition coil in a car is a step-up transformer, and the primary is powered up by the vehicle's 12-volt DC system. (And yes, in actuality the voltage is a bit over 13 volts. Some other voltages are possible.) The primary winding of the coil is intermittantly "pulsed" by the breaker points in the car, or the electronic ignition system in newer cars. For older cars, at the proper moment (the so-called "timing"), which is determined mechanically by the cam that operates the breaker points (and the adjustment of the breaker points themselves), the points close and the electrical system is connected to the primary winding for a moment. This delivers a pulse to the primary of the coil. Let's look at the electronic ingition systems a moment. In an electronic ignition, there is a sensor in the distributor to enable the control module to sense the position of the distributor shaft assembly. At the correct time, which is "calculated" by the control module and based on information like crankshaft position, speed, throttle position and a bunch of other stuff, the control module pulses the primary winding of the ignition coil. Now let's see what happens. The voltage pulse in the primary is stepped up many times by the many turns in the secondary winding, and a high voltage pulse is developed in that secondary by the inductive action of the coil. This high voltage pulse is routed to the appropriate plug through the rotor and distributor. Zap! The plug fires and ignites the fuel-air mixture that has been "sucked" into the cylinder by the piston on the intake stroke and then compressed on the compression stroke. The power stroke will commence with the ignition of the fuel-air mixture by the arc across the gap of the spark plug.