File:Vibrator ignition coil.png

English: Drawing of vibrator-type ignition coil (trembler coil) used in early automobiles around 1900 such as the Model T Ford. It is an induction coil wired as an autotransformer. The two righthand terminals are attached to the car's battery, the lefthand terminal is the high voltage output to the distributor. The mechanism visible on the end is the vibrator interruptor, a magnetically activated switch contact which repeatedly breaks the DC current in the coil's primary winding to provide the flux changes needed to induce voltage in the secondary. When current starts to flow in the primary, the iron core of the coil which projects through the end of the box becomes a magnet. This pulls the springy interruptor arm, opening the switch contacts, turning off the current in the primary. With no current the magnetic field from the coil collapses, and the vibrator arm springs back, closing the contacts again, turning on the current. This cycle is repeated many times per second. Each time the contacts "break", the collapsing magnetic flux in the coil induces a high voltage pulse in the secondary winding. Typical secondary potential is 10,000 to 20,000 volts. Caption of figure: "Pfanstiehl box type vibrating coil". Alteration to image: cropped out distracting background.