This page was last edited on 15 August 2015, at 00:hillier’s fundamentals of automotive electronics pdf free download. A trembler coil, around 1915. The mechanism on the end is the “trembler”.
The switch contacts are on a springy iron arm, which holds them closed. The arm is mounted near the iron core. The magnetic field of the core is switched off, allowing the arm to spring back, closing the contacts again. Then the primary current is turned on again, and the magnetic field opens the contacts again. This cycle repeats many times per second, while power is applied to the coil.
In the trembler coil, in contrast, each “break” of the trembler contact produces a pulse of high voltage from the coil. During the time the points in the timer are closed, the vibrating trembler arm produces a series of high voltage pulses, producing multiple sparks. In the Model T, a battery was used for starting, but once the engine started the supply was switched to the engine’s own generator. In these early days, this was not rectified and so the alternator’s output remained as AC. This was entirely adequate to operate the ignition system, and after 1915 to power electric headlights, although it could not be used for battery charging.
It was simply adopted for use in automobiles. When the piston was at the right point, the contact breaker opened, breaking the battery current. The drawback of the low tension coil was that the high ignition voltage was generated in the same circuit as the low voltage battery current flowed in. In the Model T, four trembler coils were used, one for each cylinder. This was a precursor of the modern use of individual plug-top coils, where each cylinder has its own coil, thus avoiding the need for a HT distributor.
For correct operation, each cylinder must be fired in turn, and at the right time. Both of these tasks were conducted by the ‘timer’ or low-voltage distributor, a rotary switch. The Timer switched the primary current to each coil in turn and also started the coils at an appropriate time in the cylinder’s cycle. Starting a cold engine could require dexterous manipulation of the control to get the engine to start. Modern engines control such timing even more carefully, but this is now automatic and not obvious to the driver.
A significant difference from modern ignitions is in the strength and number of sparks produced. A modern system produces one, large, spark at exactly the time commanded. The trembler coil systems cannot produce such a high energy spark, but it does produce a continuous stream of sparks for as long as the timer circuit is closed. These were both less sensitive to the accuracy of ignition timing and their mixtures also benefited from having a sustained ignition source. Trembler ignitions were particularly suitable for igniting these mixtures. These systems used a single ignition coil for the engine, supplying the spark to each cylinder in turn. The high voltage distributor evolved from the timer and it too was a rotary switch driven at camshaft speed.
The wide availability of the Model T made their component parts equally widespread. Their trembler coil in particular became a popular component for electrical hobbyists and backyard tinkerers, and was one of the first factory-made electrical components to be available in such numbers. The Model T coils remained so popular for non-car use that they remained in production for some years after the car itself. As this application is more frequency sensitive, the vibrators were generally a separate unit, with a more stable frequency tuned reed, apart from the transformer.