Prewar Workshop: Trembler coils

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Recently in the workshop I had ignition problems with a <1900 vehicle. The car would not really want to work well when cold and had problems finding the correct ignition timing.  The ignition system was a modern set of contact breakers and coils and seems to have been converted at some point in history from its unknown original battery operated ignition type.

In this case, I decided to use trembler coils for this car. The system best known from the Model T Ford. The main advantage of these is that they give a continuous spark as long as the contact is made. Unlike the contact breaker ignition, that charges the coil and releases the spark only once per powerstroke.

The way the trembler does this is that it has a coil inside that acts like an electromagnet. When the trembler is supplied with current, the primary coil charges and magnetizes an iron core its wound around. The magnet pulls open the trembler points that are mounted on top of the assembly.

The trembler points open, causing the current in the primary coil to stop and the magnet to be demagnetized. At the same time, the secondary winding has generated a high tension current which arcs over the spark plug. Demagnetizing the iron core in the primary winding closes the trembler points again and the process repeats. This process repeats multiple times per second which looks as a continuous spark as long as the assembly is supplied with power.

Power to the assembly comes from a distributor on the camshaft. This distributor has a brush that makes contact for a few degrees of rotation, giving the coil a spark for some length of piston travel.

For questions or remarks, please comment on the artice or ask me via [email protected]

Article by Jos van Genugten

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