Trembler Coil



NEW 11-16-2013  I have been asked recently if the trembler coil shown on this page would drive a Jacob's ladder. I told him “I don’t know but I will find out”. It turns out it will drive a Jacob’s ladder. Two pieces of #14 wire were added to the coil to form the “ladder”. 4 pictures were added to the gallery showing the Jacob’s ladder in operation. This is a rather puny Jacob’s ladder when compared to one made with a neon sign transformer, but it does work.


8-8-2013 There is a good explanation of how a Trembler coil   works on Wikipedia, so I will not go into a lengthy explanation of how they work.

The circuit presented here is not a true trembler coil circuit because the magnetic field of the spark coil does not open the contacts to create the spark.  A relay is used to interrupt the coil primary circuit. 

This circuit does not use any electronics, only parts which can be obtained at an auto parts store.  I wanted ignition parts for a pre-electronic ignition car so I ask the NAPA parts man for a coil and capacitor (condenser) for a 1961 Chrysler.  The relay is an automotive type obtained from an electronics store. The relay is a Bosch type labeled HKE cma 31-c.  Any relay with a 12 volt coil and one set of normally closed contacts rated at 10 amps or more should work.  This circuit is so simple someone must have tried it before.  I do not remember seeing this circuit in any literature nor could I find any thing like this on the internet. 

This circuit is essentially a Kettering system with the relay  replacing the points.


These pictures are in a thumbnail format, click on the picture to see a larger version.   

Set up.

Showing the 3 components making up the trembler coil setup. Capacitor, relay, and coil.



Coil in operation

Showing the spark in still air. The column of hot ionized air provides a low resistance path for the arc holding the voltage down.

Coil in operation.

Showing the spark in a stream of moving air from a fan. The conductive column of ionized air is blown away between each HV pulse generated by the coil. Each pulse put out by the coil reaches a voltage great enough to break down and ionize the air. Voltages reached with the arc being blown out are much greater than than shown in the previous picture.

Jacob's ladder.

Two wires were added to the trembler coil to form a Jacob's ladder.

Jacob's ladder.

Arc starting at the bottom of the "ladder".

Jacob's ladder.

Arc climbing the ladder. Several high voltage sparks occured during a rather long shutter opening. Note the bright spots on the left wire and the blue arc crossing to the right wire.

Jacob's ladder.

The arc has climed to the top of the "ladder" and is about to blow out, restarting the cycle.

Spark plug.

If a spark plug is operated at one atmosphere pressure as shown here it is not necessary to use a small spark gap as would be used in a piston engine. The ground electrode has been removed from this plug and it provides a large arc surface all the better to ignite a gas mixture. The arc has established its self across the shortest distance. This is in still air.

Spark plug.

A small gust of air caused two arcs to be established while the camera shutter was open.

Spark plug.

A gust of air will blow out an established arc causing new ones to be established at each HV pulse. Such a condition would exist when starting a pulse jet engine.

Spark plug.

A gust of air caused multiple arcs to be established.







                                                               How it works:    

Battery power is supplied to the relay coil through a set of normally closed contacts on the relay.  When power is applied the relay is energized and opens the contacts removing power from the relay coil, the contacts then close starting the cycle over again.  The ignition coil primary is connected in parallel with the relay coil and is pulsed every time the relay switches.  An ignition system capacitor (condensor) is connected across the relay contacts just as it would be across the points in a distributor.  The spark rate is determined by how fast the relay opens an closes the contacts.  The high voltage return of the coil's secondary is not shown on the schematic but is internally connected to one of the primary terminal bolts.  Use either one as a return.

Parts used:

B1     any 12volt battery or source

RL1   Bosch automotive relay  MCM Electronics part#  26-534

C1     ignition capacitor (condenser) NAPA part# AL868   Any capacitor with a value of .2 to .25

          mfd and a voltage rating of 600 volts or more will probably work in this position.

T1      Ignition coil NAPA part# IC12SB

V3      Spark gap,  a piece of wire inserted in the coil tower and spaced 3/8 inch from one of the coil

           primary terminals, or what ever you want to do with the high voltage.



        Tester for ignition coils and condensers.


        Used with a HV rectifier and a HV filter cap this would make a HV low current power supply.

         the HV rectifier from a color TV might work if it has a high enough PIV rating.


          Use it to pre charge the belt on a Van De Graff generator.


           Use it to start a  Valveless Pulsejet Engine


            Light off fuel in a diesel engine intake manifold for a cold start.


               Drive a Jacob's ladder.


The use of the trembler coils in model T Fords is well known.  The last model T was made in 1927 and was probably one of the last autos to use this kind of ignition system.  One of the last uses of a trembler coil that I am aware of was on a 1953 Massy Harris model 55 tractor with a Continental Diesel engine.  There was a valve and primer pump on the dashboard which would squirt Diesel fuel into the intake manifold.  A trembler coil would fire a sparkplug in the manifold and light off the Diesel fuel.  The engine would always start no mater how cold it was.  This system was replaced by 1955 with a giant glow plug in the intake manifold.



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