Ignition coils for small engines

[Ian S CParticipant @iansc]

On some of the full size hit & miss engines some of the blokes use the (I think its) ballast transformer for fluoresent lights,using the back emf, no transistors allowed.Ian S C

[John Wood1Participant @johnwood1]

Hi Ian, when I was at the Internal Fire Museum earlier this year the owner told me that they use fluorescent light transformers for some of their old engines, unfortunately I wasn’t able to press him for any circuit information. I have looked at a transformer from an old light fitting and find only a two-wire connector so not sure how that would be used. We need someone clever enough to be able to describe how such a unit might be used in ignition systems, however, the transformers I have seen are really quite large so may not be suitable for smaller engines.

 

John

[Engine BuilderParticipant @enginebuilder]

John, The flourescent transformers are chokes and would be used on an engine with low tension ignition. I have some of these on some of my models (the one as my avatar is one).

If anyone is not familular with this type of ignition let me explain. There is no spark plug but in its place is a set of points inside the cylinder head. The circuit consists of a just a battery ,the points ( called an ignitor) and the coil all connected in series. There is a mechanical arrangement that pushes the points together and breaks them at the right moment.

David

[Sub MandrelParticipant @submandrel]

Finally I think it is a nice juxtaposition to have an old style hit ‘n’ miss engine together with a surface mount microprocessor ignition system.

 

I must admit, I am tempted by a three-cylinder steam engine with solenoid operated valves under microprocessor control – not just reversible and speed controlled – but angular control and inching like a stepper, or even waving back and forth.

 

Neil

[Anonymous]

Strange but true, I did start building a three cylinder radial steam engine (Cygnet Royal, I think) during ‘O’ level metalwork. Of course I never finished it, but I do still have the bits somewhere. I also suspect that I was the only person in whole history of the school to use the shaping machine, while making parts for Cygnet. I had to use the shaper, as we didn’t have any milling machines.

 

Of course any steam engine also deserves a microprocessor controlled steam whistle!

 

Regards,

 

Andrew

[John Wood1Participant @johnwood1]

Hi David, thanks for the gen re low tension ignition. I have of course come across mention of such systems but hadn’t found a decent explanation which you have now supplied. Presumably then the mechanical striker operates externally and is what you can see on early magnetos.

 

Good gen – thanks

 

Regards   John

[Ian S CParticipant @iansc]

Could of coarse go to a hot tube and forget electric, but its difficult in little engines. The original design of the motor I’m sort of putting together had this type of ignition, but I’v gone sparky, the engine has a bore of 2″ and a stroke of 4″, The design is about 120yrs old. Ian S C

[Billy MillsParticipant @billymills]

Flourescent chokes are NOT designed with Kilo Volts in mind, they have pile windings so a varnish insulation breakdown is on the cards. If you want to wind an inductor for High Voltages then you wind in a layer then insulate before winding the next layer or you wind in a former that has slots i.e. small partitions along the core to insulate the windings. Impregnation with a good epoxy is not a bad idea.

 

Backlight invertor transformers ( from LCD displays) produce about 2.5KV pk-pk in a very small high frequency transformer ( 30-60KHz). They might be a starting point for a small ignition system. There are certainly enough of them thrown away by people who service displays.

 

 

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