Model petrol Ignition solution

[Chaffe]

My appologies if this has already been covered. I have for my model IC petrol engine a 1/4" spark plug that i wish to fire with a motorbike coil. I understand the coil has a live to it (usually through the ignition switch) and that the plug will go on the lead and must be earthed. I also understand the coil earth must be earthed for the majority of the time and only when the earth is broken that a spark will occur as the coil collapses. There must be a capacitor to stop back emf accross the points also.
So my question is, i would like to use a transistor to replace the points and use a low current switch or hall sensor to activate this. Does anyone have any circuit diagrams they could prehaps share with me? many thanks in advance James.

 

[gbritnell]

There have been several schematics presented on this forum along with the following.
http://www.5bears.com/tim4.htm
I tried to post Elsmore's hit and miss ignition but the link doesn't seem to work any longer.
gbritnell

 

[Chaffe]

i have read (and tried to make) elsmores circuit, it is quite complex for the job it does in my opinion, i could do without the timer etc, i will look at the other link you have posted, thanks

 

[Chaffe]

Good link! "tim6" looks to be what i am looking for, many thanks james

 

[DaveRC]

Hi James,

There is a kit for a very simple ignition that has all the bits you are looking for at a very good price,

http://www.model-engine-plans.com/partskits/ignitionsystems/transistors.htm

I have just got one of these, not tried it yet but looks simple enough, and I like simple....

I also have a 6v bike coil to use, one thing you need to check, that the primary coil is not less than 1 ohm, if it is add a resistor in series to make it so. I am quite sure I got that right, not put it into practice yet. Any less then 1 ohm the current draw will be to much.

Dave

 

[Ken I]

A lot of new car ignition systems are using 3 wire ignitors = Pos, Neg & Fire. (BM, Merc, Audi, Turbo Golf)

Sometimes this is built into the coil/plughead assembly and in others it is a separate unit.

The pos is hard on via a surge resistor and the pos fire pulse causes a transistor to short the coil primary (the surge resistor limits the "fault" current on the input) causing field collapse and ignition voltages in the secondary.

The pos "fire" pulse needs to be very short in order to limit overheating of the (inbuilt) surge resistor.

I ran one on a square wave generator (so it was shorted 50% of the time) and it overheated in about 30 seconds.

So the fire signal needs only be long enough for field collapse - I'm guessing about 1-2 microseconds.

Ken

 

[Chaffe]

I run a VAG igniter on my cosworth v6 turbo road car, i guess something similar would work in model practice, good point

 

[Chaffe]

i piicked up an automovite (vag) smart igniter yesterday, it uses a hall sensor or set of points/switch etc as a trigger, got it sparking quite easily, ill post some pictures when i get a minute.