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Help with coil limiting Spark Duration

3BABY

Jan 26, 2011
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Jan 26, 2011
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Hi All,

just wandering if anyone would know how to limit the spark duration time on an ignition coil..

obviously we can limit the dwell time by only charging the coil for a certain amount of time.. but how do we limit the time the spark (some call it the burn time) is being produced for once the magnetic field starts collapsing?


.. oh and apart from the obvious of re-charging the coil.. is there any other way?

opinions would be awesome! thanks :)
 

neon

Oct 21, 2006
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Oct 21, 2006
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Well you could add a diode across to limit the negative ringing but then the spark plugs will need frresh repalcement often due to migration of metal. I think this is an ill concieved idea personally i would prefer longer time to make sure all fuel is burned:eek:
 

3BABY

Jan 26, 2011
3
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Jan 26, 2011
Messages
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Well you could add a diode across to limit the negative ringing but then the spark plugs will need frresh repalcement often due to migration of metal. I think this is an ill concieved idea personally i would prefer longer time to make sure all fuel is burned:eek:

thanks for the reply..

yes i agree.. more spark time makes sure all the fuel is burnt.. but the problem is.. at a high rev range i.e. 10,000rpm.. if the "burn time" stayed long it would crossover into the next revolution of the engine..
 

3BABY

Jan 26, 2011
3
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Jan 26, 2011
Messages
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Sounds like you are looking for a 'Capacitor Discharge Ignition' system.
http://www.gill.co.uk/products/digital_ignition/Introduction/4_CDIvsIIS.asp
Back in 1968 I built a CDI and wired it into the points and ignition coil on the car engine, but did it through a relay that would restore the original wiring configuration if the electronics ever failed. Never had to use that relay.

Ahh yes.. that would fix the spark burn time problem..

thanks for the reply..

there must a a way to control the actual burn time though.. and not leave it up to a capacitor value..
 

Resqueline

Jul 31, 2009
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If you limit the charge time sufficiently then I guess the spark burn time would be shortened too - due to the lesser energy stored.
 

duke37

Jan 9, 2011
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Jan 9, 2011
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The coil is "charged" with 12V and "discharged" with about 300V, Thus the charge time will be 25 times the burn time. At high speeds (10,000rpm) the limit is the charging time. This is where the capacitor discharge system wins since it can input the 300V directly. Presumably, the burn time will be determined by the resonant frequency of the coil/capacitor combination. I am not sure of burn time, most descriptions give plug voltages showing resonance but I have never seen plug currents, I have a feeling that current may only be passed during the first half cycle and that there will be insufficient voltage to restrike the arc on subsequent half cycles.
 
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