Help with coil limiting Spark Duration

Discussion in 'General Electronics Chat' started by 3BABY, Jan 25, 2011.

  1. 3BABY

    Thread Starter New Member

    Jan 25, 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 :)
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Controlling the input, various electronic ignitions, etc, controls the output.

    Changing to a smaller coil will result in a shorter pulse as well. Dynamically changing the coil value at engine speeds is a different situation.
     
  3. 3BABY

    Thread Starter New Member

    Jan 25, 2011
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    Thanks for the quick reply..

    im not too sure what you would consider the input in this circuit.. as in the input supplying the coil..?


    unfortunately like you said changing the coil characteristics dynamiclly is not an option..

    basically i would like to change the burn time throughout the rev range of an engine.. i have an output of a microcontroller connected to a "coil driver".. as i can change the charge time.. im scratching my head as to how i would control the discharge time

    thanks again
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The charge time will change the discharge time, but would also reduce peak voltage.


    There may be somebody more experienced with ignition (motorcycle guys) with better ideas.

    What is the reason for a shorter spark?
     
  5. 3BABY

    Thread Starter New Member

    Jan 25, 2011
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    basiclly at Higher RPM around 10000-15000 if the spark time is too long its going to roll into the next revolution of the engine... 2 stroke engine.. no so good..

    there must be some sort of reverse polarity method or something to "Kill" spark..

    thanks for you input thus far... appreciate it :)
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Ok, I see the problem.

    Using a smaller coil and a smaller gap should keep the plug hot enough to not clog, this would keep the spark hot, but for less time.

    Another way to shorten the spark duration would be to double the load on the coil to discharge it quicker, e.g. 2 plugs per cylinder.

    I am not an internal engine engineer, BTW, just worked with "normal" ignition stuff. You are in the realm of the F1 car's RPM, or some high end off road motorcycles.
     
  7. 3BABY

    Thread Starter New Member

    Jan 25, 2011
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    in the realm of Race Jetski's... unfortunately i cant change the coil i have or do two plugs per cylinder for this application.. but good point im definitely going to look into multi plug systems..

    ill keep researching how to limit the spark time though.. :)
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Others with more info may chime in. Don't give up on us yet. :D
     
  9. 3BABY

    Thread Starter New Member

    Jan 25, 2011
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    Thanks mate :)

    by the looks of it.. thus far.. im going to have to implement some sort of Capacitor discharge system.. but how to Dynamically change the actual time the coil sparks for... we will see ..
     
  10. Jaguarjoe

    Active Member

    Apr 7, 2010
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    Build or buy a capacitive discharge ignition system. That'll take you down to 50us width.
    I think Silicon Chip magazine had plans to build a nifty one that Jaycar sold as a kit. MSD makes and sells CDI's too. They're great at high RPM's and suck with lean mixtures such as at low speed. To fix that they employ multiple sparks.
     
  11. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I'm sure if you tried a high tension lead with a different resistance value, you'll affect spark duration. T=L/R. Isn't that where the air gap came in?
     
    Last edited: Jan 25, 2011
  12. Jaguarjoe

    Active Member

    Apr 7, 2010
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    I've read somewhere that a resonant convertor ignition has adjustable spark duration. Theoretically, it can spark continouosly so it needs control. I haven't seen a circuit for it so I don't know anymore.
     
  13. 3BABY

    Thread Starter New Member

    Jan 25, 2011
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    Ahhh yes .. after a little research.. that sounds like the go.. but how does it work? its takes the invered 12VDC .. so say 475VAC to an "AC Amplifier" thats triggered by your programed controller.. then to a coupling capacitor then to you +ve terminal of your coil...

    Question.. what does the "AC Amplifier" do?


    Also.. if you were to hook the +ve end of the coil up to the 475VAC supply at say 20KHz.. could that produce a "constant" spark?
     
  14. Jaguarjoe

    Active Member

    Apr 7, 2010
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    I think that "amplifier" is a high voltage, high frequency oscillator keyed by a uP. I'm having a hard time seeing 475 volts being crammed into a 1 ohm coil primary. Resonant Convertor is another name for a switcher.
     
  15. 3BABY

    Thread Starter New Member

    Jan 25, 2011
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    Could you please explain what "keyed by a uP" means?

    take a look at this website.. under the Resonant Converter Ignition.. itd be interesting to know whats going on inside the "AC Amplifier" ..

    http://www.stlaroc.com/features/ignsyste.html

    after a little bit more research.. looks like MSD do a similar unit.. it looks like a good 300-500V is applied to the coil at a high frequency to provide a "continuous" spark.. and the processor is used to control the amount of time the voltage is applied to the coil.. thus you can alter the spark duration... sound about right with you guys?

    :)
     
    Last edited: Jan 27, 2011
  16. Jaguarjoe

    Active Member

    Apr 7, 2010
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    Keyed by uP" is "triggered by a microprocessor" or uP or uC.

    I read that website, good stuff there. Look at fig 3, the width of the HI-8 spark is 1ms, the same as an HEI system, and 10-20 times wider than a CDI spark. It's wide so it can fire lean mixtures (like at low load + low RPM).

    I think you're right about how the HI-8 works.

    I searched through the MSD website, couldn't find anything about any system like the HI-8.
     
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