Ignition module switching voltage

Discussion in 'Homework Help' started by sunshine03, Jan 20, 2010.

  1. sunshine03

    Thread Starter New Member

    Dec 30, 2007
    I am a bit confused about primary ignition circuit switching;
    Is it true that all electronic ignition modules (including waste spark systems) send a voltage pulse to the negative terminal of a coil or coil pack; to interrupt the primary circuit, and fire the plugs - then turn the ground for the primary circuit back on (all of this happening in a blink of an eye)? Also does the voltage vary with each model ? .... Text books do not explain this clearly; if this is how things work.
    Thanks to everyone for all of your help
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Oops, I just saw the text book reference - back to homework section.

    NO, the action is to turn on a device that lets current flow in the coil primary briefly. The resulting magnetic field collapses when that primary current is interrupted, and induced the high voltage in the secondary.

    This link illustrates the process - http://www.rmcybernetics.com/projects/DIY_Devices/homemade_ignition_coil_driver.htm
    Last edited: Jan 20, 2010
  3. Darren Holdstock

    Active Member

    Feb 10, 2009
    Alternatively you could dump the load from a charged capacitor into the coil primary, this makes for a very good spark, particularly if the self-resonant frequency of the primary circuit is a close match to the self-resonant frequency of the secondary circuit.

    Beware of operating with the secondary circuit open-circuit, e.g. with an ignition lead unplugged. The secondary still produces a large voltage, but with no spark plug to load it it has to go somewhere, usually flashing back into the primary circuit, destroying the electronics. There's also enough energy in a modern ignition system to kill a person several times over, so watch out for that one too.
  4. sunshine03

    Thread Starter New Member

    Dec 30, 2007
    Hi all,
    Just wanted to add;
    The reason this is confusing me; is I ran a check on my '82 nissan (old car - but still runs good) as an attempted example to what I read in my textbook. While checking the negative circuit going from the ignition module to the negative terminal on the coil (negative wire to coil removed; and with a meter in series, between the negative ignition module wire's terminal and the coil's negative terminal - cap, coil and plug wires still connected); wish I could draw a picture, I kept getting a voltage reading of 0.3v to 0.4v - while cranking the engine, and it was blinking very fast. Didn't know if this right or even what the book was trying to say.
    Thanks again to everyone for all of your time and help
    Last edited: Jan 22, 2010