Ignition Spark Generator from Auto Coil

Discussion in 'The Projects Forum' started by Jerry Dziuba, Mar 7, 2016.

  1. Jerry Dziuba

    Thread Starter New Member

    Feb 18, 2016
    I am trying to create a low cost, reliable method of making a spark to ignite the pilot of a combustor. Using a cheap automotive coil and capacitor/condensor wired thusly:


    seems to work. Sort of.
    The coil gets rather warm/hot in use, not something typical of an automotive coil in use. Is there something jumping out at anyone that I need to do with this circuit to prevent that, and also is there something I can do to just improve the circuit in general.

    As is, it generates a nice strong spark which is great. Just wondering if there might be either a better way to do it.
  2. Richie121

    New Member

    Jan 12, 2014
    If your coil is getting warm then one of your condensers/ capacitors is failing allowing a DC current though it. Had the same problem with my vehicle and the coil got hot.

    Sounds like fun. Doesn't involve potatoes does it? ;)

    I've thought of a steampunk idea where you charge capacitors slowly from a source and then discharge them through the coil when needed. As it is a slow capacitive charge you can add a LED voltage bargraph display to show it charging - looks neat.
  3. Jerry Dziuba

    Thread Starter New Member

    Feb 18, 2016
    After further investigation, it appears I have a coil that requires an external ballast resistor. I will pick up one of these next run to the auto parts store and see if that cures the warm up problem.

    Nothing fun like a potato shooter! This is for a BTEX elimination system.
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    Lower your supply to 9V, or 6v and see if it will work better.
  5. ian field

    Distinguished Member

    Oct 27, 2012
    Most motorcycle coils I've seen have a PTC LT winding and don't require a ballast resistor. Examples tested on the bench draw about 8A at room temperature and sink slowly to about 4A as they warm up. If you're using a car coil without ballast - just don't hold the button down.

    You'd get far more dependable ignition if you use a 555 to pulse the coil - by trial and error; just tune the frequency for the most ferocious arc. A good choice for the coil driver MOSFET is the type used in flyback SMPSU. 600V rating is very common which is just about enough. The TO220 style parts are usually max 6A, 2 or 3 in parallel is a good idea. If you know where to look, there's 9A 900V parts in TO247 packages.

    You could use a second 555 (or a 556 dual timer) to make a monostable that gives a timed burst of arc per button press.