Creating Inductive Pulse

Discussion in 'General Electronics Chat' started by cag2014, May 15, 2016.

  1. cag2014

    Thread Starter New Member

    May 15, 2016
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    Assume I'm a complete newbie, no electronics experience; this true

    I need to generate an inductive pulse .... described as a sinusoidal waveform.

    The source to trigger this inductive pulse is simply an automotive ignition wire attached to a
    spark plug; I assume the voltage through the ignition wire is anywhere from 8k to 45k.

    Would a 2 wire "current transformer" (maybe a split core type, possibly FeNi mag) around the
    ignition wire do this?

    What type of signal would be generated in terms of dc, ac, voltage or amps. ?

    Again, I'm totally clueless on this.

    This 'signal' will be used as an input to ignition module

    Any thoughts, questions, would help.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    The signal from such a current transformer around the plug wire will be high frequency ringing pulse, the voltage and current will depend upon the current transformer core and number of windings but the current will be low.

    Why do you want a signal from the plug wire back to the ignition module? :confused:
    Is that a different module than caused the spark you are monitoring?
     
  3. cag2014

    Thread Starter New Member

    May 15, 2016
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    Crutschow,

    Assume a 6 cylinder engine having 1 spark plug per cylinder, 1 ignition coil, a distributor with 6 ignition wires.
    The vehicles ECU (engine computer) fires the coil, coil sends high voltage to the distributor. Distributor rotor distributes the voltage
    to the spark plugs in series; a typical automotive ignition system from the 80's.

    The engine subsequently, or now, has 2 spark plugs per cylinder. The existing ignition system can't fire 2 plugs, nor at the same time.

    The "idea' (crude as it is) was to have 6 independent ignition modules wired to 6 independent coils.
    Each ignition module would have a 'sensor', or current transformer, connected to the respective existing ignition wire attached to the existing
    spark plug.

    Assume cylinder 1 has:
    its existing spark plug "A" ignition-wire-spark plug via the existing distributor,
    and spark plug "B" the added ignition module, 'sensor (current transformer)' and coil-ignition-wire-spark plug
    When 1A fires 1B's sensor to 1A's ignition wire sends the signal to the ignition module which releases the secondary voltage in
    1B's coil, power travels to 1B's second spark plug.

    That was the idea.
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    One other way to do this would be to eliminate the distributor and ECU. Switch to a crank trigger and MSD type ignition box using dual coil pack with each coil lead to the two spark plugs in each cylinder. The coil packs were originally used in the 1980's GM cars and didn't use a distributor. The original use of these coil packs had each lead going to a different cylinder, a 'waste spark' system.

    I take it this is for a high performance or hot rod engine. You could also do like dragster Hemi engines do, and use two distributors driven by a toothed belt drive. Any thing can be done with some thought and machine work. Years ago I made one of these for a friend that built a pulling tractor that used two 460CI Ford(Lincoln really) engines.

    What engine uses a distributor and ECM to generate the firing order? They usually have a reluctor wheel and pickup. And just use the ECM for advance and retard of the spark, instead of a vacuum advance canister.
     
  5. cag2014

    Thread Starter New Member

    May 15, 2016
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    Shortbus,

    Actually the ECU controls the dwell for the existing coil and there is a TDC and speed sensor on the flywheel side, firing order is naturally based upon the distributor.

    There is no room for 'twin dizzy' distributor and can't put sensor wheel on the crank pulley.
    There are rather expensive options otherwise: change the fly wheel, change the ECU, a different pickup inside the distributor
    with a different ECU..... all rather pricey options.
     
  6. cag2014

    Thread Starter New Member

    May 15, 2016
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    It seems i need a signal to the ignition module (2 wires) this described as:
    1) An AC signal
    2) at least 300 mV in amplitude
    3) 600mV peak to peak (could be higher)
    4) a saw tooth or sinusoidal waveform

    So it sounds like I need to determine what if any inductive coil can provide this signal
     
  7. crutschow

    Expert

    Mar 14, 2008
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    This article may be of interest to you.
    It converts the distributor to generate a signal for firing electronic ignition modules, one for each cylinder.
    These modules could then trigger dual output coils to fire the dual plugs on each cylinder.
     
  8. shortbus

    AAC Fanatic!

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    Did you link the wrong site? That one is for a guy making other brand distributors able to use a GM HEI module. Last update in 2008.
     
  9. cag2014

    Thread Starter New Member

    May 15, 2016
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    Crutschow
    Thanks for the site info. I spoke with the chap there. Unfortunately his designs would require either a second distributor (what we call a twin dizzy; 2 caps, 2 rotors one driving another, or a 12 cylinder cap with twin rotors). We don't have room with this engine.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    I don't understand the need for 2 rotors since you are firing two plugs at the same time(?). :confused:
     
  11. crutschow

    Expert

    Mar 14, 2008
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    No, I did not.
     
  12. cag2014

    Thread Starter New Member

    May 15, 2016
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    Well, the thread is kinda moving a lane over from my initial question as to how to send a
    sinusoidal waveform waveform (inductive pulse) signal to an ignition module.

    So, I need a 'device' with two wires, maybe a "current transformer" alike a FeNi split core type, that surrounds an ignition wire.
    The device needs to send signal that is;
    1) AC
    2) sinusoidal waveform
    3) have at least a 300 mV amplitude
    4) 600 mV peak to peak or higher is okay.

    Assuming the ignition wire this device is wrapped around has atypical spark of 8k to 30k volts

    What are the characteristics of a current transformer that would provide that signal, if a current transformer is the right description?
     
  13. crutschow

    Expert

    Mar 14, 2008
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    You might try a pickup such as this, which is used with a timing light.
    But you'd need an oscilloscope to see what the output looks like.
     
  14. wayneh

    Expert

    Sep 9, 2010
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    Getting into that mV range could be as simple as a wire wrapped around a plug wire a half dozen turns. I have an engine hour meter that gets its signal that way. You could limit the voltage by just using diodes, so that anything more or less than ~650mV conducts thru the diodes to ground. It wouldn't give a clean sine but I suspect your device doesn't need anything more than a good timing pulse.
     
  15. cag2014

    Thread Starter New Member

    May 15, 2016
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    Crutschow and Wayneh,
    Ahhh Haa. I appreciate this.
    Initially I considered using the pickup from my old timing light but I could not get any information as to what kind of signal it put out.
    Making my own coil might be the starting point.

    I'm considering finding a used oscilloscope to test this all out but, naturally, I'm not educated on what kinda of scope I need to exam the pulse width. I see so many on (cough) ebay but I'm not sure what specifics I need for a scope:
    For example, do I need:
    1) Analog or Digital,
    2) 2 channels or 4,
    3) Bandwidth
    4) Specific test cables or connectors
     
  16. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Don't see anything on that link but the HEI conversion info. Nothing about dual plugs at all.
     
  17. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    An where would this AC, siusoidal wave form come from off of a spark plug lead? An ignition spark pulse is a square wave with "ringing" after the main firing pulse. Even with getting the signal from a lead, you second plug would fire at a different time than the main spark, due to the propagation delay of the extra electronics.

    Knowing the brand of engine, there may be a distributorless ECM from a different year/model that could be adapted.
     
  18. crutschow

    Expert

    Mar 14, 2008
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    The dual plugs can be fired using a dual output coil.
     
  19. cag2014

    Thread Starter New Member

    May 15, 2016
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    Where does the wave form come from: The 'pie in the sky' idea was to have a "device", maybe a "current transformer" alike a FeNi split core type that is clamped around a given ignition wire (somewhere between the distributor and the spark plug), alike Cruschow suggested a common timing light clamp.

    An ignition spark pulse is a square wave with "ringing" after the main firing pulse.. This maybe true, however I just need a device that will create the "guessed" ... AC, sinusoidal waveform, having at least a 300 mV amplitude, 600 mV peak to peak or higher is okay. If a simple current transformer or device alike that won't do that then what will?

    Logically both spark plugs won't fire "exactly" at the same time, however we don't know the time difference until I test it. Engine wise, it the second plug fires a few degrees later (retarded) I'd be quite happy with that because I only need the secondary event (spark) to take place when the engine is at WOT near the top of its rpm range. The secondary plug handles the other side of the cylinder which is not receiving a good the flame spread.

    There are a dozen distributorless ECM, ECU, DME, etc, systems out there, and they range from $4K on up when you get done, plus the labor and dyno time (this engine is already tuned for timing and fuel; just needs 2nd set of plugs to handle the flame spread). They utilize, typically, a flywheel sensor or front crank sensor. However, I don't need the fuel management nor the timing portion of what they have because my current DME handles that.

    In order to fire a dual output coil I'd need a signal for each coil.... 6 of them.

    I've explored, for the 6 cyl, existing 12 plug distributor's and twin dizzy (6+6) distributors, they won't fit where they'd have to go.
     
  20. crutschow

    Expert

    Mar 14, 2008
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    As mentioned by others, you may be able to get an adequate signal by just wrapping a few turns of wire around the spark plug wire.
    Use two inverse parallel diodes (1N4148 or similar) to ground to limit the voltage to about ±0.7V.
    The waveform may look a little ratty if you observed it on an oscilloscope, but as long as it triggers the module, that's fine.
    You can experimentally connect that to your ignition module and see if it triggers it.
    Adjust the number of turns around the plug wire to find the optimum value.
     
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