Champion Spark Plugs - Question for Schematic

[jegervais]

My question relates to the previous "Champion Spark Plug" thread. I understand electrical theory pretty well, but something in your rfi noise response got me thinking and I would like your input/thoughts/clarification. <br /><br />The ignition coil is basically acting as a voltage step up transformer and as voltage increases current flow decreases at an expotential rate. By adding resistance to the plug wire or to the plug, does that really reduce current flow through the secondary winding? Or, is it actually reducing the current flow through the "antenna" part of the circuit (the plug and hi-tension lead)?<br /><br />For example, I've recently been doing some ignition system component testing on a 50hp Johnson. The unit has no spark on 1 cylinder. The ignition coil is good (swapped primary leads), of course the charge coil is good. Timer base shows the following: 1.5 volt output (dva) on both blue and green leads and no shorts to ground. Ohm spec is 27 +/- 5 ohms. Green is 27, blue is 500. Measured the ac current and found the blue lead only delivering 20% of the current the green lead did - figure not enough current to activate the gate on the scr. Now this current stuff has me intrigued...<br /><br />Anywho... I'm interested in your thoughts on this rfi thing, your response in the other thread helped my understanding of the how and why - <br /><br />Thanks,<br /><br />-John

 

[petryshyn]

Re: Champion Spark Plugs - Question for Schematic

Hi John<br /><br />When the primary winding has voltage applied, a current flow occurs. This current flow in the primary, creates a rising magnetic field. This rising magnetic field induces a voltage into the secondary winding. Since there is a path for current in the secondary, electrons will flow through the winding, plug wire, plug and ground return.<br />As you can see, the secondary winding, plug wire and plug are all hooked in series. Any current flow in a series circuit will be reduced when resistance is added.(as in any series circuit) <br /><br />

<br /><br /><br />The current through the secondary ciruit ignites the fuel, but also generates a magnetic field as all current flow does. Since the current in the secondary fluctuates, the magnet field around the conductors fluctuates as well. Thus giving us high frequency magnetic fluctuations (RFI) Any resistance added to the circuit will reduce the current = reducing the magnetic field = reducing RFI.<br /><br />

<br /><br /><br />Any nearby conductor (wiring harness, trigger coils, etc.) will act as an antenna. The RFI that is generated will induce voltages into them. These bogus voltages can and will be perceived by the module, packs, computers and CPU's as an input signal from a ligitament sensor. Thats when all the fun starts. Garbage in = garbage out.....<br />

<br /><br /><br />Hope this is what you were after!<br /><br />

 

[jegervais]

Re: Champion Spark Plugs - Question for Schematic

Hey Schematic thanks - the piece of the puzzle I was omitting was the return path on the secondary side (duh!). Appreciate the diagrams, they cleared up my thought process before I even started reading...<br /><br />Thanx again,<br /><br />-John

 

[seahorse5]

Re: Champion Spark Plugs - Question for Schematic

To add just a bit to this conversation, the addition of more than 5K resistance in the secondary (plug wire) circuit, greatly lowers the spark energy.<br /><br />The former OMC designed their electronic (CDI) ignitions with suppressor plugs in mind. The suppressor looks like a ballpoint pen spring that is inside the plug. If you measure the resistance, it is only about 40 ohms. At RFI frequencies, it "impedes" AC current, as resistance to AC is called impedence. Like your stereo speakers are either 4 ohm or 8 ohm, that is the impedence at music and voice frequencies. If you measure the speakers with a regular ohmmeter, it will read something quite different.<br /><br />In OMC CD ignitions, a non-resistor plug will "dump" the voltage very quickly, allow the current occillations generating RFI, and gives a short duration spark. That may result in short plug life.<br /><br />A 5K resistor plug will severly limit the voltage across the plug, lower RFI, but may make the engine hard starting and may misfire often during periods needing high voltage (acceleration). <br /><br />The suppressor allows the voltage to jump the plug gap and "holds" the arc longer since it doesn't affect the DC voltage in the system, but "impedes" the AC RFI producing current.

 

[petryshyn]

Re: Champion Spark Plugs - Question for Schematic

Hey, good stuff there seahorse5.<br />I guess we'd call that a 'choke'<br />It would be interesting to see how the newer TVRS wires perform on CDI. They are no longer straight carbon resistor, they are now very small wire wound in a coil configuration from end to end. Kind of like a long choke.

 

[jegervais]

Re: Champion Spark Plugs - Question for Schematic

Seahorse-<br /><br />To sum this all up then, would it be correct to say the suppression feature filters out to the ac signals (rfi), while NOT adding resistance to the dc, thereby not reducing spark energy?<br /><br />I wish I still had my old B.E.&E. theory books! I never thought I would say that 23 years after I gave them away...<br /><br />Needless to say this has been an interesting discussion.<br /><br />-John

 

[seahorse5]

Re: Champion Spark Plugs - Question for Schematic

A choke is the correct nomenclature for the suppressor. It attenuates the occillations from the interaction of a capacitor and a coil. If I remember right from Electronics 101, it is an LC circuit.<br /><br />John, your wording is correct and that is why it is important to use Q style plugs in most J/E outboards. NGK makes a Z numbered suppressor plug, but it costs quite a bit more than the Champions<br /><br />Special plug wires like Schematic described have been around for quite a few years. For J/E and Merc outboards, they are available from Wizard Performance for less money than OEM wires, and the end connections are stainless steel, instead of rust-prone springs.

 

[almost retired again]

Re: Champion Spark Plugs - Question for Schematic

Hi Schematic and Sea Horse Five;<br />It sure is great to see people with electronic knowledge on this board. It has been my experience that at least 60% of the problems that occure are electrical in nature. I think it is necessary for all good techs. to have a good foundation in basic electricity/electronics. By the way Schematic I don't know how you put the wonderful pictures and diagrams on the board I guess it's because I'm somewhat computer illireate. I believe that people like you two and more are a real asset to this board. Knowledge that can't be passed on is wasted and gone forever when the owner passes on.<br />Anyway great job