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Everything Else (Not Vincent Related)
Resistor Type Spark Plugs and Original Magnetos
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<blockquote data-quote="Magnetoman" data-source="post: 98638" data-attributes="member: 2806"><p>The short answer is, a resistor <em>won't</em> be less of a problem in a resistor iridium plug. The long answer is:</p><p></p><p>When the voltage from a coil climbs to ~5-7 kV the electric field across a plug is high enough to ionize the air in the gap and the plug sparks. When that happens the resistance across the gap becomes very small so the inductance L of the coil discharges its ~10 mJ of energy in a time L/R which is a microsecond or so. With a resistor plug the discharge time is still L/R, except now there is 5-10 kOhms of resistance in the circuit so the spark takes much longer to discharge. Plus some of the energy is wasted in creating heat in the resistor. </p><p></p><p>The same things happen inside the combustion chamber with an iridium electrode, except the thinner electrode in that type of plug will initiate the spark at a somewhat lower voltage because the electric field near its tip is larger (because the dia. is smaller). However, if everything is working fine in your combustion chamber now, the lower voltage at the onset of discharge won't do you any good (or any harm). What matters is the total energy of the spark, which would be the same for a "normal" or for a non-resistor iridium plug. But, irrespective of the composition or diameter of the electrode, the energy in the spark will be less for a resistor plug because of the losses in the resistor. </p><p></p><p>If your magneto doesn't have a problem with a resistor "normal" plug, it won't have a problem with a resistor iridium plug. But, if it does have a problem with one, it will have a problem with the other. </p><p></p><p> Despite resistor plugs having worse performance than normal ones, because of the energy lost in the resistor, they're used because the longer L/R time takes the radio frequency emissions from the spark down from the range ~1 MHz (i.e. 1/microsec.), where they interfere with radio and TV signals, to ~1 kHz where they don't matter. When resistor plugs were introduced to allow radios in cars to function, their battery/coil ignition systems could be easily updated by slightly redesigning the coils to provide a bit extra energy if needed. However, such a redesign isn't as easy on a decades-old magneto.</p></blockquote><p></p>
[QUOTE="Magnetoman, post: 98638, member: 2806"] The short answer is, a resistor [I]won't[/I] be less of a problem in a resistor iridium plug. The long answer is: When the voltage from a coil climbs to ~5-7 kV the electric field across a plug is high enough to ionize the air in the gap and the plug sparks. When that happens the resistance across the gap becomes very small so the inductance L of the coil discharges its ~10 mJ of energy in a time L/R which is a microsecond or so. With a resistor plug the discharge time is still L/R, except now there is 5-10 kOhms of resistance in the circuit so the spark takes much longer to discharge. Plus some of the energy is wasted in creating heat in the resistor. The same things happen inside the combustion chamber with an iridium electrode, except the thinner electrode in that type of plug will initiate the spark at a somewhat lower voltage because the electric field near its tip is larger (because the dia. is smaller). However, if everything is working fine in your combustion chamber now, the lower voltage at the onset of discharge won't do you any good (or any harm). What matters is the total energy of the spark, which would be the same for a "normal" or for a non-resistor iridium plug. But, irrespective of the composition or diameter of the electrode, the energy in the spark will be less for a resistor plug because of the losses in the resistor. If your magneto doesn't have a problem with a resistor "normal" plug, it won't have a problem with a resistor iridium plug. But, if it does have a problem with one, it will have a problem with the other. Despite resistor plugs having worse performance than normal ones, because of the energy lost in the resistor, they're used because the longer L/R time takes the radio frequency emissions from the spark down from the range ~1 MHz (i.e. 1/microsec.), where they interfere with radio and TV signals, to ~1 kHz where they don't matter. When resistor plugs were introduced to allow radios in cars to function, their battery/coil ignition systems could be easily updated by slightly redesigning the coils to provide a bit extra energy if needed. However, such a redesign isn't as easy on a decades-old magneto. [/QUOTE]
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