linkinmylog Posted August 3, 2007 Share Posted August 3, 2007 How do i make a ignition coil spark a plug? i wired it directly to the 12v battery and nothing(as i expected), then i put an old condensor(capacitor) through a relay then ran it through a ballast resistor then to the coil all had good grounds but no spark, plug is good. i need this to ignite flamethrowers in my dual exhaust. could someone show me the components and a wiring diagram to make the coil/plug spark? thanks Link to comment Share on other sites More sharing options...
FrankRizzo Posted August 3, 2007 Share Posted August 3, 2007 To understand how to make your coils spark, you need to know a bit about how coils (inductors) work. You see, when voltage is applied to an inductor, the entire length of wire that makes up that coil experiences the same voltage instantaneously. What takes time is build is the amount of current that flows through it. Once the current has reached it's maximum value (after a certain period of time), a constant magnetic field is created around each turn. The inductor tries to maintain that current flow even if the circuit is interrupted. When you open the circuit, the magnetic field around the coil collapses, and the inductance of the coil tries to maintain the current flow. Since the disconnected wires are now see as a high resistance (the resistance due to the air gap between the two wires), Ohm's law (V=IR) dictates that the voltage has to increase in order for the current to be maintained. SO, what you have to do is connect the coil long enough for a constant magnetic field to be created and then break the circuit through an air gap (the spark plug) so that a high voltage spark is created. This phenomenon can bee seen when you unplug an inductive load (a vacuum cleaner or fan for example) while it's still running...you get a spark at the outlet as the collapsing magnetic field tries to maintain a constant current. Link to comment Share on other sites More sharing options...
lja Posted August 3, 2007 Share Posted August 3, 2007 You need to quickly turn the current through the HV coil on and off. With the coil hooked to the spark plug (make sure the threads on the spark plug are hooked to the negative side of the coil and negative side of the battery) Try quickly tapping the coils positive wire to the batterys positive terminal. This quick make-break action should cause the coil to generate a pretty good spark at the plug. To actually install it in your exhaust. The easiest thing I can think of to generate a constant on-off would be to wire a relay so it's a buzzer.Get a DPDT relay, wire the NO contacts of one side through the coil, this will make the relay coil pull in and open the contacts. When the contacts open the relay coil turns off and the switch closes again. This will continue as long as power is applied. Run power for your HV coil through the other set of contacts (you may need to use the NO contacts on that side as well if the relay doesn't pull in far enough). Youl know you wired the relay correctly when power is supplied and it buzzes. You should be able to find a schematic for this in about 30 seconds on google. Link to comment Share on other sites More sharing options...
they call me 9 fingers Posted January 31, 2008 Share Posted January 31, 2008 Hey if you want to spark a spark plug try using a disposible camera flash, my spud gun has one on it right now, they spark a spark plug great. Link to comment Share on other sites More sharing options...
Boomer Posted February 5, 2008 Share Posted February 5, 2008 You putting the 300V from the electrolytic into the 12V side of the ignition coil? This is High power CDI (capacitor discharge ignition). Thouching the HV can get lethal, as the energy is no longer limited by the energy content of the magnetic field inside the coil (1/2 LI^2), but only by the capacitor (1/2 CU^2). Hook up a cap bank and you easily get ear-splitting megawatt-sparks! The spark actually is in phase with the cap's discharge current, unlike the 'old' car ignition, where switching *OFF* the current from the battery creates a spark at the output with *opposite* polarity (see what Frank explained above). These sparks are much hotter than the 'normal' ones, for the reason explained above (plus the fact they last shorter = more power from the same energy). Link to comment Share on other sites More sharing options...
fredjr Posted February 5, 2008 Share Posted February 5, 2008 The most commonly used method for flame throwers in car exhaust pipes is to use a Model T coil box. They will fire a spark plug continuously as long as voltage is applied to the coil. I have a fully restored 1920 Model T. I have replaced the coils with an electronic ignition system, so the old coils are laying in the garage. The double set of points on each of the coils are very high maintence. As would be the buzzing relay contacts mentioned previously in this thread. Link to comment Share on other sites More sharing options...
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