ionbeam
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Well, off we go into the 1% audience area... :nerdsmiley:
The following is true for motorcycle dual plug coils.
[/electron flow theory] [conventional view of electricity]
Referring to the picture you will see that the threaded part of both sparkplugs are threaded into the cylinder head, that makes the 90 degree electrodes of BOTH plugs ground.
The secondary side of the coil has no ground reference of its own, it is electrically floating. When the primary side coil is shut off, the magnetic field of the iron core collapses (core not shown in the picture). As the magnetic lines of flux cut across the secondary windings it imparts energy to the secondary side of the coil. The voltage will be determined by the gauge of the secondary side wire, the length of the wire and turns ratio of the primary to secondary side. Just for round numbers we will say the secondary side is producing 50,000 volts, here after short cut to 50kV.
For electricity to flow there must be a path, a negative pole and a positive pole. Looking at the drawing, if the center electrode of plug 1 is at 50kV then the center electrode of plug 2 would have to be ground for electricity to flow. If plug 2's center electrode is ground and the 90 degree electrode is ground there would be no spark!! WTF? Here is where it gets tricky. The secondary side of the coil 'self centers' such that plug 1 will receive +25kV and plug 2 will receive -25kV. It does total 50kV, it is just split in half. Now plug 1 will fire because the center electrode is +25kV and the 90 degree electrode is ground. SPARK jumps from plug 1's center electrode to the 90 degree electrode at ground. At plug 2 funky things happen. The center electrode is at -25kV; said another way it is 25,000 volts LOWER than ground. Electricity flows from positive to negative. At plug 2, the 90 degree electrode is more positive than the center electrode (-25kV) thus the SPARK will jump from the 90 degree electrode to the center electrode. This is how the electrical circuit gets completed. Which plug ends up with a positive center electrode and which has the negative center electrode is determined by the direction of current though the primary side coil.
Back to the original question, "Can a misbehaving plug affect the other plug's operation in their series circuit?" If one plug has a flaw such as an eroded electrode or fouling there will be reduced conduction which will reduce total energy delivered to both plugs. When either plug is disconnected there is no complete electrical path so no electricity flows, thus no spark. Here is a big BUT -- high voltage is extremely aggressive in seeking out a path for conduction. At 50kV many things become conductors. 50kV will pass right through regular wire insulation, it will leak through air, it will seek out cracks in the high voltage insulation of the plug wire. Failing to find conduction in those areas it will try to jump back across to the primary side. Should the primary side try to energize the coil while the secondary side is seeking a path to ground ugly things can happen. This is where coil wires can burn, high voltage can find its way back to normally low voltage circuits such as the ECU or coil trigger circuit. It is a Bad Thing when one plug is completely out of the circuit. Should things go perfectly wrong and the coil finds no ground path, the coil can retain the 50kV awaiting fingers and hands :stunned: If you ever have to remove a plug from the engine the plug should remain in the plug wire and a jumper cable should ground the shell of the plug.
:sleepysmiley03: :sleepysmiley03: :sleepysmiley03: :sleepysmiley03: :sleepysmiley03: :sleepysmiley03:
The following is true for motorcycle dual plug coils.
[/electron flow theory] [conventional view of electricity]
Referring to the picture you will see that the threaded part of both sparkplugs are threaded into the cylinder head, that makes the 90 degree electrodes of BOTH plugs ground.
The secondary side of the coil has no ground reference of its own, it is electrically floating. When the primary side coil is shut off, the magnetic field of the iron core collapses (core not shown in the picture). As the magnetic lines of flux cut across the secondary windings it imparts energy to the secondary side of the coil. The voltage will be determined by the gauge of the secondary side wire, the length of the wire and turns ratio of the primary to secondary side. Just for round numbers we will say the secondary side is producing 50,000 volts, here after short cut to 50kV.
For electricity to flow there must be a path, a negative pole and a positive pole. Looking at the drawing, if the center electrode of plug 1 is at 50kV then the center electrode of plug 2 would have to be ground for electricity to flow. If plug 2's center electrode is ground and the 90 degree electrode is ground there would be no spark!! WTF? Here is where it gets tricky. The secondary side of the coil 'self centers' such that plug 1 will receive +25kV and plug 2 will receive -25kV. It does total 50kV, it is just split in half. Now plug 1 will fire because the center electrode is +25kV and the 90 degree electrode is ground. SPARK jumps from plug 1's center electrode to the 90 degree electrode at ground. At plug 2 funky things happen. The center electrode is at -25kV; said another way it is 25,000 volts LOWER than ground. Electricity flows from positive to negative. At plug 2, the 90 degree electrode is more positive than the center electrode (-25kV) thus the SPARK will jump from the 90 degree electrode to the center electrode. This is how the electrical circuit gets completed. Which plug ends up with a positive center electrode and which has the negative center electrode is determined by the direction of current though the primary side coil.
Back to the original question, "Can a misbehaving plug affect the other plug's operation in their series circuit?" If one plug has a flaw such as an eroded electrode or fouling there will be reduced conduction which will reduce total energy delivered to both plugs. When either plug is disconnected there is no complete electrical path so no electricity flows, thus no spark. Here is a big BUT -- high voltage is extremely aggressive in seeking out a path for conduction. At 50kV many things become conductors. 50kV will pass right through regular wire insulation, it will leak through air, it will seek out cracks in the high voltage insulation of the plug wire. Failing to find conduction in those areas it will try to jump back across to the primary side. Should the primary side try to energize the coil while the secondary side is seeking a path to ground ugly things can happen. This is where coil wires can burn, high voltage can find its way back to normally low voltage circuits such as the ECU or coil trigger circuit. It is a Bad Thing when one plug is completely out of the circuit. Should things go perfectly wrong and the coil finds no ground path, the coil can retain the 50kV awaiting fingers and hands :stunned: If you ever have to remove a plug from the engine the plug should remain in the plug wire and a jumper cable should ground the shell of the plug.
:sleepysmiley03: :sleepysmiley03: :sleepysmiley03: :sleepysmiley03: :sleepysmiley03: :sleepysmiley03:
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