The current, at the moment of spark, can reach values like 10 amps. That's a lot for a small wire size, like the ones found in some spark plug wires, if they are resistor wires (resistor wires are often flat, spiral-wound carbon ribbons). To calculate the current in your system, use this approximate formula:
1. (Ignition voltage at the coil with points closed) x (current at the points) = WATT SECONDS stored in coil (about 36 for CB750).
2. 1 / (200 [this is 12000 RPM, in Hz)]) = DISCHARGE TIME (which = .005 seconds).
3. (WATT SECONDS) / (DISCHARGE TIME) = DISCHARGE WATTAGE per SECOND (about 7200 on CB750).
4. (DISCHARGE WATTAGE per SECOND) / (COIL RESISTANCE) = DISCHARGE CURRENT SQUARED (which=3.46 amps here).
NOTE:
these calcs ignore the energy added by the condensor and the increased spark discharge rate caused by the condensor, which acts like a "speedup" device on the order of about 12% to 15% in a well-tuned system. In other words, add about 12% to the above value (total 3.88 amps) to get your "real" results.
The resistors in the plugs (or plug caps) take a beating like this at every spark. Inside a sparkplug, the resistors are very small and depend on the heatsinking of the engine to "save their butts" from overheating and the resulting loss of carbon, which increases the resistance until it burns away into an open gap. This open gap can still fire, but it uses some of the HV energy to create a plasma first to jump the .030" (or so) gap first, then it jumps the spark gap, but weakened.
Resistor wires cause the energy to focus into a plasma field that helps the HV travel along the surface of the conductive parts of the cable. This "surface travel" mimics electricity's natural tendency, which is to travel along the outer few thousandths of any wire. By encouraging this movement, the losses drop AFTER the first spark travels the wire, and the efficiency of the wire improves with more RPM. This is one reason why they became so popular: the high-RPM "droop" in HV is reduced with resistor wires of the wound type, when compared to a stranded metal HV wire. But, this plasma carrier must necessarily be thin, so they do burn out with time.
Either way, there is resistance, whether by plug, cap or wound wire. This resistance controls the discharge rate of the coil's stored-up watts. If it discharges too fast, due to higher currents (like in a resistor-less system), then the energy is lost as heat in the trip from coil to plug. This heat destroys the wire faster than normal by overheating it, too. If the current is limited to a lower value, the voltage rises (ohm's law isn't just a good idea: it is the law, you know) to dump the wattage into the gap.
I know that's a lot of theory, but maybe with a beer or a snack, it might begin to make some sense...
Hey HondaMan - i bow at your all-knowing electrical prowess!!!
Can you explain to me however, how the condensers INCREASE energy?
I thought they were basically a capacitor - storing energy like a battery, yet releasing it in one dump of power?? With no internal magnetic coil windings, how would they increase electrical energy?
??
