Mark,
If this is better addressed in a PM let me know and I'll delete this post. I just thought maybe someone else out there wants to know why things work, too.
Perhaps you (or someone) can educate me on why there is any voltage difference at the spark gap at all?
Assumptions:
The coils develop voltage from the stored energy field collapsing. (either points opening or transistor switching off) I'm just trying to differentiate from pulse ignition triggers here, that don't rely on spark gap.
The voltage then rises as the field collapses until there is sufficient potential to ionize plasma between the spark gap electrodes.
The plasma forms an electrical conductor across the gap, that dumps the energy and effectively prevents further voltage build up at the electrodes.
If your test set up did not change the spark gap, the gap atmosphere composition, pressure, and temperature, why do you record different voltage readings in your chart?
I can see how adding extra spark gaps, or resistances, in series between the spark plugs and the coils will raise voltage developed in the coils or anywhere in the path between spark gap and coil. But, why does it take different voltages to create the arc? Are there some air currents around the spark gap? Are there spark plug capacitance/impedance effects interacting with the coils and transmission leads?
I pulled this reference off another internet forum. (Since I don't have my reference books, anymore.):
1939 handbook of chem and physics - a table of spark gap voltages (ON pg 1517 if you have the same book) - the table goes from 5 to 300KV, and shows the gap voltage for needle points, and spherical electrodes of
2.5, 5, 10, and 25 cm. of possible interest here, :
KV | 2.5 ball | 5 ball | needle
5 | 0.13 | 0.15 | 0.42cm length of spark gap
10 | 0.27 | 0.29 | 0.85cm
20 | 0.58 | 0.60 | 1.75
30 | 0.95 | 0.94 | 2.69
50 | 2.000 | 1.71 | 5.20
100 | | 4.77 | 15.5
300 | | | 54.7
according to another table, lowering air temp increases the gap length, as does increasing air pressure.
Cheers,
It's OK to discuss it here for everyone to see, if the Moderators don't mind.
The numbers I got were, simply, the numbers I measured. I did the readings 3 times each, then took the highest and lowest reading, averaged it, and let that be the value. It went like this: set at 58 Hz, take readings, go to 67 Hz, read, then 167 Hz, read, then back to 58Hz and do it again. (I don't believe in single-reading "miracles", myself...).
I agree that, theoretically speaking, the spark potential (voltage) should be the same for a given gap, and physics teaches this (so do EE courses in colleges these days). But, the variances we often see in tests like these show up, nevertheless. One thing that I could not measure, but could hear with my ears, is the sound of the spark. And, the width and color of the spark is hard to measure and record. But, there is a detectable difference at the different voltages: the Dyna generates a deeper sounding, brighter colored spark that is visibly wider in its flame than the Honda coil. And, as the voltages wax or wane at differing RPM, the color and sound goes directly with it, as you might expect. My surmise from this test revolves around the risetime of the Dyna coil vs. Honda: the faster collapse of the Dyna causes a more abrupt dump to the plug, causing the voltage to rise somewhat higher before the ionization has time to enhance the jump. (You can see this in the duoble-dip waveforms above). This would seem to fit with the Honda's performance, as it is more consistent across a wider RPM range, while the Dyna is more sensitive to the inductance in the spark wires (the Honda is copper wire) at different frequencies.
I didn't try this next part, for lack of pieces, but I used to "tune" the voltage peaks by changing the condensors to move the hottest part of the peaks to the RPMs I wanted for Race Day. You can shift the peak range (Honda coils) between 3000 and 12000 RPM by using 0.26uF and 0.22uF condensors, respectively. Standard value is 0.24uF, peaking at 6500.
More about those "double dips" in the waveforms: the first peak is the buildup before the spark actually jumps. The portion between the two peaks is the sustaining voltage while the highest current is coming from the coil, and the gap is ionized: the current rises through the plasma's conductance while the voltage drops to the "burn level" in the plasma it has now created. As the current drops and the plasma fades, the gap's resistance jumps up, the spark suddenly can't jump it anymore, and the spark fails: this causes the second peak as the coil's collapse is not yet finished. There's still energy there, but without the plasma and its lowered conductance, the voltage has nowhere to go but up, because there is no more current path. But, it hasn't the excess potential needed to re-jump, so the coil is then back-shocked, making the ringing you see after that.
It's not really complex, just quick.
