Ignition Coil Power Supply QUestions (fwd)

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---------- Forwarded message ----------
Date: Sun, 20 May 2007 14:13:00 -0400
From: "Breneman, Chris" <brenemanc@xxxxxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Ignition Coil Power Supply QUestions

Hello,

My ARSG project has been temporarily (for a few days) interrupted so I can make a small coil for someone as a gift, because they have supplied many of the parts necessary for my larger coil (old microwaves, piping, fans, etc.).  I've wound a small secondary and filter chokes, but am trying to figure out a good power supply for it that would be small and low power.  I think the cheapest way of doing this would probably be to use a few ignition coils.  (If there's a better way for about the same price and power level, suggestions are welcome.)  Anyway, I had a few questions about ignition coil power supplies relating to Tesla coils.
The first type of ignition coil power supply that I thought of would be to use one or two ignition coils as normal autotransformers.  With approximately a 1:100 turn ratio, 120V on the primary could yield a very reasonable 12kV on the secondary in a nice sine wave.  They would have to be ballasted, of course, probably capacitatively on the primary, like the common mains ignition coil driver.  The problem I see is that I think most of the voltage would be dropped at the ballast.  From searching the internet, it seems to me that the unloaded inductance of the primary of a typical ignition coil is around 3mH, yielding around 1.1 Ohms of reactance at 60Hz.  A reasonable capacitative ballast would be a 10uF motor run capacitor (which I happen to have on hand), which would yield about 165 Ohms of reactance.  This means that the majority of the voltage would be dropped by the ballast representing a corresponding decrease in the high voltage produced, right?  And is there any good way to get around this?
The second type I considered was the typical ignition coil mains power supply, consisting of a capacitor, triac lamp dimmer, and ignition coil primary in series.  I know that some people have used these to power Tesla coils, but wouldn't the high voltage waveform be far from ideal for Tesla coil use?  Examining the waveform, the first part of a cycle on the primary (before the triac kicks in) would be a normal sine wave rise, but during this portion, wouldn't the high voltage produced be severely limited by the series capacitor?  Then, when the triac cuts in and gives the inductive kick, a much higher voltage is produced, but since the gap fires at that point, it doesn't go into charging the capacitor.  Is this correct?  And am I correct in thinking that it would be a problem?  Also, the second inductive kick on the first half cycle of the 60Hz primary waveform would pretty much go to waste, as well as the part of the cycle after that before the waveform crosses 0, right?  And if these are really problems, is there a good way to fix them?
Is there any better way to drive ignition coils than these two for Tesla coil use?

Thanks a lot,
Chris