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Re: Ignition Coil Power Supply QUestions (fwd)
Original poster: List moderator <mod1@xxxxxxxxxx>
---------- Forwarded message ----------
Date: Sun, 20 May 2007 16:01:56 -0500
From: resonance <resonance@xxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Ignition Coil Power Supply QUestions (fwd)
Yes, an OBIT --- oil burner ignition transformer. Most local
heating/cooling shops would donate a used one free for a high school science
project. They provide much more current than an ignition xmfr can (usually
only 1-3 mA --- very slow charging of your capacitor). Obits are generally
rated 10 kV at 23 mA and will charge an MMC cap bank without any problems.
Jim Heagy in SFC CA has dozens of these OBITs in stock.
If you go the route of an ignition xmfr use an alternistor not a triac for
Subject: Ignition Coil Power Supply QUestions
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
Thanks a lot,