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Re: Another Short Question - (DCTC Cap Sizes)
Original poster: "Kevin Ottalini" <ottalini-at-mindspring-dot-com>
DC drive TCs can use a wider range of caps since the current
limiting is not a function of the cap size. The rotary gap can run
at very low speeds continuously up to high speeds, limited only by
how fast you can recharge the cap to the target voltage. (No sync
issues, and no external limiter inductance required either).
In DCTCs, the cap becomes a purely resonant issue ... how many
turns on the primary VS how much capacitance.
There are efficiency issues about small caps though, so the
trend for DCTCs is to immediately head for the largest bang
size that you can handle.
For an example, take a look here at this chart I made up
of measured primary inductance VS capacitance size. You
can clearly see the "sweet spot" on each curve and the
efficiency trend of larger cap sizes (same breakout for
a lower voltage).
This was made by measuring the minimum voltage that would
achieve breakout on a smooth toroid. The caps I use are
0.125ufd each at 10KVDC, so by putting 5 in series, 4, etc.
I can easily adjust the value.
Feel free to look around ... lots of info about DCTCs there.
(Just edit the line above to see higher directories with your
browser. One of these days I'll get them all on a web page).
I also found that the physical number of turns on the primary
is more important than the inductance ... IE: it takes several
turns on the inside of the primary to get so many uH, but it
may only take one or two on the outside of the primary.
I consistently found that I got better coupling from having
more turns at the same inductance ... as long as I didn't get
too close. It was easier to adjust to find the sweet spot
as well. I presume that the field generated was smoother
with more turns so more of the secondary was covered.
> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Another Short Question
> Date: Friday, December 08, 2000 7:03 AM
> Original poster: MaverickIce00-at-aol-dot-com
> Hi Everyone,
> I have another relatively short question. After reading a little about DC
> coils, I started to wonder: What are the advantages of powering a coil
> DC? At first thought, I believe that DC would offer the capacitor a
> charging source, possibly increasing the lifespan of the cap. I'm not
> sure about this one, but it would also seem as though a RSG would not
> be salient-pole synchronous because there would be no peaks or zero
> points or anything like that so one could use an 1800 RPM motor without
> having to modify it. A more specific question I have is how the DC would
> affect the level of capacitance for the cap. since frequency of the
> line is a factor involved in calculating the capacitance and therefore
> resonant frequency of the primary LC circuit.
> - Joshua -