Re: [TCML] Beginning Tesla Design

[Gary Lau <glau1024@xxxxxxxxx>]

I disagree with advice suggesting that designing capacitor strings to the DC
voltage rating will result in failure.  Designing MMC caps is commonly done
using the DC rating,

Terry Fritz performed a methodical experiment to determine the life
expectancy of CDE MMC caps, operated at a peak AC voltage equal to their DC
voltage rating.  The result (speaking from memory) was that they would last
at least 20 hours.  While this may not sound like a lot, it's probably a lot
more run time than any hobby coil would ever accumulate.

Probably the better thing to be cautious about is how gaps are set.  Merely
using a LTR cap value will NOT guarantee that a too-wide gap won't
significantly exceed the Vrms * 1.414 peak value.  If one chooses to throw
caution to the wind and open up the gap and safety gap, only then would
over-designing a cap voltage rating make a difference.

Regards, Gary Lau
MA, USA




On Mon, Jan 3, 2011 at 6:06 PM, Brandon Garretson
<garretsontech@xxxxxxxxx>wrote:

> Sorry Taylor, I didnt mean to throw you a curve ball there.
> What I was getting at is according to your TeslaMap output, your
> primary cap size is very close to resonant, which means running the
> coil in that configuration could create a condition that may cause the
> secondary voltage in your NST to rise to a point well over what it is
> safely rated to operate at and ultimately burn it out.
> Secondly, using just enough caps in the MMC to reach the desired
> capacitance, but ignoring the fact that they are rated for DC
> operation is likely to significantly shorten their lives (perhaps to
> just mere minutes).
> Im not saying that you need to spend a lot of money and build a museum
> piece, but you may find that by building it to the bare minimum that
> looks like it should work on paper could cause it to go up in smoke on
> its first test run.
> Perhaps a $65 investment on a more durable design would serve you
> better than $45 spent on burnt-out components.
> I may be wrong, these things can be strange beasts, perhaps it could
> last much longer than you need it to for the purpose its being built.
> I would just hate to see it die before you got a chance to demonstrate it.
> Ask a lot of questions and read through the TCML archives, there is a
> lot information here.
> Best of luck!
>
> >
> > On Sat, Jan 1, 2011 at 7:38 PM, Taylor Skidmore <balt11t@xxxxxxxxx>
> wrote:
>
>
> >
> > > I'm not really sure how to respond to that, other than that my MMS is
> being
> > > supplie by a friend. I don't want this to be as big as possible, but
> rather
> > > a simple, small, economic design. I have approximately $45 to make
> this,
> > > not
> > > including my NST.
> > > On Dec 31, 2010 12:27 PM, "Brandon Garretson" <garretsontech@xxxxxxxxx
> >
> > > wrote:
> > > > Your primary cap looks a little small and close to resonant size, try
> to
> > > get
> > > > it up just over 9nf like TeslaMap recommends for a static gap.
> > > > Also try to build it to handle at least 1.5 to 2 times your NST
> secondary
> > > > voltage as the caps you will likely use are rated for DC.
> > > > My 12/60 powered coil MMC is rated over 30kv.
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