Re: Tesla Coil Blunders

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "bob golding by way of Terry Fritz <twftesla-at-uswest-dot-net>" <yubba-at-clara-dot-net>

Hi Gary,all,
    At the risk of sounding pedantic I don't think you can have "DC
inductance". I think
inductance is usually measured at something like one Khz. It is on my
bridge anyway. Please feel
free to flame away if I have got this wrong. I have found that the "fudge
factor" on  the tuning
of my big coil is about 10 per cent lower than the calculated figure, and
also from measuring it
using  Johns scope s.g and counter method.  It was a bit closer with the
spectrum analyser,but
still lower. When I get this 30" sphere  i should be able to run at full
power without any
breakout. I will check the res freq with the spectrum analyser and report back.

cheers
bob golding

Tesla list wrote:

> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Gary.Lau-at-compaq-dot-com>
>
> It is well known that the operating resonant frequency of a secondary with
> streamers will be lower than the low voltage (streamerless) resonant
> frequency, due to the fact that streamers and the ion cloud about the top
> load will act to increase the terminal capacitance.  I used ETesla6 to
> calculate my secondary frequency and it was dead-nuts on.  Only the physical
> geometry and secondary DC inductance was needed, not R.  The operating
> frequency with streamers was the "usual" amount lower - I just
> experimentally tapped further out to find it, but didn't note exactly how
> much lower it was.
>
> I would guess that to calculate this fudge factor in advance would require
> an estimate of streamer behavior, something that's presently way too complex
> to predict.
>
> Gary Lau
> Waltham, MA USA
>
> >Original poster: "John H. Couture by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net>
> >
> >Tesla Coilers may be making the worst of TC blunders when doing
> calculations
> >for determining the operating resonant frequency of their coils. It is a
> >well known fact that the calculated frequencies do not agree with the
> actual
> >operating test frequencies. Many important design decisions are based on
> >this unique frequency so it is important that it be correct. To circumvent
> >this problem a fudge factor is used for all TC computer programs but this
> is
> >only a bandaid for TC design.
> >
> >The equation that coilers use for finding the TC resonant frequency is
> >
> >      F = 1/(6.283 x sqrt(LC)
> >
> >The TC secondary circuit is an RCL circuit but the "R" is omitted by
> coilers
> >in the above equation which may be the worst of TC blunders. In the Tesla
> >Coil Construction Guide page 5-1 the complete resonant frequency equation
> is
> >shown including the "R" parameter. It is also mentioned that the "R"
> reduces
> >the resonant frequency and if the "R" is large enough there will be no
> >resonant frequency. In other words the "R" could be the reason the
> operating
> >frequency does not agree with the calculated frequency when the "R" is
> >omitted.
> >
> >To my knowledge no one has ever determined how to find this very important
> >"R" for an operating Tesla coil either by calculation or by tests. TC
> >programs are hurting because of this lack of information.If anyone has any
> >comments I would be interested in them.
> >
> >John Couture
>
> --------------------------------