Re: Tesla Coil Blunders

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Mddeming-at-aol-dot-com>

In a message dated 3/28/01 8:44:41 AM Eastern Standard Time, tesla-at-pupman-dot-com 
writes: 



>
> > 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 



Hi John & All, 
        I'm not sure that a known simplification is necessarily a "blunder". 
The full original formula is: 
f=1/2pi x sqrt(1/(LC - (R/2L)^2)) 
taking the derivative of f w/resp to R gives us: 
df/dR=R/(f*(4*pi*L)^2) 
For a coil ~4"  -at-270 KHz, R would have to be>500 ohms to change the frequency 
even 1%. Since DC resistance is on the order of 20 ohms, the AC resistance 
would have to be 25 times higher to be responsible for even a 1% change. IMO, 
this is not the culprit. 

Matt D.