Re: Fw: Capacitor Help

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Malcolm,

Tesla list wrote:

> Original poster: "MalcolmTesla" <tesla@xxxxxxxxxxxxx>
>
> BTW - does this mean my coil is running very weak even when I get it tuned?

No.

> I thought I saw someone say in the past an NST powered Tesla Coil should be
> tapping around turn 9 to 10 on the primary otherwise it's not running very
> efficient?  Any truth to that?

Absolutely NOT! No such thing. But, maybe what you read was not 
interpreted as the writer intended. Regardless of NST, MOT, PIG, PT, 
or whatever power source is used, the primary frequency is determined 
by the primary inductance and the tank cap. The tank cap is 
sufficiently large enough to make the primary "not" sensitive to 
misc. changes. But the secondary is very sensitive. It is sensitive 
to external capacitance's which includes toploads, primary's, strike 
rings, etc. When I modeled your coil via the photos, I modeled the 
strike ring as well. In Javatc, this would be considered a "grounded" 
object. I used the disk input to best represent the strike ring 
(large ID and 1/4" larger OD). This is exactly why there is a check 
box for grounded or topload connection in that program.

With all the components in position, the secondary or resonator has a 
resonant frequency. The primary inductance can be adjusted (as well 
as tank C) to ensure the primary circuit is at the same frequency as 
the resonator. The number of turns is a matter of geometry and 
inductance needed for resonance, nothing more. There is no magic 
turns number for any given transformer type. There is common sense, 
but no magic values.

> What can I look at doing in the future to
> bring my turns down to the 9 to 10 range?  Add more strings of caps in
> parallel to increase capacitance?

If you need to increase L for resonance, you can keep L as is and 
lower C to attain the same resonance. As a matter of fact, JAVATC is 
recently updated with a capacitance reference output (it's within the 
primary outputs section). If you give Javatc the geometric dimensions 
of your setup including the number of turns on the primary and simply 
leave the tank cap value at 0, you can run the program and it will 
let you know the value of C needed for resonance. You can certainly 
run the coil at 9 or 10 turns if desired. Just increase C.

Take care,
Bart