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Re: [TCML] Photos of my coil.

Hi Austin,

From the collective answers that you have already received
to your post about capacitor size, the obvious answer to the
question in reference to the .005 uFd is "farther away". ;^) Al-
though transformer Z is dependant upon the line frequency
(50/60 hz) along with the voltage/current rating of the transformer,
"I" cannot seem to recall the formula for determining transformer
impedance right off the top of my head, but programs like
JavaTC from Bart Anderson's excellent Tesla coil site:
www.classictesla.com can get you pretty well situated on all
of these parameters.

Also, you should check into www.teslauniverse.com and log
into their chatroom, as there are often coilers from this very
forum chatting live about Tesla coils in there. ;^)

David Rieben

----- Original Message ----- From: "austin feathers" <kartkid1@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Monday, August 10, 2009 12:12 AM
Subject: Re: [TCML] Photos of my coil.

Thanks David,

Apparently I'm learning the hard way that NST's are pretty fickle :P. I have also consildered adding vanes to the rotor just to move some air through the
gaps for quenching. I was wondering though just how to calculate NST
impedance, and how that relates to resonance in the tank circuit such that a safe capacitor voltage can be found. Do I need to move closer to, or further
away from .005 microfarrads?

I'll contact you about the variac!



On Sun, Aug 9, 2009 at 7:42 AM, David Rieben <drieben@xxxxxxxxxxx> wrote:

Hi Austin,

Very nice looking Tesla coil project.

You're gonna find (at least I did) that NSTs are no-
toriously fragile in Tesla coil service. The Terry filter
will probably help with this but one of the main issues
that causes NST failure in TC duty is the opening of
the SG too wide, which allows the the resonant volt-
age created between the NST's HV secondary
winding and the primary capaitor to "go theough the
roof". However, since you have a synchronous ro-
tary gap, this should not really be an issue for you,
assuming that you have it synched correctly.

Also, your primary cap should be at least 2X reso-
nant for the mains frequency and your transformer's
rating. Since a 15/30 NST at 60 Hz is going to be
resonant at around .005 uFd, you are right near the
"border" with you .093 uFd. primary cap. But, as
I was saying earlier, I have personally found that
NSTs tned to be very fragile when used for this
purpose irregardless of whatever precautions that
I take and I also realize that powering a Tesla coil
is pretty much way out of the designer's intended
purpose for this type of transformer.

I may also have an extra variac that I could let go
of that would work for you. Contact me off list
for more details and check out my Flickr page
of my coil project:


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