RE: Questions (fwd)

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

Original poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com> 



>From: MaverickIce00-at-aol-dot-com
>
>1) How much do new NSTs usually run? I went down to Advance Neon Sign Co.
in 
>Denver and got an estimate on a 6 kV 30 mA NST for my first TC. And I must 
>say, the price didn't exactly thrill me: $102.68 :-( I've heard of people 
>getting new NSTs for relatively cheap compared to this, I think something 
>like $80.00 for a new 15 kV 30 mA NST and $60.00 for a new 9 kV 30 mA NST,
so 
>I'm wondering if they're totally ripping me off... BTW, the NST is a 
>Franceformer 6030 P2G. I haven't bought the thing yet, so I'm looking for a

>little advice. I'll probably end up getting a used one if all else fails.

Can't help you here, I bought a used 15/60 for $75 and recommend that route.

>2) What exactly do Faraday Cages do? I've heard that they virtually
eliminate 
>electromagnetic and radio frequency interference, and if this is true, I'd 
>like to find out how to build a nice-looking one for my coil since RF 
>grounding is somewhat out of the question (this is going to be a smaller
coil 
>being run mainly indoors away from any suitable RF ground, and I'll be 
>transporting it to lots of places which would require a small setup time).

A Faraday cage completely surrounds a given space with a conductive surface
to contain electric and magnetic fields.  This has often been suggested on
this List as a means to eliminate interference radiated by Tesla Coils, but
I'm not convinced that this can be successfully accomplished without extreme
measures (since no coilers to my knowledge have EVER made and published any
quantitative measurements of EMI with and without such a cage).  I'm not
even sure that it's necessary since we generally run our coils for only very
brief periods.  Of greater concern is the possibility of damaging electrical
appliances elsewhere in the house through voltage transients conducted
through the power cables, and this would not be helped by the use of a
Faraday cage.  Unfortunately this is one area that has received virtually no
serious attention and research (we're all too busy making the sparks
bigger!).

>3) Will non-current limited transformers automatically stop drawing
excessive 
>current when shorted after a certain amount of time? I would believe that
the 
>current would stop flowing excessively after a certain point, such as 
>saturation of the core, or after it reached the maximum current allowable
by 
>the inductive reactance of the primary winding.

The current will stop flowing only after you blow a fuse.  When a
transformer core saturates, it causes even more primary current to be drawn.

>4) Are there any negative effects of placing various components (NST, Tank 
>Cap, Filter, Spark Gap, etc.) in close proximity to the primary coil (a 
>couple inches)? I don't think this would have much effect on anything
>except 
>for small changes in the frequency of the coils, but I want a quite compact

>unit for easy transportation.

Funny you should ask!  I recently conducted some experiments to investigate
just this.  I found that if the base of my NST was 17" below my primary,
some losses were measurable, but it was not a lot.  Bringing the NST (or any
large metal object) closer to the primary rapidly increases the losses.  I
would not recommend having the NST base closer than about a foot from the
primary.  

Regards, Gary Lau
Waltham, MA USA