Re: Question on Ceiling Height/Material

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Jim,

At 11:23 AM 5/24/2006, you wrote:
> Hello List Members,
> I recently noticed that the ceiling height and material can make a 
> significant difference in a coil's secondary frequency.

You bet!!  E-Tesla was sort of inspired by situations like this:

http://teslacoil.com/images/content/sg20tc_pepsicenter.jpg

where it was hard to guess at the tuning, and ever harder to fiddle with it!!

> Case in point - I was trying to get my DF-DRSSTC working. I couldn't 
> get it to break out properly and it was drawing too much current. I 
> took the coil over to a friend's house and it was working well - got 
> 18" arcs to a ground rod - with no change in the coil configuration. 
> What was the difference? My friend said his shop which has a flat 
> metal roof, suppresses the operating frequency of his coils. When he 
> moves them outdoors, they have to be retuned. When I was trying to 
> run this coil before, I was in my garage which has no "ceiling" only 
> open rafters up to the roof.
>
> In playing with parameters in JAVATC, I see a noticeable change 
> between an 8 ft ceiling and a 12 foot ceiling. I don't see anything 
> in the program that inputs the material type for the ceiling. I 
> would think a non-conductor like gypsum wallboard would have less 
> effect than a flat steel roof. Maybe Bart could shed some light here.

In general, even gypsum will present a sufficient boundary for HV 
RF.  Probably not as good as steel and probably at a higher loss, but 
good enough.  It is not so much a conductor, but a capacitor that 
will zero the voltage out trying to charge it at that point, but the 
results are the same.

> The bottom line for me is to accurately model the room envelop when 
> running a TC modeling program. Also, if you relocate the coil - say 
> from in the garage to out on the drive way - expect to have to 
> retune (possibly reconfigure).

Yes.  If you reduce the primary to secondary coupling, it will be 
less sensitive.  But that might reduce the spark size too...  Not sure...

Cheers,

        Terry


> Jim Zimmerschied