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RE: Induction heating in torroid / short circuit of secondary

Hi Colin,
I don't think I've seen a good explanation 
re: why there is not much difference in performance
between Shorted and Open topload toroids.

I keep a few AL dryer duct types around that can be
easily separated at the junction (I keep the gap short ~1/4").

When I use the "Open" Toroid I connect it as an aiding turn.

  I am able to draw a small arc between the two "Open" edges,  
  indicating there IS energy that may be lost using the shorted turn 
  toroid; An optimized system could be theoretically create a bit 
  longer maximum Spark using the Open turn version though likely to be
  within a normal deviation distribution, so not readily apparent.
from my experience:
when Shorted, the power arc max distance difference is not discernable.

I wonder if there is a compensating alteration of Field difference.

*** Terry, have you ever modeled these two conditions ? 
           Do the Field plots differ ?
           This may be a case where you create the program,
           so the results are pre-destined to agree with
           that codes assumptions ?

I use galvanized and AL toroids interchangeably with indiscernible
 max Spark difference.
Any differences are more likely due to their surface texture
 rather than the metal they are made from.

A note: higher resistivity is likely to result in greater inductive heating
Stainless steel is more resistive than Brass
 which is more resistive Galvanized ducting (zinc plated steel ?)
 which is more resistive than AL
 which is a bit more resistive than Gold
 which is a bit more resistive than Copper
 which is a bit more resistive than Silver.

 Has anyone measured discernable max arc differences using these metals ?
(assuming similar dimension and surface texture)

Bottom Line:
Heating is a low concern as its likely to be undetectable at most TCout avg
powers
unless it affects the max spark achievable.
Spark length affect is real concern - and that appears to be zilch.

**** distantly related: I did some interesting experiments a while back,
Stacking toroids dielectrically insulated from each other but  
switched via spark gaps in an effort to provide electrical "delay"
determining WHEN the next level Capacitance was "connected"
The Sec output wire was likewise "gap switched" to the first toroid.

...attempting to effect "dynamically stepped" tuning 
as a funtion of having reached a minimal HV.

A thin little spark area appeared to be sufficient
 to effectively connect the levels,
 rather than an optimally large connecting surface area expected.

Regards, 
Dale

-----Original Message-----
From: Tesla List [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, December 18, 1999 7:18 PM
To: tesla-at-pupman-dot-com
Subject: Re: Induction heating in torroid / short circuit of secondary

Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>

Hi Colin,

	That's exactly what I use with great success.  I use two stainless
steel
pizza pans (cheaper than aluminum versions).  I get a 3/8 inch piece of
all-thread rod and a few nuts to space them out about four inches.  I then
use 8 inch duct around the outside which naturally matches the ten foot
length.  I use aluminum heating duct tape to connect the ends and tape
around the pan to duct joint to get good electrical contact.

	The shorted turn problem makes good theoretical sense, but in
practice, no
ill effects are noticed at all.

Cheers,

	Terry

At 11:36 AM 12/18/1999 +0000, you wrote:
>I'm currently building my second tesla coil and having looked at the
various
>options have decide to make a torroid out of aluminium ducting.  To provide
>a form for the ducting I was planning to use two pie tins fitted back to
>back, with the tapered rims forming a good match to the shape of the inside
>of the ducting (i.e. something like O>==<O).  
>
>I've got two worries though, where I'd be interest to hear other people's
>views and experiences.
>
>1) If I use steel pie tins will I get problems with induction heating?
>2) More generally, does the complete conducting loop of the torroid act as
a
>short circuited turn coupled into the flux of the secondary?  If so, would
>it be better to leave a gap in the torroid to minimize power loss?
>
>Thanks, Colin.