Toroids Effect on Q of Secondary
Date: Wed, 11 Jan 2006 18:39:17 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Toroid's effect on Q of the secondary
Original poster: norman@ees1s0.engr.ccny.cuny.edu
I just finished measuring the resonance frequency of my secondary by observing
the null due to the series resonance of the 1/4 wavelength coil. The toroid on
top of the coil was constructed out of 4", "semi-rigid flexible aluminum duct",
bought in Home Depot. The ID is 3.5", OD 11.5" and the center of the toroid is
hollow so that it slides over the PVC coil form. The coil is 9" x 3.5" wound
with # 24 wire and resonates at 500kHz.
I noticed that when the toroid was about 3" above the top of the secondary
winding the resonance notch was very deep, but when the toroid was moved close
to the top of the winding, the notch was not very steep. Clearly the toroid was
affecting the Q of the coil, probably by acting as a shorted turn. I have not
come across any information about how far the toroid should be placed from the
top of the coil. Anybody have any information about this? Should I place a
slit through the toroid?
Also the surface of the semi-rigid flexible duct looks like an accordion with
1/4" deep ridges spaced about 1/4" apart. Will this surface affect the
streamers? This is a low power Tesla coil that I hope will produce at least 10"
streamers.
Date: Thu, 12 Jan 2006 12:47:40 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Toroid's effect on Q of the secondary
Original
poster: "D.C. Cox" <resonance@jvlnet.com>
a 5-6" spacer should work fine in this appli.
Dr. Resonance
Date: Thu, 12 Jan 2006 19:37:17 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Toroid's effect on Q of the secondary
Original
poster: "Barton B. Anderson" <bartb@classictesla.com>
Hi Norman,
I have not heard of anyone using a slit toroid. You may be experimenting into a
topic that hasn't been looked into deeply. I generally keep my toroid as high as
possible (not allowing sparks to issue from the top winding, well, unless I'm in
a lazy mode of operation). It's been stated on the list that a toroid low or
partially covering the top windings may heat the top windings (I have not
experienced this myself). It certainly appears the Q was
definitely affected. Out of curiosity, how did you measure fo?
Take care,
Bart
Date: Fri, 13 Jan 2006 00:25:41 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Toroid's effect on Q of the secondary
Original poster: FIFTYGUY@aol.com
In a message dated 1/12/06 9:38:20 PM Eastern Standard Time,
tesla@pupman.com writes:
> I have not heard of anyone using a slit toroid.
I tried it, and it had no measurable effect either on sparks ,or amplitude of
fundamental resonance when base-driven directly with an oscillator. I didn't pay
any attention if it had any effect on the bandwidth, and hence Q, but I doubt
it.
Date: Fri, 13 Jan 2006 00:27:24 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Toroid's effect on Q of the secondary
Original poster: "D.C. Cox"
<resonance@jvlnet.com>
I slitted up a toroid once (6 x 24 inch size) and noted that it worked fine at
low levels atop the secondary, however, a solid surface toroid produced the
exact same discharge when it was properly elevated. This was testing on a coil
with a 60 inch long spark.
It's best to experiment with small blocks of wood to elevate the toroid until
you are achieving max spark discharge possible ---- very much like experimenting
with sec coil elevation until you are hitting your max.
We wind all of our "test" coils within 1 inch of the lower end and start
elevating until we hit a max using a small 10 rpm DC motor on a flex drive.
After hitting it then we just design for the proper start height on all of our
sizes, 4", 6", 12" 18" and 24". The larger size 18" (ID) requires 6.75 inches
of elevation above the primary and the 24 inch (ID) requires exactly 9 inch
elevation. Sec elevation is absolutely linear right down to the 2 inch size so
you can just make up a simple graph and get the 4", 6", 8", 10", etc. readings
right off the graph ( I will email one to Terry F for posting) and, we you do
all the testing, will get the exact same output as you will off my graph --- no
exceptions with classic coils. This could change with DRSSTCs as I have not
tested elevations on them.
Dr. Resonance
Date: Fri, 13 Jan 2006 12:03:55 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Toroid's effect on Q of the secondary
Original poster: "Peter Terren"
<pterren@iinet.net.au>
The question of a slit toroid has been raised way back by the pioneers of
toroids but experimental evidence did not show any difference. It was one of
the first questions I asked this list when I joined originally some years ago.
The toroid is generally kept sufficiently high above the secondary while still
preventing any corona off the top turn. Examples of getting it right are here:
http://tesladownunder.com/Tesla_7ft.JPG
and getting it wrong here:
http://tesladownunder.com/Tesla18inch1st2.JPG
Peter