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Re: Top Toroid
At 11:15 PM 1/31/97 -0700, you wrote:
>> Subject: Re: Top Toroid
>> Subject: Re: Top Toroid
>> >Subject: Re: Top Toroid
>
>Subscriber: tom_mcgahee-at-sigmais-dot-com Fri Jan 31 23:09:24 1997
>Date: Fri, 31 Jan 1997 12:47:15 -0500
>From: Thomas McGahee <tom_mcgahee-at-sigmais-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: Top Toroid
>
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>----------
>> From: Tesla List <tesla-at-poodle.pupman-dot-com>
>> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
>> Subject: Re: Top Toroid
>> Date: Friday, January 31, 1997 1:05 AM
>>
>> Subscriber: rhull-at-richmond.infi-dot-net Thu Jan 30 22:56:39 1997
>> Date: Thu, 30 Jan 1997 18:27:28 -0500 (EST)
>> From: richard hull <rhull-at-richmond.infi-dot-net>
>> To: tesla-at-pupman-dot-com
>> Subject: Re: Top Toroid
>>
>>
>
>Richard, Bert, Anyone Else,
>What do you actually mean when you say a toroid is 7.8pf anyway? In a
>classic capacitor the capacitance is a function of the Area of the
>plate(s), the Distance that separates the plates, and the dielectric
>Konstant of the insulating material that separates the two plates.
>
>i.e. C= (KA)/(D^2)
>
>When you say a toroid has a 7.8 pf capacitance, is this based on some
>standard distance away from earth in dry air, or what? The reason I ask
>this, is twofold:
>snipola
>2) If Toroid capacitance IS subject to such large variations in value due
>to surroundings
snip
>>It seems to me that what should be done is measure real-world toroids under
>real-world conditions, and then use the results to come up with a corrected
>formula that would generate an answer that is reasonably close to the
>observed values. Then the result from the formula would be more useful in
>practice. I think you would also have to caution people that the calculated
>value could actually vary from the real by up to plus or minus so much
>percent.
>
>Since we coilers are generally interested in the toroid as it applies to
>our secondary coil, what we need is a method for measuring toroid
>capacitance AS A TOP LOAD on the secondary. A first approach might be to
>measure the self resonant point of a secondary coil with and without the
>toroid. Or even better yet, with several different toroids! The more the
>better!! Then do the same thing with every one of your coils, each time
>also trying every one of your toroids (even ones that you think are *the
>same*). The results might be something other than what you suspect. And
>then the Hunt is ON! If results are consistent and reproducible by others,
>then one might be able to gather enough data to come up with a reasonable
>formula applicable to coiling. If not, the results in themselves would be
>useful as-is as a kind of sampling of What To Expect.
>
>My reason for proposing using the self-resonant frequency of a secondary
>with and without toroid as the meausrement means is simple: Almost all of
>us can do THAT with very simple equipment. I might not have a picoammeter,
>but I do have a sine wave generator, and two LED's. An oscilloscope and
>frequency counter are NICE, but not NECESSARY for getting some working
>data. I am still concerned by the distance factor of the toroid to earth or
>its nearest component. A reasonable isolation of the toroid from
>surrounding objects may be enough to get useable results.
>
>Just a thought.
>
>Fr. Tom McGahee
Tom,
You just figured this crap out on your own!!! Good man. I mention in
another post a bit about how to do this, but you are basically on the right
path.
The capacitance of a toroid is developed isotropically and much has been
said in recent months on this list about it. It is an electrostatic thing
and the concept is a bit illusive to many. For complete details and a super
nice read check out TCBA News vol 6 #2, 1987 for a killer article on
isotropic capacity and its full derivation complete with worthless, pie in
the sky equations, etc.
We will never develop a consistent 5% accurate equation for mounted
toroidial capacity of any toroid on any coil by figuring backwards from real
world measurement without a thousand variables, many unkowable to the
average Tesla coil "dinker".
Calculate, "plug and pray", and finally, measure.
Richard Hull, TCBOR