Re: How to rise the secondary? (fwd)

---------- Forwarded message ----------
Date: Mon, 13 Jul 1998 05:27:53 +0000
From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: How to rise the secondary? (fwd)

  Barton, All -

  Coupling is not a critical adjustment for Tesla coils and exact coupling
is not necessary. In fact, when the secondary is  raised if only the
coupling changed the only change would be a reduction in the TC output. The
reason the output does change is because the tuning changes and this is very
important and must be precisely set to obtain maximum output from the TC.

  The problem with raising the sec to prevent sparking and change the tuning
is that there is a better way to design and build Tesla coils. When a TC is
correctly designed, built, and tuned, raising the sec will only reduce the
output until it is zero. A correctly designed TC requires that the pri to
sec clearance be adequate to prevent sparkovers. This is not a critical
parameter because classical Tesla coils operate over a wide range of
couplings from about 0.10 for large coils to about 0.30 for small coils. 

If an exact coupling is desired it cannot be done by raising the sec because
chances are the tuning will not be correct. This is not true when the
primary is used to tune the coil.

  Coupling or K factor is only a numerical ratio like pi. With Tesla coils
the coupling is a ratio of inductances. Changing the coupling changes the
inductances which changes the tuning when raising the sec. This does not
happen when the tuning is changed by changing the primary coil. Quenching is
not changed by coupling but it may be changed by tuning and other adjustments.

  It is important to know that raising the sec can be used to "tweak the
tuning" but there is a better way. That is to design the primary with
sufficient clearance to prevent sparkovers instead of having to raise the
sec. The necessary clearance data has been obtained by empirical means by
many coilers in the past. I have incorporated this data into the JHCTES TC
computer program and it appears to be working. The data can only be verified
when other coilers make similar programs for comparison.

  John Couture


At 10:17 PM 7/11/98 -0600, you wrote:
>---------- Forwarded message ----------
>Date: Sat, 11 Jul 1998 00:47:27 -0500
>From: "Barton B. Anderson" <mopar-at-uswest-dot-net>
>To: Tesla List <tesla-at-pupman-dot-com>
>Subject: Re: How to rise the secondary? (fwd)
>I'm not sure I quite understand what your saying. First you say it's not
>necessary to raise the secondary "if the TC is designed properly". Then you
>finalyze by saying "I have not solved the problem of finding the exact coupling
>for a particular TC". To me, these are two conflicting messages. For myself, I
>(until I "can" calculate and build to the calculation exactly) choose to design
>slightly over coupled so that I can "raise" the secondary to adjust coupling to
>maximum capabilities without over-arcing. Maybe, you are playing
>and asking how we can calculate to precision coupling?
>Tesla List wrote:
>> ---------- Forwarded message ----------
>> Date: Fri, 10 Jul 1998 05:47:05 +0000
>> From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
>> To: Tesla List <tesla-at-pupman-dot-com>
>> Subject: Re: How to rise the secondary? (fwd)
>>   To All -
>>   Why are coilers building Tesla coils and raising the secondary to make
>> them work properly? Raising the secondary of a properly designed and tuned
>> coil only reduces the output. Why use a faulty design of excessive
>> overcoupling then try to correct it by raising the secondary?
>>   If a proper pri/sec clearance is maintained to prevent flashovers and the
>> coil properly tuned raising the secondary is unnecessary. Tweaking is part
>> of the tuning process and not necessary for coupling selection with a
>> correct design. With a properly designed TC the quenching adjustments relate
>> only to the primary circuit. Quenching always occurs after the first
>> transfer when the secondary circuit has almost zero energy and has no effect
>> on the primary circuit.
>>   Critical coupling is the same for Tesla coils as it is for any dual
>> coupled RCL system. If this condition can be determined at the time of
>> design the correct amount of overcoupling can be determined and excess
>> overcoupling avoided. It does not make engineering sense to deliberately and
>> incorrectly design a coil with excessive overcoupling and then try to
>> correct it by raising the secondary.
>>   I have studied and researched this problem with over a dozen coils. My
>> conclusion was that raising the secondary was not necessary with a properly
>> designed TC. In fact a TC that requires raising the secondary can never be
>> adjusted to produce optimum output. This is because moving the secondary
>> away from the primary will reduce the output. I have not solved the problem
>> of finding the exact coupling for a particular TC. However, coupling is not
>> critical as it does not affect the amount of energy transferred. Only
>> sufficient pri/sec clearance is required to prevent sparkovers. I agree more
>> research is needed.
>>   John Couture