RE: How to rise the secondary? (fwd)

---------- Forwarded message ----------
Date: Tue, 14 Jul 1998 19:59:43 +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)

  Russ, All -

  There is no algorithm that I am aware of that gives the coupling for a
Tesla coil to provide proper clearance to prevent sparkovers between the
primary and secondary coils. For the JHCTES TC program I collected data on
the pri to sec clearances that coilers in the past were using on successful
coils. I used this data in the JHCTES program. I have not been able to
compare this data with other programs because apparently no one has made a
similar program.

  The ideal location for the quarter wave Tesla coil secondary is to have
the bottom of the secondary at the spiral primary. Raising the sec from this
level will lower the output.

  Raising the secondary will do four things at once and not separately and
they are listed in the order of their importance; obtain the necessary
clearance to prevent sparkovers, find the proper tuning point, move the
primary away from its ideal location, and change the coupling. The coupling
is the end product of raising the secondary and may or may not be the
coupling desired. 

  The coupling is not a precise point as is the tuning. The coupling changes
the time of energy transfer but the tuning changes the amount of energy
transferred and the output. The coupling would not affect the quenching but
the tuning would. When raising the secondary the coupling cannot be changed
without changing the tuning. If the quenching changes when the secondary is
raised it is because of the tuning not the coupling.

  It is my understanding that the way to design Tesla coils is to keep the
bottom of the  secondary level with the primary spiral and as follows. The
amount of minimum clearance between the coils will determine the input
voltage that can be used. It is obvious that the clearance will increase
with the increase of input voltage. The proper amount of clearance for a
particular input voltage is found by empirical methods. This would also be
the point of maximum coupling being used. However, the coupling can be
lowered if desired by increasing the clearance which would also be adequate
for the input voltage. Some coilers believe this would reduce the output
like raising the secondary but this is not correct.  

  It should be noted that the coupling is not necessarily a critical
parameter for Tesla coils. The range for classical Tesla coils varies from
about 0.10 for large coils to about 0.30 for small coils. The so called
"critical coupling" point is always less for Tesla coils than the coupling
used so the TC is always overcoupled. It would be interesting to know but is
not necessary to know the critical coupling point for a particular TC.

 The proper tuning position is then found by adjusting the primary coil and
this is why the proper design of the primary is so important (another story)
. This design method would provide the optimum conditions for these
particular parameters without having to move the secondary away from the
primary which is undesireable as I mentioned above. The optimum TC output
also depends on other parameters and these parameters are determined by
different criteria. 

The JHCTES program gives recomended values as defaults for all the input
parameters as any program should. However, the defaults can be varied by
about +/- 15% and sometimes more and still give a workable coil provided the
system is in tune. This is why it is so important that any TC program
provide automatic tuning when changes are made. 

  Why do I keep pushing the JHCTES program? It is not perfect and someday a
coiler will produce a better program. I am hopefully waiting for that day so
I can see what I missed (without having to do all that work!). How about it
Terry Fritz? And there are others capable of doing all that work.

  John Couture


At 09:40 PM 7/13/98 -0600, you wrote:
>---------- Forwarded message ----------
>Date: Mon, 13 Jul 1998 07:20:23 -0400
>From: "Thornton, Russ #CSR2000" <ThorntoR-at-rc.pafb.af.mil>
>To: 'Tesla discussion Group' <tesla-at-pupman-dot-com>
>Subject: RE: How to rise the secondary? (fwd)
>I agree with your statement about the poor engineering practices of
>building adjustments into a system when proper design would make it
>superfluous.  However, you are implying that there is an algorithm for
>building the coils to make the required coupling.  I have collected and
>categorized quite a bit of data over the past few years that I have been
>reading from you and the other gurus on the list and after a search of
>the coupling section I am at a loss.  I have found only how to define
>and measure the coupling factors but not  anything on how to build to
>the critical coupling.  Could you please illuminate it for me(us).
>Russ Thornton
>CSR 2040, 
>Building 989, Rm.  A1-N20
>Phone: (407) 494-6430 
>Email: thorntor-at-rc.pafb.af.mil
>>From: 	Tesla List[SMTP:tesla-at-pupman-dot-com]
>>Sent: 	Saturday, July 11, 1998 12:23 AM
>>To: 	tesla-at-pupman-dot-com
>>Subject: 	Re: How to rise the secondary? (fwd)
>>---------- 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