Re: Cap Location

From: 	John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
Sent: 	Saturday, January 10, 1998 11:50 PM
To: 	Tesla List
Subject: 	Re: Cap Location

At 10:13 PM 1/10/98 +0000, you wrote:
>From: 	Greg Leyh[SMTP:lod-at-pacbell-dot-net]
>Sent: 	Saturday, January 10, 1998 5:46 AM
>To: 	Tesla List
>Subject: 	Re: Cap Location
>> Hmmm,
>>  Mr. Cox says put the gap across the transformer, not the cap.
>>  Mr. Couture says put the cap across the transformer, not the gap.
>> I respect the opinion of both of these gentlemen, and my own experiences
>> have been inconclusive either way. I can think of arguments for either
>> method being superior.
>> Anyone else have an opinion?  Discussion?
>The operation of the primary circuit is of course the 
>same for either scheme.  However, the spark gap placement 
>has an _enormous_ impact on the charging circuit. 
>It is preferable whenever possible to put the _spark gap_ 
>across the transformer, so that when the primary circuit 
>fires, the only voltage that gets kicked back to the xfmr 
>is the IR drop of the gap, rather than the full voltage 
>swing present on the primary capacitor.  This results in
>at least a 10 to 1 reduction in the RF voltage thrown back
>to the xfmr.

  Greg, All -

  Tesla in the CSNotes said he thought the gap across the transformer was
better than the cap across the transformer as you and Mr. Cox suggest. He
based this on the fact that the current from the cap did not have to go thru
the gap to get to the TC primary winding. However, he did not make
comparison tests to determine which method was preferable. Also, he did not
address the problem of the gap OPENING.

  The TC primary circuit contains an inductance. When a switch (gap) opens
on an inductive circuit with current, there can be a large voltage transient
created. This voltage is   V = L di/dt   and can be high enough to break
down the secondary winding insulation in the power transformer. I believe
this is what breaks down neon transformer insulation.

  When the gap is across the transformer and it opens the TC primary
circuit, there can be large voltage transients formed in the power
transformer secondary winding. This voltage can damage neons and under
special conditions even damage pole transformers. When the cap is across the
transformer with a safety gap the safety gap will provide voltage limiting
for the transients comimg from the operating spark gap.

  The problem is we do not know how to design a spark gap to keep these
transients under control. A few years ago when I saw the "rotgit" program by
Jamison I thought it could be used to solve this problem. It is an excellent
simulation of the spark gap but is based on theory only and I was not able
to find a method to relate it to real world spark gap design.

  It is obvious that more research is needed in this region of TC operation.
As I mention in one of my books the design parameters that need to be
coordinated in a computer program are the spark gap and primary capacitor
charging  characteristics, and several other parameters. If a rotary spark
gap is used the RPM, number of electrodes, breaks/second, etc, would also
have to be considered. In fact this program would be more complicated than a
program to design the Tesla coil.

  John Couture