JHCTES TC Program (was Round vs flattened primary tubing)

From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Friday, June 12, 1998 7:27 PM
To:  Tesla List
Subject:  Re: JHCTES TC Program (was Round vs flattened primary tubing)

At 10:39 PM 6/11/98 -0500, you wrote:
>From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
>Sent:  Wednesday, June 10, 1998 11:46 PM
>To:  Tesla List
>Subject:  Re:  Round vs flattened primary tubing
>Tesla List wrote:
>> > You are absolutely
>> > correct about maintaining the conductive skin area (this
>> > configuration may actually be slightly better in this respect than a
>> > round conductor because the RF currents will tend to concentrate on
>> > the inner side) and how the round edges would be better for corona
>> control
>> > than the sharp edge of copper ribbon, but I think the real advantage is
>> how you
>> > could gain more inductance for a given sized flat pancake while
>> maintaining the
>> > same generous turn-turn spacing.  I prefer to make my flat primaries
>> > smaller in diameter than say the length of the secondary or the
>> > diameter of the topload.  This allows the coil base to roll through
>> > more doorways than would otherwise be possible, and helps reduce
>> > primary strikes by keeping this component _tucked-in_.  My 15-1/2 inch
>> > diameter secondary MTC-1 system rolls through a normal 31 inch wide
>> > man-door.
>> Robert:  
>> RE the increased inductance for a given sized primary.  Since my
>> post, I played around with the Wintesla2 program to see the effect of more
>> compact primary windings.  Interestingly, the inductance was about the
>> minimum for wire diameter equal to the turn to turn spacing for 1/4 inch
>> wire or tubing.  The inductance goes up a little as turn to turn spacing is
>> either decreased (mutual coupling effect?) or increased (wire length gets
>> longer).  However, the change in inductance only amounted to that which
>> would be gained by increasing the total number of turns by a tenth of a
>> turn!  (I have no idea if Wintesla2 is producing completely correct
>> results.)  Except for fitting through a doorway, the other benefits don't
>> seem worth the effort.
>> --Steve
>There can be a significant advantage! Let's build a pancake style
>primary from 3/8" copper tubing with 1/4" clearance between turns. Let's
>also specify an inner diameter of 10", and a maximum outer diameter of
>3/8" round tubing:
>In order to have 1/4" clearance between turns, we'd need a turn-turn
>spacing of 5/8". This limits us to a primary with 14 turns, resulting in
>about 72 uH of inductance. 
>Flattenned 3/8" tubing:
>Now lets make a primary using the same tubing that's been pre-flattenned
>to form a copper "strap" that's approximately 1/2" wide by 1/8" thick.
>Using this material, we can decrease the turn-turn spacing to 0.375"
>while still maintaining 1/4" clearance between turns. We can now fit 20
>turns in the same space, resulting in a primary with about 201 uH of
>inductance, or about 2.8X the inductance!
>-- Bert --

  Bert, All -

  I get 12 turns instead of 14.  (25 - 10 = 15/2 =7.5 inch width of spiral
  7.5 / 5 / 8 = 12 turns (72 mh)    7.5 / .375 = 20 turns (201 mh)
  I ran the numbers thru the JHCTES program and found that the 20 turns of
flattened tubing would apparently not make a practical Tesla coil because
the inductance is too great. The secondary coil would be too large to fit
the primary. Some of the 46 JHCTES parameters are shown below.  (Pri spiral
avg rad = 8.75 inches    pri width = 7.5 inches)

  Pri turns                      12          20
  Pri ind mh                   72        201 
  Pri cap uf                 .0205       .0074 

   Sec dia ins                 6.0       6.0
   Sec turns                1000      1000  (45 TPI)
   Sec AWG                  24         24    (.0201 dia)
   Sec ind mh                36          36
   Sec term pf                30         30 
   Pri/Sec clear ins       2.0        2.0
    Oper. freq  KHZ      130       130
   Note that  LpCp = LsCs  so both coils are in tune. The 12 turn 
   TC parameters would make a good coil.  However, the
   .0074 uf pri cap necessary to keep the 20 turn system in 
   tune would not make a good coil because the pri cap
   is too small for this size TC.
  The pri spiral 10 inch inside dia limits the sec dia to a max
   of about 6 inches to obtain proper clearance between
  coils. This limits the winding length to about 22.2 inches
  for an H/D of 3.7 ratio. 

  The advantage of the JHCTES program is that all of the
  parameters can be varied to find many "what if" combinations.
  Many coils have been designed and built using the 
  JHCTES program and they have all worked properly.

  Other combinations are possible but appear to present 
  problems. A larger toroid? Smaller sec wiring, etc?
  Coilers who have the JHCTES program may want to try
   other combinations. 

  Any comments?

  John Couture