Re: Coil blueprint

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi John,


 > Original poster: "John Richardson" <jprich-at-up-dot-net>
 >
 > I'm finalizing my design for my new coil system, and want to share the
 > parameters with all, and hopefully obtain some input in the process:
 > Transformers:  Two paralleled 12/120 NSTs for a total of 12kv at 240ma.  I
 > don't plan to ramp up the input voltage beyond 120 volts
 > Secondary:  Eight inch PVC with 36" of  #24 heavy build.
 > Primary:  14 turns of 1/4 inch copper tubing.
 > Topload:  Homebrew 8x36 toroid placed 4" above final winding.
 > Gap:  Forced air tungsten, adjustable from 1 to 10 individual series gaps.
 > Cap:  .134 LTR MMC

For a static gap, I thinking 83nf might be a better choice (Cres *pi/2).
Your 134nf would be a good choice for a SRSG.

 > 1)  I was planning to start with the sec. elevated 2" above primary, and
 > adjust from there.  Should I design for an equal pri. and sec. height, and
 > adjust up?  It's a pain to try and cut off excess PVC after the sec. is
 > done, but easy to shim up if one places the start of the windings close to
 > the end of the form.

Good to start with primary 2" below the bottom turn of the secondary (lower
coupling).  This can be done by having starting the winding on the sec about
2-3 inches from the bottom of the coil form.  You can then raise the primary
to increase coupling making sure you don't overcouple and cause racing arcs
that can destroy your coil.  Some people raise and lower the secondary and
some raise lower the primary.  Results are same.

 > 2)  Inner primary turn 2" from secondary.  O.D. about 23", as I'd like to
 > keep the assembly around two foot square.

1 inch clearance should be fine.  If you find out it is not, you could
always insulate.  If you use 1/4 copper with 1/4 space, and start the inner
turn at 10 inch dia (1 inch clearance), 23 inch OD will give you room for 13
turns.  Personally, I would like to have a few more turns.

 > 4)  I would like two place the transformers, PFC caps, and 30 amp Corcom
on
 > the first tier of my plywood cart, and place the gap, cap bank, safety
 > filter on the second level, with the coil it self on the third and top
 > level.  Try to keep that big mass of transformer iron about 15-20 inches
 > away from the primary.  Is this really necessary, or am I being paranoid?
I
 > remember a thread a while back on this, but don't recall any definitive
 > answers.

If you do place the  transformers on the first shelf, I would offset the
transformers to each end of the shelf (as much off to the side of the
primary coil's axis as possible) and only connect the cases together via the
one ground wire (dont make a ground loop).  I would also put the safety
filter with the transformer on the bottom shelf (maybe between them).  Be
sure to use the RC filter and not the LC filter.  The cap, safety gap, and
main gap should be fine on the second shelf.

 > 5)  I'm thinking about total gap spacing being no more than .375.  I would
 > prefer a slight loss of spark length to ensure NST survival.  Sound like a
 > good starting point?

.375 for the main gap seems a little on the large size.  If you make it to
adjust this large, it will be very important to set your safety gap
appropriately (with Cp and TC primary disconnected, maybe to just fire with
the variac at 130 Vac).  Be sure to use a three terminal safety gap with the
center terminal grounded to the NST chassis.

Gerry R
Ft Collins, CO