General Coil Design

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

Original poster: "Ian McLean" <ianmm-at-optusnet-dot-com.au> 

Hello Coilers,

I have been lurking on this list awhile.  I have been playing with
electronics and high voltage for a long time in one form or another but
still have not built a coil.

I have done a lot of research over the last few years on the Web on Tesla
Coils, and am in the process of building my first Tesla Coil now :)  Whilst
I am no newbie to electronics or high voltage I am certainly a newbie to
coiling, so I have some general design questions for obtaining optimal
performance.

I have built my HV supply.  I have 2 x 15/60 NST's.  I have built a HV RC
filter and protection gap for the NST's.  I have built an AC control box
with a 2kVA variac.  I have tested this setup on a Jacob's Ladder, and it
works real well.  Tested AC draw from the wall.  With a single 40uF PFC cap
for both NST's, and the Jacob's Ladder running, AC current draw from 240
volt mains averages out between 5 and 6 amps.  I have an 8 Amp breaker in
the AC control box and it has not tripped yet.  So far so good.

I have ordered 60 x Cornell Dubelier 942C20P15K 0.15uF 2000V caps from
Richardson Electronics here in Sydney Australia.  They arrive in 2 days.  I
am so excited.  I can build my MMC now :)  Getting closer ....

I seem to be building this coil back-to-front compared to a lot of people.
I haven't built the actual coil primary or secondary yet ...  I am building
it from the power supply up rather than the other way around.

For my MMC, I am planning on building 5 strips of 12 caps.  I'll build the 5
units separately so I can play with cap size.  I'll use 10M 1/2W resistors
as bleeders as suggested by the Geek Group.

If I use all five strips in parallel, that gives me 67.5nF  tank cap.  This
is very close to the LTR cap size recommended for an SRSG gap by the Geek
Group for a 15/120 supply.  If I use 2 or 3 strips, this gives me roughly
the LTR cap size for a static gap (about 37.5nF).  I have a 600W motor, and
am planning to modify it for salient pole synchronous operation.  I am
building a sucker gap as well, so I will have the ultimate in flexibility.

Now you have my history, comes my question.  Secondary coil design.  I
originally thought 1mm enamelled copper.  About 750 turns on 200mm form.
160kHz resonant frequency.  I thought this would give me some headroom if I
decide to get a pig later.  Got these design specs from a coil on Herb's
tesla Page for a similarly powered transformer.  Then I spoke to Claude,
also here in Sydney, and an experienced coiler, whom suggested that my
selection for copper was too thick, and turns too few.  He suggested that I
choose 0.6mm copper and go for 1000-1200 turns on a 6 inch former for a
secondary length of 30-32 inches.  I have plugged these figures into JavaTC
and cannot for the life of me get the results I am expecting.  The
calculated resonant frequency is below 100kHz, which can't be right.

I am after the same thing as everyone else of course, the longest possible
streamers, so my question is what secondary design would be optimal for a
15/120 supply with the tank circuits I have described ?  This really is a
general question for everyone's benefit I figure, as this seems to be about
the power level that many coilers are using.

Sorry for the long email.

Rgs
Ian