# No Subject

• From: I am the NRA <pierson-at-cimcad.enet.dec-dot-com>
• Date: Mon, 28 Nov 94 21:11:41 EST
• >Received: from inet-gw-1.pa.dec-dot-com by csn-dot-org with SMTP id AA19003 (5.65c/IDA-1.4.4 for <tesla-at-grendel.objinc-dot-com>); Mon, 28 Nov 1994 19:14:50 -0700

```>Coil design:
>	Given a bunch of 22 ga. magnet wire and a 4" thin wall PVC pipe for
>	a form, design a coil that works well.  I plan on figuring out
>	if the wire diameter will allow between 400 and 1000 turns and
>	produce a coil with a height to width ratio of about 4:1.
>	Then, calculate this length, and figure out the 1/4 wave frequency
>	based on this length.
How?  Its NOT the same as the length of the wire.  The wire length will
turn out to be _roughly_ twice the 1/4 wave, for most coils.  That is,
100 meters of wire will resonate at 50 meters.  ROUGHLY.  Ther is cut
and try here.

>	Given the frequency, coil size, and number of turns, find the
>	inductance.  Then calculate the capacitance that is needed to make the
>	LC secondary circuit oscillate at the desired frequency.
hmmmm?  Usual secondary has no capacitors, per se.  Soem model it as
the inductance and teh stray capacitance.  Some treat it as a helical
resonator.  The second apprach is the one i fancy, as do the Corum's.

>	Then, once I have the secondary designed, design the primary coil so
>	that it is about 3x the diameter of the secondary coil.  Figure out
>	the size of the capacitor that I need based on the size of the primary
>	coil and my transformer output.
Primary capcitiance should resonate the primary to the same frequency
as the secondary.  Matching to power transformer secondary is nice, but
not convinced of its need.  Some do it.

>	Now the question:  Does anyone who has successfully designed a tesla
>	coil see any problems with this approach?
Usually, i understand:
Pick secondary pohysical size (how mush room, how much wire on
hand.
Pick coil form.	(Tesla and others end up with short, fat
secondaries.  Most home coils are tall and
skinny....)
Wind until out of wire.
Measure resonant frequency of finished secondary.
Wind primary and add caps to make it resonant to secondary.
(some will have the primary LC matched to the power transformer
secondary.  Not sure i concur, but may be right...)
Caps should eb big enough to utilize energy from power
transfomer.  Which sorta sets the size, and fulfills the
matching criteria....  This can the be used to guide the
design of the priomary (in which ther is fair freedom:
Wires are short, so expense is nto an issue, voltages are
semi low, so mechanical construction is straight forward and
design can be fiddled til it works.

I reccomend TC TUTOR, by the Corum brothers, runs on a PC.  There
are other desing sw packages that may be of assistance.  For
understanding Corum's Vacuum Tube Tesla Coils is good.  Poor title
as it is about key elements of ALL coils.

>Performance:
>	I frequently read that the old coil designs are less efficient than
>	the modern ones.  The question is why?
Dunno,  Speculation:

>	Is it strictly the materials,
Partially.

>	or is it some choice bits of knowledge such as "don't make your
>	coil over 4 times taller than it is wide".
Some truth to that, but Tesla knew that. Took a while for it to get
rediscovered.

>	I would appreciate it if I could hear about specific design
>	enhancements made to the primary/secondary system designs.
DO not skimp on secondary wiore size.  #22 is ok.  Some do #30.  Too
small.

Consider making mechanical arrangements for a tertiary coil...

>	I figure that I can get the spark gaps figured out later, though that
>	may not be a good idea:  perhaps a coil system is also designed around
>	a specific type of spark gap.
The Gap is A LOT more critical than is commonly thought.  BUT, it like
the primary, can be easy to tweak later.  Its hard to tweak a secondary.
I don't understand that a particularly close linkage exists between gap
desing and coil design...  Cettainly a better gap can "always" be
"plugged in".

regards
dwp

```