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Re: "The Mighty Corona Cone" (fwd)
---------- Forwarded message ----------
Date: Sat, 14 Feb 1998 15:46:03 -0600
From: Chuck Curran <ccurran-at-execpc-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: "The Mighty Corona Cone" (fwd)
Steve:
Sounds like you've made some nice project with this coil. The debugging is
always fun, especially with everyone one the list able to offer suggestions
and tips from past experiences. Thanks for explaining the details of your
current circuit, that makes it easier to offer advice. One thing you might
want to review is the load that the .018 mfd cap is placing on your 30 ma
transformer. I believe this is too large of a capacitance for this size
transformer. Your secondary is really begging for more power, I'd go on a
serious hunt for more transformers to parallel in your system.
If I understood correctly you have used a vertically wound primary that is
traveling up the length of the secondary. Most of the Tesla systems built
by list members have used either perfectly flat primaries or in lower power
systems wound with about a 30 degree angle from the flat. This is basically
the by-product of flames, arcs and failures that led to the successful use
of the primary type I just mentioned. If you decide to try the full 15,000
volt capability of your transformer, the circuit below is one that has been
proven successful by many and I believe it is still available for
downloading along with many others from either Chip's Web site or the ftp
site--I haven't looked for awhile, so that's a guess.
TESLA COIL SCHEMATIC ---------
| | T1
---------
O
X1 C1
O
| |
O L2
O-----------------------------| |------- O
||O | | | | | L1
O
||O | | | O
O
-----O||O * SG * |--->O O
O||O----------*---|Gnd G1 O O
-----O||O * * O
O
120 ||O | | O
O
Volts ||O | | O
O
O----------------------------------------------O O
|
|
Gnd
X1 = Neon Sign Transformer, grounded center tap
SG = Safety Gap.
G1 = Main system (tank circuit) Spark Gap.
C1 = Tank circuit capacitor
L1 = Primary Coil.
L2 = Secondary Coil.
T1 = Toroid discharge terminal
Gnd = RF Ground.
I am never sure if a keyboard created drawing will end up distorted in
another's computer, so try looking at either http://www.pupman-dot-com or
ftp://nic,funet.fi/pub/sci/electrical/tesla. You will find a wealth of
photographs and information that will be very helpful as your coil work gets
further along. If you did your initial setup and then tuned your coil close
to other objects, you may have a mismatch in the primary secondary tune.
Another item to check out as you go further. I would cut the capacitance
back to about .004 mfd for this 30 ma transformer. That does create a
problem with matching with your high inductance secondary. Unless you can
get allot more power, you should also consider going with a smaller
secondary coil that will resonate at a point where your power available can
handle the correct cap. A 6" x 24" secondary would be a better match for
your transformer. Good Luck with your design
Chuck
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Saturday, February 14, 1998 12:40 PM
Subject: "The Mighty Corona Cone" (fwd)
>
>
>---------- Forwarded message ----------
>Date: Sat, 14 Feb 1998 11:57:28 -0500 (EST)
>From: SBJohnston-at-aol-dot-com
>To: tesla-at-pupman-dot-com
>Subject: "The Mighty Corona Cone"
>
>
>Chuck Curran wrote:
>
>>Your secondary dimensions are close to my unit that is 15"
>>dia. x 56". I use a 10 1/2" x 56" toroid whose centerline is
>>12" above the top turn of the secondary. I have not seen
>>any discharge in the top turns at all--so far!
>>I would suggest that you may need to make a larger toroid,
>>if your system has the power to handle something like
>>40"-60" in diameter.
>
>If I add a larger topload that will reduce the secondary resonant frequency
>even lower, meaning I will need to add capacitance to keep the primary in
>tune, which I believe will result in a serious mismatch to my half-a-15
>kV-30ma transformer.
>
>>It would help to have more detail on your coil design--maybe
>>I already missed that?
>
>15 kV 30 ma neon xfmr with half of the secondary in use (ground to one
end).
>
>
>Capacitor : four old heat-sinked mica caps from 1920's Navy spark
>transmitter in parallel - marked .004 each at 12.5 kV. Ought to end up
with
>.016 but I measure .02 uF cold, so I've been using .018 uF in my
>calculations.
>
>Primary: 11 turns of 3/8" copper tubing, 26" inches in diameter, 1 turn
per
>inch, solenoidally-wound, ends up about 12" high.
>
>Secondary: 5' long, 16" diameter cylindrical form made of narrow wooden
>strips air spaced. 48" of #22 coated windings, space-wound for about 13
>turns per inch. Secondary sits about 2/3 of the way into the primary.
>
>
>>I ran through several checks on the
>>resonance of your secondary bare and with toroid similar to
>>yours. I would "estimate (guess)" that the toroid provides an
>>additional 18 pf which would suggest that your secondaries
>>resonant point of 134 Khz would drop to around 101 Khz--
>>I'm curious why you indicated yours is 119 Khz with
>toroid, pretty big difference.
>
>A Tesla-coil design program I downloaded calculated the secondary at 148
kHz.
> I measured the secondary's resonant freq as134 kHz bare and 119 kHz with
>the top loading. But it is certainly possible that nearby metal objects
>were loading the coil down. Since my garage is over-stuffed clearance is
no
>more than 4 feet between coil and other objects. I run it out in the
>driveway, of course, but I was measuring with the nearby objects.
>
>>Did you run the wire from your secondary all the way up and connect it to
>the toroid?? Yes, I even confirmed it by ohming-out the connection
between
>top of the coil and the toroid (since I cannot see the wire when it ducks
>behind the wooded form-end).
>
>Thanks for going over this with me -- I'm eager to get more dramatic
results
>(you know, I've got the spark "fever"). I just borrowed a .05 uF at 15 kV
>oil-filled cap from work which I could place in series with the .018 uF
>parallel combination for a higher voltage capability with .013 uF value.
> This would allow me to use the whole neon secondary at 15 kV. Hmmm...
I'll
>have to figure out how to handle the center-tap grounding versus grounding
>the low end of the primary to get that circuit going...
>
>Steve Johnston
>
>sbjohnston-at-aol-dot-com
>
>
>