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Re: This week is the week...need help on spark-gap spacing
Subject: Re: This week is the week...need help on spark-gap spacing
Date: Sat, 31 May 1997 06:58:43 -0500
From: Shawn Collins <rubidium-at-worldnet.att-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
At 03:32 AM 5/31/97 +0000, you wrote:
>Subject: Re: This week is the week...need help on spark-gap spacing
> Date: Fri, 30 May 1997 15:34:59 -0400 (EDT)
> From: Esondrmn-at-aol-dot-com
> To: tesla-at-pupman-dot-com
>
>
>In a message dated 97-05-30 06:58:20 EDT, you write:
>
><< I am finally at the end of a three month endeavour and need help on
> setting
> my spark gaps.
>
> I have a 15KV 60mA neon, 15 turn 3/8" tubing primary with .0105 uF flat
> plate cap (freezer bags and aluminum foil), 1050 turn 6 " secondary
>(#22
> AWG) and 24"x4" torroid. I am using a single forced-air gap.
>
> I have checked the resonant frequencies of my primary circuit with
> scope,
> sine generator and freq counter set up and have an incredibly high-Q
> primary. (deviating 5% from center frequency I almost lose the signal).
> I
> have made some 180uH protection chokes for the neon and have protection
> spark gaps made on the neon side.
>
> Would someone please help me with a startup procedure for this? I
>intend
> to
> mount the secondary tonight and find its resonant frequency and then
> match
> the primary to it before any startup.
>
> I would assume I should start with the protection gaps pretty wide
> open
> and a fairly narrow main spark gap and a low variac voltage. I then
> intend
> to slowly increase everthing until I am running at 110Vac on the
>variac.
> What should I expect for approximate final gaps for the main spark gap
> and
> the protection gaps (just ball-park).
>
> Also, how can I best tune this ? I have heard of holding a discharge
> ball
> near the torroid and tuning, at low power, for maximum discharge
>length.
> I
> am concerned about over/under coupling (my conical primary (30 degree
> rise)
> is 8.5" diameter on its center with an insulating plastic between it
>and
> the
> secondar). THe base of the secondary winding is about even with the
>base
> of
> the primary.
>
> Thanks alot for your help.
> Shawn
> >>
>Shawn,
>
>The physical geometry of your secondary and primary is almost exactly
>the
>same as mine. I would start with the safety gaps set at about 1/2".
>For the
>main gaps I would use a series of gaps to add up to about .15". I think
>my
>static gaps that I used to use for up to 12kv 120ma was 6 gaps of .030"
>each.
> Set the tap where you think it should be. Place a small wire or other
>sharp
>object on the toroid and then suspend a ground wire (to the main RF
>ground)
>about 24" away. Slowly bring up the variac voltage. Arcs should break
>out
>with about 40 to 50% of variac full power. Run it all the way up for
>several
>seconds and make sure there are no problems - like arcs where there
>shouldn't
>be.
>
>The sparks should be hot and heavy to the ground at this point. Now
>slowly
>move the ground farther away and retest. Get it to the point where it
>just
>barely hits the ground wire at full power. Now try going up and down
>one
>full turn on the primary and compare the results. Once you find the
>best
>spot, try moving it up and down maybe one half turn. Tune for best
>sparks.
> When you get done and remove the wire on the toroid, the full power
>best
>tune spot will probably be about 1/2 turn farther out due to a more
>intense
>ion cloud around the toroid and effective more capacitance and thus
>lower
>frequency. Set the safety gaps so they just ocassionally fire. I think
>mine
>are set at about .50 to .65".
>
>Keep us posted.
>
>Ed Sonderman
>
>
Well, I am happy to say, SUCCESS !!!
At 110 VAC on the Variac I have seen 42" discharges to the garage door
tracks. With the coil isolated from anything to discharge to, I get
mulitple
2'-3' purple discharges all over the center edge of the torroid. Do
these
discharges sound like everything is working as well as it could ?
I used Ed Sonderman's Excel spreadsheet to do all the calculations and I
must say it worked VERY WELL, as my calculated primary and secondary
resonances came out EXACTLY as predicted (calculated a 167kHz torroid
loaded
secondary and it came out at 170kHz and secondary tapped where
predicted) !
I ended up running the safety gaps at 5/8" each (neon) and the main gap
at
5/8" also. (For my main gap, I cut a finnned heat sink, for a TO-3 style
transistor, in half and then mounted 1/2" stainless bolts on each
half.
Those halves were then mounted with a single screw each to the inside of
a
6" plastic pipe with a squirrel cage fan from a microwave oven mounted
behind blowing a good stream of air through the tube. I can run for 5
minutes and they are barely warm !)
Back to my main question....
I am concerned that I may be overcoupled because the system doesn't seem
to
be very sensitive to tuning.I tried changing the primary by a whole turn
and
didn't see any perceptible discharge length change. Also, once in a
great
while, I will get a solitary arc out of the secondary about 1.5" from
the
bottom to the primary. I put some hot-glue on the sharp edge at the
connection point of the primary near the secondary and this stopped. The
secondary bottom winding is flush with the bottom of the primary. There
is a
1.5 inch gap between the primary and secondary with a 3" high acrylic
barrier between them.
Since I have access to a good sine generator, scope, and freq counter I
will
attempt to measure K using Mark Rzeszotarski's timely post on methods of
measuring this.
Does anyone know how to do L calculations using this equipment rather
than
using an L meter ?
One other question.... I would like to get pictures of this coil on the
web
somehow, does anyone have a page and would like to post them ? The
construction is entirely out of Lexan and acrylic (including the
capacitor,
base, gaps, and secondary coil) and looks really good. All the
components
sit on a 24" square acrylic sheet with another sheet above on which is
mounted the coil itself. Under the first sheet is a 3/16" sheet of
aluminum
that serves as my R-F ground and ground connnection point.
Also I have reformatted Ed's spreadsheet to make it prettier and cleaned
up
some of the internal references on the formulas. How do I share that ?
Thanks for all the posts from you tireless experimenters !!!!
Shawn Collins
in WA.