Re: Very strange problem, please help

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

Original poster: "David Kronstein by way of Terry Fritz <twftesla-at-qwest-dot-net>" <david_kronstein-at-telus-dot-net>

Hi. here's the answers to you're questions, in order.

Does the frequency or pitch of the sound change as the spark gets longer?
I'm not sure, I wasn't listening.

Does the cap get warm in operation?
No, not at all, but I haven't run for more than about 20 seconds

Do I understand that your cap gap is a safety gap across the cap only?
Yes.

Is that cap a part of a bulk buy that took place a number of years ago?
No, I got it form from Plastic Capacitors through Interworld Electronics in
early 2000.


The current really fluctuates, but the highest peak I saw was around 10
amps.


It seems the gap requires a higher voltage to fire over time, maybe because
of overheating.
I'm redoing the fan for the gap, I'm now going to use a Muffin fan blowing
air through the tube, instead of drawing air trough slits between the gaps
with a flat radial flow fan, as used previously.
I'll test it out with the new gap when I'm done.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, August 12, 2001 10:57 AM
Subject: Re: Very strange problem, please help


> David (?),
>
> I've seen this "growing of sparks" in other coils too, and I'm
> not 100% sure what causes it.  It could be caused by the caps
> if their value changes as they heat up.  This would depend on
> the cap's dielectric.  In some coils, I suspected the break-rate
> may be increasing as the gaps heat up and fire at a lower
> voltage, but this seems less likely in your case, because the
> cap value is not small.  Here's a question?  Does the frequency
> or pitch of the sound change as the spark gets longer?  This
> would suggest that the breakrate is changing.  If the pitch
> doesn't change, than it may be a tuning change that occurs
> after it runs awhile.  Does the cap get warm in operation?
> The cap may be somewhat underrated  voltage-wise, but
> whether it survives depends a lot on your gap spacing.
> A narrow gap spacing will keep the voltage low and protect
> the cap.  I think you said the gap spacing was quite narrow
> overall, at less than 1/4".  I'm surprised the coil even gives
> 36" sparks with such a narrow gap.  In thinking about this
> more, I must have mis-read your gap spacing, because
> since your cap gap begins to fire at 1/2", this means your
> main gap must be wider than I thought.  Do I understand
> that your cap gap is a safety gap across the cap only?
> It's a good idea to put a suitable resistance or inductance
> in series with the cap gap to prevent abuse to the cap
> when that gap fires.  Alternatively, you can put the
> safety gap across the main gap, so the inductance of
> the primary reduces the cap current when the safety
> gap fires.  Some say this may subject the cap to a higher
> voltage in certain cases. A 1/2" gap is probably too wide for
> that capacitor.  Is that cap a part of a bulk buy that took
> place a number of years ago?  Some of those blew up
> for various reasons..... a combo of poor cap design, and
> over-volting perhaps.
>
> John Freau





Original poster: "Jason Johnson by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<hvjjohnson13-at-hotmail-dot-com>

Well, your capacitor is right near resonance for your transformer. It could
be that once your gaps heat up they make it easier for breakdown to occur,
and then your breakrate goes way up, putting more power through your coil.
This should be able to happen because w/ a resonant sized cap, the ratings
on the transformer don't mean anyhting and it can start sucking power like
you wouldn't believe. Get an analog amp meter, put it on the LV side of your
NST and see how far the current draw goes up as the sparks are growing.
Conditions like this are not favorable for your components, but as long as
you have properly set saftey gaps it shouldn't kill anything (note: I've
never owned an NST, and I don't plan on owning one, so talk to somebody else
w/ an NST that knows if yours could die, I've hear they can rather fragile).

<< Jason R. Johnson >>
G-3 #1129
The Geek Group
http://www.thegeekgroup-dot-org/



Original poster: "Alex Madsen by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<alexmadsen-at-yahoo-dot-com>

My coil does the same thing but not so badly. I think the air begins to
Ionize around the coil. I reset my gap after the safeties begin to fire(easy
to do on my coil).
Alex Madsen
www.geocities-dot-com\alexmadsen
#1147




Original poster: "brian by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<ka1bbg1-at-mcttelecom-dot-com>

Hi, well i'm gonna guess this one, sounds like the cap is warming up and
coil is comming into tune,most caps tend to drift when warming up. cul brian
f.





Hi David....

sounds like the cap is warming up and the plates are getting closer
together which increases the capacity
just enuf to change variables in the setup ALSO ... is the coil being run
in a room with little or no
ventilation?? it can make a difference due to the production of ozone and
the such which increases the
streamer length.
Another situation is since you went to 4 gaps, the amount of energy between
those gaps is a bit more than it
was when it was 10 gaps...  the metal from the gaps begin to ionize a bit
more than normal ( the 10 gap
setup) and this allows more energy to conduct thru the plasma arc of the
gaps...

try going back to 6 gaps or more and put some type of air flow on them if
it isnt there already... also try
ventilating the room some more too...  and last but not least  set up a
strike rod ( an old microphone stand
or something connected to the RF ground ) off to the side of the coil to
draw the streamers away from the
light   ( no noooo dont go into the light ;)  )  and if you want
directional streamers... put a breakout
point on the toroid ( aluminum tape works great ) .....



Scot D



Origanal Message



I took out my coil after not using it for a long time, and I decided to use
only 4 gaps out of 10 for now, so I put a CD on top, and I turn it on. I'm
getting sparks about ten inches, but after a few seconds, the arcs start
getting longer, and longer, and longer, until about 12 seconds later there
about 30 inches long, so I turn it off, and go searching for something else
to put on, and I find a tin can, so I put that on top, and turn it on.
Again I start out with 10 inch arcs, and they grow, over about 15 seconds,
to about 36 inches long, so long they started striking the fluorescent light
above, also the capacitor safety gap starts firing about once a second, so I
shut down.

Transformer is a 15/60 neon, cap is a 0.01uf 20 KVAC Plastic Capacitors,
primary is tapped at 12.6 T, using quarter inch pipe spaced at 1/2 inch
centre to centre, secondary is 1000 T #24 wire on 4 inch PVC toroid is 4
inch TD by 17"OD, spark gap is a cylinder gap, built on a 6 inch PVC pipe,
electrodes are 1.5 inch copper pipe couplings, spaced at 0.03(Most of the
gaps are larger than this, maybe ~0.04)with ten gaps, cap safety gap is made
of 2 stove bolts, heads facing together, with a gap of a little less then
1/2 an inch.

Any idea what's causing this? Please help.
Also, is the cap rated high enough?