Re: 4 Inch tesla coil - Inquiries

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: G Hunter <dogbrain_39560@xxxxxxxxx>

I think the primary heat is cause by high RMS currents
due to poor tuning and non-quenching.

Try a better quenching spark gap.  I suggest a
two-horned sucker gap made of 1" or 3/4" copper pipe
fittings.  Use plenty of copper to sink lots of heat.
Mount the gap atop an old vacuum cleaner motor and let
it run full throttle.  A Hoover or Bissell upright
motor/blower assembly should do fine.  Either one will
draw 10-12 Amps from a 120vac outlet.  I collected a
few such vac blowers just by grabbing discarded vacuum
cleaners from the curb.  The motors are always good.
The vacuum cleaners are being thrown out beacsue all
the cheap plastic body parts are broken.

Cheers,

Greg

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Hydrogen18"
> <hydrogen18@xxxxxxxxxxxxx>
>
> I've got a 4 inch tesla coil that I've pulled out of
> storage and set
> about improving and trying to make into a more
> logical setup. Specs
> are as follows
>
> Secondary - 4 inch Schedule 80 pipe, 1500 turns 28
> awg, 18 inches long
>
> Primary - Coil of 1/4 inch copper pipe, about 13
> turns worth. laid
> out flat and zip tied to plexiglass. 1/4 spacing
> between turns. about
> 2 foot overall diameter.
>
> Spark gap - Static style, 1 inch spherical brass
> drawer pulls mounted
> to 1/2 inch copper pipe. This can be adjusted really
> easily. A cheap
> blower supposedly running at 25000 rpm blows alot of
> air in an
> uncontrolled fashion across these. They get pretty
> dang hot, but the
> arc seems to be quenched pretty well, although I
> have no first hand
> experience with spark gaps outside of my own design.
>
> Topload - 12 inch toroidish thing with a section of
> 4 inch dryer duct
> stacked around it. Seems to discourage primary
> strikes pretty well,
> although it was designed for such
>
> Tank Cap - 942C20P15K's(2000 VDC 0.15MFD) in strings
> of 8, up to 3
> strings of these in paralell(plenty more strings
> ready to be
> assembled). Mounted in a wooden box but the
> capacitors themselves are
> in 180 degree sections of PVC pipe for insulation.
> Connection is made
> at all junctions to the strings by means of 1/4-20
> brass bolt.
>
> Power supply - 4 MOTS producing around 9500 volts
> RMC AC, current is
> limited by 10 lbs 10 AWG wrapped around a 3 inch
> piece of Schedule 80
> with an adjustable iron core(I have also left the
> shunts in the MOTS,
> as I see no need to drive them as hard as some
> people do; mine are
> not under oil but epoxy potted). Driven by a 30 Amp
> 240 VAC outlet, I
> do not feel this is the limitation in my setup.
>
> So far my recent attempts have yielded point to
> point strikes of 28
> inches or more; longer arcs accounting for the bend.
> That was with 2
> capacitor strings. Attempting to use 3 capacitor
> strings seems to
> make finding a tuning point impossible, all I
> suceeded in doing was
> getting the primary so hot I burned myself(this was
> in just a second
> or so of having the spark gap firing). I am dumb
> tuning this coil,
> just starting at turn one and moving out until I get
> a large
> response, and then making smaller movements from
> there. I've made the
> following conclusions:
>
> - Steel anywhere in the primary circuit basically
> destroys
> performance and likes to get really hot.
> - Tuning seems to be very pecuilar on a lower
> coupling coil(I had 3
> inch coil in the past with 'high' coupling between
> the primary and
> secondary, you could make turns of adjustment to the
> primary without
> noticeable output in spark).
> - The charging current available to the coil doesnt
> seem to affect
> things much, other than the spark gap getting
> louder.
> - This spark gap is better than the last, because I
> don't have to
> wait for it to cool down between runs. It takes a
> very long time run
> time for the initial breakdown voltage to change due
> to tempature of
> the electrodes. They are hotter than a car brake
> rotor at the parts
> you can observe, but I suspect where it matters they
> are remaining
> cool. They also dont require a resurfacing every 30
> seconds of runtime.
>
> And I've got these concerns:
>
> - My primary is very poor. The spacing is
> nonuniform. I think tuning
> is changing because the turns are not held very
> securely.
> - Should I add another gap to my static spark gap?
> Are there any
> telltale signs of an overloaded static power gap? I
> know that the
> signs of a 'power arc'(the deep orange-reddish arc
> that does not
> quench) or rapid electrode erosion are two to look
> for, and I have neither.
> - I have a safety gap on my transformer, so I'm not
> concerned about
> opening my spark gap up too much. But is there a
> primary side side
> RMS VAC that I shouid aim to have the spark gap
> breakdown at?
>
> My questions are from here:
>
> - Should I bother improving the primary? I'm not
> getting turn to turn
> arcing, it's the inconsistency of the shape that's
> my concern.
> - What's the maximum size capacitor for this coil I
> can reasonably
> expect to run?(I know my limitation is the spark
> gap, and probably
> will be for all my coiling years given the easy
> availability of large
> dangerous HV transformers)
> - Why is my primary getting so darn hot? Is off
> resonance driving of
> the coil the cause of this?
> - Is there a better(intelligent, mathematical)
> method of tuning the
> coil I can employ?
> - What kind of spark length performance should I
> expect from this coil?
> - Any other obvious mistakes?
>
>
>




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