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?