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First coil I built (More tests!)

First coil I built (More tests!)

I posted a message about a month ago about my first Tesla Coil, which
I was impressed by the performance per watt of power input.

Firstly thank-you to Bart, Bob Golding and John Couture who took
interest in this message,  and even fed some values into their
computers.  Sorry I didn't provide more information.

Since I am now currently out of work,  my Telsa Coiling has taken
a back seat due to lack of money and job hunting.  However I have
operated my coil some more in order to do some testing with an
oscilloscope.

My new (more comprehensive) coil specification is as follows:-

Power supply:		240 VAC, 50 Hz, roughly 6 Amps RMS.
Supply filter:		250 VAC 16 Amp RFI filter.
Transformer:		2 x 6Kv 100mA Neon Sign Transformers in parallel
			(With centre-tapped secondary,  made by
			Tunewell transformers of London, England.)
			Open circuit voltage 6.4Kv RMS,
			Short circuit current 130mA RMS,
			Secondary Inductance 150H.
Primary capacitance:	33 nF Total,  (made of 6 x 22 nF Polyethylene
			caps in oil, series/parallel connected.)
			Each tested to 18KVDC from TV-Flyback power supply.
Spark gap:		Static RQ-gap,  5 gaps of roughly 0.5mm each,
			Fires at roughly 10Kv.
Primary Coil:		9.5 Turn Saucer shape spiral inclined at 20
			degrees.  Tapped at 6 Turns for biggest sparks.
			Overall diameter 450mm.
Secondary Coil:		Roughly 1000 Turns of 0.6mm enamelled wire,
			100mm diameter x 700mm length varnished PVC tube.
			Measured 16.5mH
			Resonates at 430KHz with no toroid,
			 indicating 8.2pF of interwinding capacitance,
			Resonates at 304HKz with 300mm toroid,
			 indicating 16.4pF total capacitance,
			Resonates at 272KHz with 2x 300mm toroids,
			 indicating 20.5pF total capacitance,
Discharge Terminal:	2x 300mm Toroid from 100mm Aluminium vent ducting.
Safety gaps:		None yet,  (woops)


Secondary resonant frequencies were found by feeding the primary from
a powerful signal generator,  and watching the brightness of a nearby
8 inch flourescent strip-light.  I found that if I stood too close
to the TC during the test,  the resonant frequency would be lowered.

I also took some measurements with my oscilloscope using a standard
probe fixed in the air about 15 feet away from the OPERATING Tesla Coil.
With Y-gain set to 1V/div the damped oscillations were easily visible.

In my last message I speculated about whether my spark-gap may be
firing more than once during each half cycle of the supply.
Using the oscilloscope it could clearly be seen that there were roughly
7 or 8 damped RF oscillations fired off during each half cycle of the
mains supply.  This corresponds to a break rate of around 800 BPS.
I assume this is due to the relatively small tank capacitance being
re-charged many times in each mains cycle by the large current
available from the neons.

All this means my calculated power figures were out by a factor
of about eight!   Not 70 Watts but about 600W.  This agrees with the
supply current.

I have recently read much about small tank caps versus big tank caps,
Maybe small caps fire more times per second giving similar overall
power too big capacitors.  Any thoughts ?

I found all this very interesting,  but had to cut short my testing
due to the noise.  I would liked to have tried tests with one neon,
two neons,  various combinations of capacitors,  and tried altering
the coupling.  Maybe another time.

I have already fitted two 4inch fans to the RQ-gap to increase run-time
from about 10 seconds to several minutes.
Can anyone suggest any improvements to my design as I seem to be
having trouble beating the 3 foot barrier,  for streamers into the air.


PS. I don't have a reliable source for neons,  I got mine second hand
from a neon sign maker in Gateshead.  He only had two of this type which
had been taken off "burnt-out" signs.  He let me have them for 15 pounds
each as he said that 100mA was too powerful !  I just pray that these
units are robust and last long,  as they are over 100 pound each new !

If anyone has any feelings about my test results or suggestions for
future tests please let me know,

					Cheers,

						Richie,

				(Making some noise in sunny Newcastle.)