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Tuning and Performance Questions (6.5" coil)
Hello,
I've been tuning my 6.5" coil and have reached a new personal best of
consistent 60" strikes to a grounded rod with 1.6kva input.
I have two questions/concerns:
1) Toroid height affects my coil operation dramatically. Not just spark
length but consistency and smoothness of operation. With the toroid set at
it's current height above the secondary, I get a faint purple corona from
the top of the secondary down to the strike rail. Is this OK? If I raise
the toroid 1/2" I get breakout from the top turns of the secondary.
Lowering the toroid 1/2" destroys performance.
2) My capacitor bank consists of four rolled poly caps in a parallel/series
arrangement for a total of .042mfd with a total dielectric thickness of
.072" (spread over two capacitors). I also have a safety gap across the
capacitor bank. It's made of two 1/4" stove bolts with their heads facing
each other and a gap of .3" When the system is in tune my safety gap starts
to fire whenever my variac voltage gets to 100v (when out of tune it fires
much sooner). Am I being too conservative with this gap?
3) Performance was in the 34-36" range until the last marathon tuning
session where I did a lot of work on toroid height and fine tuning of the
tap. I now achieve consistent 60" strikes. Is this good performance for
1.6kva into the system or should I look for more?
Settings:
Current limited to 17amps using three MOT's (with shorted secondaries) and
6.2 ohms (all in parallel).
Maximum Variac setting is 95volts
Primary Tap is at 7-5/8 turns
Spark Gap is RQ type (with a blower) using five gaps for .150"
Secondary windings start .5" above the primary
Toroid is 4.5" above the top secondary winding
Coil specifications are as follows:
Primary Transformer
Input Voltage 95 VAC
Input Current 17 Amps
Output Voltage 12,000 VAC (-at-120v in)
Input frequency 60 HZ
Primary Design
Inside Diameter 9.5 inches
Average Radius 8.88 inches
Wire Diameter .025 inches
Total Diameter 26.0 inches
Wire Spacing 0.25 inches
Wire Length 79.0 feet
Total Turns 17.0
Secondary Res. Freq. 124.2 khz
Inductance 0.1407 mh
Primary Cap to Res. 0.0117 uF
Angle of Windings 0.0 degrees
Secondary Design
Diameter 6.50 inches
Radius 3.25 inches
Winding Length 27.5 inches
Circumference 20.42 inches
Wire Gauge 22 awg
Wire Length 1698 feet
Turns per Inch 37.4
H/D Aspect 4.23
Inductance 34.56 mh
Resonate Frequency 248.1 khz
Medhurst_K 0.72
Res. Freq. w/Toroid 130 khz
Self_C 11.91 pf
Top Load
Type Direr Duct Toroid
Size 6" chord x 30" diameter
Top Load C 32.1pf
Tank Capacitors
Number of Capacitors 4
Capacitor Configuration Series/Parallel
Type Rolled LDPE
Overall C .042 uf
C of each unit .042 uf
Dielectric Constant 2.0
Plate Length 120 inches
Plate Width 14 inches
Dielectric .036 inches (6-at-.006")
Pictures available at the following:
http://www2.hughes-dot-net/~brianb/teslahome.html
Thanks in advance (hope this isn't too much information)
Brian D. Basura