4" Demo Coil Spec.
Please note, the following information is merely a design summary for a particular system. It is presented "Out of interest" and it does not represent a set of plans which you should follow to construct a finished Tesla Coil....
LV SUPPLY 

Supply voltage: 
240 
Vrms 
Supply frequency: 
50 
Hz 
Real power draw: 
2550 
W 
VA draw: 
2832 
VA 
VARs: 
1232 
VAr 
Uncorrected power factor: 
0.90 
(lagging) 
Optimal PFC capacitance: 
68 
uF 
Supply current with PFC: 
11.2 
A rms 
. 

SUPPLY BALLAST 

Ballast type: 
Primary Inductive 

Primary ballast inductance: 
51 
mH 
Primary ballast resistance: 
0.21 
Ohms 
Effective L referred to HV sec: 
88 
H 
Effective R referred to HV sec: 
361 
Ohms 
RMS voltage across ballast: 
232 
V rms 
Average ballast voltage: 
190 
V avg 
Peak ballast voltage: 
554 
V pk 
RMS ballast current: 
11.8 
A rms 
Peak ballast current: 
17.0 
A pk 
Ballast IČR dissipation: 
29.2 
W 
. 

SUPPLY TRANSFORMERS 

Type: 
Oil filled plate xfmr 

Primary rating: 
230 
V rms 
Primary resistance: 
0.24 
Ohms 
Primary inductance: 
2.24 
H 
Secondary V rating: 
9540 
V rms 
Secondary I rating: 
200 
mA rms 
Secondary resistance: 
460 
Ohms 
Secondary inductance: 
3850 
H 
Transformation ratio: 
41.48 

Open circuit HV supply: 
9955 
V rms 
Short circuit (ballasted) HV supply: 
360 
mA rms 
RMS Primary voltage: 
258 
V rms 
Peak primary voltage: 
445 
V pk 
Average primary voltage: 
210 
V avg 
RMS sec voltage when running: 
10698 
V rms 
Peak sec voltage when running: 
18465 
V pk 
Average sec volts when running: 
8725 
V avg 
RMS primary current: 
11.8 
A rms 
RMS secondary current: 
284.5 
mA rms 
Primary IČR dissipation: 
33.4 
W 
Secondary IČR dissipation: 
37.2 
W 
Total IČR dissipation: 
70.6 
W 
. 

PRIMARY CAPACITOR 

Tank capacitor value: 
70.5 
nF 
Tank capacitor rating: 
32 
kV pk 
Charging circuit Res. Freq.: 
63.9 
Hz 
. 

ROTARY SPARK GAP 

Rotary type: 
Salient pole synchronous 

Motor speed: 
1500 
RPM 
Motor rating: 
1/8 
HP 
Disc diameter: 
7 
Inches 
Electrode centres: 
3 
Inch radius 
Flying electrodes: 
1/8" 
Zirc. Tungsten (x8) 
Fixed electrodes: 
1/8" 
Zirc. Tungsten (x2) 
Firing rate: 
200 
BPS 
Electrode spacing: 
Unequal 
(stagerred 44/56%) 
Electrode locations: 
0, 40, 90, 130, 180, 

220, 270, 310 degrees 

1^{st} firing point: 
1.06 ms 
after supply zero cross 
2^{nd} firing point: 
6.62 ms 
after supply zero cross 
1^{st} firing voltage: 
18430 
V 
2^{nd} firing voltage: 
18430 
V 
1^{st} bang energy: 
12.0 
J 
2^{nd} bang energy: 
12.0 
J 
Total power throughput: 
2400 
W 
. 

TC PRIMARY WINDING 

Winding type: 
Inclined spiral 

Material: 
1/4" Soft Cu tube 

Inclination: 
15 
Degrees 
Inside diameter: 
7 
Inches 
Outside diameter: 
19 
Inches 
Turn spacing: 
0.75 
Inches 
Number of turns: 
8.5 

Tap point: 
7.5 

Tapped inductance: 
24.7 
uH 
Resonant frequency: 
120.6 
kHz 
Primary tank surge impedance: 
18.7 
Ohms 
Peak primary current: 
986 
A 
RMS primary current: 
45 
A rms 
Pri/Sec coupling coefficient: 
0.18 

. 

TC SECONDARY WINDING 

Winding type: 
Closewound helix 

Secondary diameter: 
4.32 
Inches 
Secondary diameter: 
21.3 
Inches 
Number of turns: 
1500 

Turns per inch: 
70.4 

Secondary inductance: 
45.6 
mH 
Secondary resistance: 
82 
Ohms 
Secondary self resonant freq: 
272.1 
kHz 
Secondary self capacitance: 
7.5 
pF 
Loaded sec resonant freq (small signal test): 
126.0 
kHz 
Secondary surge impedance: 
36.1 
KOhms 
. 

DISCHARGE TERMINAL 

Terminal type: 
Hollow toroid 

Toroid dimensions: 
24" x 4" 

Toroid capacitance: 
27.5 
pF 
Total sec capacitance (without corona): 
35 
pF 
. 

DISCHARGE CHARACTER 

Maximum spark length: 
72 
Inches 
Average spark length: 
54 
Inches 
ADDITIONAL COMMENTS:
The aim of this project was to produce a small demonstration coil, that would produce an arc of approximately 6ft in length from a secondary coil of under 2ft in length.
The coil produces a very characteristic sound due to the use of unequally spaced electrodes in the rotary gap. The tone is somewhere between that of a 100BPS and 200BPS gap, but appears harder and more aggressive.
I believe that the offset electrodes contribute significantly to the performance of this coil. In particular the unequally spaced electrodes have been found to delay the onset of saturation, allowing the power transformers to be worked harder before saturation starts to become noticeable.
200BPS operation was chosen for a number of reasons:
A fully synchronous design was chosen to prevent surging and allow accurate measurements to be taken.
It is also felt that this coil would have benefit from a slightly larger and much smoother toroid. At full power the toroids are covered with corona forming at edges and imperfections in the toroids. This represents a large area where power is being wasted. The relatively low 200BPS firing rate seems to demand a smooth toroid surface, although it is not nearly as critical as 100BPS operation.
Any comments are welcome,
Richie,