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NST's shorting out.

Original poster: MARTINFRYML@xxxxxxx


Hello all,



I just rebuilt my Tesla Coil and have run into problems at higher power inputs.
I first operated this coil with one 12000v 60 ma Neon transformer and it operated quite well and consistently with no problems, giving 31 inch sparks to ground.. I had a safety gap and choke directly in front of the NST.
Later I decided to parallel two NSTâ??s together, and the results were great for a few tries with a real performance boost ( 50 inch sparks to ground), but then one NST burned out (lost one side).
I proceeded to add a second safety gap, this one to discharge into the primary coil, and set this gap narrower than the other so it would fire first. I also added a safety capacitor-- five 8 kv .0047 mfd caps in series, across the NST safety gap.
I tried the system again with 2 other NSTâ??s , and first it blew out the safety caps (shorted between two of the caps ? bllew out of one and into another), shorting the NSTâ??s so nothing worked. I removed them and tried again. Again, one NST burned out one side (incidentally always the second one in the parallel, not the first one, which I operated as a single before).
Next, I unpotted one of the burned out NSTâ??s , soaking in mineral spirits, removed as much of the pitch as needed to take the coils apart. Tested the unit-- both sides worked perfectly, and then removed half of the shunt plates (10 out of 20). I reassembled and had a current draw of 18 amps on the mains (vs. original 6-8 amps on a working NST), so I figured I was getting between 120-180 ma output from the unit. I only planned to operate this rebuilt unit for 15 seconds at a time to prevent overheating and now I only needed one transformer, not two.
I installed into the coil and again, it worked great for 3 tries. Then one side burned out again, this time permanently, as the resistance reading was very high compared to the other side. Now Iâ??m back to square one. 



My speculations on the problems, possible causes/solutions:
The fact that this has happened three times seems to indicate to me that the problem lies AFTER the NST, with the coil design itself, not with the NST, and that some strong pulses are making it past the safety gaps and chokes.
Perhaps setting the safety gaps narrower would give more safety at the expense of performance, but they are already firing every second or more now. I had to widen them when using the two NSTâ??s as opposed to one because they were firing continuously. Was this a mistake? Primary safety gap is about 7/8 inch, and gap just before NST is 2 X 5/8 inch with ground tap in center.
I perhaps need a safety cap again, but probably need 100kv+ to stand the pulses coming backward. I have seen several opinions in the past about size (mfd) but think low is better to prevent secondary resonance in the system. Thoughts?
My rotary gap is a little warped so the gap distance varies per revolution, but the I keep the contact gap distances to the minimum anyway ( much less than safety gaps) so donâ??t think this is major.
Perhaps I need to find some ferrite toroids for much better choke protection. I now use one inch pvc pipes with 25 turns of 12 ga wire. These were originally air core coils, but I filled the air core with steel nails thinking this should increase inductance and could only help.
I have pasted in the Java program results below to give a better idea of the coil dimensions if you have time to read it. 



Anyhow, I would appreciate any suggestions anyone may have.



Thank you.



Martin Fryml



System details:



Capacitor 35 kv .03 mfd Maxwell pulse capacitor



Sunday, February 26, 2006 2:53:53 PM

J A V A T C v.10 - CONSOLIDATED OUTPUT

Units = Inches

Ambient Temp = 60°F

----------------------------------------------------

Surrounding Inputs:

120 = Ground Plane Radius

120 = Wall Radius

100 = Wall Height

102 = Ceiling Radius

119 = Ceiling Height



----------------------------------------------------

Secondary Coil Inputs:

Current Profile = G.PROFILE_LOADED

6.33 = Radius 1

6.33 = Radius 2

31 = Height 1

81.4 = Height 2

735 = Turns

16 = Wire Awg



----------------------------------------------------

Primary Coil Inputs:

8.83 = Radius 1

15.23 = Radius 2

32 = Height 1

35.75 = Height 2

9.6 = Turns

0.25 = Wire Diameter

0.03 = Primary Cap (uF)

0 = Desired Coupling (k)

----------------------------------------------------

Top Load Object Inputs (dimensions & topload or ground connection):



Toroid #1: minor=8.36, major=32, height=88.4, topload



----------------------------------------------------

Secondary Outputs:

115.09 kHz = Secondary Resonant Frequency

90 deg° = Angle of Secondary

50.4 inch = Length of Winding

14.6 inch = Turns Per Unit

0.01775 inch = Space Between Turns (edge to edge)

2436.1 ft = Length of Wire

3.98:1 = H/D Aspect Ratio

9.61 ohms = DC Resistance

26439 ohms = Forward Transfer Impedance

26176 ohms = Reactance at Resonance

19.04 lbs = Weight of Wire

36.199 mH = Les-Effective Series Inductance

33.844 mH = Lee-Equivalent Energy Inductance

38.915 mH = Ldc-Low Frequency Inductance

52.829 pF = Ces-Effective Shunt Capacitance

48.415 pF = Cee-Equivalent Energy Capacitance

90.659 pF = Cdc-Low Frequency Capacitance

9.46 mils = Skin Depth

36.302 pF = Topload Effective Capacitance

55.2 ohms = Effective AC Resistance

474 = Q

----------------------------------------------------

Primary Outputs:

107.14 kHz = Primary Resonant Frequency

6.91 % high = Percent Detuned

30 deg° = Angle of Primary

60.47 ft = Length of Wire

0.523 inch = Average spacing between turns (edge to edge)

2.5 inch = Primary to Secondary Clearance

73.561 µH = Ldc-Low Frequency Inductance

0.026 µF = Cap size needed with Primary L (reference)

340.655 µH = Lm-Mutual Inductance

0.201 k = Coupling Coefficient

4.98  = Number of half cycles for energy transfer at K

22.63 µs = Time for total energy transfer (ideal quench time)

----------------------------------------------------

Transformer Inputs:

120 [volts] = Transformer Rated Input Voltage

12000 [volts] = Transformer Rated Output Voltage

60 [mA] = Transformer Rated Output Current

60 [Hz] = Mains Frequency

120 [volts] = Transformer Applied Voltage

0 [amps] = Transformer Ballast Current

0 [ohms] = Measured Primary Resistance

0 [ohms] = Measured Secondary Resistance

----------------------------------------------------

Transformer Outputs:

720 [volt*amps] = Rated Transformer VA

200000 [ohms] = Transformer Impedence

12000 [rms volts] = Effective Output Voltage

6 [rms amps] = Effective Input Current

720 [volt*amps] = Effective Input VA

0.0133 [uF] = Resonant Cap Size

0.0199 [uF] = Static gap LTR Cap Size

0.0346 [uF] = SRSG LTR Cap Size

133 [uF] = Power Factor Cap Size

16968 [peak volts] = Voltage Across Cap

59982 [peak volts] = Recommended Cap Voltage Rating

4.32 [joules] = Primary Cap Energy

342.7 [peak amps] = Primary Instantaneous Current

41.1 [inch] = Spark Length (JF equation using Resonance Research Corp. factors)



----------------------------------------------------

Rotary Spark Gap Inputs:

1 = Number of Stationary Gaps

21 = Number of Rotating Electrodes

540 [rpm] = Disc RPM

0.44 = Rotating Electrode Diameter

0.25 = Stationary Electrode Diameter

12.25 = Rotating Path Diameter

---------------------------------------------------

Rotary Spark Gap Outputs:

21 = Presentations Per Revolution

189 [BPS] = Breaks Per Second

19.7 [mph] = Rotational Speed

5.29 [ms] = RSG Firing Rate

30 [ms] = Time for Capacitor to Fully Charge

0.88 = Time Constant at Gap Conduction

1.99 [ms] = Electrode Mechanical Dwell Time

58.6 [%] = Percent Cp Charged When Gap Fires

9943 [peak volts] = Effective Cap Voltage

1.48 [joules] = Effective Cap Energy

247504 [peak volts] = Terminal Voltage

280 [power] = Energy Across Gap

45.6 [inch] = RSG Spark Length (using energy equation)
WITH 2 NSTâ??S the Rotary gap speed was increased to 525 PPS to prevent overcharging the Caps.