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Re: [TCML] poor coil performance again- help!

Hi Thomas,
A perfect example of a small coil and problems associated with them. First, the salt water caps are lossy (I hope you know that) and your caps have sharp points everywhere, so lots of loss and corona is expected. But, something else, I see in your data. Your setting your sec and pri bottom values at 0? This puts them at the same level horizontally with the ground place. They should be set to the actual level above the ground place. Makes a difference in frequency (from a calc standpoint).
Your lead length you show as 50cm? Looks much longer to me. It should be the length of the wire from the cap to the primary plus the length from the primary back to the spark gap. I would think it would total about 100cm or more from the picture. This makes a significant impact on your coil. We were just talking about this in the other posts and here is a perfect example. If the lead length is really 100cm or near, by the time you tune it to 3 turns (1.9uH), then your lead inductance is nearly half at 1.3uH. This does affect tuning, but Javatc is accounting for that (which is why it identifies around 3 turns (would have been near to 5 if the leads were not included, and in which case, you will still end up at 3 via trial and error). It's always good to keep leads as short as necessary so that you can use as much of the primary as possible. This is not a spark enhancement comment, but simply tuning and something to be aware of (it's part of what makes small coils hard to do).
Losses seem to be the main problem. The cap is obvious. But there may be losses elsewhere also. I noticed banana jacks on the gap? I don't think their a big problem, but I would keep them out of the high current path. For wiring, it looks like white GTO (14 awg?)which should be fine. It does look long however. Coupling is fine and at 3 turns 8cm above ground, about 0.135. This is not the problem. The Terry filter looks good also. The gap looks fine (about 2mm total?). It is narrow but this is due to the low 6kV transformer.
The coil has low turns which is a factor especially with such a small cap size, but you can't do much about that. Your main problems are cap losses, difficult low voltage, small cap size resulting in high bps. Small coils rarely do perform well , but with the added losses, I think it's just making life difficult for you. I know the JF spark length formula would predict 25" lengths based on input power for your transformer, but not easy on a small coil. However, you should be doing better than 5cm. I suspect your getting a bunch of little brushy discharges around the upper edge of the cylinder? There's no doubt that the NST can pull a decent current and ideally would like to use a 35 to 40nF cap size, but your coils not set up for that. It's running a very high bps with the 11.6nF (400 to 500 range probably). This is also another area affecting losses. They all add up, and for a small coil, makes it very difficult and the spark length is a direct result.
This coil may never do well, even with an MMC. A little better I suspect, but nothing like you desire. You can't increase your cap size either unless you could reduce the sec frequency (top load) because the primary won't allow it. A 3" x 15" toroid would get you down to 640kHz and allow a 20nF cap size at 3 turns. This would help (a little) and cut the bps down by 200. You've chosen a hard choice for a coil (low turn secondary, small, high frequency, low voltage transformer, small cap size, bottle caps, etc.). I know I sound depressing here, but I just see a lot of problems that are all likely adding up to a poor performer. 

Take care,
Bart



Thomas Ryckmans wrote:

Hello,


I rewired my small coil to get this:

http://lh3.ggpht.com/Thomas.Ryckmans/SAuuyEC3o6I/AAAAAAAAAXw/4l1Z3jR_wm8/s14
4/Tom_rewired_coil.JPG


(I am adding the JavaTC file below)


My NST is 6kV 50 mA


Primary is 8mm copper tubing, spacing (centre to centre) is 1.8 cm; inside
diameter is 11 cm, outside diameter is 30 cm, 5 turns (I am tapping at 2 or
2.5 or 3 or 3.5 turns) as per scope and calculation). I modified the spark
gap spacing, the spacing of the Terry Filter…


I am using a salt water bottles cap at 11.6 nF


Secondary is 3.2 uH with Diameter=70 mm, 480 turns, 15 turns/cm, 32 cm
height (AWG 22)

Top load is a cylinder 13 cm diameter, 18 cm high, 1 cm above end of
secondary Secondary and Primary start at the same level – JavaTC gives me a k=0.129 


I have added a stationary spark gap

http://lh4.ggpht.com/Thomas.Ryckmans/SAuuyUC3o-I/AAAAAAAAAYQ/h8QQxf8Wvzo/Tom
_Spark_gap_on_PPE.JPG?imgmax=512


and a Terry filter (with adjustable number of MOVs – I hope to get a bigger
NST one day!)


http://lh4.ggpht.com/Thomas.Ryckmans/SAuuyUC3o8I/AAAAAAAAAYA/ESiTnSNkQTg/Tom
_Adjustable_Terry_filter.JPG?imgmax=512

http://lh4.ggpht.com/Thomas.Ryckmans/SAuuyUC3o9I/AAAAAAAAAYI/JXld0yjBiC4/Tom
_Adjustable_Terry_filter2.JPG?imgmax=512


I am using a counterpoise (aluminium foil about 8 cm below the
primary/secondary; radius about 60 cm or 2x height of coil). I have no RF
ground in this apartment!


but still get pathetic sparks! About 5 cm tops from top load to a
screwdriver I am holding above it. 
On the other hand… I get massive corona on my saltwater bottles – it is much
more spectacular than the coil! Here is a picture of my saltwater cap (off
power)


http://lh3.ggpht.com/Thomas.Ryckmans/SAuuyEC3o7I/AAAAAAAAAX4/gCKeTU3n5ek/Tom
_saltwater_cap.JPG?imgmax=512


Quite ugly but I’d like to see the coil working before I invest in a MMC.


Could anyone help me nailing the issues with this coil?


Many thanks!


Thomas


J A V A T C version 11.7 - CONSOLIDATED OUTPUT

20 April 2008 22:44:40


Units = Centimeters

Ambient Temp = 20°C


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

Surrounding Inputs:

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

300 = Ground Plane Radius

300 = Wall Radius

300 = Ceiling Height


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

Secondary Coil Inputs:

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

Current Profile = G.PROFILE_LOADED

3.5 = Radius 1

3.5 = Radius 2

0 = Height 1

32 = Height 2

480 = Turns

22 = Wire Awg


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

Primary Coil Inputs:

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

5.5 = Radius 1

15 = Radius 2

0 = Height 1

0 = Height 2

5 = Turns

0.8 = Wire Diameter

0.0116 = Primary Cap (uF)

50 = Total Lead Length

0.3 = Lead Diameter


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

Top Load Inputs:

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

Cylinder #1: diam=13, bottom_h=33, top_h=51, topload


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

Secondary Outputs:

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

830.58 kHz = Secondary Resonant Frequency

90 deg° = Angle of Secondary

32 cm = Length of Winding

15 cm = Turns Per Unit

0.02287 mm = Space Between Turns (edge to edge)

105.56 m = Length of Wire

4.57:1 = H/D Aspect Ratio

5.545 Ohms = DC Resistance

15344 Ohms = Reactance at Resonance

0.305 kg = Weight of Wire

2.94 mH = Les-Effective Series Inductance

2.734 mH = Lee-Equivalent Energy Inductance

3.166 mH = Ldc-Low Frequency Inductance

12.488 pF = Ces-Effective Shunt Capacitance

11.405 pF = Cee-Equivalent Energy Capacitance

25.768 pF = Cdc-Low Frequency Capacitance

0.0784 mm = Skin Depth

8.506 pF = Topload Effective Capacitance

48.8876 Ohms = Effective AC Resistance

314 = Q


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

Primary Outputs:

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

601.84 kHz = Primary Resonant Frequency

27.54 % high = Percent Detuned

0 deg° = Angle of Primary

322.01 cm = Length of Wire

1.1 mOhms = DC Resistance

1.1 cm = Average spacing between turns (edge to edge)

1.568 cm = Proximity between coils

0 cm = Recommended minimum proximity between coils

5.453 µH = Ldc-Low Frequency Inductance

0.00609 µF = Cap size needed with Primary L (reference)

0.576 µH = Lead Length Inductance

16.981 µH = Lm-Mutual Inductance

0.129 k = Coupling Coefficient

0.125 k = Recommended Coupling Coefficient

7.75  = Number of half cycles for energy transfer at K

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


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

Transformer Inputs:

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

0 [volts] = Transformer Rated Input Voltage

0 [volts] = Transformer Rated Output Voltage

0 [mA] = Transformer Rated Output Current

0 [Hz] = Mains Frequency

0 [volts] = Transformer Applied Voltage

0 [amps] = Transformer Ballast Current

0 [ohms] = Measured Primary Resistance

0 [ohms] = Measured Secondary Resistance


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

Transformer Outputs:

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

0 [volt*amps] = Rated Transformer VA

0 [ohms] = Transformer Impedence

0 [rms volts] = Effective Output Voltage

0 [rms amps] = Effective Transformer Primary Current

0 [rms amps] = Effective Transformer Secondary Current

0 [volt*amps] = Effective Input VA

0 [uF] = Resonant Cap Size

0 [uF] = Static gap LTR Cap Size

0 [uF] = SRSG LTR Cap Size

0 [uF] = Power Factor Cap Size

0 [peak volts] = Voltage Across Cap

0 [peak volts] = Recommended Cap Voltage Rating

0 [joules] = Primary Cap Energy

0 [peak amps] = Primary Instantaneous Current

0 [cm] = Spark Length (JF equation using Resonance Research Corp. factors)

0 [amps] = Sec Base Current


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

Rotary Spark Gap Inputs:

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

0 = Number of Stationary Gaps

0 = Number of Rotating Electrodes

0 [rpm] = Disc RPM

0 = Rotating Electrode Diameter

0 = Stationary Electrode Diameter

0 = Rotating Path Diameter


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

Rotary Spark Gap Outputs:

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

0 = Presentations Per Revolution

0 [BPS] = Breaks Per Second

0 [kmh] = Rotational Speed

0 [ms] = RSG Firing Rate

0 [ms] = Time for Capacitor to Fully Charge

0 = Time Constant at Gap Conduction

0 [µs] = Electrode Mechanical Dwell Time

0 [%] = Percent Cp Charged When Gap Fires

0 [peak volts] = Effective Cap Voltage

0 [joules] = Effective Cap Energy

0 [rms volts] = Terminal Voltage

0 [power] = Energy Across Gap

0 [cm] = RSG Spark Length (using energy equation)


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

Static Spark Gap Inputs:

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

0 = Number of Electrodes

0 [cm] = Electrode Diameter

0 [cm] = Total Gap Spacing


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

Static Spark Gap Outputs:

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

0 [cm] = Gap Spacing Between Each Electrode

0 [peak volts] = Charging Voltage

0 [peak volts] = Arc Voltage

0 [volts] = Voltage Gradient at Electrode

0 [volts/cm] = Arc Voltage per unit

0 [%] = Percent Cp Charged When Gap Fires

0 [ms] = Time To Arc Voltage

0 [BPS] = Breaks Per Second

0 [joules] = Effective Cap Energy

0 [rms volts] = Terminal Voltage

0 [power] = Energy Across Gap

0 [cm] = Static Gap Spark Length (using energy equation)

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