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



Thanks Bart.. a bit depressing :-). Shall I just ditch my secondary and
start again from scratch? It seems the best option... Or is anything to do
to salvage the thing? I should have designed it at the start, but just
wanted to have a go at building it

Cheers

Thomas

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of bartb
Sent: 21 April 2008 07:59
To: Tesla Coil Mailing List
Subject: 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)
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
>   
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