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modularduck

Sun Sept 05 2010, 11:21PM

Registered Member #3094 Joined: Tue Aug 10 2010, 03:12AM
Location: portland, or
Posts: 30

Hey all,
So i though i would share my most recent foray into the TC world. While i have built a couple of coils in the past it hasn't been for nearly 20 years. This coil was started after getting laid off and finding Deep Fried Neon. After a couple failed attempts at debugging ( i found there just wasn't enough info for me at DFN) I let it sit until recently i had the extra funds to get it back out and make it work for real. If anyone has suggestions about how to get it functioning better i would welcome them!

Here are the Javatc stats:
J A V A T C version 12.5 - CONSOLIDATED OUTPUT
September 5, 2010 4:15:14 PM PDT

Units = Inches
Ambient Temp = 68Â°F

------------------------------------------- ---------
Surrounding Inputs:
------------------------------------------ ----------
100 = Ground Plane Radius
100 = Wall Radius
100 = Ceiling Height

------------------------------------------ ----------
Secondary Coil Inputs:
------------------------------------------ ----------
Current Profile = G.PROFILE_LOADED
1.75 = Radius 1
1.75 = Radius 2
11 = Height 1
31.25 = Height 2
900 = Turns
24 = Wire Awg

--------------------------------------------- -------
Primary Coil Inputs:
------------------------------------------ ----------
Round Primary Conductor
3 = Radius 1
7.49 = Radius 2
11 = Height 1
11 = Height 2
8.9805 = Turns
0.25 = Wire Diameter
0 = Ribbon Width
0 = Ribbon Thickness
0.0088 = Primary Cap (uF)
24 = Total Lead Length
0.0641 = Lead Diameter

---------------------------------------- ------------
Top Load Inputs:
------------------------------------------ ----------
Toroid #1: minor=3.25, major=15.25, height=32, topload
Disc #1: inside=0.125, outside=7, height=32, topload

----------------------------------------- -----------
Secondary Outputs:
----------------------------------------- -----------
342.37 kHz = Secondary Resonant Frequency
90 degÂ° = Angle of Secondary
20.25 inch = Length of Winding
44.4 inch = Turns Per Unit
0.0024 inch = Space Between Turns (edge to edge)
824.7 ft = Length of Wire
5.79:1 = H/D Aspect Ratio
20.9953 Ohms = DC Resistance
23894 Ohms = Reactance at Resonance
1.01 lbs = Weight of Wire
11.108 mH = Les-Effective Series Inductance
11.755 mH = Lee-Equivalent Energy Inductance
11.474 mH = Ldc-Low Frequency Inductance
19.455 pF = Ces-Effective Shunt Capacitance
18.384 pF = Cee-Equivalent Energy Capacitance
29.426 pF = Cdc-Low Frequency Capacitance
5 mils = Skin Depth
15.622 pF = Topload Effective Capacitance
86.5903 Ohms = Effective AC Resistance
276 = Q

----------------------------------------------- -----
Primary Outputs:
----------------------------------------- -----------
342.38 kHz = Primary Resonant Frequency
0 % = Percent Detuned
0 degÂ° = Angle of Primary
24.66 ft = Length of Wire
4.09 mOhms = DC Resistance
0.25 inch = Average spacing between turns (edge to edge)
1.115 inch = Proximity between coils
1.1 inch = Recommended minimum proximity between coils
23.859 ÂµH = Ldc-Low Frequency Inductance
0.0088 ÂµF = Cap size needed with Primary L (reference)
0.8 ÂµH = Lead Length Inductance
59.254 ÂµH = Lm-Mutual Inductance
0.113 k = Coupling Coefficient
0.128 k = Recommended Coupling Coefficient
8.85 = Number of half cycles for energy transfer at K
12.82 Âµs = Time for total energy transfer (ideal quench time)

------------------------------------------- ---------
Transformer Inputs:
------------------------------------------ ----------
120 [volts] = Transformer Rated Input Voltage
9000 [volts] = Transformer Rated Output Voltage
30 [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:
----------------------------------------- -----------
270 [volt*amps] = Rated Transformer VA
300000 [ohms] = Transformer Impedence
9000 [rms volts] = Effective Output Voltage
2.25 [rms amps] = Effective Transformer Primary Current
0.03 [rms amps] = Effective Transformer Secondary Current
270 [volt*amps] = Effective Input VA
0.0088 [uF] = Resonant Cap Size
0.0133 [uF] = Static gap LTR Cap Size
0.0231 [uF] = SRSG LTR Cap Size
50 [uF] = Power Factor Cap Size
12728 [peak volts] = Voltage Across Cap
31820 [peak volts] = Recommended Cap Voltage Rating
0.71 [joules] = Primary Cap Energy
245 [peak amps] = Primary Instantaneous Current
23.7 [inch] = Spark Length (JF equation using Resonance Research Corp. factors)
11.5 [peak 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 [mph] = Rotational Speed
0 [ms] = RSG Firing Rate
0 [ms] = Time for Capacitor to Fully Charge
0 = Time Constant at Gap Conduction
0 [Âµs] = Electrode Mechanical Dwell Time
0 [%] = Percent Cp Charged When Gap Fires
0 [peak volts] = Effective Cap Voltage
0 [joules] = Effective Cap Energy
0 [peak volts] = Terminal Voltage
0 [power] = Energy Across Gap
0 [inch] = RSG Spark Length (using energy equation)

--------------------------------------- -------------
Static Spark Gap Inputs:
------------------------------------------ ----------
3 = Number of Electrodes
0.75 [inch] = Electrode Diameter
0.125 [inch] = Total Gap Spacing

----------------------------------------- -----------
Static Spark Gap Outputs:
----------------------------------------- -----------
0.063 [inch] = Gap Spacing Between Each Electrode
12728 [peak volts] = Charging Voltage
10860 [peak volts] = Arc Voltage
38140 [volts] = Voltage Gradient at Electrode
86879 [volts/inch] = Arc Voltage per unit
85.3 [%] = Percent Cp Charged When Gap Fires
4.406 [ms] = Time To Arc Voltage
227 [BPS] = Breaks Per Second
0.52 [joules] = Effective Cap Energy
237600 [peak volts] = Terminal Voltage
118 [power] = Energy Across Gap
25.6 [inch] = Static Gap Spark Length (using energy equation)

I plan on changing the MMC by adding another row of 1600v .047uf caps to come closer to the recomendation of Javatc.
Also i plan on rewiring all of the connections with 10awg wire instead of the current 14 gauge stuff i had laying around.
I will most likely add a fun to the gap to quench it at some point though it seems to run fairly well without it.
A strike rail was part of my original build on this coil and i am going to add another once i get the coupling adjusted just right and get the tuning all worked out. 8" sparks aren't quite long enough to warrant it right at the moment.

modularduck

Mon Sept 06 2010, 10:23PM

Registered Member #3094 Joined: Tue Aug 10 2010, 03:12AM
Location: portland, or
Posts: 30

So I replaced all the wiring with 10g and checked the tuning a couple times and can only muster about 12" streamers...I must say I am a bit disappointed with this. any ideas guys? perhaps a better torroid? perhaps some of it may be to dirty spark gap electrodes, my basement where i do most projects has been about 60% humidity and i noticed that the spark in the gap doesn't seem to move the way it used to so maybe a good cleaning and adjusting may be in order

Sulaiman

Tue Sept 07 2010, 05:49PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

As you seem to be using a static spark gap,
are you blowing enough air through it?
Probably the most critical part of a sgtc.

The arc should be blue/white and very loud/sharp sounding,quite thin.
If there is any yellow/orange or the arc is thick then forced air is required.

modularduck

Tue Sept 07 2010, 06:56PM

Registered Member #3094 Joined: Tue Aug 10 2010, 03:12AM
Location: portland, or
Posts: 30

thats great info, the sparks are white in coloration but were a much more blue color originally so i will hook up a higher CFM fan and give that a shot i suppose i could just build a small manifold system and hook it to my little air compressor like i have seen here. THANKS! i appreciate the insight Sulaiman!

quicksilver

Tue Sept 07 2010, 07:20PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

What type, brand, etc of capacitor do you have there?
I tried to make them out from the picture but I couldn't get in close enough.

modularduck

Tue Sept 07 2010, 08:26PM

Registered Member #3094 Joined: Tue Aug 10 2010, 03:12AM
Location: portland, or
Posts: 30

Quicksilver

here is link to the caps on digikeyhttp://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=495-3619-nd&x=0&y=0

I thought these would work as they are polypropylene caps perhaps i am wrong in that assumption. certainly if they are of the wrong type i didn't do very good designing of the MMC and will need to rebuild it. that certainly will affect the output from the secondary

Herr Zapp

Wed Sept 08 2010, 06:09AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Mr. duck -

Please provide specific information (ratings or model number) of the Epcos capacitors you are using; your Digikey link is non-functional. It looks like they are probably metallized polypropylene pulse caps, but what is the voltage rating?

Did you look closely at the data in your JAVATC output file, especially the spark gap section? Assuming you are not using a variac to boost the input voltage to your 9kV NST, the peak output voltage, and the voltage your MMC charges to, is ~12.8kV. However, your two-segment spark gap (.063" gap spacing) has a firing voltage of only 10.8kV. Your gap is not allowing your cap to charge to the maximum supply value before it fires. Add at least two more copper pipe segmentso your static gap, and make sure that you have high velocity airflow directed through the gap segments. Make sure that your gaps are clean and free from oxidation (clean with #320 or #400 sandpaper).

Also, what is the value of the bleeder resistors in your MMC?

Be advised that your .0088uF tank capacitor value is what's termed a resonant value, and can result in extremely high voltages in the primary circuit that can destroy both the NST and the MMC. See Richie Burnett's extraordinary Tesla coil "Theory of Operation" website for a concise writeup on the dangers of resonant capacitor values:

(Home page at:

Finally, is that a funky little alligator clip that you are using as a primary tap??? After you change your primary wiring from #14 AWG to #10 AWG, and made all the primary wiring as short and direct as possible, make a better primary tap from a clip-in fuseholder, or a piece of copper strap with a pinch-bolt that will clamp it tightly around tour primary tubing for a tight, large-contact-area, low-resistance connection.

After optimizing the coil in its present configuration, increase the value of your MMC to around .014uF. This will prevent excessively high primary voltages due to resonant rise, and will also increase the energy dumped into the primary coil at every gap firing, which should further increase streamer length.

Properly tuned, you should be able to get 12-16 inch streamers out of this coil fairly easily.

Herr Zapp

modularduck

Wed Sept 08 2010, 02:48PM

Registered Member #3094 Joined: Tue Aug 10 2010, 03:12AM
Location: portland, or
Posts: 30

Herr, the caps are 1600v .047uf 3 strings of 16, and after doing some research here i know i need to change it a bit and will be ordering additional parts to make this happen.

the bleed resistors are 1M 1/2w are these ok or should they be more in the 10M ohm range?

Adding additional electrodes to my spark gap is no problem as i am in the process of building a new one that is more adjustable. i will increase the number to 5 and cut the spacing down.

the primary tap is in fact a a fuse holder soldered to the end of the lead its just at a funky angle in t he photo from me monkeyin with it and stiffer older wire.

thanks for the link and the info! i really appreciate it! I'll get this sucker firing on all cylinders soon i hope.

quicksilver

Wed Sept 08 2010, 04:45PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

The reason why I am interested is that common thought is that CDE caps are the MMC material of choice. Yet others have had good results with other manufacturers. Polypropylene manufacture is not the only criterion for a well functional MMC cap: very high dV/dt plays an important role.
The issue Herr Zapp brings up (resonant value) is extremely significant and if not heeded can result in damage to a NST in addition to poor performance.
The concept of NOT using a Variac to slowly introduce the power to the coil is a significant issue. You are not allowing anything but full Mains power to jump into your design. That issue alone can be very costly.

I am unsure if there are any "warning signals" as to the approach of Resonant Value. - So other than mathematical formula; the best idea is to heed that agenda.....although there may be some "warning signs". *
But again without a Variac you may not be able to see them coming! I had once heard that there was an audible "hum" or noise at a certain level but I have nothing what so ever to back that up. However that would only be available via the slow addition of power through such a variable transformer; otherwise the full power level would do whatever damage it would, with no available warning (if such a thing is anything but "hear say").

The addition of more gaps (5 in total as an example) allows several elements to take place. Additionally it will reduce noise, cool the sparks, & permit a wonderfully exercise in frustration to take place getting them all to be equal in length to be achieved.

But seriously, it is a very significant issue when taking into account the material on Richie Burnett' site.

* The issue of "warning signs" came up from a discussion of putting together a SGTC with parts available rather than purchase of parts. So that tuning became a major feature & the ability to move from Resonant Value became all the more significant. The discussion of Resonant Value became more confusing due to the use of such issues as voltage alone ("the MMC should be the NST x 1.6880", etc) which I believe is a over simplification of the Resonant Value issue.

modularduck

Thu Sept 09 2010, 12:30AM

Registered Member #3094 Joined: Tue Aug 10 2010, 03:12AM
Location: portland, or
Posts: 30

I redid the calculations on my MMC and if i add 2 more strings of 16 of the same cap it will bring my ohm loading to .0146 which should take me out of the danger of resonant capacitance as described. plus well seing 80 caps lined up should be fun to look at if nothing less.

I know of a local surplus shop that has a few old variacs so i will have to look into getting one. Too, I have been thinking that building a "terry filter' couldn't hurt, while I paid next to nothing for my NSTs I dont want to blow them up.

This brings me to another though, since I will need to adjust the MMC anyway, I would think that if i were to parallel the outputs of 2 identical NST this would increase performance no? perhaps I should just wait on that idea till I get all the bugs out of this one lol.

I hope to get the new adjustable spark gap built this weekend, provided I can gain access to my friends shop. I ran my new idea through Javatc and found that with 5 - .75" diameter electrodes with a total gap spacing of .153" will give me 99.2% charge on firing as opposed to what I have now of 85%. I am wondering if this is safe for the MMC, I noticed if I go over that total spacing I go over charge and get warnings from javatc, can someone exlain this to me? I would assume that its an issue of performance, i.e. that you want the gap to fire as close to 100% charge without going over and wasting charging time.

Thanks again guys for all your help! this is what happens when you let a low voltage guy loose on the HV world i suppose lol

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