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Secondary advice for first coil

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LAN_403

test_tube_tony

Tue Jul 13 2010, 02:51AM

Registered Member #2970 Joined: Mon Jul 05 2010, 06:14PM
Location: dallas tx
Posts: 17

ive decided to build a proper coil. so far ive got a 9kv 30ma nst, 17x .15uF 2KV caps for the tank capacitor to be connected in series (this should be a match for the nst with plenty of voltage headroom), and some 18 gauge high voltage wire rated at 30KV. for the SG i plan to start out with a simple 2 electrode setup for ease of adjustment with a strong fan to cool it. later ill build a nice one with copper pipe. im having a hard time with my secondary sizing. it was suggested to go with 3.5" dia but i can only find 3" or 4" pvc and flanges. from what i understand if i get the setup right i should be able to average 20" sparks. i read at deepfriedneon.org that a 3" coil should be 18" long and a 4" should be about 20", then add a few inches to get the total form length. my questions are, is there any difference in using cellular vs solid core pipe (i wouldnt think here is), how long should i make the pipe from a structural standpoint to avoid zapping down to the primary, what gauge wire should i use (i was thinking 30), and lastly how many turns should i shoot for? 1000? 2000?... i may just be over thinking all this but id like to do this right the first time :)
any advice would be greatly appreciated. ill post to this thread with any further questions about my first coil

thanks in advance!

dmg

Tue Jul 13 2010, 02:55AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

look at many coils that are built, they can be anywhere from a 1:3 to 1:5 and all around that (I think your coil, 3 X 20 has the aspect ratio of about 6.6 or so)
I would aim for 1000 turns on an SGTC.
a 3inch 20 inch coil is not a bad place to start though
for the secondary, to get 1000 turns, the gauge will have to be 26gauge
if I understood the question about the pipe, Ill assume it is for the primary, I would use hollow tubes, they have less losses from skin effect, lighter and cheaper, but if you have solid wire it will still work.
also, here is a neat programm for you to play with:

it will let you see what you are building, and give some specs for it at the same time, personally, I dont use this programm for SGTCs, I just build away and then tune the primary so that it will work for the secondary, but however, this can give you a very nice idea to what your finished product will look like, its turns, resonant freq, etc.

this is a calculator within javatc, which ive used to figure out that on the former, 26awg will be close to 1000turns.

test_tube_tony

Tue Jul 13 2010, 03:28AM

Registered Member #2970 Joined: Mon Jul 05 2010, 06:14PM
Location: dallas tx
Posts: 17

Gatedbreakdown wrote ...

look at many coils that are built, they can be anywhere from a 1:3 to 1:5 and all around that (I think your coil, 3 X 20 has the aspect ratio of about 6.6 or so)
I would aim for 1000 turns on an SGTC.
a 3inch 20 inch coil is not a bad place to start though
for the secondary, to get 1000 turns, the gauge will have to be 26gauge
if I understood the question about the pipe, Ill assume it is for the primary, I would use hollow tubes, they have less losses from skin effect, lighter and cheaper, but if you have solid wire it will still work.
also, here is a neat programm for you to play with:

this is a calculator within javatc, which ive used to figure out that on the former, 26awg will be close to 1000turns.

my pipe question was in reference to different types of pvc to use for the form. theres solid pvc, and theres pvc with a dense foam in the core of the pipe walls. seems to be much lighter. the store i was at today had 3"x24" pre cut lengths of the cellular core stuff. i was actually just playing with javatc. it needs so much data lol. doesnt seems to function quite right on this linux lappy tho so ill try it at work tomorrow. thanks so much for the info. it helped me figure out how i was supposed to figure it out on my own :)

dmg

Tue Jul 13 2010, 03:36AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

my bad, I missread your post,

for the secondary former, the popular choice is hollow, thin walled white PVC pipe, I cant say solid core is bad, but Ill still advice against it if you have other hollow options.

but I would think it would be best to leave the core of the pipe hollow, since it will be cheaper and lighter, that, and you can drill into the pipe itself and attach your wires more easier (with solid you will probably have to tap it, etc) and you can cut off the secondary to different lenths more easly with hollow pipe.

another thing is, if your PVC has markings on it (ink or whatver) give your former some sanding before hand, since this ink can be conductive at high voltages and cause issues later in your secondary,

if you dont feel like using plastic, ive used cardboard tubes that where heavly treated with polyurathane in the past without issues.

this is the pipe I am refering to:

test_tube_tony

Tue Jul 13 2010, 06:28AM

Registered Member #2970 Joined: Mon Jul 05 2010, 06:14PM
Location: dallas tx
Posts: 17

oh i see its drain pipe. cool. i was also trying to think of ways to make the height of the primary adjustable. probably going with a flat coil for simplicity unless you'd suggest angling it slightly. i know it would increase the coupling but i dont know if it would be advantageous on this coil. i thought about mounting the coil to a floating panel of sorts with some sort of adjustable screws but id like to think of something better than that. trying to use as little metal as possible in the construction. i also thought about using threaded pvc and a flange to raise and lower the secondary by twisting it. not sure how much play it needs up or down from the first winding tho. advice on how to rig this up would be awesome :) close up pics of mounting methods would be a bonus too lol. i have actually never seen one of these in person so im going mostly off pictures, creativity, and mind boggling amounts of reading. i really want this to look equally as good as i want it to work. i am so excited that im finally building one of these, mwahaha :D ive been wanting to ever since i was a kid. oh and has anyone ever tried using a relay to connect a hefty bleed resistor to the tank cap automatically when power is removed? i thought that might make a nice safety feature.

dmg

Tue Jul 13 2010, 06:40AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

I would go with flat, I found it easy to make, and it seemed to work best for me when in operation (helical was not very good)
In my 8 inch secondary I am using a bottom base plate (I used cardboard tube for secondary) and that plate has 8 holes, for bolts, and I just use miscelanious bushings or just stack up a few washers/nuts.
if you want, you can use a single plastic bolt comming from the center of your bottom, and then you can stack as many nuts and washers as you want to raise or lweor the secondary, or you can do your method as state, have the secondary screwing on or off, Id actually prefer that for a small secondary due to the ease of adjusting,

in my big coil, I could not do this, since the whimpy little bolts broke, due to the size of the secondary, any higher then an inch and the plastic couldnt hold up. but for a 3 inch secondary, it should work very well,
hope this helps.

Matt Edwards

Tue Jul 13 2010, 01:24PM

Registered Member #2838 Joined: Fri Apr 30 2010, 07:55PM
Location: tehachapi, CA
Posts: 333

Don't buy the black pipe. I have read that sometimes they use carbon for color. Measure the outer diameter of the three inch pipe that you are buying. That is what is important.

quicksilver

Tue Jul 13 2010, 03:17PM

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

I tried it (black pipe) and it was OK: no major issues.
However a good place to get coil forms is a carpet store! You can get 4-6" heavy cardboard tubes that will soak up a great deal of polyurethane whatever you decide to use. But the larger coil I wound was a carpet roll form & she worked-out rather nicely.

HV Enthusiast

Tue Jul 13 2010, 06:40PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Well, firstly, just use the standard schedule 40 white PVC pipe found in any home improvement store. Works great, cheap, and available in a wide array of sizes.

Secondly, my biggest advice is don't get caught up on all the numbers such as number of turns, aspect ratio, etc... Just design the coil with some typical ballpark values and go from there.

If you go to the design resource on my website, i have a nice write-up of "how i design my coils" which shows how i design a secondary, etc... Good reading.

Dan

test_tube_tony

Tue Jul 13 2010, 06:56PM

Registered Member #2970 Joined: Mon Jul 05 2010, 06:14PM
Location: dallas tx
Posts: 17

heres what i came up with. its a rough sketch and is not at all to scale or of great quality lol, but it gets the point across. how do i calculate how much travel is needed for proper adjustment? how far below the bottom of the secondary should it be able to sit? how far above should it be able to reach? been trying to find that info today and not having much luck. anyway, in this mounting idea, 3 nylon bolts support the primary coil assembly. there is a short length of plastic ruler attached to the base at each bolt so the same height can be adjusted at each one easily. the bolts will rotate freely in the coil's mounting plate and will be held up by a nut that will be glued in place on the bolt. the bottom of the bolt will screw into a nut attached to the tc base. turn the screws to the right and it lowers the coil and left to raise it.

1279047383 2970 FT92607 Primary Mounting

edit: i got all the data thrown in to javatc. heres what it spit out at me. some of the values are eyeballed or estimated. i figured i can make adjustments as i start assembly of the main components to get actual exact values. hows this look?

J A V A T C version 12.4 - CONSOLIDATED OUTPUT
Tuesday, July 13, 2010 3:58:50 PM

Units = Inches
Ambient Temp = 68Â°F

----------------------------------------------------
Surrounding Inputs:
----------------------------------------------------
1000 = Ground Plane Radius
1000 = Wall Radius
1000 = Ceiling Height

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
1.5 = Radius 1
1.5 = Radius 2
13 = Height 1
33 = Height 2
1105 = Turns
26 = Wire Awg

----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
2.75 = Radius 1
12.885 = Radius 2
13.115 = Height 1
13.115 = Height 2
8.8764 = Turns
0.25 = Wire Diameter
0 = Ribbon Width 
0 = Ribbon Thickness 
0.0088 = Primary Cap (uF)
10 = Total Lead Length
0.0403 = Lead Diameter

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=4, major=14, height=38, topload

----------------------------------------------------
Secondary Outputs:
----------------------------------------------------
320.76 kHz = Secondary Resonant Frequency
90 degÂ° = Angle of Secondary
20 inch = Length of Winding
55.3 inch = Turns Per Unit
0.00216 inch = Space Between Turns (edge to edge)
867.9 ft = Length of Wire
6.67:1 = H/D Aspect Ratio
35.1324 Ohms = DC Resistance
24956 Ohms = Reactance at Resonance
0.67 lbs = Weight of Wire
12.383 mH = Les-Effective Series Inductance
13.256 mH = Lee-Equivalent Energy Inductance
13.038 mH = Ldc-Low Frequency Inductance
19.882 pF = Ces-Effective Shunt Capacitance
18.572 pF = Cee-Equivalent Energy Capacitance
29.283 pF = Cdc-Low Frequency Capacitance
5.2 mils = Skin Depth
14.893 pF = Topload Effective Capacitance
107.9637 Ohms = Effective AC Resistance
231 = Q

----------------------------------------------------
Primary Outputs:
----------------------------------------------------
320.76 kHz = Primary Resonant Frequency
0 % = Percent Detuned
0 degÂ° = Angle of Primary
36.33 ft = Length of Wire
6.03 mOhms = DC Resistance
0.892 inch = Average spacing between turns (edge to edge)
1.117 inch = Proximity between coils
1.1 inch = Recommended minimum proximity between coils
27.665 ÂµH = Ldc-Low Frequency Inductance
0.0088 ÂµF = Cap size needed with Primary L (reference)
0.313 ÂµH = Lead Length Inductance
52.225 ÂµH = Lm-Mutual Inductance
0.087 k = Coupling Coefficient
0.126 k = Recommended Coupling Coefficient
11.49  = Number of half cycles for energy transfer at K
17.83 Âµs = Time for total energy transfer (ideal quench time)

----------------------------------------------------
Transformer Inputs:
----------------------------------------------------
110 [volts] = Transformer Rated Input Voltage
9000 [volts] = Transformer Rated Output Voltage
30 [mA] = Transformer Rated Output Current
60 [Hz] = Mains Frequency
110 [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
2.45 [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
59 [uF] = Power Factor Cap Size
12728 [peak volts] = Voltage Across Cap
31820 [peak volts] = Recommended Cap Voltage Rating
0.71 [joules] = Primary Cap Energy
227 [peak amps] = Primary Instantaneous Current
23.7 [inch] = Spark Length (JF equation using Resonance Research Corp. factors)
101.4 [peak amps] = Sec Base Current

----------------------------------------------------
Static Spark Gap Inputs:
----------------------------------------------------
2 = Number of Electrodes
0.25 [inch] = Electrode Diameter
0.265 [inch] = Total Gap Spacing

----------------------------------------------------
Static Spark Gap Outputs:
----------------------------------------------------
0.265 [inch] = Gap Spacing Between Each Electrode
12728 [peak volts] = Charging Voltage
12695 [peak volts] = Arc Voltage
34569 [volts] = Voltage Gradient at Electrode
47907 [volts/inch] = Arc Voltage per unit
99.7 [%] = Percent Cp Charged When Gap Fires
5.15 [ms] = Time To Arc Voltage
194 [BPS] = Breaks Per Second
0.71 [joules] = Effective Cap Energy
276350 [peak volts] = Terminal Voltage
138 [power] = Energy Across Gap
26.3 [inch] = Static Gap Spark Length (using energy equation)

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