Secondary advice for first coil / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Secondary advice for first coil

previous 1 2 3 next

Move Thread

LAN_403

Herr Zapp

Tue Jul 13 2010, 10:32PM

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

ttt -

In conventional spark-gap Tesla coils, primary-secondary coupling factor values typically fall between .12 and .16.

Using JAVATC, adjust your primary position to deterimine the heights that will yield coupling factors of .10 and .18. Then, design your adjustment mechanism with enough range of travel to reach these extremes, and you will almost certainly have enough adjustment range to optimize your coil's coupling factor.

You mentioned that you obtained some 18ga HV wire for the "SG". It would not be recommended to use wire this small anywhere in the tank circuit. Remember that every time the spark gap fires, the peak current in the tank circuit can exceed 100 amps, so you would be better off using heavier gage wire (I'd suggest #12 AWG minimum). You don't need HV insulation if you route the wire carefully. Also remember to keep all tank circuit wiring as short and direct as possible.

Don't waste your time with a single gap. Spend a little extra time and build a multi-gap array using 1/2" or 3/4" dia copper water pipe, with a total of at least three gap segments (four pieces of pipe). The quenching of a single segment gap will usually be very poor unless you build a high-velocity air-blast setup.

For a first coil powered by a 9-30 NST, I'd recommend 4" dia thin-wall PVC pipe (SDR-35) wound with #26, #27 or #28 AWG magnet wire. You'll find #30 AWG a real challenge to wind unless you build a winding jig and have some experience with larger gage wire. Make the form about 24" inches long, with a 20" winding length (about 1100 - 1400 turns). 3.5" diameter gray PVC electrical conduit also will work well; useful lengths of both the SDR-35 pipe and the electrical conduit can frequently be obtained at no cost from construction sites (ASK the site foreman!!).

When using a design tool (like JAVATC, etc.) to determine the resonant frequency of your coil, remember that "4 inch PVC pipe" is NOT 4" in OD, and 6" PVC pipe is NOT 6" in OD.

4 inch PVC pipe is actually ~4.22" in diameter, and 6 inch PVC pipe is ~6.28" in diameter.

Regards,
Herr Zapp

test_tube_tony

Wed Jul 14 2010, 12:51AM

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

thanks eastvolt, that pdf was pretty awesome. very easy to follow.

herr zapp, ill run some numbers with the 4" form. seems like the size vs length looks a little happier in my mind, as 3" seems a bit small. ill also look into the 3.5 size i just have to find the form. im a very visual type of designer with anything i do and things usually work out. tesla was the same way only to an unearthly extreme :) *snarls at j.p. morgan's name*. imagine where we would be today if tesla had found a deferent source of funding. its truly a shame. but anyway im off track. i started playing with the tesla coil cad program and i noticed it has a quarter wavelength resonant frequency number that it spits out. i hadnt heard this term before in my reading so i did some searching on the googles. seems it has to do with wireless power transmission if two identical coils are built but i cant seem to find a very good explanation of the hows and whys. wireless energy transmission seems like it would be something fun to play with tho so if i can incorporate it into the design it would be a bonus lol. one more question i have, is if the coil can in theory throw 20+" sparks, and the form is only 24ish" in total length, whats to keep all the sparks from nailing the primary/strike rail? do i have to keep them more than 20+" apart or do the sparks simply tend to not travel downward unless things are excessively close?

test_tube_tony

Wed Jul 14 2010, 05:10AM

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

cool im getting better at this. heres a to-scale string layout of the 4" tc design. max dimensions are 39" tall by 26" wide. ill probably change the base size tho. it seems a bit big but ill work on that when i get most of the parts together. the toroid is 15x4. im also depicting 20" sparks in the pic which i should be able to pull off with lots of ocd fueled tuning lol. hows the position of the 20" coil on the 24" form look compared to the height of the toroid? ive got it at 3" from the top and 1" from the bottom. or is the positioning not all that critical? the flange at the bottom will add about another .75" to the height so the primary should line up like it needs with plenty of primary assembly space. i assume i should run a nice hefty 3" or so piece of wire from the top turn of the secondary to the metal toroid? i cant imagine that running a little length of the magnet wire to it would be a good idea. this thing's getting expensive so im double checking my designs with you folks (the pros) first so i dont toast $200 or so haha.

1279083578 2970 FT92607 4 Inch Tc Layout

here are the pretty much final parameters except the primary will have 15 turns instead of 11.7439. i keep reading that its a good number for adjustability.

J A V A T C version 12.4 - CONSOLIDATED OUTPUT
Tue 13 Jul 2010 11:53:15 PM CST

Units = Inches
Ambient Temp = 80Â°F

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

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

----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
3.5 = Radius 1
9.377 = Radius 2
14.549 = Height 1
14.549 = Height 2
11.7439 = Turns
0.25 = Wire Diameter
0 = Ribbon Width 
0 = Ribbon Thickness 
0.0088 = Primary Cap (uF)
32 = Total Lead Length
0.1019 = Lead Diameter

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=4, major=15, height=37, topload

----------------------------------------------------
Secondary Outputs:
----------------------------------------------------
241.17 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)
1157.2 ft = Length of Wire
5:1 = H/D Aspect Ratio
48.0727 Ohms = DC Resistance
33281 Ohms = Reactance at Resonance
0.89 lbs = Weight of Wire
21.963 mH = Les-Effective Series Inductance
23.182 mH = Lee-Equivalent Energy Inductance
22.668 mH = Ldc-Low Frequency Inductance
19.829 pF = Ces-Effective Shunt Capacitance
18.786 pF = Cee-Equivalent Energy Capacitance
29.693 pF = Cdc-Low Frequency Capacitance
6 mils = Skin Depth
15.226 pF = Topload Effective Capacitance
127.4276 Ohms = Effective AC Resistance
261 = Q

----------------------------------------------------
Primary Outputs:
----------------------------------------------------
241.16 kHz = Primary Resonant Frequency
0 % = Percent Detuned
0 degÂ° = Angle of Primary
39.59 ft = Length of Wire
6.74 mOhms = DC Resistance
0.25 inch = Average spacing between turns (edge to edge)
1.367 inch = Proximity between coils
1.1 inch = Recommended minimum proximity between coils
48.454 ÂµH = Ldc-Low Frequency Inductance
0.0088 ÂµF = Cap size needed with Primary L (reference)
1.038 ÂµH = Lead Length Inductance
135.921 ÂµH = Lm-Mutual Inductance
0.129 k = Coupling Coefficient
0.129 k = Recommended Coupling Coefficient
7.75  = Number of half cycles for energy transfer at K
15.9 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
171.6 [peak amps] = Primary Instantaneous Current
23.7 [inch] = Spark Length (JF equation using Resonance Research Corp. factors)
55.6 [peak amps] = Sec Base Current

----------------------------------------------------
Static Spark Gap Inputs:
----------------------------------------------------
4 = Number of Electrodes
0.5 [inch] = Electrode Diameter
0.17 [inch] = Total Gap Spacing

----------------------------------------------------
Static Spark Gap Outputs:
----------------------------------------------------
0.057 [inch] = Gap Spacing Between Each Electrode
12728 [peak volts] = Charging Voltage
12718 [peak volts] = Arc Voltage
36593 [volts] = Voltage Gradient at Electrode
74810 [volts/inch] = Arc Voltage per unit
99.9 [%] = Percent Cp Charged When Gap Fires
5.159 [ms] = Time To Arc Voltage
194 [BPS] = Breaks Per Second
0.71 [joules] = Effective Cap Energy
275254 [peak volts] = Terminal Voltage
138 [power] = Energy Across Gap
26.3 [inch] = Static Gap Spark Length (using energy equation)

Voltage and Current distribution along the length of the secondary coil.
Length       Voltage        Current
0.00          0.00          8.2
0.2          1534.1          8.3
0.5          5137.7          8.3
1.2          13820.4          8.3
2          23455.4          8.3
2.7          33615.6          8.3
3.4          44081.4          8.3
4.2          54728.1          8.3
4.9          65479.7          8.2
5.6          76286.7          8.2
6.4          87114.7          8.2
7.1          97938.2          8.1
7.8          108737.2          8.1
8.5          119495.2          8.1
9.3          130197.9          8
10          140832.6          7.9
10.7          151387.5          7.9
11.5          161851          7.8
12.2          172212.1          7.7
12.9          182458.8          7.6
13.6          192578.7          7.6
14.4          202557          7.5
15.1          212375.8          7.4
15.8          222010.6          7.3
16.6          231425.7          7.2
17.3          240565.1          7.1
18          249334.4          7
18.8          257562.4          7
19.5          264904.7          6.9
19.8          267927.9          6.8
20          269215.6          6.7

Herr Zapp

Wed Jul 14 2010, 08:15AM

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

ttt -

The toroidal topload shapes the electroststic around the top of the coil, and will tend to direct the discharges outward, rather than straight down to the base of the secondary.

A three inch standoff distance from the top turn on your secondary to your toroid may be a little too much. Again, this depends on the diameter of your toroid, and how it shapes the electrostatic field around the top of the coil. If there is too much distance from the top turn to the toroid, the top turn will generate a lot of corona.

Your JAVATC data shows a 4" X 15" toroid; will this be spun aluminum, corrugated aluminum duct material, or ???

Regards,
Herr Zapp

test_tube_tony

Wed Jul 14 2010, 01:56PM

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

Herr Zapp wrote ...

Your JAVATC data shows a 4" X 15" toroid; will this be spun aluminum, corrugated aluminum duct material, or ???

if initial tests go well i'll purchase a nice machined aluminum one but for the time being ill probably use 4" corrugated aluminum duct material wrapped around something 7" in diameter. if i use a metal disk ill be sure to add it into the design. if i cant find a suitable metal disk i guess ill use some 1/4th" wood and cut out a circle. i just have to wander around the local home improvement stores to see what i can piece together. i chose the size base on availability, and it offered the almost right amount of capacitance according to tc cad for quarter wavelength operation (still not sure of exactly what this means). it was off by a couple tiny decimal points.

dmg

Wed Jul 14 2010, 03:46PM

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

Herr Zapp wrote ...

Your JAVATC data shows a 4" X 15" toroid; will this be spun aluminum, corrugated aluminum duct material, or ???

hmm, Herr zapp, does the surface of said torriod affect the resonant frequency to any noticable extent?

test_tube_tony

Wed Jul 14 2010, 03:59PM

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

i got the nst in the mail today. the paperwork says the transformer has a fault detection circuit that shuts off the unit if it detects an arc. seems to me like this could present a problem as the coil uses a spark gap. should i try to bypass or remove this circuitry?

edit:
i found another thread on this gfci nonsense. sounds like it may be pretty hopeless to modify it. there was no info either way about the gfci in the listing. should have asked i guess. oh well.

edit 2:
just for the heck of it i connected the hv leads to a test spark gap i made from a couple bolts and i do get arcing. maybe i got lucky and itl only shut off if it shorts to ground. i guess ill try using it and if things dont seem to work ill replace it.

Herr Zapp

Wed Jul 14 2010, 05:13PM

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

Gatedbreakdown -

"Hmm", no, the surface finish of the toroid doe not have a direct effect on the resonant frequency of the coil. The effective capacitance of the topload is what counts.

I was asking because I wasn't sure if ttt had just arbitrarily selected the 4" X 15" dimensions; these may not be "standard" dimensions for any commercially available spun toroids.

ttt -

Select your toroid dimensions to match the input power level of your coil. A larger toroid may ultimately give the longest single streamer, but a more pleasing appearance may be obtained with a slightly smaller toroid, which allows the coil to generate multiple simultaneous streamers darting in all directions.

Do some research (Tesla Coil Webring, etc.) on coils powered by single 9/30 NSTs, and see what toroid dimensions were used and what the resulting streamer appearance was.

Your new NST with the integral GFI may or may not be usable, depending if you can access and disable the GFI circuit. It may be easier to just obtain an older non-GFI NST. And, if you're going to get another NST, go for a 12/30 or 15/30. There should not be a huge difference in cost between these ratings for used NSTs.

Regards,
Herr Zapp

test_tube_tony

Wed Jul 14 2010, 07:13PM

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

ill definitely do some more research on the toroid. i have the nst hooked to a jacob's ladder setup. its 4" tall and at its closest point between electrodes its about 1/8th". had it running for several minutes. no issues noticed. like i said, ill try it with the initial setup for testing the tc. if it doesnt work out ill upgrade. if it works with no problem im golden. it does shut its self off if it arcs to ground tho which could be useful in a safety gap/protection setup.

edit:
im having more doubts about that transformer. ive found a way to make it trip quite easily. if i hold a nail in pliers and bring it very near one leg of the ladder when the arc breaks down you see a spark jump to the nail and it trips the gfci. im trying to land a 12kv 30ma proper nst. this ones pretty beefy looking. ive also found that if i add 5 more caps to the string i have already ordered it puts me at about .0002uf over for that supply. close enough lol.

quicksilver

Thu Jul 15 2010, 12:35AM

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

QUICK QUESTION ABOUT SECONDARIES & FUNCTIONALITY

My nephew is building a coil and his first attempt at a secondary is not too pretty. There are no kinks, but there ARE overlaps; quite a few. I hate to tell him he has to wind that thing over again if it's possible that it will function, but the amounts of overlaps are great. I know that kinks can create corona points, what problems is he facing with overlaps?
He saw mine and wanted to try to build one. He's a really fast learner & generally quite responsible with dangerous items but I am very far from knowledgeable on TC building idiosyncrasies.

I don't have a camera handy but basically it's 3" coil with tight 28awg coated wire with overlaps just about every inch; occasionally multiple overlaps. They are tight and the first layer of clear-coat lacquer made the unit quite solid - no slips of wire, it's firm.

Is it really a much better idea to have him re-wind a new coil form than attempt to push on with this? I was thinking that if the thing were coated heavily it may be OK. But I'm not sure, as I have not made one like this. He's 16 and just getting the concept:this is his first one.
If I need to tell him to wind it over, what is the reason why overlaps are ruinous?

Thank you

previous 1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob