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building my first sgtc

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SilentPhoenix

Sun Jan 27 2008, 09:12PM

Registered Member #1258 Joined: Wed Jan 23 2008, 11:52AM
Location: Haarlem, Netherlands
Posts: 20

i have found my copperwire and the form for the secondary and started winding. right now i have 1000 turns of 24 awg wire wound on an 8 cm diameter form giving me 55 cm wind height.
i have some copperwireleft on the spool, is it preferred to wind some more turns? teslamap's audit says that the ratio (7:1) is rather high, is this negatively affecting my coil's functioning?
btw i've decided to use just the 8kV transformer rather than putting the two in parallel.

Shaun

Sun Jan 27 2008, 09:25PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

7:1 is rather high; I would say 5:1 at most for a coil of this power. Don't worry too much over the exact # of turns, as long as you are in the ballpark it won't affect your coils performance.

And if your NST is large and heavy, then yea its the right type. Switchmode NSTs are tiny plastic boxes.

For your capacitors, bottle caps will work. However, they are bulky and heavy and can be messy to work with. It would be easier to spend the extra $40 or so for a bunch of those CDE942C caps. Then you dont need to worry about measuring the capacitance either. Its just that you said this is a demo coil for school, meaning you are gonna need to be able to cat it around easily.

Ultra7

Sun Jan 27 2008, 10:57PM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

There is always the party cup cap. . .

I personally use the 942's, and have never had any issues with them, but for a nice cheap cap, the party cup works like a charm.

Logan Kennedy

Mon Jan 28 2008, 01:07AM

Registered Member #1103 Joined: Mon Nov 05 2007, 06:02PM
Location: Houston
Posts: 80

Shaun is right. The ratio should be close to 5:1. I use 4.5:1 for most of my coils. This ratio seems to provide the best bang for my buck.

Try to wind around 900-1200 turns. Anything higher and the resistance of the secondary becomes too high.

If you do decide on using the party cup capacitors, please be sure to enclose them in something. People might begin to ask too many questions. ;)

Ultra7 wrote ...
Ahhh, but notice I didn't say LONGER sparks, just bigger sparks.

You're right! Sorry about that.

Shaun

Mon Jan 28 2008, 03:20AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Oh yea, I forgot about the party cup cap...apparently its gotten a lot of positive feedback since I last heard about it...

Although the party cup capacitor makes a very strong argument against the CDE caps just because of the price (less than $1 compared to 10s of dollars), I would rather pay for the reliability.

SilentPhoenix

Wed Jan 30 2008, 11:12AM

Registered Member #1258 Joined: Wed Jan 23 2008, 11:52AM
Location: Haarlem, Netherlands
Posts: 20

it looks like my messages aren't being posted or keep getting removed but i'll try to post this for the thirth time now:

i've used the bottle cap because i try to minimize the costs as much as possible but if i'd have known about the party cup cap i definitely would've tried that! right now i measured the capaccitance of the bottle cap and the meter indicates 1,320 nF where the formula

i used from deepfriedneon sais i should have 0,0198 uF (= 19,8 nF) to match my 8kV/50mA transformer...
i have three bottles in parallel in the current set-up so i tried measuring only one since it should have higher capacitance but it doesn't, it shows 0,500 nF. is there an explaination for that? i disconnected the cable at the top but the bottom of the bottles is still connected, could this be the reason of my problem?

also i was wondering if there's a minimum/maximum distance between secondary and topload... can't i connect the topload to the secondary and place it 30 cm above it to minimize primary strikes? because i'm under the impression that the coupling is between the prim and sec coil and the topload is just a capacitor. if this is true then it should be possible. am i missing something? has it been tried?

i have almost all my parts now, transformer, cap, sec. coil, sg, i only need my topload and my primary but i'm working on that. so far, the costs are only 10 euro's and i would really like to keep it that way so i'm looking for free/spare/old parts from friends and local stores.
i'm trying to figure out my primary now but i'm having some trouble... teslamap keeps saying that i need an awfull lot of turns or that it can't be tuned...

Ultra7

Wed Jan 30 2008, 02:08PM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

SilentPhoenix wrote ...

also i was wondering if there's a minimum/maximum distance between secondary and topload... can't i connect the topload to the secondary and place it 30 cm above it to minimize primary strikes? because i'm under the impression that the coupling is between the prim and sec coil and the topload is just a capacitor. if this is true then it should be possible. am i missing something? has it been tried?

I have tried moving the topload differing distances from the top of the secondary.
The higher you get, the more corona you get from the last turn of magwire you use to connect the topload, and it seems that the sparks get smaller from the topload. I had mine originally connected to a ball electrode and because of the long bolt attached to the bottom I had to have it about 8 inches away from the last turn and the corona from the wire was brighter than the spark from my breakout point on the ball. I chopped the bolt short, and shortened my last turn and after a retune, 14 in sparks were coming from the breakout and almost no corona from the wire. after I built my big toroid, and a hefty re tune, I got no corona from the wire and 26 inch sparks. I think the distance from the last turn to the topload is something you will like to play around with as it will be a learning experience.

As for Teslamap telling you that you need a large number of primary turns or unable to tune. . .
Can you copy and past the print file to the post so I may have a look at it?

I will gladly look over your design and offer my help.

-=Ultra7=-

SilentPhoenix

Wed Jan 30 2008, 02:58PM

Registered Member #1258 Joined: Wed Jan 23 2008, 11:52AM
Location: Haarlem, Netherlands
Posts: 20

sure, here's the text export from teslamap.
i haven't added a topload yet because i haven't figured out wich type is easiest and cheapest to build, i might even test it without a topload...
i used the 0,2 wire because i had it lying around, i'm looking for something a little thicker but still flexibel but it's hard to find.
i noticed that if i put the primary angle on 300 (wich results in a 60 degree downward angle) that it is tuned at 5/6 turns instead of the 17/18 it's giving now.
the 24awg that's indicated is not 100% right, they dont use AWG standard here so i took the closest. the diameter of my wire is 0,531 mm.

i hope you can find some flaws that are easy fixable so i can improve the design. i have almost all the parts lying around here, just the primary and the safety gap. and perhaps a topload... can i just roll some aluminium foil into a ball and use it as a topload for now?

specs:
8kv setup
30-1-2008

---------- Power Supply ----------
NST V Out 8 kV
NST I Out 50 mA
NST Input V 230 V
NST Input F 50 Hz
NST VA 400,0
NST Watts 412,0 W
NST Impedance 160 Kohms
Max Arc Length 34,5 in
NST PFC Cap 24,1 uF

---------- Primary Capacitor ----------
Your Cap 1.320 nF
Resonate Cap 19,9 nF
LTR Static Cap 27,9 nF
LTR Sync Cap 37,8 nF

---------- Secondary Coil ----------
Single build magnet wire
24 AWG
Wire Length 245,9 m
Wire Weight 0,99 lbs
Wire Resistance 20,7 ohms
Coil Height 53 cm
Coil Diameter 8 cm
Coil H/W Ratio 6,6 : 1
Coil Turns 978,8
Inductance 10,66 mH
Capacitance 7,54 pF

---------- Top Load ----------
Overall Diameter (1) unknown
Ring Diameter (1) unknown
Overall Diameter (2) unknown
Ring Diameter (2) unknown
Sphere Diameter unknown
Top Load Adjustment 95 %
Top Load Capacitance unknown

---------- Top Load + Secondary ----------
Resonate F 542,75 kHz

---------- Primary ----------
Wire Diameter 0.2 cm
Wire Spacing 1 cm
Hole Diameter 10 cm
Coil Angle 0 degrees
Coil Adjust 90 %

Needed primary inductance with:
Your Cap 40,93 uH
Resonate Cap 2,72 uH
LTR Static Cap 1,94 uH
LTR Sync Cap 1,43 uH

Turn 1 0,2 uH
Turn 2 0,7 uH
Turn 3 1,6 uH
Turn 4 2,8 uH
Turn 5 4,3 uH
Turn 6 6,3 uH
Turn 7 8,6 uH
Turn 8 11,5 uH
Turn 9 14,8 uH
Turn 10 18,6 uH
Turn 11 23,0 uH
Turn 12 28,0 uH
Turn 13 33,6 uH
Turn 14 39,9 uH
Turn 15 46,9 uH
Turn 16 54,6 uH
Turn 17 63,1 uH
Turn 18 72,3 uH
Turn 19 82,4 uH
Turn 20 93,4 uH
Turn 21 105,3 uH
Turn 22 118,2 uH
Turn 23 132,0 uH
Turn 24 146,8 uH
Turn 25 162,7 uH

---------- Design Notes ----------
No Notes

-- End Summary --

*edit: i forgot to paste the specs...*

Ultra7

Wed Jan 30 2008, 03:21PM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

Teslamap will tell you "Unable to tune" if you have not entered in any topload data.

The easiest to build is the dryer duct/Pie pan toroid but if you can get your hands on a Flagpole topper Ball, you can use that too.

Just so you can get an idea on where to tune, just input toroid data on the topload tab with say 4 inch ring and 16 inch total.

Also, you might need to add a few more bottle caps to raise your capacitance.
I played with your numbers and came up with 8nF as just a ballpark figure and have you in tune at turn 9-10

SilentPhoenix

Wed Jan 30 2008, 04:14PM

Registered Member #1258 Joined: Wed Jan 23 2008, 11:52AM
Location: Haarlem, Netherlands
Posts: 20

i was under the impression that the capacitance would decrease when i put more in parallel? but i'll give it a try.
i'll see if i can find the pie pans somewhere... dryer duct shouldn't be a problem...

*edit* btw, if you fill in any value for topload and then remove again it will keep calculating in the tuning screen... i beat the system :P */edit*

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