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First Tesla Coil, help appreciated!

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Jonathan Dennis

Thu Jun 04 2009, 08:05PM

Registered Member #2153 Joined: Wed Jun 03 2009, 03:19PM
Location:
Posts: 69

So there is no "safe" way to test the NST until I have all the components of my coil wired up?

Herr Zapp

Thu Jun 04 2009, 08:23PM

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

Jonathon -

I think you need to do some background research on Tesla coil design, theory of operation, construction details, etc, etc, etc. before you actually try to start building a Tesla coil. If you don't know how to power up a neon sign transformer and determine if it is "working", then you won't be able to deal with the far more complicated aspects of building and tuning a Tesla coil.

One easy thing you can do is just read through the thread "Getting the Ball Rolling..." in this forum. Blitzorn started out two weeks ago almost exactly where you are today, and has asked many of the questions that you will ask as you get ready to build your first Tesla coil.

As for "testing" your NST, perform the following:

Connect the transformer's primary terminals to an AC linecord. (if you have a variac use it to control input voltage for these tests.) Connect a piece of stiff, solid wire (#12 or #14 household wire, coat-hanger wire, etc) to each HV bushing, and form the wires so the free ends are about 3/16" to 1/4" apart. This is a spark gap that will provide visual evidence that the transformer is generating HV output. Plug in the AC linecord, and apply line voltage (or slowly crank up the variac), and there should be a continuous, bright blue arc between the ends of the wires. Unplug the transformer, and re-form the ends of the wires so the are at least 2" away from each other, and the end of each wire is about 3/16" to 1/4" from the NST's metal case. Again apply power; there should be a continuous blue arc between the end of each wire and the transformer case.

Keep your hands away from the wires during this testing; 12,000V will deliver a shock that you will not quickly forget.

Regards,
Herr Zapp

Jonathan Dennis

Thu Jun 04 2009, 08:39PM

Registered Member #2153 Joined: Wed Jun 03 2009, 03:19PM
Location:
Posts: 69

Thank you, and I have been doing non stop research for the past week. I just wanted to ask an expert to assure that I don't damage my NST, as it would be difficult to find another one.

WinTesla calculated my secondary to have 1,603 turns, several websites recommend not exceeding 1000 turns, will it affect performance?

Herr Zapp

Thu Jun 04 2009, 10:37PM

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

Jonathon -

If you've already "designed" your coil using one of the Tesla coil design applications, please post all the dimensions and parameters here for review. There's no way to effectively critique the design unless we know ALL the information.

Typically, Tesla coil secondaries have between 800 and 1200 turns. 1600 turns sounds "high", unless you intend to use very small wire gage (difficult to wind), or have an extremely tall secondary coilform.

A secondary "aspect ratio" (length-to-diameter ratio) of around 5:1 has been found to work well. With your 12/30 NST, a 3.5" or 4" diameter secondary coilform would be appropriate.

Provide the coil design data, and we can help you optimize your design before you get too far along.

Regards,
Herr Zapp

Jonathan Dennis

Fri Jun 05 2009, 02:59AM

Registered Member #2153 Joined: Wed Jun 03 2009, 03:19PM
Location:
Posts: 69

Primary Transformer
Input Voltage 250VAC
Output Voltage 12000VAC
Output Current 0.030Amps
Input Frequency 60Hz

Capacitance for Transformer Z Match 0.0066uf
PFC Capacitance 11 .4595uf

Primary Design
Inside Diameter 7.0in Average Radius
Wire Diameter 0.250in Total Diameter
Wire Spacing 0.200in Wire Length
Total Turns 10.0
Secondary Res Freq
Inductance O.0346mh Primary Cap to Res
Angle of Windings Odegrees
5.75in
16.00in
29. 58ft
163.9456khz
0.0272uf

Secondary Design
Diameter 4.00in Radius
Length 20.00in Circumference
Gauge 28 Wire Length
1/4 Wave Length (without top load C)
Turnsllnch 75.16 HID Aspect
Total Turns 1458.07
Inductance 39.01 mh Res Freq 283.00khz
Medhurst_K 0.80
Res Freq WI Toroid 163.95khz
SelCC 8.11pf

Top Load C 16.05pf
1/4 Wave Length
2.00in
12.57in
1526.89ft
869.47ft
5.00
1500.88ft

Does that look okay?

Blitzorn

Fri Jun 05 2009, 04:25AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

if you are in tennessee then the wall socket is only going too give you 120VAC input... do you have a step up transformer to connect before your NST?

Herr Zapp

Fri Jun 05 2009, 04:31AM

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

Jonathon -

If I understand your data, your 10-turn primary will require a capacitor value of .027uF.

What type of capacitor do you intend to use (salt-water bottle cap, MMC, rolled polyethylene, etc)? Have you calculated how many bottles, how many MMC caps, etc will be required to yield .027uF? And the associated cost?

You might want to add more primary turns to bring the required capacitance down to ~1.4X the "resonant" value (1.4*.0066 = around .009 or .01uf).

Using your Tesla coil design application, increase the primary length and watch what happens to the capacitor value. Also, with a 30ma transformer you really don't need to use 1/4" copper tubing for your primary conductor, you can get by with #12 AWG solid wire, and reduce the turn-turn spacing so even though you have more primary turns, the overall size of the primary doesn't get too large.

You can also reduce the inner diameter of your primary to 6" without too much risk of primary-secondary flashover.

Regards,
Herr Zapp

Jonathan Dennis

Fri Jun 05 2009, 05:18AM

Registered Member #2153 Joined: Wed Jun 03 2009, 03:19PM
Location:
Posts: 69

I plant to use a MMC, was unsure how to make the primary in such a way to reduce my required capacitance. Also, I already have the copper tubing laying around, that's why I was going to use that.
The transformer is actually a 120 VAC, the 250 VAC was an error. I am just going to splice an old cord and use our houses ground. Is there any chance it could leak and damage anything? If so I will avoid using our homes ground.

Jonathan Dennis

Wed Jun 10 2009, 10:45PM

Registered Member #2153 Joined: Wed Jun 03 2009, 03:19PM
Location:
Posts: 69

I am getting close to the completion of my FIRST coil! I am so excited to see how it will run. I just finished winding my secondary, and have one question. I have a 4" diameter and 24" of coil. I know that the 5 to 1 ratio means I should stop at 20, but I thought 4 extra inches couldn't hurt. I have not cut the wire yet, and wondered if I could wind even more, seeing as how the roll still has plenty of wire. I don't know how making the secondary longer will affect my performance. Will it hurt or help?

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