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my secondary coil, is this OK?

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Coronafix

Mon Aug 31 2009, 01:03AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

I may have missed it somewhere but what are you using to drive your tank circuit? An NST? If so, then you can calculate the correct cap value quite easily.
Resonance is a function of an inductance (L) and a capacitance (C) together. It has nothing to do with the spark gap distance. You tune a coil by adjusting the primary inductance.

raff

Mon Aug 31 2009, 03:45AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

hi Coronafix

im using flyback driver(mazzilli) as input for SGTC..

this will be my 1st SGTC (or in general , a tesla coil)

how do I know if my tesla coil is IN RESONANCE?

I know for sure one of them is LONGER spark output

Coronafix

Mon Aug 31 2009, 08:17AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

raff wrote ...

im using flyback driver(mazzilli) as input for SGTC..

In that case calculating the correct cap for that isn't so easy. I think the cap you are using will be fine.

To calculate the resonance you need to work out what the secondary frequency will be. This will be a
combination of the inductance of the secondary, its self capacitance and the capacitance of your topload.
Then plug the frequency and your chosen capacitance value into the resonance equation to work out what
inductance you need. Wind a primary with enough inductance and give it room to move because the frequency of a
coil drops slightly as it creates sparks, so adding 10% inductance to the calculated usually works better.

This is where tesla coil calculators such as JavaTC really help.

A list of the equations,

raff

Tue Sept 01 2009, 01:40AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

Coronafix,

Mads has calculated my secondary winding to be resonating at aroung 640KHz... now I have used deepfriedneon site to calculate for my primary LC.. my cap measures 7.8nF on the LCmeter... the calculator says its around 634KHz with L=9uH C7=nF .... is this my proper way of calculating/tuning it?

no problems measuring L on the primary coil once its in place because I have my LC meter in hand..

Coronafix

Tue Sept 01 2009, 03:57AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

I plug your numbers into Javatc and get 685kHz for your secondary, but once you have a topload this frequency will be lower depending on the size of it.
If you use javatc it will tell you how many turns you need, just tick the "allow javatc to tune my coil" box.

raff

Tue Sept 01 2009, 06:00AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

guys,

here is another mockup... secondary 640-685KHz reso

I will have a go at helical primary first..

primary = L 9.xxuH / C 7.8nF = 593KHz (not quite close enough) I think ill have to reDO my helical primary.. it was 8T.. will try 7.5T or 7T.... wish this primary was BARE so I could just TAP into it

as for this topload, its NOT done yet..and its HELD by a plastic screw(bolt/nut found on toilet seat covers LoL) I still have to PUT "something" in the sides so it could be like a torroid.. maybe a crumpled aluminum foil and made into a ROLL so I could put it in the "sides"

still not sure what to put in there.. also shown my flyback driver(done in IRFP250) in its board.. together with the DC flybaCK and my cap...

starting to look like a tesla coil

hahaha

Coronafix

Tue Sept 01 2009, 07:20AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

The output of your flyback will be DC. This changes things somewhat as you will need a charging reactor.

Someone correct me if I'm wrong here.

Steve Conner

Tue Sept 01 2009, 09:22AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

In practice, people seem to just hook the output of a DC flyback across the spark gap of a Tesla tank circuit and it works fine. The flyback is naturally current-limited so it charges capacitors happily.

raff

Tue Sept 01 2009, 10:22AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

guys,

can someone pls explain whats the importance of adjusting the sparkGAP? is it part of the fine-tuning process?

Coronafix

Tue Sept 01 2009, 10:43PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

The adjustment of the sparkgap is for setting the voltage that the cap will charge to. The spark will jump across the gap when it gets to a certain voltage.

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