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Calculating a tesla coil's resonant frequency?

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Dr. Dark Current

Tue Nov 12 2013, 12:31PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I would say so, killing a 6 kilowatt bridge is no fun, and the antenna driver sometimes produces random/undefined states during ground arcs.

StormInABottle

Tue Nov 12 2013, 12:42PM

Registered Member #9252 Joined: Fri Jan 04 2013, 06:27AM
Location: Andromeda
Posts: 253

I see.
Can you guys throw me a PLL control schematic that would be better suited for this?
And yes. Killing a bridge is not fun. Specially that those mosfets will dine on my money. That's why i will do low power testing using IRFP 460s. When i reach a stable condition i will switch onto the higher power mosfets.
(Removing a turn from the primary coil will make the coil more power hungry right?)

TwirlyWhirly555

Tue Nov 12 2013, 03:44PM

Registered Member #4104 Joined: Fri Sept 23 2011, 06:54PM
Location: Uk .
Posts: 122

yes , in a SSTC varying the number of primary turns will vary the current drawn

More turns = more inductance = less current draw ,
Less turns = less inductance = more current draw .

You should start off at a higher number of turns and reduce them as you go and stop at what you feel is safe for the inverter to output / switch

twist2b

Tue Nov 12 2013, 04:54PM

Registered Member #2086 Joined: Tue Apr 21 2009, 02:33AM
Location:
Posts: 117

StormInABottle wrote ...

I see.
I will make sure to put the primary right at the very bottom of the coil.
I plan my primary to be 6 AWG wire. Will be a pain to wind that's for sure.

Diameter of secondary coil : 12.00in
Winding height of secondary coil : 12.00in
Wire diameter for secondary coil : 0.01in
Spacing between windings : 0.00in
Secondary turns : 1200.00
Secondary wire length : 3769.91ft
Secondary inductance : 297.93mH
Approximate resonant frequency : 81.61kHz
Secondary quarter wavelength resonant frequency : 65.27kHz
Secondary self capacitance : 12.77pF
Toroid capacitance required to form quarter wavelength coil : 7.19pF

Tesla coil CAD told me all that.
The topload should get the resonant frequency down to 50-60 khz.
I will also mount the driver / control circuit on a pcb to minimize stray inductance and stray capacitance.

The coil is based on this

The control circuit has slight modifications. Like higher filtering capacitance and other diodes.
The full bridge sports shiny mosfets

Higher power diodes
C8/C9 are a string of 8 capacitors each
3000 UF filtering.
100 Amp , 1000 volt rectifier.
High wattage resistors.

All seems good :o?

HAHA! You would have a skin effect depth of 228.2162 um (micro-meters) (81.61kHz - just for safety of measurement I used the secondaries Fr to make decisions)
So with

AWG:AC Resistance
6:6.91433 Ohms
18:32.23073 Ohms
26:151.58234 Ohms
20:43.86964 Ohms
28:239.27048 Ohms
29:300.83076 Ohms
30:378.01742 Ohms
32:601.99992 Ohms
34:959.63591 Ohms

I take my original answer back... because you want to run CW so long I would actually suggest staying above 29AWG because you could avoid heat issues so drastically the farther you go up in AWG.. Also with a topload you are looking at even LESS resistance because the Fr goes down.

So if you calculate your output to your secondary you can choose the lowest possible AWG for your application.

I still think it doesn't have to be so drastically wide of a diameter but it might help with winding the guy...

StormInABottle

Tue Nov 12 2013, 05:28PM

Registered Member #9252 Joined: Fri Jan 04 2013, 06:27AM
Location: Andromeda
Posts: 253

I 've had experiences with 30 awg before. It's really sloppy but still manageable. Let alone 34 awg.. I'm not sure I will be able to find that.. LET ALONE WINDING IT
I MIGHT find it. But will the difference in efficiency be more than 50-100 watts?

HV Enthusiast

Tue Nov 12 2013, 10:16PM

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

StormInABottle wrote ...

I 've had experiences with 30 awg before. It's really sloppy but still manageable. Let alone 34 awg.. I'm not sure I will be able to find that.. LET ALONE WINDING IT
I MIGHT find it. But will the difference in efficiency be more than 50-100 watts?

30 AWG is very easy to wind. Its very manageable. 34 AWG much more difficult because the wire is much more fragile.

50-100 watts? Where is that number coming from?

Are you saying a secondary would dissipate that much heat as loss?? My 34 AWG secondaries are cool to the touch, even after long duration runs. Not sure where you are getting these loss numbers. That's a LOT of heat!

Dr. Dark Current

Tue Nov 12 2013, 10:38PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

EVR: We are talking about CW coils here. With such, it is almost an impossible task to keep the secondary from melting during longer runs, without forced air cooling. 100 watt loss for a moderately sized coil seems reasonable, maybe more.

twist2b

Wed Nov 13 2013, 01:36AM

Registered Member #2086 Joined: Tue Apr 21 2009, 02:33AM
Location:
Posts: 117

Right, there is no break like pulsed Tesla Coils.... since we are working in khz 60,000 times a second makes a big difference than 100,000 times. 6 AWG should have a good thermal covering too, so that should be helpful....... The more we talk about this kind of TC the more I am getting excited.
StormInABottle - can you post pictures of the results? :D

StormInABottle

Wed Nov 13 2013, 05:43AM

Registered Member #9252 Joined: Fri Jan 04 2013, 06:27AM
Location: Andromeda
Posts: 253

Sure. I will try
Dr.dark current
I want to decrease the heat / eddy current as much as possible
Also I've got exams so the project will get slightly delayed
Sorry if my grammar is bad. Writing on a mobile phone atm

StormInABottle

Wed Nov 13 2013, 10:29AM

Registered Member #9252 Joined: Fri Jan 04 2013, 06:27AM
Location: Andromeda
Posts: 253

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