Air-Core Transformers with applications in Tesla Coil design
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 21st March 2010, 08:27 PM #1 thadman   diyAudio Member   Join Date: Dec 2005 Location: west lafayette Air-Core Transformers with applications in Tesla Coil design YouTube - Tesla Guitar demonstration As you're probably aware, Tesla Coils are pretty ridiculous. I've done some research with regards to the underlying mechanisms and am interested in potentially building one. It appears a fundamental component of the Tesla Coil is its transformer. I'm interested in designing an Air-Core transformer. However, I'm not sure how to calculate the coupling coefficient (k) for a given geometry. Could anybody offer further insight on this? If we are able to define the Q factor and resonant frequency (f0), would design be fairly straightforward? What other variables should an engineer consider? Temperature is obviously a factor. How close is the behavior of real world transformers compared to simulations? Would it simply be a matter of winding two coils around an insulator (ie cardboard, plastic, etc)? At this point I'm just interested in creating an electrical resonator (electrical input / output) with a given resonant frequency and Q factor. Shouldn't I be able to easily measure its behavior with an Oscilloscope? Intuitively I would assume the coupling coefficient affects the amount of leakage inductance. Would it have any effect on the resonant frequency or the Q factor? Would it be desirable to maximize the coupling coefficient? What geometries would achieve this? Thanks, Thadman __________________ "It is a profound and necessary truth that the deep things in science are not found because they are useful; they are found because it was possible to find them."
 22nd March 2010, 12:01 AM #2 Sch3mat1c   diyAudio Member     Join Date: Jan 2003 Location: Milwaukee, WI k is very, very roughly the ratio of cross sectional areas. For a tall secondary inside a short primary, it will be less (because the top end sees hardly any of the primary / the flux lines are not vertical). You can test small signal performance quite easily with a sweep generator and oscilloscope, or spectrum analyzer, or network analyzer, or etc. With sufficiently weak coupling, you can tune the primary and secondary independently, and you'll see gain as two humps if they aren't tuned equally, flat-topped if adjecent, or one sharp peak if very close. Q multiplication is a series-resonant thing. I don't really know how much use it is for a low-k transformer. The low k looks like a big series inductor, which can resonate with some of the parasitic capacitance; the remaining capacitance is parallel resonant with the secondary's self inductance. Thus, it looks something like an LLC network, which is series-parallel resonant. Add a parallel resonant primary and you've got at least five elements in the equivalent circuit. Notice two things: one, the voltage will NEVER "ring up and increase without bound". Q is always finite and therefore the voltage for a given power input is well-defined. Two, when voltage reaches breakdown, Q goes to pot, so for all your small-signal tuning, it doesn't really mean much, because all those sparks are going to smear it out quite nicely. I don't know how much value there is in low-k Q multiplication (in terms of attaining a voltage gain higher than N2/N1). It seems to me you'll get fine performance just blasting amps into a transformer. You can tune it if you want, and you probably should, since these turns ratios make for big reflected capacitance. By working with transformer action, you don't have to worry about tuning different components, and you can get much hotter sparks out by enforcing a constant-voltage characteristic (or by driving it series-resonant, you can safely limit inverter current while retaining the high-O/C-voltage characteristic). As for air-core transformers, they're perfectly calculatable, if you don't mind doing an insane amount of computation. Using a suitable model in an E&M simulator, you can get numerical results arbitrarily close to reality. Using a cheezy model, you can get "close enough" results. Using a circuit model, you can get similar results, making whatever assumptions of topology you like. In "close enough" terms, you can get excellent results from a lumped-constant model consisting of the secondary's parallel RLC equivalent, the series leakage inductance, and the primary's RLC equivalent, plus whatever you're driving it with (constant voltage, resonant, coupled, etc.?). Tim __________________ Seven Transistor Labs, LLC Projects and Resources / Electronic Design and Consultation
 29th November 2010, 01:56 PM #3 ontoaba   diyAudio Member     Join Date: Nov 2009 Location: Kudus, Malang, Dieng The magnetic field is only around primary, but it is creating electromagnetic field that transfered and trapped at secondary. It is wireless power transfer that he applied to radio.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         Dx Classic Amplifiers         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post Workhorse Solid State 14 4th April 2016 01:26 PM slhijb Multi-Way 16 20th November 2009 03:12 AM poolorpond Pass Labs 24 29th March 2008 10:55 PM gearheaddruid The Lounge 5 22nd March 2008 09:10 PM gnomus Swap Meet 0 30th July 2004 01:28 AM

 New To Site? Need Help?

All times are GMT. The time now is 04:07 PM.