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3mhz Class-E coil try 2

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cjk2

Sun Apr 12 2009, 04:53PM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

About a year ago, I decided i wanted a class e coil. I made a nice secondary with maybe 200 turns of 23awg magnet wire. I have found that it resonates at almost exactly 3mhz. This seems like a nice frequency because it is not too hard to drive, but probably out of the range of what is practical without class e.

My first attempt at class e was a failure, probably because I was inexperienced and used a hex inverter based driver. I have always had bad luck with the simple [antenna > buffer > UCC > GDT > MOSFET] drivers so i decided to try a PLL this time. I have to say, now that Ive tried PLL ill never go back.

Feeding the coil 12v, i was able to get breakout. The coil is likely not in perfect class e tune at this point, but Ive gotten up to 24v (mains isolated) in with only moderate heating. The secondary coil actually gets rather hot so i may either need a redesign or to operate at a lower duty cycle to keep heating down. My circuit is based on Steve Connors design. Audio modulation seems to work well on this coil. As soon as i get breakout I can inject audio and hear it pretty clearly in the corona.

One of the major goals of this coil was to run it unisolated from mains. It seems silly to build a tiny SSTC and then lug around a big isolation transformer to make it work. The driver i designed should allow me to power the output section of the coil from 170v of unisolated mains power.

Here's audio modulation:
http://www.youtube.com/cr99991

Does my circuit look good?
Any thoughts on working with unisolated mains?

Arcstarter

Sun Apr 12 2009, 05:14PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Hey, it looks great! I love small high frequency class E coils.

You might want to use 12 volts to the PLL IC though. It is rated for i think 1mhz at 5 volts, but 2.7mhz at 15. All i know is that the higher the voltage the better, for high freq. Unless the gate drive chip cannot handle a 12 volt input.

cjk2

Sun Apr 12 2009, 05:20PM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

My PLL is rated for 14mhz max at 5v. Its an MC74HC4046N.

aonomus

Sun Apr 12 2009, 06:01PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Nice job cjk2, it looks like its going to be a very neat and tidy minicoil...

If you want to use unisolated mains, a variac will result in variable power, but if you are confident that you can run it at full power (and want no specific control), just add a tiny 12V transformer into the enclosure.

Alternatively you could use just a DC powersupply at low voltage, but then you get the craving for bigger sparks.

Don't forget to heatsink the rectifier bridge...

cjk2

Sun Apr 12 2009, 06:40PM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

I plan on using a variac, I guess I just don't want the isolation transformer. Id like to eventually use no variac, and set my interrupter for a very low duty cycle. Im heatsinking everything to the aluminum box, which is .125" thick.

Im about to go mill holes in my box for input and output, wish me luck!

uzzors2k

Mon Apr 13 2009, 01:36PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Looking good so far. I have problems with heating of my secondary too, at only 1.4MHz. I'm not sure if it's the excessive skin effect in the secondary wire, or dielectric losses in the former, but it would melt my secondary if I let the coil run for too long.

You guys need to sharpen up your prefix use, it's M for 10^6, m is 10^-3. That's an error in the order of one billion, not a petty mistake.

MRacerxdl

Mon Apr 13 2009, 05:40PM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

I made one 1.5Mhz coil, and I did have heating problems, but that was because the power that I was running it... It have been 600W with 1.5Mhz at 36AWG Wire =P

Proud Mary

Mon Apr 13 2009, 09:58PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

That is an interesting piece of work.

I see you have a note on the primary saying "optional tune" - were you thinking of putting a variable capacitor etc there?

uzzors2k

Tue Apr 14 2009, 01:07PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Sometimes a small portion of the primary is uncoupled from secondary in order to adjust the primary inductance without affecting coupling, so it's just a minute inductor as shown.

Proud Mary

Tue Apr 14 2009, 01:41PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thank you, Eirik!

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