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Avalanche

Sun Nov 12 2006, 06:53PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

48hr double post...

I'm not having much luck with using a primary. Using config 'B' from the picture below, I can get a tube to light again, but that's about all, no breakout. I've tried both methods below, and I'm not sure which is best. I think richie uses config 'A', but his site seems to be down still. So how is everyone hooking the primary up? I've drawn both methods I've tried so far, and I don't think I'm missing anything?

Another odd thing I am seeing is a 24Mhz signal between D-S when I put it under load. Could my whole setup be oscillating because I have added extra gate capacitance?

This thing's a nightmare

Marko

Sun Nov 12 2006, 06:59PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I used primary itself as RFC (b schematic). It seems to work as well as richie burnett design (amp separate from primary), only it needs good decoupling cap close to mosfet, and all inductance 'after' the cap counts as your primary leakage inductance.

Your coil must be mistuned if you aren't getting any sparks, no matter of class-e tunage.

Use long wire to move the breakout point away from topload.
What power/voltage are you putting into coil?

With my config I was getting 4cm sparks with some 20V in.

PS. you may sometimes double-post as this is only going to make steve conner post something funny and merge threads..

Just kidding, don't do it actually..

Avalanche

Mon Nov 13 2006, 12:11AM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

It must just me my mistuned coil then... although I am only putting in 13.8 volts. I'll just use config 'B' then and try a decent decoupling cap. And a tuned coil.

I won't make a habit of double posting, but I think it was legit (or at least bordering on

)

Marko

Mon Nov 13 2006, 12:26PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Posting 48hrs after last post is allowed, but before that isn't.

Decoupling cap must be polypropylene, and possibly something better than single metallization (high continuous currents) for low ESR.

Other types heat up like nuts, change capacitance and frequently blow everything up after detuning away enough from class E.

Are you using feedback or oscillator to drive the coil?

Avalanche

Mon Nov 13 2006, 12:41PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I'm using a crystal oscillator to drive it.

I'll have to get a few decent capacitors I guess, I'm just using whatever I can find at the moment. Thanks for the help!

Steve Conner

Mon Nov 13 2006, 12:47PM

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

We do take the no-bumping rule seriously. I might "Post something funny" but, along with all the other moderators, I keep a tally of how many double posts each user has to their name, and too many gets you pwn't.

Marko

Mon Nov 13 2006, 08:42PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Avalanche wrote ...

I'm using a crystal oscillator to drive it.

I'll have to get a few decent capacitors I guess, I'm just using whatever I can find at the moment. Thanks for the help!

I think it's really easy to set up antenna feedback, just use a 74HC14 or something similar in place of your crystal.

You'l have problems with startup, though, so <ou need some simple oscillator to 'ping' the system while it's 'out of lock'.

You can maybe just keep the existing crystal osc and weaken it's signal enough that antenna easily overrides it.

If you plan to continue using oscillator, you'l have to slowly remove turns from secondary until you get best tune.

You can also use a trick with telescopic whip antenna topload, wich you can pull in or out for finetune.

ragnar

Wed Nov 15 2006, 03:13AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

The fact my signal generator goes nuts when I run this coil really, really isn't helping, BUT:

Here's first light from the 13.56MHz coil:

Very hot lil arcs... but I'm drawing 2A at 22V to get this to happen -- I think it'll be hopeless until I can get the class-E tuned correctly... and stop the siggen going crazy every time I approach Fres. =D

Still, it makes sparks!

...

Wed Nov 15 2006, 05:44AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I can concur that frequency generator going crazy when you hit resonance is very much not cool. Like hot as plasma not cool

I blew out at least one fullbridge cos of that

I had a bridge made of irfp250's and was running ~50v in, sweeping the frequency around (I needed a finer knob on my sig gen) when I managed to get it really in tune, but then the gen went crazy and sent it far enough out of tune to blow up the bridge in all of the flaming glory you love (although I had the foresight to include a fuse as to prevent the ripping the cord out of the wall)

Hmm, only 40w for like 1mm... You are approaching my all time record of 5" off 1.4kw

ragnar

Wed Nov 15 2006, 07:50AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

I tweaked the shunt capacitor to 63pF (40kV :P) which makes the coil a lot more stable. It's interesting how big the shift is (~1MHz) between drawing an arc from the coil, and then tuning it to emit corona by itself. The system really has to be started at a different frequency from where you intend to run it.

The first breakout and corona has to be coaxed out with a knifeblade or similar. I also increased the drive voltage to 32V and it's drawing ~1.4A in these pics. The class-E operation seems almost spot on with the new capacitor(s), but something's still not quite right -- my gate waveform is much spikier, with a much lower duty (as a result of me putting in a UCC37321 instead of UCC37322 in my signal generator), and only hits about 10V peak.

To get a proper 50/50 duty cycle I'm going to try and go for a 74HC14 oscillator which won't drop into weird modes (even when grounded, pin2, pin9 and pin14 on the PLL chip is going nuts just by being nearby)... and I guess when I want audio modulation, I'm going to have to do it properly (class-G or class-H modulator)...

Even though there's a long way to go, first (and second) light is very rewarding!

This is one HOT lil' breakout.

What do you guys think?

This is the DS waveform, 40nS/20V per div., supply voltage is 32V.

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