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It's time for an SSTC

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Ken M.

Tue Oct 16 2007, 07:51PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

IF by "tightly couple" you mean, how close can you make the primary and secondary? As I said before I have them ontop of each other.

How ever if you mean "tightly couple" as in magnetic coupling to increase mutual inductance I don't think too much considering the skori coil I have, has a gap of about 1/2" and another1-11/2" down the pvc pipe and I still get some primary to secondary arcing through the insulation.

Dr. Dark Current

Sat Oct 20 2007, 11:44AM

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

OK, as I now got it working reliably, I wanted to draw some arcs. It didn't blow a FET as before, but as the streamers start hitting the ground electrode, they become very thin sparks. Why is this?

Ken M.

Sat Oct 20 2007, 12:15PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Thin? Mine get thik as hell almost MOT style just really long, the only time when i got small sparks was when I had it set to think spark pulses flyback style.

Dr. Dark Current

Sat Oct 20 2007, 01:49PM

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

WhiteArc wrote ...

Thin? Mine get thik as hell almost MOT style just really long, the only time when i got small sparks was when I had it set to think spark pulses flyback style.

Are you using CT or antenna? I'm now running halfwave CW with start-up osc and CT with a circuit I posted before.

Here's a video with ground sparks, they get almost invisible!
]1192888198_152_FT31895_pict0185sparks.avi[/file]

Tom540

Sat Oct 20 2007, 06:28PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Posts: 617

It Looks like you're detuning the coil whe you bring the ground closer.

Steve Ward

Sat Oct 20 2007, 07:12PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

This is in fact the main problem with using feedback from the secondary circuit. When you ground out the circuit, it tends to either 1) simply disturb the oscillations, and cause a minor "hiccup" in operation, or 2) completely destroy the self-sustained oscillation, and the SSTC stops once the spark connects with ground (instead of pumping more power in, so you get the nice flaming ground strikes).

Antenna feedback seemed slightly better for ground arcs, but it seemed to depend on a few factors, which i never quite figured out (since i left that route awhile back). Some of my SSTCs would work great for ground arcs, and others would make the "thin" weak sparks because oscillation would cease. It never really seemed too detrimental to the MOSFETS, but it was annoying. Any time i tried using CT feedback (without aid of PLL) this was the exact problem i had, so that is why i never posted any CT feedback SSTCs on my site.

Ken M.

Sat Oct 20 2007, 08:19PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Hmm I guess that would make the difference, I was refering to antenna feedback since I have yet to rebuild it with CT feedback. Although From the skori coil the arc stays the same and its ct feedbak...

Zum Beispiel

Sat Oct 20 2007, 08:44PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

When I play with the arcs I use an ungrounded chicken stick to draw arcs. I have a small toroid on the end of the stick and a sharp metal point pointing away from it.

Like this:

=========0----

== insulator
0 toroid
---- sharp metal thingy.

I get some very hot arcs this way

Dr. Dark Current

Sun Oct 21 2007, 08:20PM

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

Well, I changed the resistor in series with CT back to 10k (I was using 4k7). I got a nice arc to ground and one dead FET as a bonus.

I'm going to rebuild it, I'll trash the CT and use an antenna probably.

Can anyone advise what SSTC self-tuning driver is the most reliable and allows ground arcs without flying silicon? PLL maybe?

Dr. Dark Current

Tue Oct 23 2007, 01:56PM

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

I noticed one weird thing.. With no topload, sparks are small and power draw is low. With small topload, sparks got almost 2x big and the input power too.
Now I made a new bigger toroid, put it on- the sparks are still the same (maybe even little shorter) but the power draw is really large, probably 1.5x as much as with the small topload!
Where did the power go? I didn't notice any huge dissipation in the fets. Is there something I still don't understand, such as power factor? (I measured the input power "visually" by watching a large bulb in series).

On the same topic, I also noticed that (at very low power) drawing an arc from the topload results in very noticable input power decrease, while I think the heat generated by the ~1" hot arc is at least few times larger than the heat from the little ~1/2" purple discharge alone...

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