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SSTC has odd behavior

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LAN_403

Killa-X

Sat Dec 18 2010, 01:57AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
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Posts: 1039

I have 2 120V feeds to my SSTC. Bridge, and 12V-5V PSU.

First 120V fed:
It feeds into a 120V to 18V transformer. with a 12V and 5V regulator, to feed the chips the correct powers.

Second 120V feed:
Variac, goes to a voltage tripler, then to the bridge.

Schematic: Steve Wards Mini SSTC

Behavior:
I first have the transformer on, so the fans kick on, and the red core-glow is lit. When I turn on my variac, Nothing happens. We exact this, as it's 0V. I have a 9V battery to a 555, pulsing a frequency to the driver board. When i turn the variac up, the FL tube starts to glow. But, i hear the fans get a little slower, and the LED fades.

I noticed this in the past with my last setup. It was still able to kick out the huge arcs, but it freightens me that the fans slow a tad, and the LEDs dim. It's not due to power draw, as its only a few mA at 10VAC input. What causes this?

Does Hot/neutral really matter on a voltage tripler? I didnt think this would do a thing.

Edit

I just wanted to add, that i got it more defined to a specific detail now. If i have a high duty cycle, the power dims, and UCCs get hot. If its higher, they are fine.

Gunboat

Sat Dec 18 2010, 10:19AM

Registered Member #338 Joined: Thu Mar 23 2006, 12:28PM
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Posts: 41

Just a thought here,are you using the same circuit to plug into? it could be drawing power from somewhere else.Try using a different outlet for each plug.Just my two cents worth.

Killa-X

Sat Dec 18 2010, 01:58PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
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Posts: 1039

Gunboat wrote ...

Just a thought here,are you using the same circuit to plug into? it could be drawing power from somewhere else.Try using a different outlet for each plug.Just my two cents worth.

No, couldnt be it. 15A breakers, the variac amp meter doesnt even move up to 1A...and that PSU for the 12V/5V is a 70W rated transformer. If the coil doesnt pulse, it doesnt 'dim'

My only guess, I wouldnt know how to go at fixing, but here it is.

Obviously it dims only when the coil bursts out streamers. So clearly, it has to do with the RF or CT, which can be lead to the UCCs, as they get hot if it dims like that for more than 5 seconds. They are fine else wise. If I run low duty, they seem to be happy no matter what I do.

Just a thought. Is this picture below the correct way to connect a CT for feedback, replacement of the antenna?

Usually this setup works fine. As I was able to slow-burst pulse 7" streamers with a low power test. I just wondered if the way I've ALWAYS done it, is actually correct. This is exactly how my CT is connected. If the part isn't in the picture, it means I don't have it in real thing.

Wolfram

Sat Dec 18 2010, 02:08PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Is the CT on the primary or on the ground wire of the secondary? What is the ratio of the CT?

Killa-X

Sat Dec 18 2010, 02:10PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Anders M. wrote ...

Is the CT on the primary or on the ground wire of the secondary? What is the ratio of the CT?

The CT is on the secondary ground wire, as its a SSTC. The ratio, giver take a couple turns, is 1:130. This is the same CT I have used in the past when I first built this coil, and never experienced this. I just wondered if the CT connection was right, as I have heard people say they use capacitors and resistors on their CTs...

Wolfram

Sat Dec 18 2010, 02:15PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Put a scope on the +5V rail when this is happening and see if it's stable. The CT is pushing some current into this rail via the germanium diodes, with a 1:130 this current shouldn't be very large, but it might be able to upset something.

Killa-X

Sat Dec 18 2010, 02:30PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
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Posts: 1039

well, given my connections are correct for the CT, Yeah..It should work. But something miss-oscillates, other wise there would be no reason for both UCCs to get really hot to the touch during pulse. I must ask though, not that it matters, but a single turn means a 100% solid turn around right? Not just passing a wire through, but a full true turn correct?

Wolfram

Sat Dec 18 2010, 03:21PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Any time the wire passes through the center of the core is a turn.

Killa-X

Sat Dec 18 2010, 08:35PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
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Posts: 1039

Ah...So far it does like to behave better on a single wire going through it. That means I had a 2 ratio, now a 1..Now it works over 40V, it use to fully stop.

It does seem to work a bit better actually. Just by changing that simple 2 into 1 turn. Wouldnt think it would do that much of a difference really. I updated my SSTC project page with pics/sparks, just going to 50V on the variac, with 7-8 inch burst tests.

So far, 60VAC, aka 250VDC, kicks out 13-15 inch streamers. So 120V, or 500VDC, hopefully will give me 24-30 inches. Yet, my mosfets are rated 500V, so that is really pushing it =)

Gregory

Sun Dec 19 2010, 03:48AM

Registered Member #2922 Joined: Sun Jun 13 2010, 12:08AM
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Posts: 226

put a resistor between the capacitor and the CT for reduce heat on all CIs and turn the circut less sensitive to interferences

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