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First SSTC's first light! What tweaks/refinements are possible?

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Coronafix

Wed Oct 01 2008, 11:54AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Nice work! You got to try and fix that corona leak at the bend in the wire though, at higher power it will
eventually burn it out. I space wind the last 5 or so turns of the secondary to encourage this, but
you could try curving the last turn on more of an angle towards the top and try and take the bend out.
Epoxy or varnish will really help it. Cutting a curving channel in the side of the end cap where the leak is
and filling it with epoxy would really help.
The further away from 90 degree bends the better.

Love your layout, it shows a lot of thought.

aonomus

Wed Oct 01 2008, 12:00PM

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

Yea, unfortunately since I didn't think that far ahead in terms of the secondary I'll be a bit of a loss but I'll just get the copper pipe sometime this week and try to fix it. In terms of the layout, I found myself backpedaling because the rubber feet on the bottom took up too much space in the end which could have given me more stability (ie: mount the GDT somewhere so it doesn't break wires so often).

I will definitely re-engineer the secondary for my next SSTC (likely a musical SSTC) to get around these problems, cutting a groove in the acrylic and filling in with some kind of epoxy sounds like a very good idea. The first piece of my SSTC built was the secondary, and I hadn't done as much research until now. Since I live in a small apartment I won't build beefy DRSSTCs till I have more space, and most importantly money (I have the parts for another SSTC lying around, but not for a DRSSTC).

uzzors2k

Wed Oct 01 2008, 09:06PM

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

You still haven't provided any details on the primary winding. Given that the coil actually dies from low voltage tests unless interrupted, I assume you're using way too few turns. Beef it up man! Your coil should do CW from 40V without the mosfets so much as breaking a sweat. Toploads increase current by lowering fres (and other effects I'm not sure of) so you'll need more primary turns to keep the impedance the same. All of your problems are a matter of tuning! You can always remove turns once you have the coil under control.

aonomus

Wed Oct 01 2008, 09:51PM

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

Well, details:

Currently 4.5 primary turns of 16AWG, the coil doesn't fail with low voltage tests, however they fail cold. I'm trying to find a suitable primary form to lower the coupling (and add more windings).

I'm still stumped overall as to why it fails with the topload. Since the coil runs off its own feedback via a 74HC14 it should stay in tune correct?

MRacerxdl

Wed Oct 01 2008, 10:20PM

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

4.5 Primary turns? I was used for my IRFP250 coil 7 Turns for a Half Bridge, and I get 20cm sparks :D

It can fail with topload because low turns, and the antenna can get massive signal and stops to work for a few nS, that can kill the mosfets.

Try to increase the turns to 10, and test it, if runs ok with no heat at mosfets (not on the heatsink, some times the mosfets heat in the front of it, but not on the heatsink) reduce the turns by 1, and try again.

Coronafix

Wed Oct 01 2008, 10:45PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

4.5 turns is way too few turns, that explains why they are blowing.
Do about 20 and as Uzzors said, you can always remove some later. The impedance of the secondary wants to suck amps into it, if the primary impedance isn't enough to supply it, then the pump is going to blow (mosfets).
I'm sure there are better analogies but that's mine on the run this morning. :)

aonomus

Thu Oct 02 2008, 12:37AM

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

I just followed the schematic :/

With 20 turns should I have a low BPS or higher BPS?

I'm trying 10 turns now and I can support a topload at low BPS with easy breakout, and hard breakout at high BPS (near CW).

Yet another edit:
With primary at 10 turns with about 5 BPS and topload w/ breakout point I get nice 7" sparks

Overall, about 7-8" sparks

Full power, 1/5th second shutter speed

Full power, 1/50th second shutter speed

And video:

uzzors2k

Fri Oct 03 2008, 03:36PM

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

Haha, nice. First light with power always rocks. More turns will decrease the current draw, allowing you to use a higher duty cycle on your coil. I would find the interrupter setting which gives the best sparks, and then remove as many turns as you're comfortable with from there.

Ken M.

Fri Oct 03 2008, 03:42PM

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

Very nice, you got it running and its looks similar to steves arcs and mine (I'm still dicking around fixing mine ><). Congradulations again!

MRacerxdl

Fri Oct 03 2008, 09:56PM

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

You can try to use HalfWave retified mains. That will make the sparks grow a little and current gets down.
Now the arcs are looking good :D

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