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4hv.org :: Forums :: Tesla Coils
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Medium size DRSSTC - Primary Flat or Helical

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Killa-X
Fri Jun 08 2012, 03:53AM Print
Killa-X Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
My DRSSTC currently features a Helical primary. It's climb height is about 5 inches, and maintains 3 inches from the secondary. As it sits, i never had issues with it flashing over to the secondary. However, I want the best out of this coil, and I see a lot of the large DRSSTCs using flat primary coils instead of helical or cone. Steve wards for example. I just want peoples suggestions on if i should keep mine as is, a Helical coil, or change it into a flat coil. Changing isnt a problem. I just have to cut out 8 new peices of acrylic that attach to my clamps that extend outward.

Let me know what you guys think.

Link2 I have had tuning issues in the past.

Link2 Primary

Thanks for your time. My last setup, a CM300 halfbridge, peaked at 7ft sparks for the power I gave it. This round, its CM300 fullbridge. I'll do proper tuning, but I want to make sure my primary is best suited for operation. Also ... I will get a better clamp for primary tap :D
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Goodchild
Fri Jun 08 2012, 06:07AM
Goodchild Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Flat hands down for any DR. There is really no reason to do a helical primary in my opinion. With a flat primary you get a coupling in and around 0.2k which is more than plenty for most DRs and it is out of the way much less likely to be hit by racing sparks and toroid to primary flash overs. And on top of all of this flat is also way easier to build.

I used a helical on a DR once, my first DR, never again....

The only time I have really needed a helical primary is with my QCW where a coupling of 0.3k and greater was needed for proper operation and the top voltage was low enough that flash overs were not a problem, <70Kv in my case.

EDIT:

Also looking at your photo tuning was not the only problem, your coupling had to be insanely high with the secondary all the way down in the helical primary.
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Steve Conner
Fri Jun 08 2012, 07:45AM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
To my understanding, the tighter the coupling the better your coil will perform, until you reach the point that it starts flashing over because the gap between primary and secondary is too small. The flat primary doesn't have the optimum coupling coefficient, it just has about the highest coupling possible without flashovers in a high-powered coil. I think DRSSTCs would perform even better if this limitation could be overcome, perhaps by filling the coil system with oil or SF6.

I had this problem once, and rather than rebuild the primary, I rewound the bottom 2" of the secondary (which had been burnt up by the flashovers anyway) with a heavier gauge of wire.
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Uspring
Fri Jun 08 2012, 10:46AM
Uspring Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711
What about using a conical primary? Seems like a compromise between flat and helical ones. JavaTC will do the math, e.g. coupling for you.
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Dr. Drone
Fri Jun 08 2012, 02:31PM
Dr. Drone Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673
shades
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Goodchild
Fri Jun 08 2012, 02:48PM
Goodchild Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Steve Conner wrote ...

To my understanding, the tighter the coupling the better your coil will perform, until you reach the point that it starts flashing over because the gap between primary and secondary is too small. The flat primary doesn't have the optimum coupling coefficient, it just has about the highest coupling possible without flashovers in a high-powered coil. I think DRSSTCs would perform even better if this limitation could be overcome, perhaps by filling the coil system with oil or SF6.

I had this problem once, and rather than rebuild the primary, I rewound the bottom 2" of the secondary (which had been burnt up by the flashovers anyway) with a heavier gauge of wire.

Well there is a way to overcome this limitation turn that DR into a QCWDR and get those top volts way down. wink

In that case I'm all for high coupling and helical primaries!


Also Dr. Spark I almost smashed my screen thinking there was a bug on neutral
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brandon3055
Fri Jun 08 2012, 03:11PM
brandon3055 Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271


Well there is a way to overcome this limitation turn that DR into a QCWDR and get those top volts way down. wink
[/quote1339168145]

What is a QCWDR?
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Dr. Drone
Fri Jun 08 2012, 04:56PM
Dr. Drone Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673
shades
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Goodchild
Fri Jun 08 2012, 08:13PM
Goodchild Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Destroyer of mosfets wrote ...



Well there is a way to overcome this limitation turn that DR into a QCWDR and get those top volts way down. wink
[/quote1339168145]

What is a QCWDR?


A QCW is a DR the full name of the coil is a QCWDRSSTC. A QCW is DRSSTC with a high tank impedance and control over the current envelope. Same basic principles as a DR apply.
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Killa-X
Sat Jun 09 2012, 12:46AM
Killa-X Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Well, Is it suggested that I rise my DRSSTC secondary so its not so far deep into my helical, or is it best I just rebuild the primary flat, and adjust coupling from there. I can do either. Obviously it be easier to keep the current design, and just rise the secondary, but, If flat primaries seem to run performance better, then I maybe should just build things that way..?
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