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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I don't think dissipation factor really matters either. I've seen Richie B. fire up a SSTC with a damp cardboard coil former, clouds of steam came out and condensation formed on the topload, but the spark output still seemed fine. The sheer power available seems to make it irrelevant.
If you are worried about dissipation factor, you can get a very rough impression of it by placing a small piece of the material in a microwave oven, along with a cup of water to prevent damage to the oven. Microwave on high for 20 seconds, then feel the material to see if it got hot. This is a very hard test because of the extremely high frequency: any material that can pass it should breeze through in a Tesla coil.
From a design perspective, if dissipation factor matters that much, the design is bad (excessive loaded Q)
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Hello Steve,
I agree it probably doesn't matter as far as subjective output, e.g., "spark length" is concerned. And for the average person, it may not matter in any other sense, either, as I assume that most tesla coils are not operated continuously for very long periods of time.
It would matter for me simply because I want to know what kind of losses I have and what kind of temperature rise I'm dealing with.
As far as a quick test with a microwave oven, one potential problem I see is that for many materials, the loss factor varies alot with frequency (e.g., for PVC, one of my references says the loss is actually three times worse at lower frequencies than at 3 Ghz); also, off the top of my head, I don't know how the field strength in the oven would correlate to the field strength near the secondary.
In any case, if Herr Zapp's coils work fine and give him no problems, that's great, and they certainly look good...more "power" to him!...my "anal" design methodology simply requires me to dwell on it a little bit.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
> I've seen Richie B. fire up a SSTC with a damp cardboard coil former, clouds of steam came out and condensation formed on the topload, but the spark output still seemed fine.
Yep, that@s true. I@ve ran my SSTC coil CW at a couple of kW for a few hours, and on returning the table around the bottom of the secondary was covered with pools of water. It had evaporated from the varnished cardboard form, and condensed on the aluminium toroid, then dripped down onto the table top! The room also had a characteristic smell that I can only describe as "hot cardboard"
It proves that cardboard does absorb a lot of water when stored in the garage for long periods.
I think the secondary being damp affects SSTC@s running in CW mode more than disruptive coils. When tuning up my CW coil you could definitely tell if the former was damp because it would draw noticeably less current from the supply than when it had dried out. Then again, most people probably don@t run their TCs from an accurately metered supply, so wouldn@t notice the difference. If there was any change in spark length, however, it was minimal.
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What's the best way to secure the ends of single layer windings on a plastic form?
