RE: troubleshooting tesla coil, continued (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Sat, 22 Sep 2007 01:15:39 +0000
From: david baehr <dfb25@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: RE: troubleshooting tesla coil, continued (fwd)


Where are you located ???  I have a large roll of 30mill Poly I may sell ,
you could double it up , dont know if Ill ever use it. if intrested, email
me at dfb25@xxxxxxxxxxx
> Date: Thu, 20 Sep 2007 20:05:54 -0600> From: tesla@xxxxxxxxxx> To: tesla@xxxxxxxxxx> Subject: Re: troubleshooting tesla coil, continued (fwd)> > > ---------- Forwarded message ----------> Date: Thu, 20 Sep 2007 21:42:27 -0400> From: Marko Ruban <Marko@xxxxxxxx>> To: Tesla list <tesla@xxxxxxxxxx>> Subject: Re: troubleshooting tesla coil, continued (fwd)> > I've upgraded my design with 1/4" copper tubing primary and a toroid > topload (3"x12") made from aluminum air duct. I can now pull about 2" > sparks off the topload. I'll work on new spark gap next, current > (temporary) one seems to stop working properly after a minute or so.> > I also decided to give polyethylene a try for capacitor, but it didn't > work. Burned a hole right away (3 layers of 4mil), think I'll need more > or better quality PE. When I was putting the Mylar cap back together, I > noticed soot on the margins from arcing. Looks like I'll need more than > an inch margin for my next cap.> > > Tesla list wrote:> > ---------- Forwarded message ----------> > Date: Sun, 16 Sep 2007 22:06:17 -0700> > From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>> > To: Tesla list <tesla@xxxxxxxxxx>> > Subject: Re: troubleshooting tesla coil, continued (fwd)> >> > Hi Marko,> >> > Yes, now that you identified 4 pairs of copper sheets and the 1" > > clearance using Mylar, 7nF is just about right! And yes, Mylar has a > > dielectric constant value of 3.2 and breakdown at 7,500 V/mil. But there > > is a problem here that you have identified in this particular post. The > > problem is Mylar (aren't you sick of people bringing up bad news?). > > Sorry, it's just that it sticks out like a sore thumb. You accounted for > > the volts/mil and dielectric constant, but you didn't account for how > > dielectrics behave with alternating currents such as RF (Tesla Coil > > frequencies).> >> > Dielectrics have what is termed a "dissipation factor" identifying > > losses (always in the form of heat) when the dielectric is operated in > > an alternating current. The higher the frequency, the more losses that > > are generated. Some dielectrics have a high dissipation factor and > > others a low dissipation factor. What is desired for high frequency is a > > low dissipation factor. Mylar unfortunately has a high dissipation > > factor and makes them unsuitable for Tesla Coil tank caps. It's always > > best to go with a known dielectric which has a low dissipation factor > > such as polypropylene, polystyrene, polyethylene, etc.. just as the cap > > manufacturers themselves go with. Even with our MMC's, we account for > > the dissipation factor (tangent loss) as specified by the cap manufacturers.> >> > There are a lot of things you'll be working on, but I just wanted to > > point out that Mylar is not a great choice for tank caps (even if the > > volts/mil is high and dielectric is in the medium range). Your cap being > > a plate cap would likely do better than a rolled mylar cap simply due to > > the thermal dissipation of the plates, so you may want to give it a go > > anyway and see how it reacts. Of course, if breakdown occurs (even a pin > > hole punch through), that will end the caps use. I personally used oil > > in my plate cap, mainly for the self healing ability.> >> > If you are ever curious as to what constitutes a good dielectric or not, > > copper vs. steel in the primary, etc.., just do a search at > > www.pupman.com of the list archives. Cap dielectrics are one of those > > items where there is a lot of information available.> >> > Take care,> > Bart> >> >> > Tesla list wrote:> >> > > >> ---------- Forwarded message ----------> >> Date: Sun, 16 Sep 2007 16:43:56 -0400> >> From: Marko Ruban <Marko@xxxxxxxx>> >> To: Tesla list <tesla@xxxxxxxxxx>> >> Subject: Re: troubleshooting tesla coil, continued (fwd)> >>> >> As I mentioned a bit earlier, I made an error in units, my cap was an> >> estimated 7nF (not pF). I finally got the multimeter, and that value was> >> confirmed since initial post.> >>> >> Capacitor is constructed with 4 pairs of 10mil copper sheets (6" x 8")> >> separated by 10mil Mylar sheets with 1" margin on the sides. I picked> >> Mylar because it has a high dielectric value and high breakdown voltage.> >> 10mil sheet is rated at 70kV.> >>> >>> >> Tesla list wrote:> >>> >> ---------- Forwarded message ----------> >> Date: Fri, 14 Sep 2007 18:17:24 -0700> >> From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>> >> To: Tesla list <tesla@xxxxxxxxxx>> >> Subject: Re: troubleshooting tesla coil, continued (fwd)> >>> >> Hi Marko,> >>> >> Your inserting 0.007uF into Javatc so the frequency's do match as they > >> should at that capacitance. However, your "saying" 7pF and that is way > >> off from both Javatc and what the plate cap really is. Judging by your > >> plate cap configuration, it is about 0.7nF (not 7nF) if your using glass > >> as an insulator. If air is your insulator, then it's down to 0.1nF.> >>> >> So you are way out of tune. The fix is the cap. For a plate cap using > >> glass with about 0.2" spacing, you would need a plate surface area of > >> 900 square inches (30" x 30").> >>> >>> >> If your going to use a plate cap, you might want to consider Castor oil > >> which has a high dielectric of 5. About 15 plates (8" x 11") with a 0.2" > >> spacing between plates would yield near 7nF (which is 0.007uF). Plate > >> caps are fun to play with, but when you start building to a capacitance > >> such as this, it can get bulky and messy. I of course recommend an MMC > >> for performance.> >>> >> Take care,> >> Bart> >>> >> Tesla list wrote:> >>> >> > >>> >> ---------- Forwarded message ----------> >> Date: Thu, 13 Sep 2007 19:19:45 -0400> >> From: Marko Ruban <Marko@xxxxxxxx>> >> To: Tesla list <tesla@xxxxxxxxxx>> >> Subject: troubleshooting tesla coil, continued> >>> >> Hello guys, I'm back from a long summer vacation. As per previous > >> suggestions I have acquired an old NST transformer (12kV, 60Hz, 60mA > >> output). And the spark gap does run now with capacitor/primary in > >> circuit. However, there's no visible effect on the topload, still. > >> Could it be that badly un-tuned?> >>> >> Please see the photo of my simple setup and make any suggestions...> >> http://marko.dppl.com/TC_setup.jpg> >>> >> The flat rectangular thing in front, is the capacitor, which should be > >> about 7pF. Can't make a more specific measurement since my new > >> multimeter is still in the mail. Spark gap is on top of the NST, and > >> consists of two screws facing each other (about 0.2" adjustable > >> spacing). Wire running in the back to the right is the ground.> >>> >> Also, here's a dump of JavaTC for my coil...> >> http://marko.dppl.com/coil.txt> >>> >> Thanks in advance for any assistance.> >>> >>> >> > > > 
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