From: "Terrell W. Fritz"
Date: Sat, 09 Sep 2000 22:09:56 -0600
Subject: Re: [TSSP] Mystery of the missing loss
Hi Boris, All, At 03:52 AM 9/8/00 -0700, you wrote: snip...> >Hi All, >Althought,I have been present on TSSP list from its >first days,this is first post of mine (very occupied >lately,and can't manage to check email on regular >basis as I used before:)) > >Few comments regarding measured too low Q : >Whenever I see measured Q of unloaded secondary > in order of 50 I can claim: >If Z coil is resonably high ,which in most TC >secondaries is,low Q could be the result of following >things: >1.)Rdc is too high becouse of too thin wire diameter >used. Using wire gauge tables, my Rdc should be 68.986 ohms. My coil measures 69.5968 ohms (OK, I have a nice meter ;-)) I examined the trusty o'l secondary and despite a few minor cosmetics it seem in excellent shape. Certainly no spots that would worry me in the least. > 2.)Something is poorly made in secondary construction >such as shorted turn top isotropic capacity effect >apperance,nonlinear wounding and eddy currents loss >area presence etc. The secondary is in excellent condition. I probed around for a shorted turn, but a simulation test with an extra shorted wire showed the dramatic effects such a thing would make. Since the inductance and other basic parameters are the same as years ago and the secondary is not normally a surface arcer or anything like that, I will rule out damage and shorts. >3.)Possibly extra high dielectric loss in coil form > (unlikely here I think) Now this I can NOT rule out! The secondary seemed to have much higher loss at low frequencies than at high!! Using my vacuum cap (which actually showed a loss higher than my super cap!) I could clearly see that higher frequencies had higher loss. Here is a little chart I made of the effective secondary resistance vs. frequency. I made it with the vacuum cap by varying the capacitance and finding the effective Rac. http://216.160.168.190/TeslaCoils/Misc/PaulNich/BRacvF.gif Basically, it says something is getting very lossy very fast as frequency increases. I have no idea what, but the larger toroid case was probably less lossy due to the frequency being lower rather than the fields and such. This secondary is a 1/8 inch thick cardboard impregnated with paraffin wax "sonotube" used for circular concrete forms. This wire may have had an oxide layer at the surface before it was coated. The vacuum cap is probably more lossy at low capacitance than high Maybe the polyurethane coating is doing something... The list goes on... but I seem to be getting super high loss as frequency increases. >4.)EM Coupling of secondary with enviroment and losses >outside a coil structure. I have done such tests a number of times in a number of places and gotten similar results. I don't have an oxygen free silver plated room coated with a gold anti-oxidation layer or anything, but the room is not all that unusual... I would guess the previous option three... > >I don't belive that Terry made serious mistakes >relating 2 and 3.Neither that the reason for very high >Garry Johnson's secondary coil Q in order of 500 >is some kind of superior secondary construction. >But I do belive it is due to point 4. >That would be the reason:Enviroment and resonator >position in it. >I'm quite convinced Terry's secondary coil Q results >would be much better in different enviroment >conditions. I have played with some modelling and I think the "room" is far enough away that it should not be a factor. It is raining now so outside is not an option. There are a number of things in the Rac loop but the coil form really does seem lossy to me... The science goes on... Cheers, Terry > >Regards, >Boris > >__________________________________________________ >Do You Yahoo!? >Yahoo! Mail - Free email you can access from anywhere! >http://mail.yahoo.com/
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.