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Re: [TCML] My Hemisphere/Toroid with Unconnected Top Sphere results
Hello Ed,
This thread was meant to move the specific discussion on the hemisphere/toroid combination unit with top sphere, from the original build thread "My first tesla coil" to here as a seperate offshoot topic. Based on what you stated, it doesn't sound like you saw those beginnings. So I will restate in brief the whole thing here. There is a reason for the top sphere not being directly connected - more below.
Essentials are that I finally build this combined 11" diam. hemisphere plus toroid underside top load. The hemisphere is a plastic form the outside of which is covered smooth in metal foil tape and the bottom inside edge also with metal foil tape (wrapped around the bottom edge connected with the outside surface, and an metal duct toroid shoved carefully
in the bottom, then the
outside edge meeting joint between the hemisphere and toroid covered with metal foil tape. Now the plastic form had a flattened area on the zenith/top section with a hole in the top, so I did not cover that area in foil on first testing.
Before I continue, check some pics showing the topload for clarity:
http://i230.photobucket.com/albums/ee64/ncc1701_photos/tech/my_tesla_coil_fullview_01.jpg
http://i230.photobucket.com/albums/ee64/ncc1701_photos/tech/my_tesla_coil_hemi-toroid_sphere_GA.jpg
http://www.freewebtown.com/baitzobservatory/tesla/index.html
To continue, even though I went through steps of tuning the primary, I was not getting quite the streamer length output I was looking for (noting the power is 270Watt 9kV 30mA NST with terry filter and safety gap and a 6-gap spark gap, so theoretical max 27" streamer possible). Again, not getting the results I hoped for, I chanced to add a 6"
hollow all metal sphere rested on top of the hemisphere on the plastic part. For clarity of the connection between sphere and hemisphere see here again:
http://i230.photobucket.com/albums/ee64/ncc1701_photos/tech/my_tesla_coil_hemi-toroid_sphere-1.jpg
http://i230.photobucket.com/albums/ee64/ncc1701_photos/tech/my_tesla_coil_hemi-toroid_sphere_GA.jpg
To continue, the result (without any further primary tuning) was what I would call rather "spectacular", I suddenly was getting 18-20" max streamers and easily 15-18" often, with a constant arc between the hemisphere and top sphere. Additionally the top sphere would sometimes break out in a perfect single steamer and the "serpent" was visible too! See video:
http://www.youtube.com/watch?v=YoUesr9L3cg
Following the session, I later realized the arc between the sphere and hemisphere was arcing through the plastic into the metal foiled hemisphere. I
also tested removing the sphere as well as directly connecting the sphere both directly to the secondary top winding and also seperately by foiling up the zenith area of the hemisphere. When the top sphere was directly connected, I could not achieve the same streamer lengths - no more then 12 inches max - it was quite obvious difference.
So with the zenith area of the hemisphere partially rimed in foil so the arcing to/from the sphere would be able to hit metal, not plastic (for safety reasons more than anything) I got the better results again. Again, this pic shows the closeup of the connection as I modified them finally:
http://i230.photobucket.com/albums/ee64/ncc1701_photos/tech/my_tesla_coil_hemi-toroid_sphere_GA.jpg
So to reiterate, the top sphere has to be unconnected through any metal to the hemisphere for the the streamers to get 18-20", but when directly connected, the result is
diminiished streamer length, back to maybe 12". My current hemisphere now has the metal foil 'peeled back' as it were just enough so the plastic is not affected like it was in the first run, but there is an arc through the air between the sphere and hemisphere to make this work.
As such this is why I do not connect the sphere directly. I don't have an explanation for why this works.
Peter
>I've been reading this series of notes and in spite of what you've written still can't f
>figure out if you have a solid ELECTRICAL connection between the sphere and the
>toroid. You say the top sphere is metal but then speak of "arcing into the plastic".
>What is the construction of the top sphere and is there a thick layer of plastic over the
>metal? In any case you should be able to run a sheet metal screw into the bottom of
>the top sphere, attach a wire to it, and connect to toroid and eliminate all of this arcing.
>Ed
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