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A question about the base material of a VDG

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  • Craig Fuller
    I have been tossing around the idea that it may be better to make the base of a VDG out of a conductive enclosure similar to the upper terminal. It just seems
    Message 1 of 3 , Oct 31, 2006
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      I have been tossing around the idea that it may be better to make the
      base of a VDG out of a conductive enclosure similar to the upper
      terminal.

      It just seems that this would ensure maximum charge transfer of the
      lower brush in the same way that the upper enclosure ensures maximum
      charge transfer on the upper brush. I have only seen a few units
      (mostly commercial) that have a conductive base, but it seems like it
      would make a worthwhile experiment. I have a suspicion that this
      would have little effect on a unit that has a HVDC supply.

      I think I may experiment with my machine by just placing the whole
      thing in some kind of grounded metal box (decent gauge aluminum) with
      a hole in it for the column. Who knows, it may work.
    • Richard R. Linder
      Craig: There are some commercial VDGs on the web that go both ways. I would suggest that the shape of a conductive shroud would be optimum if it were a mirror
      Message 2 of 3 , Nov 2, 2006
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        Craig:
         
        There are some commercial VDGs on the web that go both ways.  I would suggest that the shape of a conductive shroud would be optimum if it were a mirror image of the bottom half of the top terminal, namely a hemisphere with an involute hole for the column.  I would not spend any time or money on any kind of a conductive lower shroud that had any surface feature that even resembled an edge or corner facing in the upward direction. 
         
        You can get more bang for the buck by increasing the conveyance of electrons up to the top terminal. This would include incorporating a higher belt speed, belt width and optimizing the belt material to be complementary with the roller material.  At 60 mph and a belt width of 6" I can easily generate over 100 microamps of charging current. 
         
        Dick Linder
      • Craig Fuller
        That s an excellent point. I forgot how the base of the machine tends to draw charge from the terminal. Adding grounded points to the base (like the corners
        Message 3 of 3 , Nov 3, 2006
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          That's an excellent point. I forgot how the base of the machine
          tends to draw charge from the terminal. Adding grounded points to
          the base (like the corners of an enclosure) would just make it worse.

          As it is now, my acrylic support column is attached to the base by
          an acrylic flange that I solvent welded to the bottom (it's quite
          strong!). There are steel bolts holding this flange to the base,
          and in the dark I can see faint corona streams coming from bottoms
          of them. I don't want to get close to the tops of the bolts to see
          corona (although I know it must be there) because the zaps from the
          machine feel like short but painful headaches, you may be familiar
          with the sensation. I am going to check McMaster and see if I can
          replace those steel bolts with nylon.

          While I am VERY happy with the performance of my machine, I wish
          that I had made the base out of something other than particleboard.
          A polycarbonate base might be nice!

          Craig


          --- In VanDeGraaffGenerator@yahoogroups.com, "Richard R. Linder"
          <linder@...> wrote:
          >
          > Craig:
          >
          > There are some commercial VDGs on the web that go both ways. I
          would suggest that the shape of a conductive shroud would be optimum
          if it were a mirror image of the bottom half of the top terminal,
          namely a hemisphere with an involute hole for the column. I would
          not spend any time or money on any kind of a conductive lower shroud
          that had any surface feature that even resembled an edge or corner
          facing in the upward direction.
          >
          > You can get more bang for the buck by increasing the conveyance of
          electrons up to the top terminal. This would include incorporating a
          higher belt speed, belt width and optimizing the belt material to be
          complementary with the roller material. At 60 mph and a belt width
          of 6" I can easily generate over 100 microamps of charging current.
          >
          > Dick Linder
          >
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