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Re: two months silence - the ebb and flow of interest

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  • jpiperson2002
    ... Well, it s mid-winter here in Chicago and many of my projects are on hold until Spring when the garage warms up. I d spent spent a considerable amount of
    Message 1 of 6 , Feb 3, 2008
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      --- In VanDeGraaffGenerator@yahoogroups.com, "saihager" <saihager@...>
      > Nobody making these anymore??????????????

      Well, it's mid-winter here in Chicago and many of my projects are on
      hold until Spring when the garage warms up. I'd spent spent a
      considerable amount of time and effort on a VDG without finishing it
      last Fall and finally bought a commercial one with ~17in top from
      Science First. Both of my sons are in grade school and I'll probably
      leave the completion of the home made VDG to one of them as a school

      I ran into 2 situations which which side tracked me a bit while
      finishing my VDG (4 inch PVC column, 19" garden gazing globe top, DC
      universal motor with Variac speed control). First, I used a large
      stainless steel garden globe, large for the money but almost
      impossible to cut an access hole. Found someone who works on cars with
      a plasma torch, that cut a nice though rough-edged hole into the globe
      in just a couple of minutes. The rough edge of the hole access hole
      needed to be covered with anti-corona putty and metal cannot be
      pressure bent into an inward curve. It's simple enough to cover the
      rough edge to prevent corona, just slit a piece of clear vinyl tuning
      along the long side and fill it with anti-corona putty, then slide it
      over the edge of the access hole. It works but the putty is very
      expensive and there's no easy way to produce a smooth inward curve
      along the access hole (ideally it would funnel into the globe). If you
      don't have easy/free access to a plasma torch for cutting a hole into
      a garden globe I'd recommend just buying a commercial VDG globe from
      Science First, it might cost you 50% to 100% more than using garden
      gazing sphere and cutting the access hole yourself but in the long run
      you'll spend much less time and effort to get a usable globe.

      The other problem I ran into was balancing the rollers at high speed.
      I didn't expect that part to be difficult difficult since I have a
      decent drill press, but in fact I chewed up a couple nice $35 pieces
      of solid Nylon rod (roller) without getting the axle hole completely
      centered correctly and the wobble in the heavy nylon rods at high
      speed was too much. If I had a lathe I could have trued the roller, in
      retrospect I should probably have used 3in PVC pipe for rollers and
      glued in end plugs. That way I could have drilled center holes in a
      bunch of end plugs for short PVC roller tubes and then tested the
      rollers for balance, the rollers would only have cost a few cents each
      so testing a bunch of them for balance wouldn't have cost much.

      Since I started the VDG last year I did make a stack capacitor to go
      with it using six 3.5 gallon buckets each lined with foil . It gives a
      satisfying though not especially scary crack at discharge of about 1
      inch after charging with my Science First VDG for a minute or so, the
      total capacity of the stack was 3.4nF at about 60,000V (1.1 inch gap
      between 1 inch spheres) giving almost exactly 6 Joules. That would be
      a substantial shock to say the least but not usually considered to be
      life threatening. Buckets are very expensive way to get capacitance
      though. It's nice for a concept demo to show people since buckets look
      big and impressive, but a HV capacitor as big as a flashlight battery
      can hold many times the capacitance charge of a stack of buckets.
      There are lots of big HV capacitors of all sorts on eBay for the
      fearless. Stay away from them unless you are very knowledgeable in
      electronics and a total safety freak, and can guarantee that others
      won't get into them when you aren't around to supervise.

      The VDG project did get me off on a HV tangent of interest though. We
      got a nice 80KV induction coil, and we made a small sparker box out of
      an old cigar box which uses a small 100KV battery operated HV coil
      (another eBay find for about $20 used in taser type stun batons), push
      a button on the front of the box and a fat 1 inch spark crackles
      between 2 electrodes on the top of the box. It's a nice toy but it
      produces a fair amount of ozone and is so loud that people come by to
      see what the problem is. Also got a solid state Tesla coil, that's one
      to be careful if used inside, you need separate grounding (wire to a
      rod pounded into the earth) otherwise you may fry all electronics
      hooked to your electrical outlets if the main sparks from tesla ever
      manage to ground to your regular electrical system ground.

      Surprisingly to me, our favorite HV device has turned out to be a 12
      dia Megavolt plasma globe, it's a large out-of-production lightening
      globe with beautify long blue lightening bolts which snake around
      inside and which turn pink as they hit the glass of the globe. There
      are many 8in dia plasma globes available maybe $35 if I recall which
      are also impressive, I got lucky on finding a used 12" dia (A 12" tall
      globe will only be 6" or 8" in globe diameter and sellers almost
      always hide this fact in the small print). The plasma globe lets you
      see large sinuous sparks close up without the ozone or danger - I use
      that plasma globe a hundred times for each time I use the induction
      coil. The plasma coil cost considerable more but the noise and ozone
      make the induction coil an occasional thrill at best.

      So as the weather warms up in a few moths we'll dust off our
      unfinished projects and we'll bounce our way from one to another. Each
      of these interests and discussion forums becomes a springboard to many
      things new and unexpected. People come and go as their interests
      evolve but the forum provides a nice place for us to leave our
      impressions and small discoveries for those who may show up years later.

      I'm hoping to get to 'Lightning on the Lawn' in Baraboo Wisconsin this
      fall, it's hosted by Dr Resonance who produces commercial VDGS and
      tesla coils. Check out this youtube link to see some short videos on
      his huge Big Bertha tesla coil and singing tesla from the 2006 and
      2007 Lightning on the Lawn gatherings;


      John Piper
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