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New to Group and Building a Van de graff

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  • nickademusss
    Hi All, Im new to this group, and have some questions reguarding Van de graff Generators. I have constructed a small one about three foot tall. Using a fan
    Message 1 of 6 , Jan 7, 2005
      Hi All, Im new to this group, and have some questions reguarding Van
      de graff Generators. I have constructed a small one about three foot
      tall. Using a fan motor, 2" PVC pipe, nylon bottom roller, silicon top
      roller, plastic belt (shoulder strap from my 60's geiger counter) and
      a small speaker cab. The collector is a 8" diameter Stainless sphere,
      made from a small air tank. all the sites I have been to show the
      machines using a rubber belt. something like a very large wide rubber
      band. Were can I get one? and is it going to work better than what I
      have? Right now I can get a 12" faint spark out of it. this spark can
      only be seen in the dark, but can be done almost 40 times a minute. I
      can get a bright spark around 8" long. any feedback about the
      construction of this simple yet fun machine would be great. Thanks,
      Nickademusss
    • colt45hal@aol.com
      Nickademusss: Welcome to the group! If you re getting an 8 BRIGHT spark from an 8 terminal, I think we should be consulting YOU! Harold Pollner
      Message 2 of 6 , Jan 8, 2005
        AOL Email
         
        Nickademusss:
         
        Welcome to the group!
         
        If you're getting an 8" BRIGHT spark from an 8" terminal, I think we should be consulting YOU!
         
        Harold Pollner
      • Richard R. Linder
        Hi Nickademusss all the sites I have been to show the machines using a rubber belt. something like a very large wide rubber band. Were can I get one? and is it
        Message 3 of 6 , Jan 8, 2005
          Hi Nickademusss
           
           all the sites I have been to show the
          machines using a rubber belt. something like a very large wide rubber
          band. Were can I get one? and is it going to work better than what I
          have?
          --------------------------------------------------
          There are many materials which are suitable for VDG belts. There are also many considerations when choosing the optimum material for your particular VDG. You should familiarize yourself with the triboelectric list of materials. Logically, the belt material should be between the materials used for your rollers. The weight of the belt material enters into the equation also. If the belt is heavy you will experience tracking problems at high belt speeds due to centrifugal force tending to lift the belt off the rollers. The belt will also collide with the spray and collector points since the typical point-to-belt gap is about 1/32". The belt material should be easy to splice. Also, if there is to be a long distance between rollers and if the belt is stretchy, the sides of the belt, which are opposite in polarity,  will attract each other and ultimately rub or stick together...not good.
           
          FYI in both my VDGs I am using vinyl impregnated nylon for the belt. It's very strong, only .003" thick therefore very light. It can be spliced with plexi solvent cement which results in a tough "weld". Since it is only .003" thick you can splice with an ovelap rather than a difficult butt joint. It does not stretch very much therefore the belt sides cannot touch each other. My bottom rollers are nylon and top rollers are teflon in the small VDG and PVC in the large machine. Belt widths are 3" and 6" respectively. Belt speeds are  in the vicinity of 60-70 mph. The small VDG has a sphere of 18" in diameter with a 6" hole cut for the column. The sharp edge of the hole is covered with liquid plastic to minimize corona.  The large 36" in diameter sphere has an involute hole of 8" in diameter. The small column is 4" plexi tubing and the large column consists of 4 fiberglass posts.
           
          I have posted many pictures of the small VDG and some of the sub assemblies of the large one. I'll be posting pictures of the large one in a few weeks after I finish touring the schools for this year's static electricity show.
          --------------------------------------------------------------
          Right now I can get a 12" faint spark out of it. this spark can
          only be seen in the dark, but can be done almost 40 times a minute. I
          can get a bright spark around 8" long. any feedback about the
          construction of this simple yet fun machine would be great. Thanks,
          -----------------------------------------------------------
          You will find that the geometry of the tip of your ground wand will have a significant effect on the length and intensity of the spark. The only hard data that I have regarding ground wand tips is what I have experienced and that is a 1.5" diameter chrome steel ball will give me a respectable spark 3 times longer than a 7" diameter ball but the 7" ball produces a much hotter spark.
          Hope all this is of some help.
           
          Dick Linder





        • nickademusss
          Thanks Richard, for the the info, I forgot to tell everyone that the almost totaly enclosed box im using causes the fan motor im using to overheat. To fix this
          Message 4 of 6 , Jan 8, 2005
            Thanks Richard, for the the info, I forgot to tell everyone that the
            almost totaly enclosed box im using causes the fan motor im using to
            overheat. To fix this problem I put a 120v 90mm fan that draws in air
            from the back and blows it across the motor. This had a great effect
            on the opperation of the unit. After a few minutes the air gets heated
            by the fan motor and then moves up the PVC pipe to the Sphere. It
            seems to be drying the air out inside it. After I added the fan was
            when I was geting the large 6" to 8" sparks bright enough to be seen
            in daylight. and faint ones or rather groups of faint sparks up to a
            foot in lenth. The very loud and bright sparks are around 4" to 5".
            Also I did check out the triboelectric list and thats why I used Nylon
            on the bottom and silicone for the top roller. I read somewere that I
            should use materials as far apart on the list as possible. Would it be
            better to use a larger sphere? if so whats to big for a smaller setup
            like this? Also I have thought of using a hair dryer to dry the sir
            inside the VDG any thoughts on this?
            Thanks for the info, Zac/Nickademusss











            --- In VanDeGraaffGenerator@yahoogroups.com, "Richard R. Linder"
            <linder@c...> wrote:
            > Hi Nickademusss
            >
            > all the sites I have been to show the
            > machines using a rubber belt. something like a very large wide rubber
            > band. Were can I get one? and is it going to work better than what I
            > have?
            > --------------------------------------------------
            > There are many materials which are suitable for VDG belts. There
            are also many considerations when choosing the optimum material for
            your particular VDG. You should familiarize yourself with the
            triboelectric list of materials. Logically, the belt material should
            be between the materials used for your rollers. The weight of the belt
            material enters into the equation also. If the belt is heavy you will
            experience tracking problems at high belt speeds due to centrifugal
            force tending to lift the belt off the rollers. The belt will also
            collide with the spray and collector points since the typical
            point-to-belt gap is about 1/32". The belt material should be easy to
            splice. Also, if there is to be a long distance between rollers and if
            the belt is stretchy, the sides of the belt, which are opposite in
            polarity, will attract each other and ultimately rub or stick
            together...not good.
            >
            > FYI in both my VDGs I am using vinyl impregnated nylon for the
            belt. It's very strong, only .003" thick therefore very light. It can
            be spliced with plexi solvent cement which results in a tough "weld".
            Since it is only .003" thick you can splice with an ovelap rather than
            a difficult butt joint. It does not stretch very much therefore the
            belt sides cannot touch each other. My bottom rollers are nylon and
            top rollers are teflon in the small VDG and PVC in the large machine.
            Belt widths are 3" and 6" respectively. Belt speeds are in the
            vicinity of 60-70 mph. The small VDG has a sphere of 18" in diameter
            with a 6" hole cut for the column. The sharp edge of the hole is
            covered with liquid plastic to minimize corona. The large 36" in
            diameter sphere has an involute hole of 8" in diameter. The small
            column is 4" plexi tubing and the large column consists of 4
            fiberglass posts.
            >
            > I have posted many pictures of the small VDG and some of the sub
            assemblies of the large one. I'll be posting pictures of the large one
            in a few weeks after I finish touring the schools for this year's
            static electricity show.
            > --------------------------------------------------------------
            > Right now I can get a 12" faint spark out of it. this spark can
            > only be seen in the dark, but can be done almost 40 times a minute. I
            > can get a bright spark around 8" long. any feedback about the
            > construction of this simple yet fun machine would be great. Thanks,
            > -----------------------------------------------------------
            > You will find that the geometry of the tip of your ground wand
            will have a significant effect on the length and intensity of the
            spark. The only hard data that I have regarding ground wand tips is
            what I have experienced and that is a 1.5" diameter chrome steel ball
            will give me a respectable spark 3 times longer than a 7" diameter
            ball but the 7" ball produces a much hotter spark.
            > Hope all this is of some help.
            >
            > Dick Linder
            >
            >
            >
            >
            >
            >
            >
            >
            >
            ------------------------------------------------------------------------------
            >
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            >
            > a.. To visit your group on the web, go to:
            > http://groups.yahoo.com/group/VanDeGraaffGenerator/
            >
            > b.. To unsubscribe from this group, send an email to:
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            >
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            Service.
          • colt45hal@aol.com
            Nickademusss: Yes, there is a theoretical relationship concerning sphere size vs maximum attainable potential: It is 30KV per centimeter of sphere radius, or
            Message 5 of 6 , Jan 8, 2005
               
              Nickademusss:
               
              Yes, there is a theoretical relationship concerning sphere size vs maximum attainable potential: 
               
              It is 30KV per centimeter of sphere radius, or 76.2KV per inch of sphere radius.  Thus, a sphere with  a diameter of 12 inches (radius 6 inches), could THEORETICALLY develop a potential of 6 x 76.2, or 457.2KV, or 457,200 volts D.C. 
               
              In pratice, however, the theoretical values are never reached, due to local anomalies, humidity variations, local atmopheric pressure, departure from the theoretically perfect sphere, etc.
               
              Happy HV Discharges...
              Graaffer Hal
               
               
               
               
               
               
               
               
            • Richard R. Linder
              Zac: I have read that heaters are often used inside the base of VDGs exactly for the purpose of dehydration. Humidity is a killer of VDGs. Keep in mind that if
              Message 6 of 6 , Jan 9, 2005
                Zac:
                 
                I have read that heaters are often used inside the base of VDGs exactly for the purpose of dehydration. Humidity is a killer of VDGs. Keep in mind that if your column material tends to absorb moisture, it will take some time to dry it out maybe hours or even days so it pays to keep it dry all the time if you want it to work every time you turn it on.
                 
                When you do experiments to improve the operation of a VDG be sure to note the temperature and relative humidity. You might try something that is a real improvement but be fooled by a high humidity day.
                 
                You can also buy packets of silica gel that will absorb moisture and help dehydrate the innards of the VDG. These packets usually have an indicator that shows when the packet is saturated and has to be baked in the oven to dry the silica gel.  They can be found on the web.
                 
                By the way if you are using a motor with brushes be aware that a brush motor will produce carbon dust as a byproduct of brush wear. If this stuff gets on the belt the belt will start to become conductive and worse yet, the dust will get transfered to the rollers.....a bundle of problems.  Brush type (universal) motors are desireable since you can control the speed and you get the most HP for a given size motor. I have my universal motor enclosed in a tunnel with a muffin fan on one end. The air drawn over the motor is discharged at some distance from the lower roller.
                 
                Sphere size: The diameter of the sphere determines the practical voltage limit that it will tolerate before significant corona will occur. So, I would not try to charge a 10" sphere to a million volts no matter how high the column is. In addition, the size of the sphere determines its capacity and therefore the energy in the spark. Since there are a lot of other factors effecting the maximum voltage, I don't think you can precisely calculate these values. My 6 foot VDG uses an 18" sphere and the 8 foot one uses a 36" sphere. I tried the big sphere on the small VDG and observed a definite difference in performance. But, as I mentoned, the column leakage is different and the charging rate is different due to difference in belt width so, comparisons can only be considered approximations.  I would visit various sites of the web and see what the other enthusiasts are using and try to judge their successes and failures. Determining the exact optimum sphere diameter can be elusive and expensive. I can only suggest to err on the safe side. If I had a choice between an 18" or a 20" I'd get the 20".  I had a choice between a 30" and a 36" and chose the 36".  Even though it's a bit hard to handle, I don't regret the choice
                 
                Dick
                 
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