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High voltage Direct Current

  1. Dec 24, 2009 #1

    taylaron

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    Happy holidays everyone!

    I'm searching how to produce high voltage, high current DC electricity to be used for statically charging a giant electroscope. The explanation why is very elaborate, so to put it simply, I need to energize a giant electroscope.

    I have limited electrical engineering education, but a thorough explanation would be appreciated.

    Perhaps using a Telsa coil to generate high voltage AC current and then rectify the current. Evidently this is not an option because rectifying circuits can not handle such extreme voltages.

    Any Ideas?

    Regards,
    -Tay
     
  2. jcsd
  3. Dec 24, 2009 #2

    vk6kro

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    Probably a Wimshurst Machine would be OK. These generate a good spark and it is DC at about 50000 volts. You have to wind a handle to get the voltage.

    The next step up would be a Van Der Graaf machine, but that may be too high a voltage for your project. Good ones generate sparks that are a foot long, or more.

    Another choice, at your own risk, is a defunct color TV set which has a source of 30000 volts DC in it. If this part of the circuit was still working, that would be plenty for an electroscope.

    For you and anyone else reading this, be aware that any voltage over 50 volts can kill you, especially if it is on a capacitor capable of delivering a lot of current.

    Don't operate Van Der Graaf machines anywhere near electronic equipment.
     
  4. Dec 27, 2009 #3
    How giant is that electroscope?
    There is a giant Van de Graaff generator that should be perfect for charging giant things.
    http://www.mos.org/sln/toe/
    However I don't think they will borrow it to you.
     
  5. Dec 27, 2009 #4

    taylaron

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    I'm attempting to energize 10 grams of activated carbon to the highest static potential possible. I will then use the discharge to power a circuit, regulating the flow of electricity with a "current potentiometer" I designed. The surface area is calculated using the activated carbon surface area to weight ratio of 100m^2 per gram [Figure from http://www.cee.vt.edu/ewr/environmental/teach/wtprimer/carbon/sketcarb.html] [Broken]. Imagine an electroscope with 1,000 m^2 of surface area made of conductive carbon....
     
    Last edited by a moderator: May 4, 2017
  6. Dec 27, 2009 #5

    vk6kro

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    That link doesn't seem to be working, but maybe you could explain why you think this would be a good idea?

    One key to getting a high voltage onto something without it discharging is to have a very smooth surface. Charge tends to spark away at any sharp point.
    So, you always see Van Der Graaff generators with a highly polished dome on them.

    I have to wonder if your conductive carbon would act like a lot of sharp points.

    What circuit are you thinking of powering after your "current potentiometer". I'm not even sure what that is, so you could explain that, too, if you like.
     
  7. Dec 27, 2009 #6

    dlgoff

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    http://www.cee.vt.edu/ewr/environmen...sketcarb.html" [Broken]
    The OP has an extra ] at the end.
     
    Last edited by a moderator: May 4, 2017
  8. Dec 27, 2009 #7

    vk6kro

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    This one works:

    http://www.cee.vt.edu/ewr/environmental/teach/wtprimer/carbon/sketcarb.html [Broken]
     
    Last edited by a moderator: May 4, 2017
  9. Dec 27, 2009 #8

    taylaron

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    I apologize for the broken link and yes, http://www.cee.vt.edu/ewr/environmental/teach/wtprimer/carbon/sketcarb.html [Broken] is the correct link.

    The device i'm describing is similar to modern super capacitors according to http://scitizen.com/screens/blogPage/viewBlog/sw_viewBlog.php?idTheme=5&idContribution=174 [Broken]

    an appropriate diagram of a modern super capacitor cell can be found here:
    http://www.nanomac.uq.edu.au/pdfs/Fact%20SheetSupercapicitors.pdf [Broken]

    Instead of having multiple cells in a super capacitor, i'm attempting to merge the layers into one block and provide a more compact, powerful version. I realize that combining the cells eliminates the possibility of putting multiple cells in series or parallel and thus dramatically increases the discharge voltage (if I am correct).
    To prevent premature discharge, the activated carbon would be placed in a very resistive dielectric container.

    To best illustrate the device and DC circuit I intend to build, think of two classic gold foil electroscopes, each discharge probe spaced apart from one another. One of the electroscopes is charged with static electricity and the other is neutral. Between the charged scope and the circuit is a "current potentiometer or c-pot". After the c-pot is a resistor and then the resistor is connected to the neutral electroscope. This is illustrated in the image attached. The electrons flow from the high concentration in one electroscope to the other neutral electroscope until both scopes have reached static equilibrium.

    I realize that the definition of a circuit is along the lines of 'current traveling in a closed loop' and that the "circuit" described above doesn't exactly describe this definition. But for simplicity sake, I will continue to use the word circuit, although it is the wrong term.

    The c-pot I describe works by varying the conductivity of a material. Unfortunately I intend to patent the concept so I can not give much detail.

    I am concerned that the electrons stored on the surface area of the activated carbon will not be able to travel freely within the body of activated carbon itself and reach the conductive terminal on one end. Activated carbon supposedly is conductive, but can charge on one side of a clump freely move to the other side? I sure as heck hope so, because modern super capacitors do it on a smaller scale. The increased thickness concerns me.

    The dielectric containing the activated carbon would of course be filled with a liquid. Can the liquid be conductive and still be able to store electrons on the surface of the activated carbon?

    According to http://www.theactivatedcarbon.com/page/activated-carbon-properties/" [Broken] 10 grams of activated carbon would provide 15,000m^2 of surface area to store electrons on.
    Thoughts?

    Thank you for your help

    -Tay
     

    Attached Files:

    Last edited by a moderator: May 4, 2017
  10. Dec 28, 2009 #9
    Your c-pot sounds like a simple transistor.
    If you statically charge a piece of activated carbon, it won't store much more charge then an equally big sphere.
    In a super capacitor the large surface area gives you a large capacitance, however if you just put that activated carbon into an insulating liquid and apply a charge to it you don't get a capacitor effect. The capacity will be very small. The charge will not distribute over the entire surface area. It will only be at the outside. All the surface area on the inside will stay free of charge.
    To get a large capacitance the carbon needs to be in a conductive liquid. But then you can only apply a small voltage.
     
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