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Building an HV AC capacitor for a tesla coil

  1. Feb 5, 2009 #1
    I also have a membership at scienceforums.net and posted this to try to figure out what went wrong, but my post has been up for a week with 100 views and 2 replys both saying that they have no idea what I'm talking about. Hopefully I will have better luck here.

    Quick introduction: im 16 years old and i like to build things with high voltage. I have never taken any courses in electronics or physics so all i know is what i have researched on my own, therefore i desperately need a good forum so that i don't kill myself and my projects actually work.

    I need to build an HV capacitor somewhere between 1 and 40 nF rated for close to 28k volts to account for surges and gains in the capacitor. so i did some research... eventually i chose plexiglass for my dielectric. I picked up some .093 inch plexiglass at Home Depot, and proceded to cut out 3 inch squares. i then made 2.5 inch circles of aluminum foil using the bottom of a can and alternated between aluminum and plexiglass, lining up the circles to the best to my ability, putting out tabs of aluminum to the right side for the first aluminum circle and then to the left for the second, etc. I hot glued around each plate to prevent contact between plates of the opposite charge. I used 20 plates. I then linked all the tabs on either side by folding them together. i attached the leads of my 10k volt 30mA 60Hz neon transformer to the tabs, then added a second set of wires going off that i could short to discharge the capacitor. I submerged the entire apparatus in mineral oil as an additional precation against arcing.
    Well, as I'm sure anyone with any knowledge of basic electronics (not myself) has figured out, it didn't work. I got small sparks off of the secondary wires when i touched them (while the apparatus was plugged in), but not even enough to make an arc. There was nothing after i unplugged it. The capacitor retained no charge. I figure that, of all the possible reasons, two of the most likely are that either: a. i accidentially made a short when building the capacitor (no visible arcs existed) or b. the aluminum foil isn't conductive enough and i should get copper sheets.
    i suppose the AC could have something to do with it...
    But the bottom line is i dont know why it didn't work. So any help would be appreciated.

    P.S. i understand that the capacitor doesn't match my goal of 1 to 40nf, but that was because i decided to test it before i finished. The one i built should have been about .9nF according to my calculations.

  2. jcsd
  3. Feb 8, 2009 #2
    Sorr y didnt read the whole
    but this should help you :)


    The capacitor is made in like 10 minutes and the one in this tut can handle 20Kv just fine.

    capacitance of this bottle capacitor is 1842pF (1.8nF)! That is very high for a cheap high voltage capacitor!

    If you need more then that depends on the thickness of the bottle. If the bottle's plastic if flimsy, it can handle about 10Kv to 15Kv. If the plastic is thick and hard, it can handle 15Kv to 30Kv.

    But remember the capacitance will keep on increasing :)
    but not very much though :)
    Last edited by a moderator: Apr 24, 2017
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