DC Cap Bank

Discussion in 'General Electronics Chat' started by gt4awd, Nov 21, 2006.

  1. gt4awd

    Thread Starter New Member

    Nov 19, 2006
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    I was reading about capacitors and found that a capacitor blocks DC current. Voltage across the capacitor is constant and the current through the capacitor is zero when using DC current?

    How can I construct a capacitor that will store up a higher DC voltage than that of the input voltage? I am trying to setup a basic spark gap circuit. Where the gap is set at a certain distance and the connection cannot be made until a capacitor builds up enough stored voltage to discharge across the gap. Any help is appriciated, thanks.
     
  2. EEMajor

    Well-Known Member

    Aug 9, 2006
    67
    4
    Umm, as far as I am aware, that would violate the law of conservation of energy. If a capacitor is in series in a DC circuit, you won't have current flow. If your capacitor is in parallel then you will have current flow around the capacitor, and into the capacitor UNTIL it reaches the source voltage, at which point it will sit and wait for the source voltage to shut off and then it will discharge its power back into the circuit.

    Are you trying to setup a spark gap for a Tesla coil? If so, I can point you to some other resources for that. It is a dangerous undertaking if you don't know some basic electronics and HV safety rules....
     
  3. gt4awd

    Thread Starter New Member

    Nov 19, 2006
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    Well, as you can see from my first post there is a lot I do not know, but I have been trying to learn as much as possible. I do know basic HV safety rules, and yes I am trying to setup a spark gap configuration for a tesla coil. First I would just like to test the spark gap configuration without the rest of the coil setup, if this is possible.

    I would appriciate it if you would direct me to some good resources to do this, and thanks for the reply.
     
  4. EEMajor

    Well-Known Member

    Aug 9, 2006
    67
    4

    Hey no worries, I am a student myself, and still have much to learn. I will in fact, never be done learning.

    Anyway, I wish you luck in building your Tesla coil. I have one half built sitting in storage from my younger years, and hope to complete it someday.

    I don't want to sound like a broken record, but I will just make mention of safety again real quick. Tesla coils are lethal, and must be treated as such. Please be ever so cautious while working on this, and take measures to make sure that others who are not educated in electronics will not be able to turn it on and hurt themselves. Many times people take extra caution with the HV side, and forget that the normal household mains are deadly as well. Sorry to sound like your mother! :eek:

    That said, here are some links that I used back in the day when I began my project. Some of the better links I had no longer work, but here is what is left, enjoy:

    http://www.ttr.com/rotary_spark_gap.htm

    http://www.kronjaeger.com/hv/hv/src/tesla/index.html

    http://members.tm.net/lapointe/SparkGap.htm

    http://www.connecticut-business.com/Users/Steve/tesla.htm

    This would be a good starting point for a first time coil builder: (mini version)
    http://www.abrownson.f2s.com/10183/minisgtc.htm



    Again, be safe and have fun!
     
  5. EEMajor

    Well-Known Member

    Aug 9, 2006
    67
    4
    These formulas come from one of the pages that no longer exists. I was smart enough back then to save the formulas, but too dumb to save the rest of the site. Unfortunate.

    Anyway, these formulas can help you calculate all aspects of your coil.
     
  6. gt4awd

    Thread Starter New Member

    Nov 19, 2006
    8
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    EEMajor, thanks a lot for the links, and additional information. In the field of electricity there is always room for extra safety reminders. You usually dont get a second chance when a mistake happens with high voltage.

    I have not checked out the links yet, but i'm sure they contain good information. By the way, I was wondering if you could look back at my first post "Volts/Amps" and comment on my transformers setup. I would like to know if it is setup correctly and safe. As far as I know it is, except for the fact that i'm using a surge protector as my on/off switch. I remember hearing mechanical switches are not that safe to rely upon.

    The transformer makes a noticable sound however, that would be hard to miss, and I think almost impossible to know it is not powered. Anyways, agian I really appriciate your help, and good luck on finishing your own telsa coil sometime.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Just to chime in - a Tesla coil is a geneator of high voltage and high frequency AC. If you are using a vacuum tube driver, then you will need a filter capacitor for the B+ supply, but the value is not large. A few tens of microfarads at a rating above the plate voltage is enough. The coil output is not rectified or filtered.
     
  8. gt4awd

    Thread Starter New Member

    Nov 19, 2006
    8
    0
    The link to the mini coil does seem like a good place to start. I noticed a lot of the pages I have already read through advice not to use to main AC power of your house with a tesla coil. Yet, when I first started learning about tesla coils many people seem to use a neon sign transformer connected through the AC main. This is the reason I purchased a neon transformer.

    The transformer is 120v primary, secondary mid point grounded 9000v 30ma, no Ground fault interrupter. I noticed all the sites say that a tesla coil uses AC current. Am I correct at assuming it is the spark gap setup that coverts the DC current to AC?

    I am slightly confused on exactly how a static spark gap would work. After building several jacobs ladders and seeing how they work, one would think a static spark gap with small gap (around 1mm) would keep a constant arc? I can see how the rotating spark gaps works though.

    If someone could further explain these aspects of the tesla coil which are still confusing me that would be great.

    By the way beenthere, I can not follow your post. This is obviously due to my lack of understanding.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    A Tesla coil is just a step-up transformer. It is driven by a (relatively) low-voltage circuit. Quite often, the primary is in the plate circuit of a tube. The tube is either driven by a radio-frequency oscillator, or can sel-oscillate. The coil's secondary has many more turns than the primary, so it steps up voltage. It's the radio-frequency that helps ionize air and let the arc carry over several feet.
     
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