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Charging 1 kV capacitor?

Discussion in 'General Electronics Discussion' started by z0tx, Sep 27, 2010.

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  1. z0tx

    z0tx

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    Sep 27, 2010
    Hello!

    I have a 1 kV 300 µF capacitor and wish to fully charge it to observe its discharge through various material. Ideally the charge circuit would be working on a battery, anything between 1.5 to 12 V... So basically what I would like to know is how to turn standard battery voltage into 1 kV DC. Something small would be preferable. I have read about boost converters, is this what I need? I don't have much knowledge about electronics so any help would be welcome!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Please convince us you know the safety aspects of working around a 1kV 300uF capacitor first.

    What are the potential risks and what precautions do you plan on taking?
     
  3. z0tx

    z0tx

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    Sep 27, 2010
    Always discharge the capacitor before handling, and don't give it a higher voltage than it can tolerate of course. I'll work with plastic gloves.
     
  4. shrtrnd

    shrtrnd

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    Jan 15, 2010
    And some safety glasses, I hope.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    And someone to perform CPR as required.

    Start with the innards of a disposable camera. You'll get 300 to 350 volts with enough energy to kill yourself, but only if you try hard.

    Work with that for a while, if you get as belt from that you will have a good chance of surviving to learn from it.

    If you're keen you can use a voltage multiplier to charge the capacitor (slowly) to a higher voltage.
     
    Last edited: Sep 28, 2010
  6. z0tx

    z0tx

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    Sep 27, 2010
    This was a question about a 1 kV capacitor. I said I wasn't an expert but that doesn't mean I have no knowledge at all... I have already worked with disposable camera capacitors, got a nice shock quite a few times. I simply want to construct something similar with a 1 kV capacitor... And so I ask, how?

    Steve what do you mean by 'slow'?
     
  7. Militoy

    Militoy

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    Aug 24, 2010
    I get the feeling that your choice of words wasn't by accident - A 300uF cap charged to 1000V is going to have 150 Joules of energy stored in it. Coincidentally - that's the exact starting energy level used in a defibrillator to stop the heart - so it can return to a normal rhythm.
     
  8. z0tx

    z0tx

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    Sep 27, 2010
    Okay I guess I asked in the wrong place as no one seems to be competent enough to answer my question...!
     
  9. Militoy

    Militoy

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    Aug 24, 2010
    I wouldn’t say it’s as much a matter of competence as it is a matter of willingness. Steve actually gave you enough information so that with a quick Google search, and a little self-motivation, you could figure out what you need to accomplish the task. My current employment is in the field of high voltage Engineering – and I’ve seen enough inexperienced people get injured over the years to make me somewhat cautious about what information I share on a public forum.
     
  10. NickS

    NickS

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    Apr 6, 2010
    Another customer not happy with the service he paid for...
    The problem here is not competency its responsibility. By which I mean it can be seen as irresponsible to give out information that enables someone to produce a device capable of accidentally killing its maker.

    I do subscribe to this reluctance but it is not as though this sort of device is top secret. There are plenty of sources online for developing lethal circuits. And if you are adequately motivated then you have likely already found other alternatives.

    I too enjoy high voltage projects. But the place where yours kind of crosses a boundary is the size of your cap. 300u is some serious storage! And you should know you are almost certainly going to take a hit from it at some point in your project.

    But I am sure you grow tired of warnings so now for the options.
    (1)Voltage doubler: This is probably my least favorite option because it requires so many stages. Each stage at best buys you twice the level as before. And this will take quite a while to charge the likes of a 300u cap.

    (2)Transformer: This is probably the most efficient way of doing what you want. But transformers with the step up you need are hard to find. That means the analysis of trying to design one(which is not my forte but I am trying to learn).

    (3) Collapsing field in a Inductor: This is my favorite because of its simplicity. You basically dump current into an inductor and then try to cut the flow instantly. The result is a huge voltage spike since the inductor is resisting an instant change in current. You would capture this energy and keep cycling. This too will take a while to charge the massive cap but it does keep other parts to a minimum.

    So if you like any of those ideas then post back and I will go into more detail.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    He should ask Ian for a full refund.
     
  12. z0tx

    z0tx

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    Sep 27, 2010
    Thank you for your reply NickS!

    I only mentionned competence to get answers...
    I had already researched the possibility of transformers and indeed this is sort of step up must be quite rare. What do you mean by designing one?
    Also, while researching, I found DC-DC converters such as boosts and flybacks. Would these be of any interest in this case or cannot they be used?
     
  13. NickS

    NickS

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    Apr 6, 2010
    Transformers are not rare but when you need one with that high of a turns ratio it is usually very specific to one design so they are custom ordered/made. Designing a transformer takes many factors into account(there is way more to it than just turns ratio).

    DC-DC operates with the same principles as my option 3.

    Flyback circuits converters require flyback transformers.
     
  14. Militoy

    Militoy

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    0
    Aug 24, 2010
    Actually..this would be the most common method of charging a cap to 1KV. Usually, the secondary of the transformer will be selected to limit dielectric stress on the transformer itself - by using a Villard cascade - either a doubler or quadrupler.
     
  15. security_man

    security_man

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    Feb 10, 2011
    I say, use a microwave oven transformer, they give 2kV AC on the secondary winding. Then you just need to make a circuit to rectify the voltage.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    security_man: You're really hot on microwave transformers aren't you?
     
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