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Question about capacitor charging

  1. Dec 8, 2009 #1
    Other than a power box which can be incredibly expensive, can someone show a good way to charge a capacitor in the 300-450 volt range, and as i am designing a circuit around multiple capacitors would i connect them in series or parallel, and yes they are polarized
     
  2. jcsd
  3. Dec 8, 2009 #2

    Integral

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    If you cannot answer for yourself, the questions you ask. I doubt the wisdom of your taking on this project.
     
  4. Dec 9, 2009 #3
    I guess that is my fault for not being clear, the rig I was using was broken when someone knocked over the box. What kinds of alternate methods can be used?
     
  5. Dec 9, 2009 #4

    vk6kro

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    You charge up a capacitor by connecting it across a DC power supply with or without a series resistor.
    Given enough time (determined by the capacitance and the resistance of any series resistor) the capacitor will eventually have a voltage across it equal to the power supply voltage.

    So, to charge a capacitor, first you need to find a power supply that can supply the voltage required.

    Not sure what you mean by a "RIG".

    Power supplies don't have to be expensive, but they can sure be dangerous if you are talking about high voltage supplies. So, you might like to read about them on Wikipedia:

    http://en.wikipedia.org/wiki/Power_supplies

    http://en.wikipedia.org/wiki/Rectifier

    Especially read about the use of bleeder resistors. These are placed across capacitors so that the capacitor discharges into them when the power is removed. Otherwise, some low leakage capacitors can carry a lethal charge for months.

    Capacitors can be charged individually and placed in series for discharge. This doubles the voltage available.
    Connecting them in series while they are charged would be a risky process unless you did it with a switch inside a box with the capacitors.

    Always play it safe with electricity. Anything over 50 volts can potentially kill you.
     
  6. Dec 10, 2009 #5

    sophiecentaur

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    Charged capacitors can be very scary! The capacitor in a camera flash unit can give a healthy smack if you touch it by mistake, days after it was used / charged! Be very careful and always discharge capacitors through a resistor, rather than just 'shorting' them out. When you see how hot the resistor can get, you'll realise the actual amount of energy stored.
     
  7. Dec 11, 2009 #6
    Baycon,

    Perhaps Integral has got it about right, if you had enough knowledge and experience to tackle this sort of thing safely, you ought to be able to work out a cheap but adequate solution to your power supply problem.

    Some time ago, an over-confident student did know enough to get some capacitors charged to a dangerous voltage. He did not know about discharge resistors though, and this nearly cost him his life. The circuit was switched off when he touched it by mistake, but the residual charge was still sufficient to give him a horribly painful shock. Luckily he survived, but sadly he still grew up to become an Electrical Engineer. Don't follow his example!

    Regards.
     
  8. Dec 11, 2009 #7

    sophiecentaur

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    I guess that student could have been well known to Baycon?
    But there are worse fates than becoming an Electrical Engineer.
     
  9. Dec 11, 2009 #8
    A boost converter would probably be the easiest approach, but I must agree with the others in that you must be very careful when working with voltages above 50V. Don't be misled by the size of capacitors your using either, a typical photo flash capacitor for example, is about the size of a "C" battery, yet holds 16.5J of energy when it only takes 16J to kill you. You can also get electrical burns to your inside tissue from current passing thru muscle and skin. A good habit to get into when working on circuits like this is to keep one hand in your pocket to reduce the chance of passing current through your heart, use a voltmeter to verify that everything is discharged before you touch it, and put bleeder resistors on all high voltage capacitors as they can regain some charge even after they have been discharged. Here is a good site about electrical safety
    http://ehs.okstate.edu/modules/electric/index.htm [Broken]
     
    Last edited by a moderator: May 4, 2017
  10. Dec 11, 2009 #9
    Thanks for all the help guys, I decided to take my own advice and get the help of an electrician that lives across the street. My project worked out after all :)
     
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