Capacitor value

Discussion in 'General Electronics Chat' started by Gdrumm, Apr 25, 2009.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Is it possible to discover a capacitor's value without clear markings?

    Is there some type of measurement I can do with a voltmeter?

    I have a small blue cap, with the numbers 104 on the side, and I want use it to set up a parallel RC circuit, to re-create a lab we have done at school.

    Thanks,
    Gary
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    2,536
    A LOT of newer DVMs have capacitance meters as a feature, but I don't think that is what you're talking about, is it?

    104 is 10000pf, or .01µF.
     
  3. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    Yes, it can be measured.

    Yes, some methods can use a voltmeter, but not a voltmeter alone. You can use an AC sinusoidal voltage source with an RC circuit. O-scopes are better to use however.

    OK, good luck! By the way, the 104 is a clear marking of the capacitor value. - Just in case you didn't realize that.
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Well yes if you had a sufficiently large value resistor, in relation to the capacitor, you could measure the charge and/or discharge with your voltmeter and your wristwatch.
     
  5. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Thanks Bill,
    I suppose that is what I'm talking about, but I don't have a meter with that ability.

    I have an Oscilliscope, a benchtop Fluke meter, and an old Function Generator.

    Might I be able to apply a voltage, get a reading, and do some math to help me identify it?

    Thanks,
    Gary
     
  6. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    By clear, I meant discernable. I have others that specify their unit of measure, such as 10 micro farad, 50 v, etc.

    Do you think that would work with a low voltage?
    I'm looking at a 8.78 V ac power supply, with a 4.7K resistor, and a capacitor (I thought the smaller the better?).

    Gary
     
  7. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Forgive me for not reading Bill's reply completely.

    Thanks Bill (and everyone).

    I will read and print this off later.

    The answer of 1 micro farad is what I needed.

    Gary
     
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
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    People often forget that a scope can also be pressed into service as a voltmeter, currentmeter, chargemeter, AC or DC...the list is nearly endless.
     
  9. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Is there a way to guestimate what components would be necessary to make up a reasonable test circuit?
    For example:
    My AC Power supply is only 8.78 V AC
    The Frequency if 60 HZ
    The capacitor is .01 micro farads
    The resistor is 4.637K Ohms

    In solving, I'm getting some weird answers
    XC = 265 K
    IR = 1.91 mA
    IC = 33.1 micro A
    IT = 1.91 mA
    Z = 4.59 K
    PC = 263 K
    PR = 4.59 K
    PT = 4.59 K
    Phase = 992???
    P.F. = 1

    What component would work best?
    I have a wide range of resistor sizes to choose from, a few capacitors, and not many choices on voltage / frequency?

    Thanks, Gary
     
  10. leftyretro

    Active Member

    Nov 25, 2008
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    You better read it again, the answer given was .01 not 1 microfarad ;)

    Lefty
     
  11. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    No.
    104 is 0.1uF not 0.01uF. 103 is 0.01uf.

    10 followed by four zeros is 100,000pF. 100,000pF is 0.1uf.

    Why can't the Orientals label it 0.1uF or 100nF instead of 104??
     
  12. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Why do you credit Orientals for this convention?
     
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