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Help With Capacitors

Discussion in 'General Electronics Discussion' started by Casablanca, Jan 6, 2010.

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  1. Casablanca

    Casablanca

    5
    0
    Jan 1, 2010
    This is my second post on this forum. As I mentioned in my first post, I am trying to teach myself basic electronics. Since I got so much invaluable help the first time, here are 2 more questions.

    I bought a variety of capacitors. The electrolytic caps are well marked and I have no trouble in determining their capacitance.

    The problem I am having is making sense of the markings on the ceramic, and mica caps. For example, I have a green capacitor that is about 3/8 inches long and about the same width. The only marking on it is: “2A334J.” I don’t have a clue on how to decipher what the rated capacitance is. I also have some much smaller caps that are more or less circular, with a diameter of about 1/16 of an inch, and are orange in color. The only marking on one of them states: “221.”

    QUESTION 1: Could someone teach me how to read the capacitance value of these caps?

    Since I couldn’t figure out the values, I bought an Extech LCR meter, model 380193. The “2A334J” cap I described above measures 350 nF at 1Khz with a Q of 176. If I change the frequency of the meter to 120hz, the capacitance stays the same, but the Q changes to 362.

    The second cap I described above (with the marking “221”) measures 208 pF at 1Khz, with a Q of 73. At 120hz, the capacitance stays the same, but the Q changes to 140.

    QUESTION 2: What does the “Q” reading mean? It is not explained in the manual for the meter and I can’t find it in my textbook.

    Thanks in advance for help with these 2 questions.
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Q1. Yes.
    The key numbers are 334, which are interpreted just like a resistor value, meaning 33 + 4 zero's = 330000pF (picoFarads) = 330nF (nanoFarads). Likewise 221 = 22 + 1 zero = 220pf. Letters may indicate the rated voltage and/or tolerance.

    Q2: The Q is an old term and stands for quality factor. The higher the number is the less are the losses within the capacitor.
    There are both series and parallell resistances in a capacitor that leads to less than ideal properties - & losses. ESR is a crucial parameter of modern electrolytics. Search for "capacitor equivalent diagram" and you'll see how it works.
    Capacitance, ESR, & Q can all change with frequency, temperature, & applied voltage (depending on type of capacitor).
     
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