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Capacitor

RogerInHawaiiRogerInHawaii Posts: 87
edited 2009-05-14 10:23 in Propeller 1
I'm interfacing my Propeller circuit to another circuit. The design for that other circuit calls for several 15pF capacitors. I purchased them at a local electronics store. But now that I'm looking at them I'm not sure they're actually 15pF capacitors. They have the normal shape for capacitors. But nowhere does it say 15pF. They're bright orange and are printed with 15M R2G 1KV. Can you tell from those numbers whether or not they're actually 15pF capacitors?

Comments

  • LeonLeon Posts: 7,620
    edited 2009-05-13 21:48
    They don't sound like ordinary 15 pF ceramic capacitors.

    Leon

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  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-05-13 21:54
    Roger,
    if you have a brand name, you might enter the word "capacitor" in the search box on a parts supplier like Digikey.


    www.digikey.com/

    In their search menu, chose the brand name, the value of the capacitor, and any other characteristics of it (whether it's a radial capacitor shape, etc.) that might apply. If they have that part, they should have a link for a data sheet, which you can download. Inside the data sheet the manufacturer will list codes that tell you what the capacitor is rated for. For example 1KV is probably something like 1000 volts. The other numbers should tell you the rest of what you need to know. I guess the trick is knowing who was the original manufacturer if all you have are the naked parts.

    I hope that helps,
    Mark
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-05-13 21:57
    The markings seem right. "15" is the value in pF; "M" is a tolerance code (±20%).

    -Phil

    Reference: www.radio-electronics.com/info/data/capacitor/capacitor-markings.php
  • mikedivmikediv Posts: 825
    edited 2009-05-14 00:02
    RogerInHawaii bright orange sounds like they are tantalum capacitors, do they have a positive +++ on one side they would work the same but are polarity sensitive and a bit costly
  • Mike GreenMike Green Posts: 23,101
    edited 2009-05-14 00:06
    15pF 1KV is a reasonable combination for a ceramic capacitor. It's probably way higher a voltage rating than you need and that means a much larger capacitor than you probably want, but it might work depending on your circuit.
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2009-05-14 00:24
    Rummaging through my parts drawer, common capacitor markings would be 0.001 to 0.1 with no letter, implying uF. Some have n at the end, for nanofarad, eg 10n. Ones over 1uF usually are bigger so have enough room to write the uF as well as the number. Some have pF. But all the ones with just a number >1 and no letter marking like u or p or n, they are all picofarad (thanks to my trusty LCR meter!). So I think your capacitor is correct.
  • RogerInHawaiiRogerInHawaii Posts: 87
    edited 2009-05-14 00:30
    mikedive,

    Nope, no +++ indication on them. I sure hope it's not polarity sensitive. The design I'm building from doesn't mention voltage rating for the capacitor, just that it's 15pF. And when I went to the local electronics store and asked for 15pF capacitors this is what he gave me. He didn't ask about voltage. The circuit is +3 volts. So I'm hoping that the 1KV, although huge, is OK with the +3V circuit. And, yes, this is in combination with a ceramic capacitor.

    - Roger
  • RaymanRayman Posts: 15,390
    edited 2009-05-14 00:31
    If it's rated for 1 kV and not really big, it probably is in the pF range... So, I'll agree that the marking is consistent with a 15pF cap.

    Are you sure you need 15 pF caps?· That's pretty small...· Usually see things like that only in RF·or high voltage circuits...

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    Post Edited (Rayman) : 5/14/2009 12:36:27 AM GMT
  • mctriviamctrivia Posts: 3,772
    edited 2009-05-14 00:54
    Unless your design is very high frequency where the shape may be important i would not worry about the voltage rating. It is a max voltage not a normal operating voltage. local places usually store high voltage ratings for low values like that because they can be used in more applications and most people buying from them are not worried about space.

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  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-05-14 09:56
    On a lot of disc ceramics in the pF range the number is just as the value up to 99pF -> where they turn to 101 etc, ie 10 with one nought added = 100. The low values often have a black tip/ridge above the number

    The down side of having a much higher voltage than needed is not just the pysical side but there will be extra lenth of signal path, more inductance, and cross coupling to other parts/earth. Unless you are working at very high frequencies these should not be a problem.
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-05-14 10:23
    Just looked up some more data

    R2G is one of the codes for its temperature coefficience they say it is -220 ppm/C or N220.

    They also say that they should be yellow, close(ish)
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