Does it matter which capacitor I get?

Discussion in 'General Electronics Chat' started by zero_coke, Nov 28, 2011.

  1. zero_coke

    Thread Starter Active Member

    Apr 22, 2009
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    There's some rated 500V and some 20V, if my application is <10V, can I use the 500V capacitor? I mean, can I use any capacitor assuming the voltage I apply to it is less than the one written on it?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Yes, you can use a 500VDC capacitor for 10V application. It will be large, but electrically it is still whatever capacitance that is marked on the case.
     
  3. zero_coke

    Thread Starter Active Member

    Apr 22, 2009
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    So I shouldn't be worried so as long as it is the capacitance I need and the voltage rating is above what I'm using on the design right? Why are there so many types of capacitors then? Some are polar, some are bipolar...etc..
     
  4. ajm113

    Member

    Feb 19, 2011
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    Naw it shouldn't really matter if your replacing a capacitor that was originally 330uF 10v with something like 330uf 500v, as long as you have the right capacitance and capacitor type. Now if you used a 5v 330uF as a replacement, expect that thing to blowup. Just keep in mind capacitors don't change the voltage when they discharge.

    http://www.radio-electronics.com/info/data/capacitor/capacitor_types.php

    That link should answer most of your questions on difference and types.
     
  5. bertus

    Administrator

    Apr 5, 2008
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  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Generally, as long as it isn't an electrolytic, you can use over voltage rated caps.

    Value in uF or pF, and hopefully voltage, are normally the only considerations when it comes to choosing a capacitor for a hobby circuit. This is usually fine as they operate in a controlled environment at room temperature and generally low frequencies and voltages.

    If you are working on a project an need a 100nF/0.1uF bypass capacitor, you will most likely grab a yellow disc looking one, which is often ceramic. The reason for this is they are extremely cheap and can be found anywhere.

    Electrolytics are large value(tens to thousands uF) "can" type aluminum or the high cost, smaller "dipped" looking tantalum. Both are polarized and will explode if hooked up backwards. "Can" type (Aluminum Electrolytics) have relatively high ESR (Equivalent Series Resistance), which has caused "Capacitor Plague" in the past decade from counterfeits skimping on the electrolyte formula, and plain bad batches. They can also vary from 50% to 200% of their printed value, unless high quality (and higher priced) caps are specified. Electrolytics (Aluminum and Tantalum) should be used within 50% of their rated voltage, but NEVER over their rated voltage, otherwise they have a tendency to turn into conductive confetti that shorts out everything else on the board. Essentially, the same behavior as a cap is hooked up backwards, or one that loses electrolyte and has it's ESR increase which increases the temp.

    "The others" have a wide variety of dielectrics, there are entire books written on dielectrics from paper/oil to polypropylene to mica. Some have faster response times to certain signals, some have lower ESR, although ESR typically is too low to matter in most small values (<1uF). Variation from printed value and value over temperature range are what differentiate the cheap capacitors from the more expensive ones of the same value but different dielectric. The worse specs for these is also -50% to +200%, but more often is around -30% to +100%, but at room temp, they are usually close to printed value. The more expensive, such as mica and metalliized film have great specs, and high prices to match.

    Don't get me started on "Audio Grade" capacitors, that is a phrase they print on them so they can charge an extra 100x to 10000x the price of an otherwise well spec'd cap for the purpose without the printing.
     
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