Question about buying caps...

Discussion in 'General Electronics Chat' started by thakid87, Jul 12, 2010.

  1. thakid87

    Thread Starter Active Member

    May 23, 2009
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    Should I just spring for the cheaper ceramic disc caps? Should I get some polarized caps? Aluminum, tantalum, etc?

    Are there situations where I would need a specific type of capacitor.

    Thanks.
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Are you wanting to set up a kit?

    Ceramics are cheap, as are polyesters. I generally get them as I need them, except for a few values. The ones I've stocked up on are electrolytics.

    It all depends what you're wanting them for.

    Tantalum caps are the deluxe models of electrolytics (quiet, stable), though they can have the undesirable side effect of catching on fire like a match head if abused.
     
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  3. thakid87

    Thread Starter Active Member

    May 23, 2009
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    I am just looking to fill up an order with enough parts to justify the shipping and I realized I don't really have many capacitors.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Been there. There are quite a few members here from the area you live, there are local stores I believe.
     
  5. Ghar

    Active Member

    Mar 8, 2010
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    Personally I would buy capacitors from various ranges of capacitance, like a bunch of pF, nF, uF, and some mF.
    Mix up the capacitor types and by going through those ranges you'll necessarily run into several anyway.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Keep in mind that ceramic and metal poly caps have practically an indefinite "shelf life". You can leave them sit for 50 years, and one day plop them in a circuit and they will work just fine.

    Tantalum and aluminum electrolytic caps are not that "user friendly". If these type capacitors have been "on the shelf" or otherwise in disuse for a period of time, they will require re-forming before being placed in service.

    In a nutshell, the re-forming process is charging a capacitor slowly via a current limited source to it's rated voltage, until its' leakage rate is acceptable. Trying to hurry this process will likely result in a bright flash, accompanied by a loud (((<<***BANG***>>>))) and some very stinky smoke. :eek:

    I'm not often at odds with Bill_Marsden, but I suggest that you stock up on the range of ceramic/poly film caps that you are likely to use in the future. 100nF/0.1uF is a mandatory size to have on hand for IC bypass capacitors. EVERY IC requires at least one bypass capacitor across it's power pins; and 0.1uF/100nF is the most often recommended value.

    The 78xx/79xx series regulators specify 0.33uF/330nF caps across the input and ground terminals. However, in the interest of stocking fewer parts, an 0.1uF and 1.0uF cap in parallel will more than satisfy the requirements.

    If you plan on using 555/556 timers, then also pick up a bunch of 1uF ceramic or metal poly film caps, and some 10nF caps. 555 timers require (as a minimum) of one 0.1uF and one 1.0uF caps in parallel across their supply pins. For best stability, you should also use a 10nF cap from pin 5 (control) to ground.

    I do have a number of aluminum electrolytic and tantalum caps on hand, but I am also in a position to re-form them properly before placing them into service. A novice is best served by buying only the electrolytic caps they need immediately from a large vendor like Mouser, Digikey, Newark, AvnetExpress, etc. who are authorized distributors of many manufacturers, and have such a high volume of sales that it is very unlikely that you will receive "stale" capacitors.
     
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