Quality Capacitors

Discussion in 'General Electronics Chat' started by cldudley, Jan 11, 2010.

  1. cldudley

    Thread Starter New Member

    Oct 7, 2009
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    Hello again group!

    Firstly, I must say that this is by far the best community website I have come across for the subject of hobby electronics, and all of the posters here are great!

    I will soon be ordering components (from Mouser) to put together a sturdy bench power supply to power my later experiments. Basically all I have now is a breadboard with some 78xx regulators and associated caps/protection diodes, so I am putting together something much nicer with an actual enclosure, adjustable voltage (LM723-based) and current limiting.

    My question here is, I know this power supply will be used for a long time, and will need to be pretty reliable. I am confident in the design, but now I wonder if the manufacturer of the components I purchase will be a major factor in the reliability of the unit.

    I will order some pretty large electrolytics for this thing, and having had very bad experiences with equipment in the past that blew caps, I am wondering if there is a particular brand or line of caps that are good quality?

    I hear good things more or less about Nichicon and Panasonic, are there others? Am I worried about something that is a non-issue?

    Similarly, there will be quite a few transistors etc in here (PN2222 mostly), these are made by many companies, Fairchild, ON Semi, etc, is there any brand difference there? Prices differ on the order of pennies or nickels.

    Hopefully some of the old hands in here can shed some light on the subject for me. :)
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    I prefer anything that is mil speced, this is a pretty good guide in and of itself. For example, the PN2222A and the 2N2222A are the same transistor more or less, but I believe the 2N2222A is mil speced. Generally you can't go wrong using these ratings, sort of a looser version of subsafe.

    There is another rating used for switching power supplies, I think it is called ESR (Equivalent Series Resistance). The lower this number the better (obviously). Wikipedia has a decent article on caps.
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    I do not think the hobbyist need to spend the extra cost on purchaseing mil speced components. Standard commercial types will do the job. It is like thinking your standard car will go faster if you fill 98 octane gasoline, instead of 95 octane gasoline. It is better to put extra money in say a proper solder iron.
    For your filter capacitors you may gain something by selecting a low esr type.
     
    Last edited: Jan 11, 2010
  4. someonesdad

    Senior Member

    Jul 7, 2009
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    I concur with using off the shelf components (as opposed to the extra cost of mil-spec). However, I have some suggestions:

    1. Buy some extra components that you fear may fail and store them against the day that the original ones used might fail. Label them carefully so you remember when you got them, part numbers, costs, and what they're for. Include a copy of the schematic too.

    2. When you've built your circuit, make measurements of voltage and take scope traces at various points. Then document this somewhere (e.g., lab notebook) so you'll have it when you need to fix things a decade or two in the future.

    By going to all this trouble, the hardware will sense it and a corollary of Murphy's law says that this circuit will operate reliably for the next 100 years... :p
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    I tend to use surplus parts myself. Most electronics types do, but if you want reliability the standards are out there.
     
  6. radiohead

    Active Member

    May 28, 2009
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    In case the beginner doesn't know, MIL SPEC stands for military specification. Parts that carry the MIL SPEC rating are authorized for all military applications from avionics to receiver-transmitters. For example, coaxial cable RG-58 versus RG-58A/U. Standard RG-58 has one layer of shield-to-ground while the RG-58A/U (MIL-Spec) has multiple layers to make it a better tempest proof cable. The bottom line is you get what you pay for.
     
  7. loosewire

    AAC Fanatic!

    Apr 25, 2008
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    What are the standards for the products that last for 2-3 years.
    Computers,plasma t.v.s
     
  8. Tahmid

    Active Member

    Jul 2, 2008
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    Hi,
    For PN2222, I use the ones from Phillips and also some Chinese ones(much cheaper), but none ever failed, so I guess it's okay to use it from any manufacturer.
    I've had plenty of capacitor failures before when I used non-brand ones. But, later, I decided to use only those from Nichicon, and mostly, almost 80% of the time, Nippon Chemicon. Ever since, I've had zero capacitor failure issues, not even in my switching power supplies, where the capacitors are even more greatly put under stress.
    I don't think ESR plays that much of an effect in linear power supplies, only for switching power supplies. I've had a few not-so-low ESR caps from Nichicon in linear regulators, didn't fail, but, failed within a few hours in switching power supplies.
    Hope this helped.
    Tahmid.
     
  9. radiohead

    Active Member

    May 28, 2009
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    Vishay, Sprague and Kemet are just a few capacitor manufacturers that have never let me down. With a well designed circuit, the capacitors should last 10 years or more. Be sure to observe the voltage rating on the capacitors and the polarity on polarized types.
     
  10. t06afre

    AAC Fanatic!

    May 11, 2009
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    My point was that more expensive versions of integrated circuits. In most cases will not work any better for the hobbyist. Mil spec circuits do have as an example wider temprature range. But then do the hobbyist need a -55°C ~ 125°C temprature range? Not very often I guess;)
    As an example. The OP is working on a power supply project using the LM723 IC. Digikey have this chip in many versions (http://search.digikey.com/scripts/D...ge_link=hp_go_button&KeyWords=lm723&x=19&y=30)
    I doubt very much the OP will see any functional improvment at all. If he use the LM723H/NOPB version (7.1$) instead of the LM723CN (0.81$) version. This can actually be tested. By bending the legs of a LM723H version somewhat it will fit in a dip version circuit.
     
  11. cldudley

    Thread Starter New Member

    Oct 7, 2009
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    I am very grateful for all the help in this forum!

    I agree with most here also in that while I want reliability, MILspec is probably a little more than I really need. Since I am building it, I will should be able to service it myself.
    =)
     
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