capacitor values

edited January 2013 in Everything Else
I bought a bag of about 100 (got almost 120)10 uf 16v capacitors from China, super cheap. They are in rows in some old synths, change em 20 at a time.

Watching RED Dwarf I decided to test them with an esr, call me bored. All the esr values were oaky, everything fell between 1-2 ohm (trouble for that value and voltage is any above 16, none were) so I figure they are "fresh". The machine beeped away and also gave value readings.

I sorted them into three piles. True values 10.nnuf, below 10uf and above 10.99uf. None were lower than 8uf and none higher than say 11.25uf with lots of variations.
Only 8-10 were actually 10 uf, about 100 were divided into the other piles, slightly more were lower. I was suprised it was 90+% of them off value.

I know there are 1% or better resistors, but I have never thought about variation in capacitors, other than for audio outputs.

so, did I get a normal batch, or a bag of culls from a factory out of the off value bins?

Is this a normal range in new average capacitors?

Should capacitors be matched precisely in circuit? Or is this sort of variation range close enough for rock n roll.

Comments

  • Hey Sealion --
    Aluminum Electrolytics have notoriously loose tolerance. That having been said, if you can live with that, they are cheap and make decent low frequency bypass caps.
    The best tolerance you can get from Digikey for a new 10uF, 16v radial package electrolytic is +/- 20%, so you're well within that.

    ESR is also a hard exact stat to measure. Generally, AE capacitors have pretty high ESR values. However, ESR depends on case type / dimensions as well as capacitance and frequency.
    1 ohm doesn't sound crazy to me. This value is also wildly temperature dependent.

    In bypass applications, generally nobody worries too much about capacitance tolerance. Other things -- dielectric, temperature rating, lifetime, etc -- matter a lot more.

    If you were making a sample and hold, or a precise filter, you would not likely use AE caps if you could help it. Film caps, or C0G ceramics are a better choice, and DO come in tighter tolerance.

    If you were bypassing a high current or high frequency circuit -- and by bypassing I mean filtering the power supply of -- you would likely use an aluminum electrolytic cap AND a smaller value ceramic cap. Some people use tantalums, I tend to avoid them.

    So, your caps are probably fine. If you're replacing caps of a similar dielectric, value, and size, you're not going to be any worse than whatever was in there before.

    If you're curious, you MUST check this site out:
    http://my.execpc.com/~endlr/index.html
    More than you ever wanted to know about capacitors.

    Also:
    http://electrochem.cwru.edu/encycl/misc/c04-appguide.pdf

    If you can get ahold of a copy of Horowitz and Hill, their section on capacitors is funny, easy to read, and informative.

    Hope this helps!
    Todd
  • Todd: Cool answer, learning learning, learning! So bulk bags of AE from HK are indeed a good deal. Thanks.
    Also just arrived an MN3004 for the jupiter's chorus.
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