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From: vaso@mips.COM (Vaso Bovan)
Newsgroups: sci.electronics
Subject: Re: Capacitor questions
Summary: Be careful
Keywords: electrolytic capacitors
Message-ID: <30715@buckaroo.mips.COM>
Date: 3 Nov 89 07:32:28 GMT
References: <109@cupcake.sal.wisc.edu>
Reply-To: vaso@mips.COM (Vaso Bovan)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 52

In article <109@cupcake.sal.wisc.edu> jwp@larry.sal.wisc.edu (Jeffrey W Percival) writes:
>I am getting a B/W TV back into working order, and want to replace a
>few capacitors. 
>
>My TV parts list gives a capacitance and voltage for each capacitor.
>The parts catalog (Digi-Key Corp.) lists many capacitors, but not
>always of the exact value I need.  So, how do I choose?  Always go to
>the next higher voltage rating?  Thence to the next higher
>capacitance?  Does it depend on what role the cap is playing in the
>circuit?
>
>Example:  I need a 15V, 5uF cap.  The catalog has this:
>
>	voltage	capacitance
>	6.3	47
>	6.3	100
>	6.3	220
>	10	22
>	10	33
>	10	47
>	16	10
>	16	22
>	16	33
>	16	47
>	25	3.3
>	25	4.7
>	25	10
>	25	22
>
>Do I go all the way up to 25 volts to get the 4.7uF?  Or do I
>simply find a better catalog?  Do caps come so finely graded?
>
>Another question:  does "bi-polar" mean the same as "non-polarized"?
>-- 

Such reseller catalogs generally do not give enough information for a
buyer to pick out the exact repalcement capacitor he needs. The buyer needs
to match not only electrical characteristics, but also mechanical
dimensions. I'd get a better catalog, from Sprague, or Nichicon, for
instance.

The degree of required electrical "match" depends greatly on the circuit 
application. An electrolytic cap using for filtering might not need to match
closely. A (generally high grade) electrolytic cap used for timing
applications had better be right on.

Non-polarized is the preferred designation for a cap constructed so that it
can be installed "backwards". The word "bi-polar" is best left to describe
semiconductors. Most electrolytic caps are polarized ("non-polarization"
exacts a volume penalty). If you install a polarized cap backwards, it will
very likely explode.  Therefore, you're not going to get any recommendations
from me, except to be careful.   :-)