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[DPRG] Capacitor Question

Subject: [DPRG] Capacitor Question
From: Earl Bollinger earlwbollinger at comcast.net
Date: Tue Aug 12 23:31:01 CDT 2003

In my opinion....
Well actually we have many kinds of capacitors.
  Electrolytic  comes in several types, paper foil, paper foil oil
filled, aluminum oxide types, tantalum, some types actually behave more
like a battery with potassium hydroxide electrolyte, and others look
more like a nickel cadmium battery. Electrolytics are all polarized and
you need be careful with the plus and minus poles on the caps. There are
some 1+ farad caps that aren't polarized though, Panasonic usually makes
these and they behave like a non-polarized nicad battery with a high
internal resistance.
  There are some special oil filled caps with paper and foil innards,
these are non-polarized starter caps for motors and florescent lights.
There are also some non-oiled filled versions too.
  The paper and foil condenser in old car point and ignition systems is
actually an electrolytic cap. The paper dielectric would eventually get
damaged by the arcing across the points and temperature and humidity and
start to shortout or go open, thus causing you to have to replace them
often.
  Tantalum caps are polarized, they are low impedance devices.You do
need to check the brand's specs though, they haven't standardized on
which end is marked positive and negative. Tantalums spew a lot of
smoke, and foul smelling stuff all over the inside of a PCB when they
let go. You need to allow for about 40% or higher max ratings for
voltage.
Of course the electrolytics in general blow up nicely anyway. But
tantalums still stink up the PCB no matter how much you clean it.
  Ceramic caps, not much to say here except there are several different
kinds. The differences deal with their impedance and how the caps
respond to radio frequencies and clock speeds, their internal inductance
and capacitance and how it changes at different clock speed and RFI
needs.
There are special high voltage caps with thicker glass or ceramic
dialectrics and shields for really high voltages.
These are the most common caps everyone uses. Jillions o different kinds
and shapes and sizes.
  PolyPropylene and other plastic and foil caps, these usually have low
impedance and react well at high frequencies. Thus you see them a lot
for filtering electric motor RFI noise, etc.
  Mylar caps more or less behave like the polypropylene ones above.
  Mica caps, you usually don't see these much anymore, but they used
them a lot in the good old vacuum tube days.

  Air dielectric caps, these are usually tuneable caps used in radio
receivers and transmitters. But they are sensitive to humidity. 

Microwave circuits, the capacitance is actually the PCB traces and the
ground shields and cases at these really high frequencies. You sometimes
have trim the PCB traces to change the capacitance. Or use a disc
mounted on the end of a long bolt to tune things sometimes. I remember
adding and removing solder on traces to tune a circuit once. Another
circuit had a small strip of metal that you bent and twisted a little to
tune the circuit.

It all boils down to choosing the capacitor for the task you need it to
perform.


-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org] On Behalf
Of Kenneth Maxon
Sent: Tuesday, August 12, 2003 9:58 PM
To: rten at new.metronet.com; Randal Matthew
Cc: dprglist at dprg.org
Subject: Re: [DPRG] Capacitor Question

Correction:  Many tantalum caps are polarized, are not electrolytic and
are
used/distributed extensively.

     -Kenneth
      (Unit 3's in trouble and it's scared out of its wits) -Geddy Lee
----- Original Message -----
>From: <rten at new.metronet.com>
To: "Randal Matthew" <rmatthew at drivesandcontrols.com>
Cc: <dprglist at dprg.org>
Sent: Tuesday, August 12, 2003 12:05 PM
Subject: Re: [DPRG] Capacitor Question


> Randal:
> All capacitors that are not electrolytic are normally not polarized
and
> can inserted with into the board with impunity.
>
> Polarized caps such as electrolytics of most kinds will at least
overheat
> and short, or outright explode with reversed polarity.
> Ralph
>
> On Mon, 11 Aug 2003, Randal Matthew wrote:
>
> > Ok, now I am feeling really stupid. I see several drawings with
capacitors
> > showing polarity and several drawings with capacitors that show no
polarity.
> > As far as I knew capacitors always had polarity? Can somebody shed
light
on
> > this for me?
> >
>
> _______________________________________________
> DPRGlist mailing list
> DPRGlist at dprg.org
> http://nimon.ncc.com/mailman/listinfo/dprglist
>

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