Subject:
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Re: Electrolytic Capacitor Ratings [was Re: Choosing Parts?]
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 22 Apr 1999 16:12:22 GMT
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Original-From:
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Patrick Cutts <patrick@surfari(StopSpam).net>
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Reply-To:
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<patrick@surfari.(AvoidSpam)net>
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Viewed:
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951 times
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Capacitance is calculated using the area of the plates, the dielectric
constant, and the distance between the plates.
It does not have anything to do with the voltage.
If a thicker dielectric is formed, it will reduce the capacitance. This is
not because of the voltage it was made at, or the voltage it is going to be
used at, it's simply because the dielectric is thicker, hence the distance
between the plates is greater, and capacitance is inversely proportional to
the distance between the plates.
Admittedly, this is just theory from the textbook, but I doubt that the
value of a capacitor is going to change if used in a circuit with a working
voltage that is lower than what the capacitor is rated at.
just my $0.02
----------
| From: FThompson9@aol.com
| To: handyboard@media.mit.edu
| Subject: Electrolytic Capacitor Ratings [was Re: Choosing Parts?]
| Date: Thursday, April 22, 1999 5:52 AM
|
| In a message dated 4/21/99 8:18:41 AM Central Daylight Time,
| tgb@cozy.core.wamnet.com writes:
|
| > > For electrolytic capacitors, you want the printed voltage to be the
| > >closest voltage above the voltage you are operating at. The voltage
| listed
| >
| > >on the can is the one it works best at.
| >
| > I don't mean to be harsh, but this isn't exactly correct. The voltage
| > is the highest the capacitor is rated for. if you have a 12 V circuit
| >
|
| Your comments aren't taken as being harsh, but I'm still not sure I
| agree. Now I must say that my comments are based on something I heard in
the
| rummer mill, but it still sounds plausible. What I heard goes like this.
| Electrolytic capacitors are formed by metal plates placed in a
| conductive solution. A thin dielectric coating formed on one of the
plates.
| The rummer states that the thickness of this dielectric coating varies
| slightly with applied voltage. So (according to the rumor), if you want
the
| capacitor to operate at its rated capacitance, you must operated it at
its
| rated voltage.
| That is the rumor as I've heard it. I have not really heard anyone
| speak against it other than to say that it is common practice to use
| capacitors larger than is needed. In most power supply applications such
| attention to detail is usually not called for. And if your using
capacitors
| in tuning applications, you probably aren't using electrolytics.
| Is there anyone on the list that is involved in the manufacture of
| electrolytics that can speak about the truth of this rumor?
|
| Pherd
|
|
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