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Path: utzoo!hcrvax!hcrvx1!paulb
From: paulb@hcrvx1.UUCP (Paul Bonneau)
Newsgroups: net.analog
Subject: Re: large capacitors -- low resistance??
Message-ID: <1024@hcrvx1.UUCP>
Date: Wed, 5-Dec-84 20:33:19 EST
Article-I.D.: hcrvx1.1024
Posted: Wed Dec  5 20:33:19 1984
Date-Received: Thu, 6-Dec-84 00:24:23 EST
References: <17@tekig5.UUCP>
Organization: Human Computing Resources, Toronto
Lines: 28

[Out Vile Jelly!]

>> So it was with great expectation that we charged this thing up.  Got a piece
>> of 16 gauge wire.  Taped it to a stick.  Sloowly approached the terminals
>> with it ... and ... nothing happened.  Apparently these things have a fairly
>> low internal resistance so they discharge shortly after the current is
>> removed.  Sigh.

>     Where did you learn your physics?  These capacitors have a large internal
>resistance.  That is one of the trade-offs that had to be made in order to make
>a capacitor with 3.3 F of capacity.  They certainly would not be too useful
>if they discharged shortly after the current was removed.  The main use of these
>capacitors is for such things as battery backup.  They will produce a small
>current for a long time, but don't try to filter the high frequency ripple
>out of a power supply with them.  It won't work.  If you want to melt wires,
>get a large computer power supply capacitor.  That is what they were made
>for (and you thought it was to filter power supplys).

I stand corrected!  My thinking on the matter was that they had a small
PARALLEL resistance (ie across the plates) not a large series resistance.
However I am by no means an expert on the subject (I was only making a
guess).

However if there was a such a beast (low resistance across the plates) the
time constant would restrict its use to such things as power regulation.
-- 
I'm a man!  I'm not a horse!		Paul Bonneau
					{decvax|ihnp4|watmath}!hcr!hcrvax