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Path: utzoo!watmath!clyde!bonnie!akgua!sdcsvax!sdcrdcf!darrelj
From: darrelj@sdcrdcf.UUCP (Darrel VanBuer)
Newsgroups: net.analog
Subject: Re: The difference between capacitors and batteries
Message-ID: <1538@sdcrdcf.UUCP>
Date: Fri, 7-Dec-84 11:32:55 EST
Article-I.D.: sdcrdcf.1538
Posted: Fri Dec  7 11:32:55 1984
Date-Received: Sun, 9-Dec-84 05:41:24 EST
References: <158@decwrl.UUCP>
Reply-To: darrelj@sdcrdcf.UUCP (Darrel VanBuer)
Organization: System Development Corp. R+D, Santa Monica
Lines: 36
Summary: 

John williams said batteries are nonlinear capacitors because charging
changes the dielectric???
I've never seen a battery in which any dielectrics played an important role
(relegated to such roles as hard rubber spacers to prevent contact between
poles).  All batteries contain an electrolyte, but it's a conductor, not an
insulator.  Not all batteries display any significant changes in the
electrolyte with charging either (lead batteries as in cars do change,
nickel cadmium and Edison batteries do not change the electrolyte).
The mechanism of storing the charge is a capacitor is forcing either a
surplus or deficit of electrons on the electrodes.
The charge stored in a battery involves transport of (charged) ions between
the electrodes balancing the transport of electrons into the electrical
circuit, and the energy stored in the different strengths of chemical bonds.
Batteries have a discharge curve which looks much more like
\
 \
  \_______________________
                          -----------------------_______________
                                                                \
                                                                 \
The tails of the curve are the result of exhaustion of active material at
the extremes of the chemical cycle (and battery switches to other reactions).
The flatness of the main curve depends on discharge rate (high rates swamp
ion transport and active surface area) and kinds of changes in chemistry in
discharge (e.g. lead battery electrolyte loses sulfuric acid, while NiCd
electrolyte remains constant 25% KOH--that's why NiCd have such constant output
till almost dead).
-- 
Darrel J. Van Buer, PhD
System Development Corp.
2500 Colorado Ave
Santa Monica, CA 90406
(213)820-4111 x5449
...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua}
                                                            !sdcrdcf!darrelj
VANBUER@USC-ECL.ARPA