Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site sdcrdcf.UUCP 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