henry@utzoo.uucp (Henry Spencer) (11/13/88)
In article <1638@adec23.UUCP> mark@adec23.UUCP (Mark Salyzyn) writes: >Does any one know the capacitance of a 60Ah battery, or is it not possible >to measure it ?!:-) It's certainly measurable -- a battery is essentially a large, polarized, highly non-linear capacitor -- but it depends on the voltage, which you didn't specify. 60 Ah is 60*3600 coulombs of charge; capacitance is charge/voltage. If we assume a car battery (12V), that's an 18 kF capacitor. (Just to head it off... Anyone who wants to argue about whether a battery is a capacitor should know that this was hashed out a couple of years ago. The obvious difference is the non-linearity of the battery, but many capacitors are detectably non-linear too. Nonlinearity is normally felt to be a feature in batteries and a bug in capacitors, which is why the difference in degree.) -- Sendmail is a bug, | Henry Spencer at U of Toronto Zoology not a feature. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
feg@clyde.ATT.COM (Forrest Gehrke) (11/14/88)
In article <1988Nov13.001657.21990@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > In article <1638@adec23.UUCP> mark@adec23.UUCP (Mark Salyzyn) writes: > >Does any one know the capacitance of a 60Ah battery, or is it not possible > >to measure it ?!:-) > charge/voltage. If we assume a car battery (12V), that's an 18 kF capacitor. > > (Just to head it off... Anyone who wants to argue about whether a battery > is a capacitor should know that this was hashed out a couple of years ago. > The obvious difference is the non-linearity of the battery, but many > capacitors are detectably non-linear too. Nonlinearity is normally felt > to be a feature in batteries and a bug in capacitors, which is why the > difference in degree.) Why should anyone want to gainsay you, Henry? One has only to look at the output waveform of the rectified output of the alternator with and without connection to the battery to be convinced that a large capacitor is involved. Forrest Gehrke k2bt
myers@hpfcdj.HP.COM (Bob Myers) (11/17/88)
>Why should anyone want to gainsay you, Henry? One has only to >look at the output waveform of the rectified output of the >alternator with and without connection to the battery to be >convinced that a large capacitor is involved. >Forrest Gehrke k2bt And again I say, nay, yon device is not necessarily a capacitor, simply because thou canst reduce an AC component with it! Question: what do you get if you connect a source supplying a combined AC and DC voltage (the rectified output of an alternator, say), across a *DC voltage source* with a fairly low series resistance (say, oh, jest fer grins...A BATTERY!)? (For further amusement, consider applying said signal across a "pure" DC voltage source - i.e., no series source resistance. Of course, this is meaningless unless you assume that the AC/DC source includes some source resistance of its own, but I think you're getting the idea by now.) Question the second: If the battery in question is really acting as a big capacitor, comment on the expected phase of the AC current through it, relative to that of the AC voltage applied across it. Hmmmmm? Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other {the known universe}!hplabs!hpfcla!myers | sentient life-form on this planet.
keithl@vice.ICO.TEK.COM (Keith Lofstrom) (11/23/88)
In article <16750005@hpfcdj.HP.COM> myers@hpfcdj.HP.COM (Bob Myers) writes: >And again I say, nay, yon device is not necessarily a capacitor, simply >because thou canst reduce an AC component with it! ... >Question the second: If the battery in question is really acting as a big >capacitor, comment on the expected phase of the AC current through it, >relative to that of the AC voltage applied across it. Hmmmmm? If I put a 1 Hz signal across a battery, I mostly see a resistor. If I put a 1 milliHertz signal across a battery, I see current/voltage waveforms that look like a capacitor. Shift the frequencies up by 1000, and the same holds true for a typical large electrolytic. In the frequency ranges I usually work in, they are both lossy inductors, and I use ceramic chipcaps, which look like open circuits at 1Hz. These are all useful in different regimes, and all resemble each other to some small extent. -- Keith Lofstrom ...!tektronix!vice!keithl keithl@vice.TEK.COM MS 59-316, Tektronix, PO 500, Beaverton OR 97077 (503)-627-4052