Magic capacitors!
in [Design]
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From: John Larkin on 9 Aug 2010 01:14 On Sun, 8 Aug 2010 21:49:35 -0700 (PDT), Bill Beaty <billb(a)eskimo.com> wrote: >On Aug 8, 8:33�pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> Cool. You must design integrators and linear ramps and timers and >> power supplies using only capacitor energies in joules. That will make >> the math much more interesting. > >Lol. > >Nah, I just choose to recognize that "time integral of I" is a concept >distinct from "charge stored on one capacitor plate." Well, we just refer to the time integral of current that flows through a capacitor as "charge", which it precisely is. It's easier to say "the charge on the cap" than "all the charge that has flowed through the cap." A cap is "charged" if it has experienced a non-zero integrated current. For Pete's sake, we all took physics. We understand this stuff. But we need to talk about these things quickly... you should hear some of the sessions around here. Even though >their values are the same, and even though the former is the cause of >the latter, they aren't measured the same. Why try to count the >excess charges on a capacitor's internal plates when we can just >measure the current in the lead wires? We don't disassemble caps and count the charges inside. We do in fact measure the currents and the voltages at the terminals. In the case of semiconductors, step-recovery diodes and such, we are downright evil about charge. "The stored charge in the DSRD junction is 800 nC". There's not even any charge separation, they are all mushed together. Physicists would despair. > >Besides endless Newsgroup fights, really this stuff is only important >when teaching basic physics/electronics to newbies and when writing >electronics textbooks. And further, it's only important if we've >decided to avoid filling students' heads with misconceptions like >single-wire capacitors or "capacitors store charge." Funny, I took physics and EE courses and never noticed a conflict. The EE profs always treated caps as storing charge. AoE resolves the situation in one sentence. John
From: Michael A. Terrell on 10 Aug 2010 02:03 John Larkin wrote: > > On Wed, 4 Aug 2010 19:39:55 -0700 (PDT), Nunya <jack_shephard(a)cox.net> > wrote: > > > It all depends on how fast you want it to get filled. In the > >long run, it does require the same power in both cases. > >So, yes, the internal resistance of the cap would > >determine the power required to fill it quickly. You > >missed the point. > > That's wronger than Always Wrong! That's Olympic class wrongness! 'Special Olympics' wrong.
From: John Larkin on 10 Aug 2010 02:05 On Tue, 10 Aug 2010 02:03:35 -0400, "Michael A. Terrell" <mike.terrell(a)earthlink.net> wrote: > >John Larkin wrote: >> >> On Wed, 4 Aug 2010 19:39:55 -0700 (PDT), Nunya <jack_shephard(a)cox.net> >> wrote: >> >> > It all depends on how fast you want it to get filled. In the >> >long run, it does require the same power in both cases. >> >So, yes, the internal resistance of the cap would >> >determine the power required to fill it quickly. You >> >missed the point. >> >> That's wronger than Always Wrong! That's Olympic class wrongness! > > > 'Special Olympics' wrong. Ha! John
From: Michael A. Terrell on 10 Aug 2010 02:07 CIC wrote: > > On Wed, 04 Aug 2010 18:00:20 -0700, John Larkin > <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > > >On Thu, 05 Aug 2010 08:41:59 +1000, Grant <omg(a)grrr.id.au> wrote: > > > >>On Wed, 4 Aug 2010 18:13:49 +0100, "markp" <map.nospam(a)f2s.com> wrote: > >> > >>> > >>>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message > >>>news:6ese46h8ne8luliofpjilue4af6d514js1(a)4ax.com... > >>>> On Wed, 21 Jul 2010 16:30:20 -0500, "George Jefferson" > >>>> <phreon111(a)gmail.com> wrote: > >>>> > >>>>> > >>>>> > >>>>>"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote > >>>>>in > >>>>>message news:rcie465itdu34iaajm1itdqslepu2i87r6(a)4ax.com... > >>>>>> On Wed, 21 Jul 2010 12:14:04 -0700, John Larkin > >>>>>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>>>>> > >>>>>>>On Wed, 21 Jul 2010 12:17:41 -0500, "George Jefferson" > >>>>>>><phreon111(a)gmail.com> wrote: > >>>>>>> > >>>>>>>> > >>>>>>>> > >>>>>>>>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in > >>>>>>>>message > >>>>>>>>news:dj7e465sga7fe3nq7hfl3f0uk601pvrem8(a)4ax.com... > >>>>>>>>> On Wed, 21 Jul 2010 11:19:31 -0500, "George Jefferson" > >>>>>>>>> <phreon111(a)gmail.com> wrote: > >>>>>>>>> > >>>>>>>>>> > >>>>>>>>>> > >>>>>>>>>>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in > >>>>>>>>>>message > >>>>>>>>>>news:s43e46la1p1vt11527eg3ptl9ulm44dfrj(a)4ax.com... > >>>>>>>>>>> On Wed, 21 Jul 2010 07:54:03 -0500, "George Jefferson" > >>>>>>>>>>> <phreon111(a)gmail.com> wrote: > >>>>>>>>>>> > >>>>>>>>>>>>Suppose you have two capacitors connected as > >>>>>>>>>>>> > >>>>>>>>>>>>--*-- > >>>>>>>>>>>>| | > >>>>>>>>>>>>C1 C2 > >>>>>>>>>>>>| | > >>>>>>>>>>>>----- > >>>>>>>>>>>> > >>>>>>>>>>>>where * is a switch. > >>>>>>>>>>>> > >>>>>>>>>>>>What is the total energy before and after the switch is closed(in > >>>>>>>>>>>>general). > >>>>>>>>>>> > >>>>>>>>>>> Energy is conserved, so it's the same, if you account for all the > >>>>>>>>>>> manifestations of energy. > >>>>>>>>>>> > >>>>>>>>>> > >>>>>>>>>>You didn't answer the question. I assume this because you don't know. > >>>>>>>>>> > >>>>>>>>> > >>>>>>>>> State the question unambiguously and I will. > >>>>>>>>> > >>>>>>>>> As I said, the puzzle is both ancient and trivial, so probably JT > >>>>>>>>> invented it. There are web sites and even academic papers devoted to > >>>>>>>>> it. Given all that, how could I not understand it? > >>>>>>>>> > >>>>>>>> > >>>>>>>>Um you don't get it. Your ignorance in basic electronics amazes me. > >>>>>>> > >>>>>>>That's funny. But people can choose to be amazed in all sorts of ways. > >>>>>>> > >>>>>>> > >>>>>>> Michael > >>>>>>>>got it(although he didn't explain where the energy went but I think > >>>>>>>>gets > >>>>>>>>it). > >>>>>>>> > >>>>>>>>Assume the second cap is initially "uncharged" and has the same > >>>>>>>>capacitance > >>>>>>>>as the first. > >>>>>>>> > >>>>>>>>Then the initial energy is > >>>>>>>> > >>>>>>>>Wi = 1/2*C*V^2 > >>>>>>>>Wf = 2*1/2*C*(V/2)^2 = 1/4*C*V^2 = 1/2*Wi > >>>>>>>> > >>>>>>>>Hence the final energy of the system 1/2 what we started with. > >>>>>>> > >>>>>>>Miraculous calculation. Yours and about 300 web sites that admire this > >>>>>>>puzzle. > >>>>>>> > >>>>>>>You didn't wxplain where the energy went - see those 300 web sites - > >>>>>>>but you are assuming losses. Another solution is that no energy is > >>>>>>>lost, and it rings forever, in which case the final state that you > >>>>>>>cite never happens. The exact waveforms are actually interesting. > >>>>>>> > >>>>>>>> > >>>>>>>>I'd really like to hear your explanation but I know thats impossible(as > >>>>>>>>you'll steal someone elses). After all your the one that believes > >>>>>>>>charge > >>>>>>>>isn't conserved... heres your change to *prove* it. > >>>>>>>> > >>>>>>>> > >>>>>>>> > >>>>>>> > >>>>>>>Check my previous posts. I noted the exact waveform across a resistive > >>>>>>>switch, for any values of C1 and C2, and an independent way to compute > >>>>>>>the energy lost in that switch. > >>>>>>> > >>>>>>>Given an inductor, one can move all the energy from one charged cap to > >>>>>>>another, uncharged one. If the C values are unequal, the C*V (charge) > >>>>>>>on the first cap obviously becomes a different C*V on the second one. > >>>>>>>I noted that here some weeks ago, too. > >>>>>>> > >>>>>>>This is all EE101 stuff. > >>>>>>> > >>>>>>>John > >>>>>> > >>>>>> Let the hedging begin... > >>>>>> > >>>>>> In Message-ID: <3b893612tjjndo8o4v1evro050nonjgp41(a)4ax.com> > >>>>>> > >>>>>> You said: > >>>>>> > >>>>>> "Right. If you dump all the energy from one charged cap into another, > >>>>>> discharged, cap of a different value, and do it efficiently, charge is > >>>>>> not conserved." > >>>>>> > >>>>>> Note the NOT CONSERVED. > >>>>>> > >>>>>> Now you say, "...the C*V (charge) on the first cap obviously becomes a > >>>>>> different C*V on the second one". > >>>>>> > >>>>>> Where did the charge come from/go to? > >>>>>> > >>>>>> John "The Bloviator" Larkin is totally incapable of admitting error. > >>>>>> > >>>>>> I truly suspect you're too ignorant to understand :-( > >>>>>> > >>>>> > >>>>>I'm glad my post got what it was suppose to get out. I kinda feel like > >>>>>Breitbart. > >>>>> > >>>> > >>>> Initial condition: > >>>> > >>>> C1 2F, 1 volt, 1 joule, 2 coulombs > >>>> > >>>> C2 1F, 0 volts, 0 joules, 0 coulombs > >>>> > >>>> Now remove all the energy from C1 and deliver it to C2. An inductor > >>>> will move the energy nicely. > >>>> > >>>> Now > >>>> > >>>> C1 has 0 volts, 0 joules, 0 coulombs > >>>> > >>>> C2 has 1.414 volts, 1 joule, 1.414 coulombs. > >>>> > >>>> John > >>> > >>>Sorry but I'm afraid you've fallen into the 'capacitor stores charge' trap > >>>John. It doesn't, as I said in another post, capacitors don't store charge, > >>>the plates are equal and opposite in the excess or depletion of electrons > >>>(they can't store electrical charge, since we all know the current going in > >>>and the current coming out of a capacitor is equal, and current is Coulombs > >>>per second). The total stored electrical charge in a capacitor is zero. That > >>>negates the whole premise of this analysis. > >>> > >>>Mark. > >> > >>Charge 1uF to 50V and put your tongue across the terminals, now tell me > >>there's nothing there ;) > >> > >>Grant. > >>> > > > >Right. And battery chargers are an elaborate public fraud, since > >batteries don't store charge. > > > >And power mosfet data sheets are all wrong. > > > >John > > > > I don't see how this applies to my flux capacitor though... > > http://kalecoauto.com/index.php?main_page=product_info&cPath=6&products_id=28 Under current ROHS regulations, all capacitors must be defluxed...
From: JosephKK on 10 Aug 2010 03:04
On Sun, 8 Aug 2010 21:49:35 -0700 (PDT), Bill Beaty <billb(a)eskimo.com> wrote: >On Aug 8, 8:33�pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> Cool. You must design integrators and linear ramps and timers and >> power supplies using only capacitor energies in joules. That will make >> the math much more interesting. > >Lol. > >Nah, I just choose to recognize that "time integral of I" is a concept >distinct from "charge stored on one capacitor plate." Even though >their values are the same, and even though the former is the cause of >the latter, they aren't measured the same. Why try to count the >excess charges on a capacitor's internal plates when we can just >measure the current in the lead wires? > >Besides endless Newsgroup fights, really this stuff is only important >when teaching basic physics/electronics to newbies and when writing >electronics textbooks. And further, it's only important if we've >decided to avoid filling students' heads with misconceptions like >single-wire capacitors or "capacitors store charge." > >Some educators say things like "what's good enough for me is good >enough for them," and so proceed to infect their students with their >own muddled thinking. This might work for most purposes, and the >misconceptions in question might not act as very large learning >barriers. But over decades and generations it's a "game of >telephone." It's a recipe for filling textbooks and classrooms with >increasing mistakes. Why not instead reverse the trend and turn your >students into physicists who happen to specialize in electronics? >It's not that hard ...just identify common misconceptions which >violate basic physics rules, then avoid spreading those misconceptions >to students. "Capacitors store charge" makes no sense to a student >with a gut-level understanding of charge conservation. Or >conversely, any student who truly believes that capacitors store >charge, might forever afterward have troubles with basic physics. >Remove the contradiction, and "Aha!" everything suddenly connects >together in your brain and makes perfect sense. Ideas like >"capacitors store charge" are bad because they prevent the wonderful >Aha. That's why they need to be taken seriously as errors, and not >just labeled as "nitpicking." > > > >> Do you think Spice uses joules for its internal representation of >> capacitor states? > >And you're certain that it doesn't just take the time integral of the >current in the capacitor leads? > Case well presented. Much appreciated. |