eklhad@ihnet.UUCP (K. A. Dahlke) (11/25/84)
I heard a rummer which I am not quite ready to believe. Someone said a company somewhere makes a 1 farad capacitor. It fits in the hand and costs $10. I took electrical engineering once, and micro farad capacitors were substantial. How can this be??!! Is it just a myth? If not, how does the damn thing work?? If it is just a rummer, what capacitance values (a few volts) are available in industry. How does cost increase with capacitance. Is the trend to increase surface area, or to use better dielectrics? -- Karl Dahlke ihnp4!ihnet!eklhad
henry@utzoo.UUCP (Henry Spencer) (11/26/84)
Farad-range capacitors are real enough, and available from several
sources last I looked. They're basically electrolytic technology
pushed hard: lots of surface area, very good dielectric formulas.
They are generally low-voltage only, as you would expect.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henrywmb@sun.uucp (Mitch Bradley) (11/27/84)
> I heard a rummer which I am not quite ready to believe. > Someone said a company somewhere makes a 1 farad capacitor. > It fits in the hand and costs $10. > I took electrical engineering once, > and micro farad capacitors were substantial. > How can this be??!! > Is it just a myth? If not, how does the damn thing work?? > If it is just a rummer, what capacitance values (a few volts) are available > in industry. > How does cost increase with capacitance. > Is the trend to increase surface area, or to use better dielectrics? It is true. I saw a data sheet for it about 2 years ago. As I recall, it was made by Panasonic, and it looked sort of like a battery. My memory isn't very good, but I recall that it was low voltage (less than 10 volts, I believe). I think it was some kind of electrolytic technology with a very thin dielectric film. The dielectric in electrolytic capacitors is a chemical film which is formed on the metal surface of one of the plates. For a given technology, physical size of capacitors tends to increase (roughly) as the product of voltage * capacitance. Cost tends to be a fixed cost plus a variable cost that is roughly linear with physical size. Of course, it depends strongly on the technology (electrolytic, tantalum, mica, ceramic, etc) and even more on the manufacturing volume. This 1 farad cap was intended for applications like keeping circuits running during power outages. I doubt that its high-frequency characteristics are very good. Mitch Bradley
sct@lanl.ARPA (11/27/84)
> I heard a rummer which I am not quite ready to believe. > Someone said a company somewhere makes a 1 farad capacitor. > It fits in the hand and costs $10. > I took electrical engineering once, > and micro farad capacitors were substantial. > How can this be??!! > Is it just a myth? If not, how does the damn thing work?? > If it is just a rummer, what capacitance values (a few volts) are available > in industry. > How does cost increase with capacitance. > Is the trend to increase surface area, or to use better dielectrics? > -- > > Karl Dahlke ihnp4!ihnet!eklhad I heard a rummer (rumor?) that you never took spelling!
waynekn@tekig.UUCP (Wayne Knapp) (11/27/84)
> I heard a rummer which I am not quite ready to believe. > Someone said a company somewhere makes a 1 farad capacitor. > It fits in the hand and costs $10. > I took electrical engineering once, > and micro farad capacitors were substantial. > How can this be??!! Yes, your heard right. There are 1 farad capacitors. In fact, there are 3.3 farad capacitors. They are only suitable for such things as memory backup and the like because they have a high internal resistance. That is the trade-off that alows such a high capacitance. They are also low voltage (5-6.3V). Also, if you heard a *rummer* it probably wasn't in electrical engineering. They spell it *rumor*. A rummer is " a large drinking cup or glass" which has little to do with capacitors unless it is a glass dielectric capacitor which would not be one farad. By the way, this was not written by the above named person (Wayne). He can't spell rumor either. John Blankenagel tekig!johnbl
dwl@hou4b.UUCP (D Levenson) (11/27/84)
Try a battery! Your car probably has an electrolytic capacitor consisting of a liquid electrolyte and lead plates...many Farads, I think. A small ni-cad is probably good for a few Farads, too. Not much bigger than some much smaller capacitors!
keithd@cadovax.UUCP (Keith Doyle) (11/28/84)
>Someone said a company somewhere makes a 1 farad capacitor. >It fits in the hand and costs $10. >Karl Dahlke ihnp4!ihnet!eklhad I can believe this. In my high-school electronics class (1970) the teacher had (for illustration purposes) accumulated enough capacitance to equal 1 Farad. This consisted of about 4 large cans, anywhere from 100,000 uF to 600,000 uF, all adding up to 1,000,000 uF (1 Farad), at about 6 volts. I would think that in the last 14 years it would be safe to assume that some progress in this area has been made, and it wouldn't take that much from that illustration in 1970. Don't know of any specifics, but I don't find it all that incredulous. Keith Doyle {ucbvax,ihnp4,decvax}!trwrb!cadovax!keithd "You'll PAY to know what you REALLY think!"
paulb@hcrvx1.UUCP (Paul Bonneau) (11/28/84)
[Out vile jelly!]
I have seen one of these suckers (1F). A friend who works for a company
called Thalamus (making in-circuit IC testers) has access to these things
(don't ask me why).
I have always had a streak of pyrophilia and used to blow up lots of
electrolytics (just plug a low voltage high capacity one into good old
120VAC - BOOM!) and explode small pieces of wire by short circuiting big
caps with them.
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.
Oh yes, this particular cap was about 2" in diameter and maybe 2" high.
Not imposing looking at all. I think it was rated at about 13WVDC.
--
I'm a man! I'm not a horse! Paul Bonneau
{decvax|ihnp4|watmath}!hcr!hcrvaxwall@fortune.UUCP (Jim Wall) (11/28/84)
Ah, yes. Supercaps. Many companies make them now, with Panasonic and NEC being the largest. They are perfect for CMOS RAM back-up (months of backup up with just one supercap). A typical 1 farad capacitor at 5.5 volts is a 1 inch diameter cylender about .4 inches high. The physics of the cap is as follows. Early capacitors stored charges between plates of material. Large caps took large plates and rolled them into tight cylinders. This worked O.K. but the surface area was still small, and the larger the surface area, the higher the capacitance. The supercaps cover smaller plates with activated carbon particles. Each particle multiplies the surface area of a portion of the plate by a large amount. A plate covered with particles has a huge surface area, and hence a very high capacitance. I have NECs liturature on them so more info is available... -Jim Wall ....!amd!fortune!wall
smh@mit-eddie.UUCP (Steven M. Haflich) (11/28/84)
The last time one of our esoteric-hardware device cooked its power supply capacitors I visited the famous emporium of Eli Heffron, purveyors of fine salvages electronics to MIT and the rest of the east coast literally for generations. While pawing though the bins of salvage capacitrongers, I noticed a large number of 140,000 mFd beauties. They were typical screw-terminal electrolytics, cylinders perhaps 2.5 inch in diameter, and perhaps 10 inches long, with (I think) a working voltage 5 V. One could bundle seven (hexagonal lattice) and hold it in one hand, yielding .98 F. Another trivium: Back in the late sixties some wag totalled the filter capacitors in the (extensively munger) MIT Research Lab of Electronics time-sharing PDP1 (arguably the *first* multi-processing minicomputer) and found it contained six Farads worth. This machine (mostly) ran on -3VDC logic which required three voltage supplies to function.
nessus@nsc.UUCP (Kchula-Rrit) (11/28/84)
> Someone said a company somewhere makes a 1 farad capacitor. > It fits in the hand and costs $10. > > Karl Dahlke ihnp4!ihnet!eklhad On my desk is a 100,000 microfarad(0.1 farad) capacitor about the size of a beer can. The voltage rating is 30 Volts. It cost me 25 cents at a surplus store in 1975. Kchula-Rrit
labelle@hplabsc.UUCP (WB6YZZ La Belle) (11/28/84)
I have some 100,000uF capacitors. This being .1F dosen't make a 1F
capacitor too inconcevable. By the way, it's rumor- not rummer!
GEORGEjcp@brl-tgr.ARPA (Joe Pistritto <jcp>) (11/29/84)
In article <4682@fortune.UUCP> wall@fortune.UUCP (Jim wall) writes: > The physics of the cap is as follows. Early capacitors >stored charges between plates of material. Large caps took large >plates and rolled them into tight cylinders. This worked O.K. but >the surface area was still small, and the larger the surface >area, the higher the capacitance. The supercaps cover smaller plates >with activated carbon particles. Each particle multiplies the surface >area of a portion of the plate by a large amount. A plate covered with >particles has a huge surface area, and hence a very high capacitance. > > I have NECs liturature on them so more info is available... > > -Jim Wall > ....!amd!fortune!wall This sounds like they should be non-polar then. Has anyone tried using these things to say, replace NICAD batteries? It would seem that they would have no memory problems. Any idea on cost? -JCP-
ron@brl-tgr.ARPA (Ron Natalie <ron>) (11/29/84)
> Try a battery! Your car probably has an electrolytic capacitor > consisting of a liquid electrolyte and lead plates...many Farads, I > think. A small ni-cad is probably good for a few Farads, too. Not > much bigger than some much smaller capacitors! Batteries are not capacitors, asshole. Maybe they should limit submissions to this list to people who know something about electricity. DC does not flow through capacitors. -Ron
cem@intelca.UUCP (Chuck McManis) (11/29/84)
[Do engineers have a fixation on batteries, or just power supplies in general?]
But the frequency response of a battery is so totally dismal. With an internal
resistance of more than .1 ohms or so and the rc constant becomes a real pain
to deal with. Now if we could get one with an internal resistance of 1e-6 ohms,
then we'er talkin' big capacitor, if you know what I mean and I think you do.
-- Chuck
[Sorry if this seems a bit weird but this has always been a big laugh of mine
ever since a friend in college (another sophomore EE like myself at the
time) designed a "super" amp with 3 farad @240V capacitors on the output
stages. It looked great in sinusoidal steady state, but those initial
conditions would kill you! :-)]
--
- - - D I S C L A I M E R - - -
{ihnp4,fortune}!dual\ All opinions expressed herein are my
{qantel,idi}-> !intelca!cem own and not those of my employer, my
{ucbvax,hao}!hplabs/ friends, or my avocado plant. :-}winkg@vice.UUCP (Wink Gross) (11/30/84)
> The last time one of our esoteric-hardware device cooked its power > supply capacitors I visited the famous emporium of Eli Heffron, > purveyors of fine salvages electronics to MIT and the rest of the east > coast literally for generations. While pawing though the bins of *** REPLACE THIS LINE WITH YOUR MESSAGE *** Oh gawd, the words "Eli Heffron" bring tears to the eyes and a lump to the throat! Some of my happiest days as a budding young nerd were spent crawling through old radar systems with a pair of dikes and a spintight in search of lost treasure. Thanks for reminding me of childhood joy! Wink Gross IC Analog Design Tektronix, Inc.
wmb@sun.uucp (Mitch Bradley) (12/02/84)
> > The physics of the cap is as follows. Early capacitors > >stored charges between plates of material. Large caps took large > >plates and rolled them into tight cylinders. This worked O.K. but > >the surface area was still small, and the larger the surface > >area, the higher the capacitance. The supercaps cover smaller plates > >with activated carbon particles. Each particle multiplies the surface > >area of a portion of the plate by a large amount. A plate covered with > >particles has a huge surface area, and hence a very high capacitance. > > > > I have NECs liturature on them so more info is available... > > > > -Jim Wall > > ....!amd!fortune!wall > This sounds like they should be non-polar then. ... Probably they are polar. The original article didn't mention that electrolytic capacitors (and I believe the basic technology of these "Supercaps" is electrolytic) use a chemical film as the dielectric. The film is formed on one of the plates by a process similar to electroplating. If you reverse the polarity, the electrolytic cell is reversed in polarity, the opposite plate doesn't have a dielectric formed on it, and the capacitor conducts DC. Generally it overheats and blows up, usually dramatically. (I am reminded of the time when a PDP11-45 blew a cap, which knocked off one of the panels. Several keypunch operators who happened to reside in the same room were terrified, and huddled in a corner. But I digress...) Electrolytic capacitors that have been sitting around out-of-circuit for a long time (like the ones you get in surplus places) should be re-formed. This may be done safely by applying a low DC voltage (of the correct polarity) to them from a current limited supply, and leaving them that way for several days. It is also possible to change the polarity of an electrolytic capacitor by very carefully applying a reverse voltage to them, which will re-form the dielectric on the other plate. I do not recommended doing this, as the conditions must be carefully controlled to prevent explosion; also, there is no point in doing it anyway. Mitch Bradley
kpmartin@watmath.UUCP (Kevin Martin) (12/02/84)
In article <6171@brl-tgr.ARPA> ron@brl-tgr.ARPA (Ron Natalie <ron>) writes: >> Try a battery! Your car probably has an electrolytic capacitor >> consisting of a liquid electrolyte and lead plates...many Farads, I >> think. A small ni-cad is probably good for a few Farads, too. Not >> much bigger than some much smaller capacitors! > >Batteries are not capacitors, asshole. Maybe they should limit submissions >to this list to people who know something about electricity. DC does not >flow through capacitors. > >-Ron Maybe we should limit submissions to this list to polite people. Lets see. Start with a charged lead-acid battery, and a charged capacitor. Measure the voltage. Wow. They can both power a voltmeter. Now, draw some DC (!) current from each. Measure the voltage. Hmmm. It has dropped a bit. I guess the battery/capacitor has discharged somewhat. Charge them up again. Aha! back to the original voltage! Leave it sit for a year. Hmm. they both discharge just sitting there. Seeing as the vague definition of a capacitor is "something which can store an electric charge", a rechargeable battery seems like a wonderful huge capacitor. Their 'capacitance' varies with their charge state (i.e. V is not proportional to Q), and they tend to have large series resistance, but they also have graceful over-charge behaviour: Lead-acid batteries just vent off H2 and O2. Electrolytics tend to explode. Oh yes... Given a large enough capacitor, DC will "flow through" it for just as long as it would through a battery. -Kevin p.s. Your average car battery has roughly 36kF of capacitance averaged over charge states from 10 to 12V (yes, I said kiloFarads).
danny@alice.UUCP (Dan Kahn @Bell Communications Research) (12/03/84)
Yes, Ron Natalie, it's true that despite many similarities, batteries are not just big capacitors. But how about not labelling as "asshole" anyone who knows a little less about electrical engineering than you. I'll take a net of people who think batteries are capacitors any day over a net that calls people "asshole" when they make a technical error. Dan Kahn Bell Communications Research
david@bragvax.UUCP (David DiGiacomo) (12/04/84)
In article <6171@brl-tgr.ARPA> ron@brl-tgr.ARPA (Ron Natalie <ron>) writes: >> Try a battery! Your car probably has an electrolytic capacitor >> consisting of a liquid electrolyte and lead plates...many Farads, I >> think. A small ni-cad is probably good for a few Farads, too. Not >> much bigger than some much smaller capacitors! > >Batteries are not capacitors, asshole. Maybe they should limit submissions >to this list to people who know something about electricity. DC does not >flow through capacitors. Talk about assholes! The original discussion was about "super-caps", and quite a bit of DC will flow through one (especially when warm). Nicads are actually a good replacement for super-caps in most filter applications-- cheaper and more readily available, much higher (effective) capacitance, but somewhat less reliable. -- David DiGiacomo, BRAG Systems Inc., San Mateo CA (415) 342-3963 (...decvax!ucbvax!hplabs!bragvax!david)
gino@voder.UUCP (Gino Bloch) (12/04/84)
[what is the bug's capacity for charged lines?] Another way of looking at the battery vs capacitor controversy is the effect that a battery can have as a ripple filter. If you put a battery (may not have to be rechargeable) across a power supply, you'd tend to see very little AC in the load. -- Gene E. Bloch (...!nsc!voder!gino) Mr Humility
zben@umd5.UUCP (12/04/84)
Sorry, but I have seen about enough pseudo-scientific garbage on this subject to breakover and add my own two cents worth of pseudo-scientific garbage: > Try a battery! Your car probably has an electrolytic capacitor > consisting of a liquid electrolyte and lead plates...many Farads, I > think. > Seeing as the vague definition of a capacitor is "something which can > store an electric charge", a rechargeable battery seems like a wonderful > huge capacitor. Begin flame: Yes, thats just about vague enough to be meaningless. A more precise definition of a capacitor is that it stores energy IN THE ELECTRIC FIELD BETWEEN THE PLATES, just as an inductor stores energy in the magnetic field that cuts the windings. Now, a battery stores the energy chemically, not as an electric field, so a battery, strictly speaking, is not the same animal as a capacitor at all. You cannot make a resonant circuit with a battery (I don't think). The discharge rate is limited by the chemical reaction rate. Thats one huge differance between a capacitor and a battery. By the way, my homebrew machine (TI9900) was made from a Technico Super Starter kit, but I designed and built the power supply. I have 1/6 of a farad on the +5 supply! (Yes, the lights dim and it goes "buzz" for a few seconds when I turn it on. But +5 is clean!). The can is 160,000 mikes at 10 volts and cost about $4.00 at the local surplus store. Buy yourself 6 or 7 and you too can have a one farad capacitor! Bailed out of EE for CS, but I can still design power supplies... Ben Cranston
ron@brl-tgr.ARPA (Ron Natalie <ron>) (12/07/84)
> > Lets see. Start with a charged lead-acid battery, and a charged capacitor. > Measure the voltage. Wow. They can both power a voltmeter. Now, draw some > DC (!) current from each. Measure the voltage. Hmmm. It has dropped a bit. > I guess the battery/capacitor has discharged somewhat. Charge them up again. > Aha! back to the original voltage! Leave it sit for a year. Hmm. they > both discharge just sitting there. > > Seeing as the vague definition of a capacitor is "something which can > store an electric charge", a rechargeable battery seems like a wonderful > huge capacitor. Their 'capacitance' varies with their charge state > (i.e. V is not proportional to Q), and they tend to have large series > resistance, but they also have graceful over-charge behaviour: Lead-acid > batteries just vent off H2 and O2. Electrolytics tend to explode. > > Oh yes... Given a large enough capacitor, DC will "flow through" it for > just as long as it would through a battery. > -Kevin > p.s. Your average car battery has roughly 36kF of capacitance averaged > over charge states from 10 to 12V (yes, I said kiloFarads). Ok, lets see, I take two 1.5 volt batteries and place them in series I get 3 volts. I take two capacitors in series, doesn't quite do the same thing. Batteries will flow DC through them much better than capacitors. You can do it continuosly. Part of my definition of capacitor is one that passes AC but not DC. More practical for designing electrical circuits that do more than blow up screwdrivers and inquisitive cats. Lets leave internal resistance out of the discussion for a moments and discuss only capacitance. -Ron
nessus@nsc.UUCP (Kchula-Rrit) (12/08/84)
> [what is the bug's capacity for charged lines?] > > Another way of looking at the battery vs capacitor controversy is the effect > that a battery can have as a ripple filter. If you put a battery (may not have > to be rechargeable) across a power supply, you'd tend to see very little AC in > the load. > -- > Gene E. Bloch (...!nsc!voder!gino) > Mr Humility *** REPLACE THIS LINE WITH YOUR MESSAGE *** Years ago I had a GE battery/AC-powered cassette recorder. There was a little slide switch in the compartment where the line cord, which was not detachable, went. One day the switch broke so that the recorder ran on either battery XOR AC, can't remember which. I, not knowing any better at the time, soldered the six leads on the switch together. Later on, I found out by accident that the recorder {re}chargered the batteries when it was plugged in to AC!! Also, when the recorder was unplugged, the diodes in the power supply were reverse-biased so the batteries did not discharge through the supply. This arrangement charged carbon-zinc batteries better than a friend's battery charger, so when one of my two sets of batteries went low, I swapped the sets and everything worked fine! Kchula-Rrit
jans@mako.UUCP (Jan Steinman) (12/10/84)
In article <6429@brl-tgr.ARPA> ron@brl-tgr.ARPA (Ron Natalie <ron>) writes: >Ok, lets see, I take two 1.5 volt batteries and place them in series >I get 3 volts. I take two capacitors in series, doesn't quite do the >same thing. You don't! O'm'gosh! Instant death to the television, X-ray, and (deep breath) computer terminal industries, all of which rely on this very property to get high DC voltages from an AC source! Go to a college EE text and look up "voltage doubler" in the index, then report back to the net that "1.5 + 1.5 does indeed equal 3". -- :::::: Jan Steinman Box 1000, MS 61-161 (w)503/685-2843 :::::: :::::: tektronix!tekecs!jans Wilsonville, OR 97070 (h)503/657-7703 ::::::
dan@rna.UUCP (12/20/84)
> The last time one of our esoteric-hardware device cooked its power > supply capacitors I visited the famous emporium of Eli Heffron, > purveyors of fine salvages electronics to MIT and the rest of the east > coast literally for generations. While pawing though the bins of > Oh gawd, the words "Eli Heffron" bring tears to the eyes and a lump > to the throat! Some of my happiest days as a budding young nerd > were spent crawling through old radar systems with a pair of dikes > and a spintight in search of lost treasure. > > Thanks for reminding me of childhood joy! > > Wink Gross > IC Analog Design > Tektronix, Inc. xyzzy Eli's is still a favorite in my book. Where else can you bargain for an 11/23 system capable of running UNIX for $2000 ? The other electronics junkyard of my past include B&F Enterprises in Peabody, MA, John Meshna Electronics in Lynn, MA, and PolyPaks in Wakefield, MA. Boston was (I guess is) a haven for such junk. The electronics junk stores on Canal Street in New York can't compare a bit. B&F was the greatest of those. Cheers, Dan