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'Super Caps'
1998\03\05@183048 by Mike DeMetz

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Anyone using super caps (.3-1F) for clock or memory back-up? If so do
you have a problem with inrush current if you let it discharge too
far?

1998\03\06@063935 by richard skinner

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No, I haven't but, I ran across something very interesting, at least to me,
but I am Ignorant to allot
of things in this world.

A SUPER CAP.   I watched a guy last week charge a roll of clx wire on a
spool, then shoot sparks
from the ends when he shorted the wire at the end.  I never much thought
about a large spool
of wire acting as a capacitor, but all the ingredients are there.  He was
telling me that you should
always short the wires on a spool before working with it as it can store
static electricity and it can get
rather high over time, if the conditions are correct.  Hum, that ought to run
a clock for sometime?

Richard Skinner
spam_OUTrwskinnerTakeThisOuTspamworldnet.att.net
http://home.att.net/~rwskinner

----------
> From: Mike DeMetz <.....mikedKILLspamspam@spam@ELKHART.NET>
> To: PICLISTspamKILLspamMITVMA.MIT.EDU
> Subject: Super Caps
> Date: Thursday, March 05, 1998 5:02 PM
>
> Anyone using super caps (.3-1F) for clock or memory back-up? If so do
> you have a problem with inrush current if you let it discharge too
> far?

1998\03\06@071838 by alex_holden

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richard skinner wrote:
>
> No, I haven't but, I ran across something very interesting, at least to me,
> but I am Ignorant to allot
> of things in this world.
>
> A SUPER CAP.   I watched a guy last week charge a roll of clx wire on a
> spool, then shoot sparks
> from the ends when he shorted the wire at the end.  I never much thought
> about a large spool
> of wire acting as a capacitor, but all the ingredients are there.  He was
> telling me that you should
> always short the wires on a spool before working with it as it can store
> static electricity and it can get
> rather high over time, if the conditions are correct.  Hum, that ought to run
> a clock for sometime?

???? Capacitance in a coil? The basic ingredients of a capacitor are two
conductors seperated by an insulator ---||---
A coil of wire on the other hand is just one long conductor. It may have
a lot of inductance, but I can't see it having much capacitance (or are
you talking about a two cored cable? Even then there would only be a
small amount between the cores).

--
------------------- Linux- the choice of a GNU generation.
--------------------
: Alex Holden- Caver, Programmer, Land Rover nut, and Radio amateur (M1
CJD). :
-------------- www.geocities.com/CapeCanaveral/Lab/1532/
---------------

1998\03\06@092733 by wwl

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On Thu, 5 Mar 1998 18:02:02 -0500, you wrote:

>Anyone using super caps (.3-1F) for clock or memory back-up? If so do
>you have a problem with inrush current if you let it discharge too
>far?
Most ones I've seen have a high internal impedance, so charge current
isn't excessive - you could always add a resistor if needed.
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1998\03\06@125036 by Claudio Rachiele IW0DZG

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I have used it with DS1302.
It works well because inside the Dallas device there is a charger circuit.
I think you can use a constant current  generator to overcome initial charge
high current, my be a limiting resistor (2K or 5K) is enough.
LMK ( let me know)

                      Claudio Rachiele IW0DZG

1998\03\06@131335 by Matt Bonner

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Alex Holden wrote:
> ???? Capacitance in a coil? The basic ingredients of a capacitor are two
> conductors seperated by an insulator ---||---
> A coil of wire on the other hand is just one long conductor. It may have
> a lot of inductance, but I can't see it having much capacitance (or are
> you talking about a two cored cable? Even then there would only be a
> small amount between the cores).
>
When the wire is coiled you have capacitance between the layers, as well
as all of the other goodies found in "real world" transmission lines:
resistance, parasitic inductance, and parasitic capacitance.  I'd draw
it, but my ASCII-art inductors look like resistors :-)

In my work, we have to deal with transitting over a sheilded coil of
3/16" wire 8000 metres long - lots of inductance, resitance, and yes -
capacitance.

--Matt

1998\03\06@134946 by Bob Blick

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flavicon
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On Thu, 5 Mar 1998, Mike DeMetz wrote:

> Anyone using super caps (.3-1F) for clock or memory back-up? If so do
> you have a problem with inrush current if you let it discharge too
> far?

The internal resistance is high, it limits the current in or out.


-bob

1998\03\06@135053 by Mike Keitz

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On Thu, 5 Mar 1998 18:02:02 -0500 Mike DeMetz <EraseMEmikedspam_OUTspamTakeThisOuTELKHART.NET> writes:
>Anyone using super caps (.3-1F) for clock or memory back-up? If so do
>you have a problem with inrush current if you let it discharge too
>far?

These capacitors have an internal resistance on the order of 100 ohms.
Often this is enough to limit the inrush current.  If not, just connect a
resistor in series with the capacitor.  Since the discharging current is
very low, the resistor won't cause a significant voltage drop.

Also they have a leakage current.  Regardless of the capacitance, even
with no load connected, they tend to discharge by themselves after a week
or so.  If your application needs to run from the backup for longer, then
a battery is the only choice.

"Discharging too far" is not a problem, unless discharged past zero, i.e.
charged in reverse.

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1998\03\06@174338 by Morgan Olsson

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At 08:22 1998-03-06 -0800, bob wrote:
>On Thu, 5 Mar 1998, Mike DeMetz wrote:
>
>> Anyone using super caps (.3-1F) for clock or memory back-up? If so do
>> you have a problem with inrush current if you let it discharge too
>> far?
>
>The internal resistance is high, it limits the current in or out.
>

Not that high! Today I«ve seen ranges from 220R (NEC 5,5V 0.047 F) down to
only 0.08R (Elna 2,5V 50F)  

Yes, 50F!!  Almost like an accumualtor.  Exept the price...
/Morgan

/  Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \
\  mrtspamspam_OUTiname.com, ph: +46 (0)414 70741; fax +46 (0)414 70331    /

1998\03\06@202103 by Sean Breheny

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At 08:58 PM 3/6/98 +0100, you wrote:
<SNIP>
>
>Not that high! Today I«ve seen ranges from 220R (NEC 5,5V 0.047 F) down to
>only 0.08R (Elna 2,5V 50F)  
>
>Yes, 50F!!  Almost like an accumualtor.  Exept the price...
>/Morgan
>
>/  Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \
>\  @spam@mrtKILLspamspaminame.com, ph: +46 (0)414 70741; fax +46 (0)414 70331    /
>

BTW, how do these super caps achieve such high capacities? Are the plates
so much closer than older electrolytics or do they use some tremendously
good dialectric, or a combination of both? At 50F 2.5V, there would be a
whopping 125 coulombs of charge on each plate, an unheard of amount of
charge in usually physics, enough to suck a statically charged comb right
through a solid brick wall from several meters away, if it weren't for the
oppositely charged plate, that is. However, that dialectric must really be
something amazing, to lower the E field enough that the force between those
plates can be mechanically supported.

Sean

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| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
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1998\03\06@202724 by William Chops Westfield

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   BTW, how do these super caps achieve such high capacities?

Capacitance is proportional to surface area, right?  Now think "activated
charcoal", "carbon fiber", and "carbon aerogel"...

BillW

1998\03\06@203733 by Sean Breheny

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At 05:26 PM 3/6/98 PST, you wrote:
>    BTW, how do these super caps achieve such high capacities?
>
>Capacitance is proportional to surface area, right?  Now think "activated
>charcoal", "carbon fiber", and "carbon aerogel"...
>
>BillW
>

Ok, but the surface area you speak of must be divided into two electrically
conductive areas, separated by an insulator. You can't just put a bunch of
grains together in a can and make a capacitor, they would all short to each
other, instead of being two conductors separated by an insulator. The only
way I can see would be to make a roll of two conductive sheets with a
dielectric inbetween, and I know some capacitors are made this way, but I
didn't think that electrolytics were, unless these super caps aren't
electrolytics?
       Clearly you must be right, the surface area must be the explanation, any
other method would be an engineering nightmare. I just can't see how they
achieve such high surface area, unless the plates are rolled up, or have a
fine pattern etched into them which has a very large surface area, etc.

Sean

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| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
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Phone(USA): (607) 253-0315

1998\03\06@210430 by William Chops Westfield

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Ah, now you're getting more complicated.  I believe that ONE conductor is
the metal/semimetal mentioned (Al, carbon, etc)  The other is a liquid
dielectric (often not "very" liquid.)  The insulating layer is the oxide
film on aluminum (very thin), which explains the polarity sensitivity
(anodizing is done electrically in the first place, so I guess wrong polarity
would remove the film...)  I'm not sure what the insulator is in a carbon
based cap...

BillW

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