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Low leakage capacitors

P

Paul

Jan 1, 1970
0
(Sorry, forgot to post to other groups.)

Hi,

I'm trying to find the lowest leakage capacitor, somewhere in the
range of 0.01uF to 1uF, *might* be able to live with 0.001uF, for DC
use. I'm not sure if PTFE (teflon) is the best choice, but here's one
-->

http://www.cde.com/catalogs/MCM-MIN.pdf

It says, "Insulation Resistance: 1000 M¥Ø*¥ìF Need not exceed 100,000 M¥Ø
at 25 ¨¬C" What exactly do they mean by "Need not exceed 100,000 M¥Ø" ?

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by placing a
voltage source on the cap for a period of time, removing the voltage
source and time it, then measure the DC voltage after a certain time
period, and calculate the parallel resistance. It appears that the
longer the voltage source is held on the cap results in more parallel
resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of caps for this
use. IOW, perhaps one cap might have less leakage after 1 minute, but
after 10 hours perhaps another type of cap might have less leakage.

I'm looking for a cap that would contain as much charge as possible
for about one day. The voltage levels are around 1 volt.

Any help is greatly appreciated!
Paul
 
(Sorry, forgot to post to other groups.)

Hi,

I'm trying to find the lowest leakage capacitor, somewhere in the
range of 0.01uF to 1uF, *might* be able to live with 0.001uF, for DC
use. I'm not sure if PTFE (teflon) is the best choice, but here's one
-->

http://www.cde.com/catalogs/MCM-MIN.pdf

It says, "Insulation Resistance: 1000 M¥Ø*¥ìF Need not exceed 100,000 M¥Ø
at 25 ¨¬C" What exactly do they mean by "Need not exceed 100,000 M¥Ø" ?

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by placing a
voltage source on the cap for a period of time, removing the voltage
source and time it, then measure the DC voltage after a certain time
period, and calculate the parallel resistance. It appears that the
longer the voltage source is held on the cap results in more parallel
resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of caps for this
use. IOW, perhaps one cap might have less leakage after 1 minute, but
after 10 hours perhaps another type of cap might have less leakage.

I'm looking for a cap that would contain as much charge as possible
for about one day. The voltage levels are around 1 volt.

Any help is greatly appreciated!
Paul


">I'm looking for a cap that would contain as much charge as possible
for about one day. The voltage levels are around 1 volt."

Aluminum Electrolytic (as long as it doesn't get too warm.)

George Herold
 
C

cassiope

Jan 1, 1970
0
(Sorry, forgot to post to other groups.)

Hi,

I'm trying to find the lowest leakage capacitor, somewhere in the
range of 0.01uF to 1uF, *might* be able to live with 0.001uF, for DC
use. I'm not sure if PTFE (teflon) is the best choice, but here's one
-->

http://www.cde.com/catalogs/MCM-MIN.pdf

It says, "Insulation Resistance: 1000 M¥Ø*¥ìF Need not exceed 100,000 M¥Ø
at 25 ¨¬C" What exactly do they mean by "Need not exceed 100,000 M¥Ø" ?

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by placing a
voltage source on the cap for a period of time, removing the voltage
source and time it, then measure the DC voltage after a certain time
period, and calculate the parallel resistance. It appears that the
longer the voltage source is held on the cap results in more parallel
resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of caps for this
use. IOW, perhaps one cap might have less leakage after 1 minute, but
after 10 hours perhaps another type of cap might have less leakage.

I'm looking for a cap that would contain as much charge as possible
for about one day. The voltage levels are around 1 volt.

Any help is greatly appreciated!
Paul

The "need not..." probably means "once our tests tell us we've reached
a
"high enough" value, testing stops.

One of the SED regulars did (is still doing?) a long-running test of
this
insulation-resistance question. Sorry, I don't recall who it was,
but
if you search the SED archives you may find what he learned. My dim
recollection was that the better capacitors were actually better than
their specs suggested (probably the better films).

Good luck!
 
J

James Arthur

Jan 1, 1970
0
Paul said:
(Sorry, forgot to post to other groups.)

Hi,

I'm trying to find the lowest leakage capacitor, somewhere in the
range of 0.01uF to 1uF, *might* be able to live with 0.001uF, for DC
use. I'm not sure if PTFE (teflon) is the best choice, but here's one
-->

http://www.cde.com/catalogs/MCM-MIN.pdf

It says, "Insulation Resistance: 1000 M¥Ø*¥ìF Need not exceed 100,000 M¥Ø
at 25 ¨¬C" What exactly do they mean by "Need not exceed 100,000 M¥Ø" ?

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by placing a
voltage source on the cap for a period of time, removing the voltage
source and time it, then measure the DC voltage after a certain time
period, and calculate the parallel resistance. It appears that the
longer the voltage source is held on the cap results in more parallel
resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of caps for this
use. IOW, perhaps one cap might have less leakage after 1 minute, but
after 10 hours perhaps another type of cap might have less leakage.

I'm looking for a cap that would contain as much charge as possible
for about one day. The voltage levels are around 1 volt.

Any help is greatly appreciated!
Paul

Polycarbonate & polypropylene are awfully good. You'll
lose more through fingerprints on the casing than leakage
through the dielectric.

Tom Bruhns filled some up and measured their discharge
over many months (on that single filling), posting the
results to s.e.d.

HTH,
James Arthur
 
I

Ian Iveson

Jan 1, 1970
0
Paul wrote:

Hi,

I'm trying to find the lowest leakage capacitor, somewhere
in the
range of 0.01uF to 1uF, *might* be able to live with
0.001uF, for DC
use. I'm not sure if PTFE (teflon) is the best choice, but
here's one
-->

http://www.cde.com/catalogs/MCM-MIN.pdf

It says, "Insulation Resistance: 1000 M¥Ø*¥ìF Need not
exceed 100,000 M¥Ø
at 25 ¨¬C" What exactly do they mean by "Need not exceed
100,000 M¥Ø" ?

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by
placing a
voltage source on the cap for a period of time, removing the
voltage
source and time it, then measure the DC voltage after a
certain time
period, and calculate the parallel resistance. It appears
that the
longer the voltage source is held on the cap results in more
parallel
resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of
caps for this
use. IOW, perhaps one cap might have less leakage after 1
minute, but
after 10 hours perhaps another type of cap might have less
leakage.

I'm looking for a cap that would contain as much charge as
possible
for about one day. The voltage levels are around 1 volt.


It may not be true that one type of dialectric is
necessarily better than another. The exact composition of
each type can vary considerably, in terms of purity,
structure, water content, etc. etc. Also manufacturing
quality can make a big difference. You may be better off
looking for caps specifically designed for low
leakage/capacitance ratio, regardless of what they're made
of.

Have you looked at C0G ceramics?

Ian
 
I

Ian Iveson

Jan 1, 1970
0
That's why it's best not to post in HTML...
 
G

Greegor

Jan 1, 1970
0
James Arthur posted the lead, here's the thread.

http://groups.google.com/group/sci.electronics.design/browse_frm/thread/c1e9a32fc3c6a53e

Newsgroups: sci.electronics.design
From: [email protected] (Tom Bruhns)
Date: 3 Jan 2003 15:46:02 -0800
Local: Fri, Jan 3 2003 6:46 pm
Subject: Low leakage parts

Some of you may recall some postings I've made over the past couple
of
years about the self-discharge rate of polyester and polypropylene
caps. The time constants I saw were on the order of a few years for
the polyester and over 50 years for the polyprops.

A month or so ago, someone asked about making a simple toggle circuit
for turning 12V lights on and off, and I posted a couple solutions.
One of them was a "this is really simple, but it probably won't work
very well" circuit using just a capacitor to hold the voltage on the
gate of a power mosfet. Well, I built that ckt, using an 0.01uF cap
across the gate-source, and toggled it "on", so the cap was charged
to
about 12V. Then I disconnected the power and went on a holiday trip.
Just came back, and it's still in the "on" state, three weeks later.
Sooo...I'd say that modern power mosfets also have pretty low gate
leakage current. To hold the voltage above the nom. 3V required to
turn the mosfet on, the average leakage must have been less than
50fA,
assuming 21 days, 0.01uF and 9V delta (and no arithmetic errors).
(It
was cool, about 18C, and likely wouldn't do quite so well inside a
car
with the windows rolled up in Phoenix in the summer...)

Cheers,
Tom
 
J

Jasen Betts

Jan 1, 1970
0
That's why it's best not to post in HTML...

No html there, what appeared to be missing was a charset header.
 
A

Alex

Jan 1, 1970
0
(Sorry, forgot to post to other groups.)

Hi,

I'm trying to find the lowest leakage capacitor, somewhere in the
range of 0.01uF to 1uF, *might* be able to live with 0.001uF, for DC
use. I'm not sure if PTFE (teflon) is the best choice, but here's one
-->

http://www.cde.com/catalogs/MCM-MIN.pdf

It says, "Insulation Resistance: 1000 M¥Ø*¥ìF Need not exceed 100,000 M¥Ø
at 25 ¨¬C" What exactly do they mean by "Need not exceed 100,000 M¥Ø" ?

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by placing a
voltage source on the cap for a period of time, removing the voltage
source and time it, then measure the DC voltage after a certain time
period, and calculate the parallel resistance. It appears that the
longer the voltage source is held on the cap results in more parallel
resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of caps for this
use. IOW, perhaps one cap might have less leakage after 1 minute, but
after 10 hours perhaps another type of cap might have less leakage.

I'm looking for a cap that would contain as much charge as possible
for about one day. The voltage levels are around 1 volt.

Any help is greatly appreciated!
Paul

Alex:
To store "as much charge as possible" at 1V only probably a supercap of
several Farades will be the best.

As far as dielectric absorbtion is concerned... I have a sample of a Russian
teflon capacitor 0.1uF/600V. I tried to measure it on an RLC bridge. On all
four test frequencies from 100Hz to 100kHz the bridge read a pure
capacitor -- just could not detect any series resistance or parallel
conductance! For comparison a polyester general purpose "greencap" does show
losses on the RLC meter and a paper capacitor would look absolutely
dreadful.

Regards,
Alex
 
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