Film capacitor as power-supply filter

On Monday, October 14, 2019 at 12:17:39 AM UTC-4, Bill Sloman wrote:

On Monday, October 14, 2019 at 2:13:58 PM UTC+11, m...@uga.edu wrote:
The rest of the story...

For those who tuned in late, I'm replacing the power supply filters in a Heathkit IT-11 capacitor checker. In the original circuit they are two 40-uF 350-V in series (to handle 600 V). I ordered a 20-uF 1-kV film capacitor to replace them.

Well, there just isn't room for that film capacitor under this chassis! So I had to resort to two 47-uF 450-V in series, like Heathkit's original..

There was debate in this thread about whether to add balancing resistors, and I didn't. John Larkin said "they take care of themselves." Indeed they do, sharing the voltage to within a few percent of equal.

I wonder if Mr. Larkin could explain further. Is there some effect that makes them equalize if they have different leakages to start with? I would expect the opposite, that the leakier one would carry a lower voltage and would form less, causing the difference in leakage to increase -- but I might be wrong.

Leakage currents have a tendency to increase exponentially with applied voltage, so you often don't need much voltage difference to compensate for significant differences in initial leakage current.

Some manufacturer's application note that I read back in 1970 was a full bottle on the subject.

snip

--
Bill Sloman, Sydney

They do no such thing. For aluminum ecaps the leakage is k x sqrt(CV), making the ratio of voltages proportional to C1/C2. That can be a pretty big disparity. My guess is the manufacturer makes some attempt at matching C before installation.
But what does your incredibly incapable and super ignorant fuck nothing of a pedophiles tell you about it?

 

[John Larkin]

On Wed, 16 Oct 2019 09:08:22 -0700 (PDT),
bloggs.fredbloggs.fred@gmail.com wrote:

On Monday, October 14, 2019 at 12:17:39 AM UTC-4, Bill Sloman wrote:
On Monday, October 14, 2019 at 2:13:58 PM UTC+11, m...@uga.edu wrote:
The rest of the story...

For those who tuned in late, I'm replacing the power supply filters in a Heathkit IT-11 capacitor checker. In the original circuit they are two 40-uF 350-V in series (to handle 600 V). I ordered a 20-uF 1-kV film capacitor to replace them.

Well, there just isn't room for that film capacitor under this chassis! So I had to resort to two 47-uF 450-V in series, like Heathkit's original.

There was debate in this thread about whether to add balancing resistors, and I didn't. John Larkin said "they take care of themselves." Indeed they do, sharing the voltage to within a few percent of equal.

I wonder if Mr. Larkin could explain further. Is there some effect that makes them equalize if they have different leakages to start with? I would expect the opposite, that the leakier one would carry a lower voltage and would form less, causing the difference in leakage to increase -- but I might be wrong.

Leakage currents have a tendency to increase exponentially with applied voltage, so you often don't need much voltage difference to compensate for significant differences in initial leakage current.

Some manufacturer's application note that I read back in 1970 was a full bottle on the subject.

snip

--
Bill Sloman, Sydney

They do no such thing. For aluminum ecaps the leakage is k x sqrt(CV), making the ratio of voltages proportional to C1/C2. That can be a pretty big disparity. My guess is the manufacturer makes some attempt at matching C before installation.

I think your equation is generic on leakage at rated voltage, across
cap ratings. It implies a declining slope for a particular capacitor,
which is not how they behave. Applied to single caps, it would make a
series string unstable.

It's surprising how rare I/V curves are for electrolytics, practically
not to be found.

https://tadiranbatteries.de/pdf/applications/leakage-current-properties-of-modern-electrolytic-capacitors.pdf

Fig 7 looks like semi-serious data, but ends at rated voltage. In my
experience, leakage increases radically above rated voltage.

But even that curve implies series cap string voltage
self-equalization.

 

[John Larkin]

On Wed, 16 Oct 2019 15:03:19 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

Phil Allison wrote:

------------------------


This link give a bit more detail to an non-simple situation.


** Oops - see same link JL posted.



.... Phil

I might just measure a couple of electrolytic caps. I think the
leakage jumps radically a bit past the reform voltage.

Here's some data on some other caps.

https://www.dropbox.com/s/dlet57gmlntxx9h/Ccap_Leakage.JPG?dl=0

https://www.dropbox.com/s/euxh4uzhoeft249/Polymer_Leakage.jpg?dl=0

https://www.dropbox.com/s/fq70y6vy854k8y8/Supercap_Leakage.JPG?dl=0

They all curve up! The polymer leakage data is entangled with its time
behavior, sort of a reform or dielectric absorption thing.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Allison]

Phil Allison wrote:

------------------------

This link give a bit more detail to an non-simple situation.

** Oops - see same link JL posted.



..... Phil

 

[Phil Allison]

Some Loony hiding behind bloggs.fre...@gmail.com wrote:

------------------------------------------------

Leakage currents have a tendency to increase exponentially with
applied voltage, so you often don't need much voltage difference
to compensate for significant differences in initial leakage current.



They do no such thing.

** Fraid they do.

For aluminum ecaps the leakage is k x sqrt(CV),

** Fraid that is not the formula for ACTUAL electro cap leakage at all.

One sees it sometimes on spec sheets describing the MAX leakage to be expected where "C" and "V" are the makers rated vales for a particular cap.

This link give a bit more detail to an non-simple situation.



> making the ratio of voltages proportional to C1/C2.

** Absolute rubbish.

But what does your incredibly incapable and super ignorant
fuck nothing of a pedophiles tell you about it?

** Kinda undoes any possibility of a sane post - don't it?


..... Phil

 

[John Larkin]

On Wed, 16 Oct 2019 15:28:02 -0700, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

On Wed, 16 Oct 2019 15:03:19 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

Phil Allison wrote:

------------------------


This link give a bit more detail to an non-simple situation.


** Oops - see same link JL posted.



.... Phil

I might just measure a couple of electrolytic caps. I think the
leakage jumps radically a bit past the reform voltage.

Here's some data on some other caps.

https://www.dropbox.com/s/dlet57gmlntxx9h/Ccap_Leakage.JPG?dl=0

https://www.dropbox.com/s/euxh4uzhoeft249/Polymer_Leakage.jpg?dl=0

https://www.dropbox.com/s/fq70y6vy854k8y8/Supercap_Leakage.JPG?dl=0

They all curve up! The polymer leakage data is entangled with its time
behavior, sort of a reform or dielectric absorption thing.

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

The data is crude, because there is reforming and dielectric
absorption going on, and I don't have a month to play with this. But
the curve is clearly radically upward. Not a zener, more like an MOV.

The current is very noisy above maybe 70 volts. I see what looks like
brief high current spikes.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Allison]

Steve Wilson wrote:
------------------

Also see

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

This paper has lots of good information, such as fig. 4, leakage as a
function of time, voltage and temperature. This precedes your later post
showing leakage as a function of voltage. The leakage is exponential.

** Fig 4 is next to useless.

Presents only the barest nominal, virtuual data.

One point that has not been discussed so far is the paper mentions the
balancing resistors will discharge the electrolytics quickly when power is
removed.

** That tiny we comment is hard to find.

And you missed this post from me here two days ago

-------------------------------------------------------------------

** The actual leakage current with HV electros is normally in the micro-amp range so dissipation causes no discernible temp rise. Ambient temp and rises in same entirely swamp it.

Where series bleeder resistors are used ( eg 100,000 Fender tube amplifiers ) they pass about 1mA which is enough to reduce and nearly eliminate mid point voltage offset.

The main benefit however is in bleeding off charge so the caps do not present a hazard if the AC supply is removed while there is no load on the PSU.

There are a couple of ways this can happen.

See typical schem:

https://schematicheaven.net/fenderamps/fender_bassman50.pdf

----------------------------------------------------------------------


** Yawwnnnn .....


...... Phil

 

[Steve Wilson]

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

On Wed, 16 Oct 2019 09:08:22 -0700 (PDT),

It's surprising how rare I/V curves are for electrolytics, practically
not to be found.

https://tadiranbatteries.de/pdf/applications/leakage-current-properties-o
f-modern-electrolytic-capacitors.pdf

I posted that link two days ago in my reply to Win on Mon, 07 Oct 2019.

Here is my post:

"When the capacitor is left with no supplied voltage, the film tends to
dissociate and become thinner. Applying a voltage to the cap restores the
film."

"An excellent description is given in"

"Leakage current properties of modern electrolytic capacitors"

https://tadiranbatteries.de/pdf/applications/leakage-current-properties-of-
modern-electrolytic-capacitors.pdf

---------------------------------------------------------------------------
Also see

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

This paper has lots of good information, such as fig. 4, leakage as a
function of time, voltage and temperature. This precedes your later post
showing leakage as a function of voltage. The leakage is exponential.

It also includes information on using resistors to balance the voltages in
series capacitors.

One point that has not been discussed so far is the paper mentions the
balancing resistors will discharge the electrolytics quickly when power is
removed. This is an important safety factor in the case of very low leakage
capacitors.

There is a huge amount of information on electrolytic capacitors on the
web. For example, see Cornell Dublier, "Aluminum Electrolytic Capacitor
Application Guide" at

http://www.cde.com/resources/catalogs/AEappGUIDE.pdf

Also see Rubycon, at

http://rubycon.co.jp/en/products/alumi/pdf/Performances.pdf

and so on.

 

[Steve Wilson]

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

See Fig. 4(b) on Page 2 in

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

The curves are exponential.

 

[Phil Allison]

Steve Wilson posted more bullshit wrote:


--------------------------------------

John Larkin

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

See Fig. 4(b) on Page 2 in

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

The curves are exponential.

** FFS - you dopey autistic wanker !!

Those alleged "curves" were drawn with a pen partially *circling* a round lid or coin.

The paper is of *low* quality - almost real information free.

Pure Google fodder.

Like you.


..... Phil

 

[John S]

On 10/16/2019 6:48 PM, John Larkin wrote:

On Wed, 16 Oct 2019 15:28:02 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Wed, 16 Oct 2019 15:03:19 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

Phil Allison wrote:

------------------------


This link give a bit more detail to an non-simple situation.


** Oops - see same link JL posted.



.... Phil

I might just measure a couple of electrolytic caps. I think the
leakage jumps radically a bit past the reform voltage.

Here's some data on some other caps.

https://www.dropbox.com/s/dlet57gmlntxx9h/Ccap_Leakage.JPG?dl=0

https://www.dropbox.com/s/euxh4uzhoeft249/Polymer_Leakage.jpg?dl=0

https://www.dropbox.com/s/fq70y6vy854k8y8/Supercap_Leakage.JPG?dl=0

They all curve up! The polymer leakage data is entangled with its time
behavior, sort of a reform or dielectric absorption thing.

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

The data is crude, because there is reforming and dielectric
absorption going on, and I don't have a month to play with this. But
the curve is clearly radically upward. Not a zener, more like an MOV.

The current is very noisy above maybe 70 volts. I see what looks like
brief high current spikes.

Great info! Thanks, John.

 

On Thu, 17 Oct 2019 05:44:51 -0000 (UTC), Steve Wilson <no@spam.com>
wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

See Fig. 4(b) on Page 2 in

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

The curves are exponential.

That fig 4b is an obvious made-up cartoon. It's certainly not
exponential. And it has no numbers.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Thu, 17 Oct 2019 06:15:30 -0500, John S <Sophi.2@invalid.org>
wrote:

On 10/16/2019 6:48 PM, John Larkin wrote:
On Wed, 16 Oct 2019 15:28:02 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Wed, 16 Oct 2019 15:03:19 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

Phil Allison wrote:

------------------------


This link give a bit more detail to an non-simple situation.


** Oops - see same link JL posted.



.... Phil

I might just measure a couple of electrolytic caps. I think the
leakage jumps radically a bit past the reform voltage.

Here's some data on some other caps.

https://www.dropbox.com/s/dlet57gmlntxx9h/Ccap_Leakage.JPG?dl=0

https://www.dropbox.com/s/euxh4uzhoeft249/Polymer_Leakage.jpg?dl=0

https://www.dropbox.com/s/fq70y6vy854k8y8/Supercap_Leakage.JPG?dl=0

They all curve up! The polymer leakage data is entangled with its time
behavior, sort of a reform or dielectric absorption thing.

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

The data is crude, because there is reforming and dielectric
absorption going on, and I don't have a month to play with this. But
the curve is clearly radically upward. Not a zener, more like an MOV.

The current is very noisy above maybe 70 volts. I see what looks like
brief high current spikes.



Great info! Thanks, John.

Quite welcome. It's good to have some real numbers on (one) real cap.

I was impressed by how noisy the current is. There's stuff going on
inside.

I think it was Werner Von Braun who said "One experiment is worth a
thousand expert opinions."



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

On Thursday, October 17, 2019 at 11:02:13 AM UTC-4, jla...@highlandsniptechnology.com wrote:

On Thu, 17 Oct 2019 05:44:51 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

See Fig. 4(b) on Page 2 in

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

The curves are exponential.

That fig 4b is an obvious made-up cartoon. It's certainly not
exponential. And it has no numbers.

Ditto on the thanks.
The Tardin article mentions that the caps behave like they have a
zener diode in parallel... So having the current look like noisy
zener current above the 'threshold' makes some sense.

Years ago I charge an Al eletro to ~1/2 the max voltage, left it
on my bench for the weekend and came back to see the voltage had
only dropped by ~10% or so. It would be fun to hook one up
to an electrometer and let it sit there for a week or whatever
and record the voltage.

George H.

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Steve Wilson]

jlarkin@highlandsniptechnology.com wrote:

On Thu, 17 Oct 2019 05:44:51 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

See Fig. 4(b) on Page 2 in

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

The curves are exponential.

That fig 4b is an obvious made-up cartoon. It's certainly not
exponential. And it has no numbers.

The curve is exponential over the portion that is increasing. Every capacitor
will be different, so if you want the curve for your particular capacitor,
you have to measure it.

 

On Thu, 17 Oct 2019 08:53:25 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Thursday, October 17, 2019 at 11:02:13 AM UTC-4, jla...@highlandsniptechnology.com wrote:
On Thu, 17 Oct 2019 05:44:51 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

See Fig. 4(b) on Page 2 in

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

The curves are exponential.

That fig 4b is an obvious made-up cartoon. It's certainly not
exponential. And it has no numbers.
Ditto on the thanks.
The Tardin article mentions that the caps behave like they have a
zener diode in parallel... So having the current look like noisy
zener current above the 'threshold' makes some sense.

Years ago I charge an Al eletro to ~1/2 the max voltage, left it
on my bench for the weekend and came back to see the voltage had
only dropped by ~10% or so. It would be fun to hook one up
to an electrometer and let it sit there for a week or whatever
and record the voltage.

George H.

Or just check it with a DVM now and then. I did that with a supercap
for a few months.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

On Thursday, October 17, 2019 at 12:24:20 PM UTC-4, jla...@highlandsniptechnology.com wrote:

On Thu, 17 Oct 2019 08:53:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, October 17, 2019 at 11:02:13 AM UTC-4, jla...@highlandsniptechnology.com wrote:
On Thu, 17 Oct 2019 05:44:51 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

See Fig. 4(b) on Page 2 in

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

The curves are exponential.

That fig 4b is an obvious made-up cartoon. It's certainly not
exponential. And it has no numbers.
Ditto on the thanks.
The Tardin article mentions that the caps behave like they have a
zener diode in parallel... So having the current look like noisy
zener current above the 'threshold' makes some sense.

Years ago I charge an Al eletro to ~1/2 the max voltage, left it
on my bench for the weekend and came back to see the voltage had
only dropped by ~10% or so. It would be fun to hook one up
to an electrometer and let it sit there for a week or whatever
and record the voltage.

George H.

Or just check it with a DVM now and then. I did that with a supercap
for a few months.

Right... I think I used the trick of putting a Gig ohm in series
with my DMM and dividing by 100.
I'd bet it can't be exponential* 'all the way down' at some point there'll be some other constant (resistive) leakage path.

Hey are tant's any better than Al-electros. At my ppoe I made this
triangle wave generator, current source into a cap, milli second to
kilo second periods. I used a 100uF tant for the longest times...
seemed to work fine.. but I only 'really' measured the longest times
once. (otherwise just made sure it went up and down.)

George H.
*does exponential imply some thermal mechanism?

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Steve Wilson]

jlarkin@highlandsniptechnology.com wrote:

> Quite welcome. It's good to have some real numbers on (one) real cap.

Yor data is valid for that capacitor only.

Every cap will be different. There are many different electrolytes with
different characteristics, such as non-solid borax or organic, non-solid
water-based, solid manganese dioxide, solid conducting polymer, non-solid
hybrid electrolyte, etc., and the leakage characteristics will be different
for each type. See Wikipedia, "Aluminum electrolytic capacitor", at

https://en.wikipedia.org/wiki/Aluminum_electrolytic_capacitor

 

[Steve Wilson]

jlarkin@highlandsniptechnology.com wrote:

On Thu, 17 Oct 2019 08:53:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, October 17, 2019 at 11:02:13 AM UTC-4,
jla...@highlandsniptechnology.com wrote:
On Thu, 17 Oct 2019 05:44:51 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

See Fig. 4(b) on Page 2 in

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap
- Leakage-Current-AAL-2018-09-18.pdf

The curves are exponential.

That fig 4b is an obvious made-up cartoon. It's certainly not
exponential. And it has no numbers.
Ditto on the thanks.
The Tardin article mentions that the caps behave like they have a
zener diode in parallel... So having the current look like noisy
zener current above the 'threshold' makes some sense.

Years ago I charge an Al eletro to ~1/2 the max voltage, left it
on my bench for the weekend and came back to see the voltage had
only dropped by ~10% or so. It would be fun to hook one up
to an electrometer and let it sit there for a week or whatever
and record the voltage.

George H.

Or just check it with a DVM now and then. I did that with a supercap
for a few months.

That's why you need a bleeder resistor for higher voltages.

 

[George Herold]

On Thursday, October 17, 2019 at 2:01:02 PM UTC-4, John Larkin wrote:

On Thu, 17 Oct 2019 10:17:47 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, October 17, 2019 at 12:24:20 PM UTC-4, jla...@highlandsniptechnology.com wrote:
On Thu, 17 Oct 2019 08:53:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, October 17, 2019 at 11:02:13 AM UTC-4, jla...@highlandsniptechnology.com wrote:
On Thu, 17 Oct 2019 05:44:51 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

Here's possibly the only curve like this ever posted online:

https://www.dropbox.com/s/i4wwttdgqycz9rv/Alum_Leakage_63u.JPG?raw=1

See Fig. 4(b) on Page 2 in

https://jianghai-europe.com/wp-content/uploads/8-Jianghai-Europe-E-Cap-
Leakage-Current-AAL-2018-09-18.pdf

The curves are exponential.

That fig 4b is an obvious made-up cartoon. It's certainly not
exponential. And it has no numbers.
Ditto on the thanks.
The Tardin article mentions that the caps behave like they have a
zener diode in parallel... So having the current look like noisy
zener current above the 'threshold' makes some sense.

Years ago I charge an Al eletro to ~1/2 the max voltage, left it
on my bench for the weekend and came back to see the voltage had
only dropped by ~10% or so. It would be fun to hook one up
to an electrometer and let it sit there for a week or whatever
and record the voltage.

George H.

Or just check it with a DVM now and then. I did that with a supercap
for a few months.
Right... I think I used the trick of putting a Gig ohm in series
with my DMM and dividing by 100.
I'd bet it can't be exponential* 'all the way down' at some point there'll be some other constant (resistive) leakage path.

Hey are tant's any better than Al-electros. At my ppoe I made this
triangle wave generator, current source into a cap, milli second to
kilo second periods. I used a 100uF tant for the longest times...
seemed to work fine.. but I only 'really' measured the longest times
once. (otherwise just made sure it went up and down.)

George H.
*does exponential imply some thermal mechanism?

A pure RC has a exponential decay, e^(-kt). But the leakage in an
electrolytic isn't ohmic, so the decay slows down as the voltage
drops.

Pretty complex.

Right, if you monitor the voltage you'd have to integrate it to get the
current.. It's not at all clear to me what that double exponential
would look like.

George H.
something like this?
https://en.wikipedia.org/wiki/Double_exponential_function
That doesn't seem right.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com