Status
Not open for further replies.

Thread Starter

Energy forever

Joined Sep 11, 2021
46
Hello good friends. Im curious in a strait way about dielectric absorption. Particularly the current. Where does the current come from? (If i were to elaborate, i would say people familiar with a capacitor that has been shorted for long (hours/days) durations will notice that upon disconnecting the short and leaving the capacitor out on a table (not in any circuit) the voltage will rise and upon hooking the cap up to a multimeter and set it to current, there will be a current reading. Its this current which i am curious to know where it came from. Please do assist in the understanding of this situation please. Many thank yous to you all and to all a good life and many feelings of happiness :)
 

LowQCab

Joined Nov 6, 2012
1,340
The Capacitor may, or may-not, develop a charge depending upon
the surrounding environment,
which is full of all kinds of Electrical-Noise and Fields,
including Magnetic-Fields.

The Leads on the Capacitor may act as crude Antennas.
.
.
.
 

crutschow

Joined Mar 14, 2008
28,201
As noted some capacitors types have significant dielectric absorption and some don't.

Here's a example where it can cause a subtle problem:
Some years ago I had an accuracy problem with a 12-bit A/D converter in a satellite system, where the output digital word changed value slightly with time after a step input change, well beyond ten time-constants of the input analog anti-alias filter
After some testing I traced it to the capacitor in the anti-aliasing filter that was a high-dielectric type ceramic type which, it turns out, also had a rather high dielectric absorption (soakage).
(That's after I read Pease's article).
The cap was absorbing and releasing sufficient electrons with a long enough time-constant, such that it was slightly altering the varying analog voltage from its true value.
Changing to a low dielectric capacitor (NPO ceramic type), which has a much lower absorption, solved the problem.

So beware of soakage when you use capacitors where high accuracy with changing analog voltages is required (such as filters).
 
Last edited:

MisterBill2

Joined Jan 23, 2018
9,824
In summary, the charge in question that appears after some time, is part of the initial charge that had been absorbed previously. The specific mechanism of the charge absorbtion and desorbtion is a lot more complex. That is sort of discussed in some of the Bob Pease writings.
 

nsaspook

Joined Aug 27, 2009
8,904
The reversible absorptiondesorption reaction in a Lead-Acid battery has a similar electro-chemical effect. Embedded charge in the plates will slowly cause the voltage potential of a battery to recover to some extent as it moves back into the electrolyte due to diffusion forces.
1633147412832.png
https://www.mdpi.com/1424-8220/17/2/422/htm
KiBaM can model two important battery effects:
  • Rate capacity refers to the applied discharge current intensity, i.e., a larger discharge current implies faster battery discharges and, therefore, reduces its lifetime. This is due to the battery voltage level, which decays slowly during the battery discharge, reducing its effective capacity for higher discharge currents [7].
  • Charge recovery refers to the ability of a battery to partially recover its charge during an idle period, after a discharge period. This phenomenon is related to the electrochemical stabilization inside the battery pack.
 

Thread Starter

Energy forever

Joined Sep 11, 2021
46

Thread Starter

Energy forever

Joined Sep 11, 2021
46
As noted some capacitors types have significant dielectric absorption and some don't.

Here's a example where it can cause a subtle problem:
Some years ago I had an accuracy problem with a 12-bit A/D converter in a satellite system, where the output digital word changed value slightly with time after a step input change, well beyond ten time-constants of the input analog anti-alias filter
After some testing I traced it to the capacitor in the anti-aliasing filter that was a high-dielectric type ceramic type which, it turns out, also had a rather high dielectric absorption (soakage).
(That's after I read Pease's article).
The cap was absorbing and releasing sufficient electrons with a long enough time-constant, such that it was slightly altering the varying analog voltage from its true value.
Changing to a low dielectric capacitor (NPO ceramic type), which has a much lower absorption, solved the problem.

So beware of soakage when you use capacitors where high accuracy with changing analog voltages is required (such as filters).
I haven't designed anything used by anyone other than myself, but i too have noticed precision depends on uniform high quality components. Peas and other readings about dielectric absorption, to me, seems trollish. To me, its kinda a bad joke. Because, of course there will be voltage in a capacitor that isn't fully discharged. No explanation so far that i have read explains why a capacitor self charges itself with usable power.
 

DickCappels

Joined Aug 21, 2008
7,981
The charge is stored in the dielectric. Watch this video to confirm your understanding of the dielectric's role, you can skip to 2:00 if you like. I think it is a very good demo. The physics of the Leiden Jar

When the capacitor is shorted the charge cannot be drained from all parts of the dielectric instantly because it is an insulator, so after the initial spark some charge may remain. Over time that charge will migrate to other parts of the dielectric and you might be able to get yet another spark from the capacitor.

Large high voltage capacitors are typically stored with the terminal shorted to soak charge eventually bleeds off. It also gives the person handling the capacitor some confidence.

I don't quite understand why you consider Pease's writings seems trollish. Granted, his use of the language is often very casual, but he know what he is talking about and is held in high regard. Robert Pease is no longer among us, having died in a car accident in June of 2011. I think a lot of us miss him and still refer to his light-hearted and informative articles.
 

Thread Starter

Energy forever

Joined Sep 11, 2021
46
The charge is stored in the dielectric. Watch this video to confirm your understanding of the dielectric's role, you can skip to 2:00 if you like. I think it is a very good demo. The physics of the Leiden Jar

When the capacitor is shorted the charge cannot be drained from all parts of the dielectric instantly because it is an insulator, so after the initial spark some charge may remain. Over time that charge will migrate to other parts of the dielectric and you might be able to get yet another spark from the capacitor.

Large high voltage capacitors are typically stored with the terminal shorted to soak charge eventually bleeds off. It also gives the person handling the capacitor some confidence.

I don't quite understand why you consider Pease's writings seems trollish. Granted, his use of the language is often very casual, but he know what he is talking about and is held in high regard. Robert Pease is no longer among us, having died in a car accident in June of 2011. I think a lot of us miss him and still refer to his light-hearted and informative articles.
Ill take a look at the link ye have previded, before i doith i'eth would like to say that one noticable human characteristic that humans will need to overcome or phase out by means of "evolution" is the natural manifestation of witholding helpful information, information that would help other humans understand. It might seem a trait of self preservation, not necessarily to preserve the ability to be alive, but to live the way they do, to preserve their lifestyle, their income, their status, their power or leverage or control of a situation. But in the so-called BIG picture, this characteristic slows the overall progress of humankind, and could ultimately lead to the premature extinction of our kind.
 

Thread Starter

Energy forever

Joined Sep 11, 2021
46
Nobody is withholding any information from you.
The only way that you could possibly know what others hold within their mind is if all human minds are connected, which if they were, i would know everything everyone else does and not need to ever ask a question. Please speak for yourself, for you only know what you hold within your mind
 

crutschow

Joined Mar 14, 2008
28,201
i'eth would like to say that one noticable human characteristic that humans will need to overcome or phase out by means of "evolution" is the natural manifestation of witholding helpful information,
What has that got to do with this thread? :confused:
Those comments belong in the Off-Topic forum.
 

nsaspook

Joined Aug 27, 2009
8,904
The only way that you could possibly know what others hold within their mind is if all human minds are connected, which if they were, i would know everything everyone else does and not need to ever ask a question. Please speak for yourself, for you only know what you hold within your mind
Yours is a typical 'WHY' physics question where the complete answer is more complex that you can currently conceive because you seem to think it's not.

 

Delta Prime

Joined Nov 15, 2019
1,191
was a nice read. Was i supposed to find the answer to my question by reading it?
Well thank you for your kind words because I wrote it. and yes you were supposed to find the answer to your question by reading it. I consider my better half to be human. That's what Don Lancaster, Joseph j Carr, Forrest M. Mims III, AAC fanatics! & distinguished members of AAC! Would say. ;)
 

Thread Starter

Energy forever

Joined Sep 11, 2021
46
Well if you want to speak in absolutes...that's fine.

But, I was referring to the helpful people that have posted in this thread.
What are your thoughts about absolutes? I need to ask because i absolutely know for absolute certainly that i absolutely do not know what you think about absolutes.
 
Status
Not open for further replies.
Top