What property determines charge current surge value in e-caps ?

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BobaMosfet

Joined Jul 1, 2009
2,123
Standard answer: iequalscdvdt, as the man behind the CapSite has named it. So there is the
capacitance to start with, and the ratio dv/dt to complete the product that ought to give you the
momentary charge current to the cap. But how ... ? Consulting textbooks and tutorials, you are
bound to find a phrase like: 'presents a near-short circuit', to describe the cap's behavior after
switch-on. Few if any specify the 'near'-part, however. The only thing to do then, is go look for an
R (i.e. in the cap itself, not the obvious resistances in source, wiring, etc.). A glance at one of the
many different equivalent circuit diagrams for an e-cap, reveals its series resistance ESR, which
indeed turns out to be less than one Ohm usually. And by applying this man's familiar law, we can
finally make more than an educated guess as to the value of the charge current surge. This is
because - while dv in the original formula is not easy to determine - V in Ohm's Law simply is the
full applied voltage, as there has not yet been generated a counter e.m.f. (where the 'm' stands for
'motive', not 'magnetic') directly after switch-on. So the inrush current surge equals the voltage
applied to the e-cap, divided by its ESR, or does it ? ....
I invite and await your comments and criticism as to method, reasoning and outcome of the above.
(Please try to apply as little math as possible - thank you).
You're not looking at this correctly. A capacitor NEVER passes current. If it does, it's failed. A capacitor is merely a device that enlarges the diameter of a conductor to outrageous proportions- upon whose surface electrons pile up unable to jump the gap (through the dielectric).

When you put voltage across a capacitor you are dropping.losing volts (ie. potential for current to move), and it appears as a short simply because current is flowing off the leg into the plate as fast as can be allowed by physics (if not impeded by a serial resistance of any sort). For all intents and purposes Dv/Dt is only applicable if an impedance exists. This why in graphs you see current start at zero in time, and voltage start at max, and they change inversely to one another. Current stops flowing and no further voltage can be dropped when the capacitor is pushing back against the supply with equal voltage.

Max current discharged, if the power-supply removed, is solely a function (ideally) of coulombs on the plate- movement is near instantaneous, so is max based on charge quantity. In physics, There is only electrons moving and the impedance to that flow- volts are an imaginary value representing the reciprocal of that ratiometric relationship between movement of electrons (neutralization of charge) and the impedance to that movement.

In short, impedance determines max charge from capacitor and the time delta.
 

Thread Starter

SYNFONIQUE

Joined Jun 5, 2021
48
@SYNFONIQUE
My experience?
30+ years of professional work in E/E - paired with university studies.
I've even worked on the quite special topic of inrush current: automotive application, so powered from a battery with maybe 20 mOhms output impedance. Believe it or not: one of these devices has been produced in some 2-digit numbers (still in production), and I've never heard of any issue. Peak inrush current is somewhere beyond 16 Amps - through a diode rated 200 mA and into a 10µF cap. (You can be sure, these 16 A are nowhere to be found in the diode's datasheet.)

Re your application:
While toroids (aka "fuse killers") are infamous for their inrush current on the primary, they still obey to Ohm's law: when "overload" by some short-circuit (uncharged caps), the secondary voltage will decrease due to the secondary winding's resistance. It's just that you cannot exceed the transformer's power rating significantly.
My (inherited) rule-of-thumb for transformer-rectifier topologies is a minimum of 1000 µF per Amp output current (50 Hz grid - 60 Hz would allow for a minimum capacitance of 833 µF). (More capacitance is better but doesn't come exactly cheap).
If your secondary overall capacitance exceed this magic minimum value, the effect of the inrush current on the capacitors will decrease as the transformer is loaded beyond the value considered "reasonable". This will not damage the transformer, just reduce the effect on the capacitors.
First of all: I seem to have done something wrong in replying to Andrew's post,
resulting in your post getting mixed up - sorry !
Furthermore, I had no intention of questioning your expertise - on the contrary, it
was clear to me right from the start: this is a voice from practice. I believe however,
that individual posts can be considered to be a mix of practical/hands-on experience
and some analysis, based upon what one has read, heard from colleagues, etc. The
fairly large discrepancy between the 'conventions' in our respective fields was the
reason for my remark. An example: an audio designer would not dream of exposing
an 1N4148 to a 16A transient, no matter how short-lived ...
On the other hand, as you're automotive-based, early 20th century no one believed
that an automobile could be started electrically ... until someone just grabbed a
(potent) battery and tried it ! And it is exactly this kind of trial and error that has let
the early electrolytic develop/evolve into the mighty e-caps that satisfy today's most
demanding designers of audiophile equipment as well as e-vehicles.
I know under- or tightly-rated transformers can act as effective brakes, but having
anything in the way of unlimited dynamics is just not-done for the die-hard audio-
phile. To avoid any misunderstandings: I am not among the audiots, as they are
sometimes called. I enjoy my music via a brick-format 30W power amp (Stan Curtis
design) driving 2-way mini-monitors. Consequently, as a designer I try to devise a
minimalist solution to the inrush surge problem that has none of the disadvantages
of conventional ICLs.
 

Thread Starter

SYNFONIQUE

Joined Jun 5, 2021
48
It seems then @SYNFONIQUE , that you have an answer,
may be you could ask for the thread to be closed as answered.
You may have noticed that we (S & Du) are still discussing the 'front end', which is
very much intertwined with the problem at hand. If you don't have a useful contribu-
tion at hand, you might consider, leaving us to it ...
 

du00000001

Joined Nov 10, 2020
120
@SYNFONIQUE
Exposing a 1N4148 to 16 A would really be an exaggeration: I'd expect the bond wires to just dissolve in thin air

If you intend to lower the peak inrush current, you might consider to insert a choke on the secondary side that doesn't hamper steady-state operation too much while lowering the peak inrush current (while somewhat stretching the duration of "inrush conditions" as the energy required to charge the cap(s) is a constant).
Just an idea...
 

Deleted member 115935

Joined Dec 31, 1969
0
You may have noticed that we (S & Du) are still discussing the 'front end', which is
very much intertwined with the problem at hand. If you don't have a useful contribu-
tion at hand, you might consider, leaving us to it ...
my apologies,
No I did not see that , hence why I asked,
I was wondering what I could do to help out ,
 

sparky 1

Joined Nov 3, 2018
785
What property determines charge current surge value in e-caps ?

The property is the material's dielectric integrity.
The causes are seen as electrochemical breakdown over time. The paper, foil or connections can be compromised more rapidly with excess heat and voltage stress. By selecting an appropriate value in Farads for a given current the effects of inrush and resistive mechanism can be reduced. For inrush thermistors have been helpful. The dielectric stress deformation charecteristics on the capacitor's materials has some interesting development like self healing and this differs according to the circuit's end use.

A common mistake is buying capacitors with expired shelf life, not testing if they are dryed out and not using reforming method.

Changing the question's sentence structure will improve the specific area of concern. I like to use a manufacturer's application note to get the terminology because the capacitor is in tolerance with the circuits function. If it is not found there it probably is a circuit question about surge suppressing methods. There are plenty of circuit simulations. I ordered more 1N5819 because of improvement when trying different diodes in simulation even though I copied a simulation I needed to modify it to meet specifications. The circuit improved as a result of replacing parts in virtual simulation the properties involved were seen on virtual instruments.

https://www.tdk-electronics.tdk.com...2da2adf2b/pdf-generaltechnicalinformation.pdf
 
Last edited:

Thread Starter

SYNFONIQUE

Joined Jun 5, 2021
48
@SYNFONIQUE
Exposing a 1N4148 to 16 A would really be an exaggeration: I'd expect the bond wires to just dissolve in thin air

If you intend to lower the peak inrush current, you might consider to insert a choke on the secondary side that doesn't hamper steady-state operation too much while lowering the peak inrush current (while somewhat stretching the duration of "inrush conditions" as the energy required to charge the cap(s) is a constant).
Just an idea...
"Peak inrush current is somewhere beyond 16 Amps - through a diode rated 200 mA
and into a 10µF cap. (You can be sure, these 16 A are nowhere to be found in the
diode's datasheet.)" Please tell me, how else I should interpret this quote from your
post. The datasheet of the 1N4148 I used for my statement, specifies 300 mA, so I
thought the comparison was legit.
The idea of inserting a (swinging) choke before the (first) reservoir cap indeed has
intrigued me since I know this topology from tube technology. However, the actual
application in a low voltage PSU certainly is no sinecure - and that is the reason one
only rarely sees it in high-end audio. In my time as an audio pro we had a pair of
Cello Encore mono-blocks in the demo room. I have never been able to acquire the
schematics of the so-called 'dual choke' PSU, designed by the late Tom Colangelo.
If anybody could help me find the circuit diagram/general circuit/white paper,
I woud be obliged.
 

Thread Starter

SYNFONIQUE

Joined Jun 5, 2021
48
He had the same answer in post #2, but ignored it.

Bob
Sorry, Bob, if we arrived at the same conclusion via a detour. But your post stated:
"There is also the output impedance of the power source, which , in some cases will
dominate." - admittedly in the "also", while the question asked for a "property of the e-cap" itself.
 

Delta Prime

Joined Nov 15, 2019
1,311
Hello there.An Belated Welcome to AAC! :)
So the inrush current surge equals the voltage
applied to the e-cap, divided by its ESR, or does it ? ....
I invite and await your comments and criticism as to method, reasoning and outcome of the above
ESR "R" is from resistance of the electrode foils, the electrolyte, the leads and each connection.The causes of leakage current in aluminum electrolytic capacitors are Distorted polarization of dielectric (aluminum oxide layer).The leakage current value can be decreased by proper selection of materials and production methods; however,cannot be totally eliminated.
Leakage current is also dependent upon time, applied voltage and temperature.The specified leakage current value is measured after the rated voltage of the capacitor is applied at room temperature for a specified time period.
 
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Thread Starter

SYNFONIQUE

Joined Jun 5, 2021
48
You're not looking at this correctly. A capacitor NEVER passes current. If it does, it's failed. A capacitor is merely a device that enlarges the diameter of a conductor to outrageous proportions- upon whose surface electrons pile up unable to jump the gap (through the dielectric).

When you put voltage across a capacitor you are dropping.losing volts (ie. potential for current to move), and it appears as a short simply because current is flowing off the leg into the plate as fast as can be allowed by physics (if not impeded by a serial resistance of any sort). For all intents and purposes Dv/Dt is only applicable if an impedance exists. This why in graphs you see current start at zero in time, and voltage start at max, and they change inversely to one another. Current stops flowing and no further voltage can be dropped when the capacitor is pushing back against the supply with equal voltage.

Max current discharged, if the power-supply removed, is solely a function (ideally) of coulombs on the plate- movement is near instantaneous, so is max based on charge quantity. In physics, There is only electrons moving and the impedance to that flow- volts are an imaginary value representing the reciprocal of that ratiometric relationship between movement of electrons (neutralization of charge) and the impedance to that movement.

In short, impedance determines max charge from capacitor and the time delta.
You do have a peculiar way of describing the life and times of a capacitor, charge,
electrons, and the like. It's not that I dislike it - in fact I'm very much interested in
original thinkers, writing likewise. What does bother me is incorrectness. For a start:
where did I state in my OP, or even suggest, that "A capacitor passes current" ? But
there is more: "This why in graphs you see current start at zero in time, and voltage
start at max, and they change inversely to one another". While the OP clearly was
about the charging process, a description thereof would show the graphs upside
down. Sorry, but this has in no way contributed to a better understanding.
 

BobTPH

Joined Jun 5, 2013
9,292
Sorry, Bob, if we arrived at the same conclusion via a detour. But your post stated:
"There is also the output impedance of the power source, which , in some cases will
dominate." - admittedly in the "also", while the question asked for a "property of the e-cap" itself.
And the inrush current is not a property of the capacitor, it is a property of the entire circuit, which is why. I said “also” when referring to the impedance if the source.

Bob
 

Thread Starter

SYNFONIQUE

Joined Jun 5, 2021
48
What property determines charge current surge value in e-caps ?

The property is the material's dielectric integrity.
The causes are seen as electrochemical breakdown over time. The paper, foil or connections can be compromised more rapidly with excess heat and voltage stress. By selecting an appropriate value in Farads for a given current the effects of inrush and resistive mechanism can be reduced. For inrush thermistors have been helpful. The dielectric stress deformation charecteristics on the capacitor's materials has some interesting development like self healing and this differs according to the circuit's end use.

A common mistake is buying capacitors with expired shelf life, not testing if they are dryed out and not using reforming method.

Changing the question's sentence structure will improve the specific area of concern. I like to use a manufacturer's application note to get the terminology because the capacitor is in tolerance with the circuits function. If it is not found there it probably is a circuit question about surge suppressing methods. There are plenty of circuit simulations. I ordered more 1N5819 because of improvement when trying different diodes in simulation even though I copied a simulation I needed to modify it to meet specifications. The circuit improved as a result of replacing parts in virtual simulation the properties involved were seen on virtual instruments.

https://www.tdk-electronics.tdk.com...2da2adf2b/pdf-generaltechnicalinformation.pdf
The purpose of my question indeed was to eventually arrive at an improved circuit
for inrush surge limiting. I hoped for exchanging views on the subject and getting a
better understanding of what really 'makes a reservoir cap tick' during the charging
surge transient. It is obviously not the complex capacitance parameter as the deter-
mining factor, but rather its ESR. I am acquainted though with the conventional ICL
circuits (and their drawbacks), most of the theory behind it, and the 'don'ts' while
selecting the appropriate caps. Thanks anyway - the 1N5819 certainly makes for an
interesting rectifier candidate, but the S/N-conscious audio designer will have to
cope with the noise of this fast-switching Schottky diode.
with
 
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Thread Starter

SYNFONIQUE

Joined Jun 5, 2021
48
And the inrush current is not a property of the capacitor, it is a property of the entire circuit, which is why. I said “also” when referring to the impedance if the source.

Bob
Your original post was a useful additional remark, not an answer to the question. And
I did not state that "the inrush current is a property of the capacitor", but arrived at
the conclusion that its ESR must be the property determining charging surge value
as far as the cap itself is concerned. That is a fact beside the fact that the entire circuit
ultimately determines the real value as you pointed out early in the discussion.
 

Thread Starter

SYNFONIQUE

Joined Jun 5, 2021
48
Hello there.An Belated Welcome to AAC! :)

ESR "R" is from resistance of the electrode foils, the electrolyte, the leads and each connection.The causes of leakage current in aluminum electrolytic capacitors are Distorted polarization of dielectric (aluminum oxide layer).The leakage current value can be decreased by proper selection of materials and production methods; however,cannot be totally eliminated.
Leakage current is also dependent upon time, applied voltage and temperature.The specified leakage current value is measured after the rated voltage of the capacitor is applied at room temperature for a specified time period.
I believe we already met in my previous thread, Delta Prime:
"Real-world behavior of series-connected electrolytic capacitors" (thread #180592)
You - and others here - may wonder, why I started this new thread on a subject so
closely related ? In one word: uncertainty. Though the sim-graphs, presented by Mr.
Gibbs, offered quite some help in believing my assumption to be true: in theory the
respective capacitances may be considered to govern voltage-division, in reality
however it is the ESRs of the caps. But being critical about sim-software, I would still
like to see some sort of peer-review-like conclusive confirmation. After all, how can
you get out what has not been put in first ? Moreover, Mr. Gibbs explicitly stated
that he had only specified the ESRs to be different from standard modelling so what
other outcome could one expect ... ? Still I tend to believe, the results are real-world.
By further narrowing the question - from two or more, to one cap - I hoped to get
'additional proof' and started the new thread.
Over to your post: I am only interested in leakage current as far as it determines the
(eventual) voltage division between series-connected electrolytics. In the late 80's
Kowalski et al. established this real-world deviation from theory, the latter stating
that the division is in the ratio of the capacitances and then inversely proportional.
When I discovered the relevant publications on the Net (decades later), this actually
started my quest for the real-world behavior of (specifically: electrolytic) caps.
 
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Deleted member 115935

Joined Dec 31, 1969
0
I believe we already met in my previous thread, Delta Prime:
"Real-world behavior of series-connected electrolytic capacitors" (thread #180592)
You - and others here - may wonder, why I started this new thread on a subject so
closely related ? In one word: uncertainty. Though the sim-graphs, presented by Mr.
Gibbs, offered quite some help in believing my assumption to be true: in theory the
respective capacitances may be considered to govern voltage-division, in reality
however it is the ESRs of the caps. But being critical about sim-software, I would still
like to see some sort of peer-review-like conclusive confirmation. After all, how can
you get out what has not been put in first ? Moreover, Mr. Gibbs explicitly stated
that he had only specified the ESRs to be different from standard modelling so what
other outcome could one expect ... ? Still I tend to believe, the results are real-world.
By further narrowing the question - from two or more, to one cap - I hoped to get
'additional proof' and started the new thread.
Over to your post: I am only interested in leakage current as far as it determines the
(eventual) voltage division between series-connected electrolytics. In the late 80's
Kowalski et al. established this real-world deviation from theory, the latter stating
that the division is in the ratio of the capacitances and then inversely proportional.
When I discovered the relevant publications on the Net (decades later), this actually
started my quest for the real-world behavior of (specifically: electrolytic) caps.
@SYNFONIQUE
Wow , is that 180592 answers to a thread,
and your confused, , Im not surprised.

Suggestion,

IMHO, confusion is partly to do with question asked, and how people listen to the answer,
In my experiance, those that don't listen, will stay confused,
 

Thread Starter

SYNFONIQUE

Joined Jun 5, 2021
48
The windmills that Don Quixote spots in the distance are always windmills; they're never giants. But Don Quixote is so convinced that they're windmills that he attacks them. I wish you a safe journey on your quest.
If you would read the publications by Kowalski et al. (physics professors), you might
develop more respect for an opinion (based upon literature study, and serious
experiments) which just doesn't fit yours.
If you can open your mind to it, surprise yourself by downloading this article:
Capacitors in series: a laboratory activity to promote critical thinking
from iopscience.iop.org .
 
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