Author Topic: Electrolytic capacitor + and - plates response to small signals  (Read 318 times)

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Offline ifrenide

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hello everyone, I want to know, how an electrolytic capacitor have the same response, for the same small square wave signal,no matter the polarization.
this is ovserved while ESR measerement of an electrolytic capacitor. how can give the same reading,for both sides.As I know, the positive and negative plates are different ,so how can they give the same response?
thanx.
best regards
« Last Edit: July 23, 2019, 01:49:50 am by ifrenide »
 

Online Zero999

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Re: Electrolytic capacitor + and - plates response to small signals
« Reply #1 on: July 23, 2019, 08:07:14 am »
By keeping the voltage very low. An electrolytic capacitor can be reverse biased by a volt or so without any damage and will still act like a capacitor.

Why scale the image up to an insane size, which just wastes bandwidth? Please refrain from posting such large files, unless it's absolutely necessary.
 

Offline ifrenide

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Re: Electrolytic capacitor + and - plates response to small signals
« Reply #2 on: July 23, 2019, 01:26:08 pm »
Hello zero999
1- How can we get the same reading, with different plate configuration" on atomic scale"?
2- Why only small voltage can be applied on the reverse polarity sens ?
 

Online T3sl4co1l

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Re: Electrolytic capacitor + and - plates response to small signals
« Reply #3 on: July 23, 2019, 02:03:13 pm »
What's on atomic scale?

Typical electrolytics can withstand several volts reverse before nonlinearities occur.  An ESR tester (is that what this is?) may only apply a few millivolts, a negligible amount in comparison.

Tim
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Offline ifrenide

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Re: Electrolytic capacitor + and - plates response to small signals
« Reply #4 on: July 23, 2019, 02:25:05 pm »
Hi Tim.
1-"On atomic scale ",I mean the anode and cathode atomic construction, do you think it's the same?
2-What make aluminum foil stripe anode. And what make the other stripe a cathode.
3-why small voltage can be applied in reverse sens " what happen to the atoms in both scenarios a small voltage ,and a high voltage? ".
4- what determine the maximum voltage applied in reverse polarity sens of the electrolytic capacitor?
Best regards

 

Online T3sl4co1l

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Re: Electrolytic capacitor + and - plates response to small signals
« Reply #5 on: July 23, 2019, 04:55:14 pm »
One of the plates is anodized to a certain voltage, and the other either a lot less, or not at all (native aluminum oxide).

Anodization is diffusion mediated as far as I know.  You can break it down to an atomic description where Al + 3H2O --> 1.5 H2 + Al(OH)3 (H2 being produced at the cathode, Al(OH)3 at the anode, as this is an externally powered, electrochemical process), but the structure develops due to the atoms and charges diffusing through the bulk material, and all that's required is a model of that bulk material.

Thickness of the [hydr]oxide layer determines voltage rating.

Probably there's also a free 1.2V or so, due to the electric double layer effect (limited by the reaction voltage of the electrodes and decomposition of the electrolyte).  When an electrolyte is used that is less prone to decomposition, this effect can be harnessed to better effect.  EDL capacitors (supercapacitors) use organic electrolytes like ethyl carbonate, which decompose above 2.7V, hence the 2.7V rating of single-cell supercapacitors.  (Combined with an extremely high surface area electrode like activated charcoal, this gives usefully large capacitances, in the farads.  Obviously, electrolytic capacitors don't have as much surface area, but they have higher voltage ratings too.)

Tim
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Offline ifrenide

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Re: Electrolytic capacitor + and - plates response to small signals
« Reply #6 on: July 24, 2019, 12:35:53 am »
Hi Tim.
thank you very much .
but you forgot questions 3 and 4  :D . important for me.
best regards
 

Online T3sl4co1l

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Re: Electrolytic capacitor + and - plates response to small signals
« Reply #7 on: July 24, 2019, 03:04:01 am »
Very well, I will explain in more detail.

Quote
3-why small voltage can be applied in reverse sens " what happen to the atoms in both scenarios a small voltage ,and a high voltage? ".

Again, the atoms aren't interesting.  It isn't a gas filled capacitor.  It is a bulk diffusion mechanism.

The voltage is proportional to the oxide thickness (or, if not exactly proportional, then related in some one-to-one manner).  The oxide is an insulator up to a certain limiting voltage, above which it is able to conduct in some manner (again, ionic diffusion is a possibility, but also impact ionization and avalanche, or conductive channel formation).

When a current flows, oxide ions are drawn into the layer from the electrolyte.  They drift through the oxide (partly propelled by the current), and eventually combine with the aluminum metal surface, forming new oxide.


Quote
4- what determine the maximum voltage applied in reverse polarity sens of the electrolytic capacitor?

Thickness of the reverse foil's oxide.  Several volts.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline ifrenide

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Re: Electrolytic capacitor + and - plates response to small signals
« Reply #8 on: July 24, 2019, 04:58:13 pm »
thank you tim  :popcorn:
 


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