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Reverse Voltage on Polarized or Electrolytic capacitors , what happens?

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When Reversing the Voltage on a Polarized or Electrolytic capacitors , what happens?
The inbetween state before it explodes or shorts out internally

If the capacitor is shorted it will make the VCC zero volts or close to zero

When a polarized capacitor is REVERSE VOLTAGE, it draws more current and pulls down the voltage between 2 volts to 5 volts

The polarized capacitor is not shorted , its REVERSE voltage and it doesn't act like a capacitor anymore

The Positive terminal needs to have more voltage than the Negative terminal

REVERSING the voltage, reverses the polarized and potential difference between the positive and negative plates cause will cause more current to draw and drops the voltage down 2 to 5 volts

- - - Updated - - -

I just don't know why it's causing it to draw more current and causing the voltage to be pulled down

When Reverse voltage on a polarized capacitor the ESR is very low?

The Potential difference is Reversed which puts a HIGH voltage on the Negative terminal and ground on the Positive terminal , This cause what to happen and why?
 

kubeek

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I am pretty sure someone allready answered those questions in the other thread.
From the link above "This is because a reverse-bias voltage above 1 to 1.5 V[4][5][6] will destroy the center layer of dielectric material via electrochemical reduction (see redox reactions). Following the loss of the dielectric material, the capacitor will short circuit, and with sufficient short circuit current, the electrolyte will rapidly heat up and either leak or cause the capacitor to burst, often in a spectacularly dramatic fashion."

Here "short circuit" is relative. For a capacitor autopsy see: http://www.pa4tim.nl/?p=1385
So to reiterate the point, the dielectric of an aluminium electrolytic capacitor is made of a thin layer of aluminium oxide. When you reverse the voltage, the oxide becomes dissolved through electrolysis. This then allows current to pass freely between the two plates of the capacitor as they are submerged in conductive liquid, making it very low resistance between the two terminals instead of a capacitor.
 
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So it is acting like a low resistance between the two terminals

What is it called when a polarized components what's a potential difference between the two leads or terminals? when you reverse the potential what is this called and what are u doing to the polarized component?
 

kubeek

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Sorry what? Please try to ask questions such that they are easy to understand..

Potential difference between two leads is also sometimes called voltage, in honor of Alessandro Volta. When you reverse the potential it is called reverse voltage, and you are usually destroying the component in the process (sometimes called operating the component outside of recommended parameters).
See? Better quiestions would have given you better answers.
 

KeepItSimpleStupid

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Think like this:

Sandwich a piece of waxed paper and two sheets of aluminum foil and you will get some sort of capacitor.

Now, do the same thing, but poke holes in the thing with a pin. Some of the edges will short. That short will have a resistance of R-pL/A. p= resistivity of aluminum, L is the length and A is the cross-sectional area of the short.

Some of those holes is a small resistor because of the jagged edges. When there are lots of holes with jagged edges, you basically have a resistor. With lots of perforations, you have a bunch of resistors in parallel. A "shunted" or "shorted" dialectic.

The dialectric in an Electrolytic cap is somewhat liquid and when the polarity is reversed, it heats up. The act of heating up creates hot spots that can turn into shorts in parallel with some finite total resistance.

It's unknown what that resistance will be for every failure.
 
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Thanks for the info. and help

To make it more clear

To focus on the potential difference is what I'm confused about

Polarized Cap
1.) Positive terminal needs a +positive or higher voltage than the negative terminal
2.) Negative Terminal needs a voltage close to zero volts

This Forward Biases the Polarized cap? so current flows from + terminal to - terminal

REVERSE Voltage Polarized cap
1.) Positive Terminal has zero volts
2.) Negative terminal has + positive or Higher voltage than the negative terminal

This Reverse Biases the cap, so the current is flowing from - terminal to + terminal


Why is it bad to put a + voltage or having a higher voltage on the negative terminal?

When having a + positive voltage on the negative terminal what happens?
When having zero volts on the positive terminal what happens?

The terminals or plates inside the cap. are polarized? the Electro-chemicals are Uni-directional not bi-directional
 

kubeek

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To focus on the potential difference is what I'm confused about

Polarized Cap
1.) Positive terminal needs a +positive or higher voltage than the negative terminal
2.) Negative Terminal needs a voltage close to zero volts...
The difference is where you seem to struggle. A properly polarized cap will have postitive voltage across it, meaning that the voltage on negative terminal is lower than voltage on positive terminal:
The potential difference is V+ minus V-, literally the difference between the two.

The inside plates of a cap are polarized, both are made of aluminium foil but one of them has a layer of aluminium oxide on it, and an electrolyte between the electrodes. See http://www.electronics-tutorials.ws/capacitor/cap_2.html
When you reverse the voltage, the electrolysis will start to happen and the oxide layer will start to move to the pure alu plate. But it will not move entirely, because the cap will be shorted very soon in some spots, the electrolyte will boil and the capacitor will went and release the gases.
 
the voltage across the cap is the difference between positive and negative terminal.
The voltage between the positive and negative across the cap in "Forward voltage" is different than the voltage between the positive and negative terminals when "REVERSE voltage"

This is my main point is that the potential differences which is the voltage between the positive and negative terminals

So it changes the Voltage drop which is the voltage across the positive and negative terminals
 

kubeek

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The bias voltage of the cap is the the voltage on positive terminal minus voltage on negative terminal.
In a "properly" biased cap this voltage is positive, i.e. +25V. In a reverse biased cap this voltage is negative, i.e. -2V. You change the voltage on the cap, the cap just reacts with passing lots of current in the reverse direction.
 
You change the voltage on the cap, the cap just reacts with passing lots of current in the reverse direction.
Why doesn't it pass a lot of current in the reverse direction?

Why does a capacitor need to be polarized? what does it do differently than a non-polarized cap?

Having a capacitor polarized will hold or store DC voltage better?
 

kubeek

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In the right direction the capacitor doesn´t pass current, because the insulating layer between the two plates is intact, so no current can flow through it. When you reverse the voltage the insulating layer dissolves and the current can get from one plate to the other, discharging the stored charge and becoming a short.
An electrolytic capacitor is polarized because of its consctruction, not because someone wanted it to be like that. A film or ceramic capacitor has much smaller size volume for a given capacity than an electrolytic capacitor. So for having small sized caps with high capacity you pay with the fact that they are polarized and will blow up if you don´t use them right.
 
oh ok so it's discharging the stored charge and drawing more currrent, pulling down the voltage

So it's polarized because why? the plates are polarized and the electro-chemicals are polarized, any reasons why?

Non-polarized cap don't have electro chemicals, any reason why?
 

kubeek

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It is just because of the way of construction. The equation of a capacitor is that capacity is equal to total plate area times dielectric constant of the insulator divided by the thickness of the insulator. So if you can get small thickness with large enough breakdown voltage, you will get a small sized capacitor for a given capacitance, and electorytics happen to do just that, the insulating oxide layer is really tiny so the capacitance is large.

There are many different ways to make a capacitor, like film caps, ceramic, electrolytic, and each with many different tipe of insulating material between the electrodes, and each type has its positive and negative features.
For example ceramic caps are more stable than electrolytics, but are hard to make in large capacitance values because the would be physically large. Other types can have better thermal stability or low inductance or some other feature that makes them good for a certain application.
And electrolytics are used mainly in power supplies, because you need large capacitance to filter the supply noise and you want them to be small. Ceramics have retain their parameters even in high frequencies, so the are used as bypassing near ic power pins.
 
They use Metalized film caps for decoupling caps from VCC to ground , circuit boards at my work

They don't use ceramics caps for bypassing or decoupling from VCC to ground, they use metalized film caps , why is that?
 

kubeek

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I don´t know, did I make that decision? Ask your boss why they use those. Could be a hundred reasons why, for example beacuse they needed just those in the past, and then they got stuck with them beacuse they don´t need any with different parameters. Or they use them beacuse they do something that ceramics can´t provide in that capacitance and voltage rating.

Please try to realize that these considerations are highly specific to the circuit the part will be in, and without seeing the schematic, knowing the function of the cap and then checking the price lists, lead times, and comparing parameters and performance of alternative parts you can´t ever tell why someone chose that exact part.
 
Yes True, just wondered if you knew as to why or had a best experience guess from it

Have you seen metalized film caps used for decoupling and Bypass?
 

KeepItSimpleStupid

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Bypassing is somewhat of an art. At times you can even find 3 or 4 different types of capacitors in parallel for bypassing.

Some considerations: Ceramic is usually better at RF frequencies. Electrolytic have a better ESR. Tantalums have a good ESR and a good frequency response.

Ripple current will also kill an electrolytic cap.
 

kubeek

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Decoupling of what from what? In which frequency range? Audio signals, video, digital data, protection earth? Each one will be different.
 
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