AC flowing through a cap. What actually happens?

[Jon Wilder]

Doesn't matter whether the active device is a vacuum tube, transistor, JFET, MOSFET, etc etc. The "coupling cap principle" works identically in either or scenario.

 

[killivolt]

Thanks, Jon. I'm not sure if we are on the same page though. Your explanation showing the a coupling principle does a good job helping me understand the circuit application and how to exploit the operational side or working translation. It does show the circuits ability to move low to high state energy in a productive manor.

However, the inner side of the capacitor is yet a mystery of how you get the energy itself to deposit, replace, displace. As in the active region without the movement of charge carriers such as electron flow as we now it through a component. e.g. The PN juntion of a transistor or through a dielectric battery.

The physical region of a vacuum capacitor use a mechanism for the lack of a better word that increases movement of force into flow again for the lack of a better word.

If I were able to look at you and tug my ear and cause you to run to home plate is the example. Only because you know the sign and I you can translate that in to moving force toward the plate running across it into the dugout. That's when an electron is conducted to operate but, just what is the signal.

I have also found some more examples of vacuum Capacitors that I did not know about. Very interesting as we continue this process.

Vacuum variable capacitor - Wikipedia, the free encyclopedia

 

[MrAl]

Hi,

Yes, the coupling cap does illustrate how we can have 100 volts average DC on the left side and -100 volts DC on the right side, yet both sides have 1 volt AC. It's like the cap isolates the two sides of the circuit.

 

[BrownOut]

But, the getter may have not been available at the time of Maxwell. I actually was hoping someone would comment on it since I didn't know. Plus if you are using a getter it would only apply to Diodes & Triodes & Pentodes when I read the wiki article, it said, to stabilize performance over time because of the high heat generated from the heater, maintaining a thermal equilibrium & vacuum.

In the instance of the Capacitor this would not apply. It does not require a heater. Only a complete vacuum without assistance from artificial methods to dry them. You wouldn't want to use RF to stimulate the A - B plate either in order to raise the temp forcing any remaining molecules. This process might also produce carbon which might influence the Chamber as well, De-stablizing the performance & altering the characteristics of the Capacitor or so you would think!

Maybe someone could explain more for me as I just don't understand. A bit confusing.

But, again I just don't understand how it was constructed back then, either.

Hi Killivolt, As Bill Clinton famously said, I feel your pain. I also had the tug of war going on in my mind the first time someone tried to convince me that current goes through the vacuum of space. I reconciled the seeming contradiction by just ignoring the displacement term. And so, I commend you for hanging in and at least keeping an open mind. The whole case for displacement current comes from Ampere's law, which says essentially that current in a wire is identical to the magnetic flux density times a length over which the flux is measured. So, in other words, if you measured the magnetic field, you could ascertain the current passing through the wire. All current measurements were done using the principle, except for some now that use a resistor and Ohm's law, along with a good amount of digital processing, to get the result. Maxwell realized, by examining experimental data, that Ampere's law was missing a term, that the current should include a term for a changing electric field, which contributes to the magnetic field, just as moving charge in a wire does. Once he added the term, the theory of charge flow was consistant with the principle of charge conservation. Sixty years after Maxwell made this important discovery, displacement current was finally measured in a lab.

Now, for the capacitor, it's been shown that the displacement current flows in the air dielectric, and as required by current continuity condition, maxwell's displacement current is equal in magnitude to the conduction current in the wires connecting the capacitor to the source of current. This gives rise to the principle of continuous current across the capacitor, even though charge does not traverse the dielectric. I understand it's difficult to think of current where there is no charge, but it's the Ampereian magnetic field, constant across the capacitor, that is the evidence that the current is there. So, current is defined by two terms, one that comes from the flow of charge, and another that comes from the change in the electric field.

It's not an easy concept, and many of the lectures say as much. Give it some time to sinc in. And remember, discovery always comes when we get results we didn't expect

 

[killivolt]

Hi Killivolt, As Bill Clinton famously said, I feel your pain. It's not an easy concept, and many of the lectures say as much. Give it some time to sinc in. And remember, discovery always comes when we get results we didn't expect

That was actually funny, when you said the "Famous Bill Clinton, Line." Suddenly, I had to read the hole thing with Bill Clintons Voice in my mind; "then" I read the last Line.

"And remember, discovery always comes when we get result we didn't expect" Good one.

 

[Mr RB]

...
We have two tanks of water, first one on the left, second one on the right. They both have 100 gallons of water in them when we start and nothing is moving.
We also have a pipe coming from the second tank going to a pump (which is not running), and the pump connected to another pipe that goes to the first tank.
Now we turn on the pump and pump water into the first tank so water flows through the two pipes and pump, but because of the piping we can only get that water from the second tank. This means that as the first tank gets more and more water, the second tank looses more and more water. Note that we did not have any other connection between the two tanks as they are separated from each other.
Question 1: We only have one pipe connected to each tank, so where is the displacement current?
...

Thank you for the wonderfully simple analogy using only flow (with no complications of field discussion).

For the water to be displaced from one tank to another, there needs to be a mechanism for displacement. That is not the pump (as the pump is voltage) the displacement mechanism is an air tube between the tanks (as ljcox said) or is a membrane between the tanls (as you yourself proposed).

But in all cases there must be an ability for the water to be displaced, which is what defines a cap as different from another 2 wire component that has no conduction. The cap has no conduction, but it has the ability for "electron displacement" from one wire to the other as this is the only way electrons can go in one side and out the other.

So for complete circuit loop current to be valid (and it must be) the pump takes water from one tank and delivers to the other, and the tank (if it acts as a capacitor) must have an ability to displace an equal amount of water from one side to the other. The "displacement current" between the 2 halves of the tank must equal the conducted current through the pump. Which sounds like what Brownout has been saying all along.

 

[MrAl]

Hello again,

The water/tanks experiment was sealed so that no air can flow. There's no displacement current. This is what i was getting at. The only communication between the water tanks is that one pipe, that's it. We can have water flow from one tank to the other without any displacement current. The flow is also constant so we have no acceleration.

Now if we add another pipe that's a different experiment.
Experiments like this are made to isolate principles.

Any measurement of displacement current in the capacitor has to rely on the field. We already know that the Electric flux change causes what we call a displacement current, we know that long time ago, when we first learned this stuff. Brownout keeps repeating this like it's new information which doesnt make sense.

 

[killivolt]

Any measurement of displacement current in the capacitor has to rely on the field. We already know that the Electric flux change causes what we call a displacement current.

So for complete circuit loop current to be valid (and it must be) the pump takes water from one tank and delivers to the other, and the tank (if it acts as a capacitor) must have an ability to displace an equal amount of water from one side to the other. The "displacement current" between the 2 halves of the tank must equal the conducted current through the pump.

This becomes a point of conclusion. But, relevancy. You have to add the value of the conductor and the wave function upon the material by which is within the field.

Gold has only 1 isotope, Silver has 2 isotopes and is balanced, Copper 63Cu 69.15% 63Cu is stable with 34 neutrons.

In a charged Magnetic Field what happens next. Is there a charged environment that is allowed a combination of factors which produce the energy that provides release of plate B ?

 

[BrownOut]

This becomes a point of conclusion. But, relevancy. You have to add the value of the conductor and the wave function upon the material by which is within the field.

Gold has only 1 isotope, Silver has 2 isotopes and is balanced, Copper 63Cu 69.15% 63Cu is stable with 34 neutrons.

In a charged Magnetic Field what happens next. Is there a charged environment that is allowed a combination of factors which produce the energy that provides release of plate B ?

The confusion comes from the fact that there is no interaction between the tanks in this simplistic example, whereas in a real capacitor, there is. As to your question, you're going down the same path as Maxwell did. There is a magnetic field due to a changing electric field, and in turn, an electric field due to a changing magnetic field. The two fields are self-sustaining and "flow" together until the electic field terminates on the 2nd plate. This continues to happen until the current stops, at which time there is only the electric field, and the magnetic field disappears.

 

[ljcox]

This increase in base-emitter current causes a large increase in collector-emitter current. In order for collector-emitter current to increase, the collector-emitter resistance must decrease, which in turn decreases the voltage drop across the emitter resistor (R3) and the transistor. This effectively pulls the collector down to ground. Remembering that the collector side of C1 has a positive charge while the R2 side has a negative charge that the cap acquired when it was pulled up to the positive supply voltage, pulling the collector side of C1 to ground effectively connects C1 across R2, but in reverse polarity, R2 now draws current from C1, but since the polarity is now reversed, this current that R2 draws is a negative going current, which causes a corresponding negative voltage drop across R2.

Jon, that is a good explanation & I agree with everything except the part highlighted in red.

Bipolar transistors are voltage controlled current sources.

So the collector-emitter resistance does not change (it is very high) it is the collector current that changes.

 

[killivolt]

The confusion comes from the fact that there is no interaction between the tanks in this simplistic example, whereas in a real capacitor, there is. As to your question, you're going down the same path as Maxwell did. There is a magnetic field due to a changing electric field, and in turn, an electric field due to a changing magnetic field. The two fields are self-sustaining and "flow" together until the electicric field terminates on the 2nd plate. This continues to happen until the current stops, at which time there is only the electric field, and the magnetic field disappears.

Ok, I'm buying into that. Which is why I mentioned earlier that there was a sympathetic region with "2" sympathetic "harmonic balanced" for lack of a better expression; separate waves acting upon them self's.

In my mind there has to be something that will kick start these to separate fields something that will act as a virtual core for the coupling to pass through.

Which is also why I mentioned the cyclotron action or rotational speed and height of an electron or electrons trapped in a field effect that alters their energy forcing them to change "State" to behave as a wave and not particle however, the electrons waiting on the other side plate B grab the energy field present now in the conductor along with corresponding "electrons present in the wire which are more than ready to behave as particles allowing them to drain toward the load?

I'm also not apposing Ratchets idea of existing kinetics generated by a form of cyclotron that produce either ions, protons, neutrons, photons or even an allusive type of electron not clearly understood. I'm seeing a highly charged atmosphere when we talk about voltage I'm seeing voltages of 5kv or 20kv being introduced to the vacuum capacitor I found in the wiki sheets.

Doesn't matter to me that the voltage might be as low as 50vac or 120vac because we know that Current and Voltage have a distinct relationship when consumed by a load. Energy can neither be created or destroyed only transformed.

 

[Ratchit]

killivolt,

I'm also not apposing Ratchets idea of existing kinetics generated by a form of cyclotron that produce either ions, protons, neutrons, photons or even an allusive type of electron not clearly understood. I'm seeing a highly charged atmosphere when we talk about voltage I'm seeing voltages of 5kv or 20kv being introduced to the vacuum capacitor I found in the wiki sheets.

Whaaat??? I never said anything about cyclotrons bombarding vacuum capacitors or anything else. I have always said that no physical charge passes through a capacitor dielectric. Capacitors work by changing their charge imbalance between their plates. This gathers charge on one plate and loses charge on the other plate for a net charge of zero. This allows a transistory current to exist in the capacitor leads. The so called displacement or virtual current is equivalent the changing electric field within the capacitor, but is is not a physical current. This changing electric field is proportional to and is caused by the imbalance of charge on the plates. This imbalance of charge is what supplies a transient current when there is no path for the charge carriers through the capacitor.

Ratch

 

[killivolt]

Your right I added the cyclotron. I meant to point out the kinetics and neutron idea. Sorry about that. But, that's when I think that the changing field might cause a microwave like condition influencing the electrons in replulsion then attraction cycle with respect to plate B. I felt the electrons had to move even if only rotationally to jump start the electromagnetic field energy.

 

[Ratchit]

killivolt,

Your right I added the cyclotron. I meant to point out the kinetics and neutron idea. Sorry about that. But, that's when I think that the changing field might cause a microwave like condition influencing the electrons in replulsion then attraction cycle with respect to plate B. I felt the electrons had to move even if only rotationally to jump start the electonagnetic field energy.
​

I have no idea what you are talking about and how it relates to the topic of this thread. Ratch

 

[BrownOut]

the electonagnetic field energy.

Electronagnetic? Is that all the warnings, buzzers, beepers they put in cars and appliances these days?

I know what you're talking about, but you're over thinking it. In modern electro-magnetics theory, the magnetic and electric fields are self-sustaining, think of a chain through space, where alternating links are the electric and magnetic fields ( they make loops sort of like a chain ) They get started when electrons move, creating the amperian current and the changing electric dispacement fields, and propagate by Maxwell's self-sustaining method. The math abstracts exactly how that happens, and it's way above my pay grade to know anyway. But it happens just as the math predicts.

 

[killivolt]

Electronagnetic?

Brownout, Thanks for the catch. Oops.

In modern electro-magnetics theory, the magnetic and electric fields are self-sustaining, think of a chain through space, where alternating links are the electric and magnetic fields ( they make loops sort of like a chain ) They get started when electrons move, creating the amperian current and the changing electric dispacement fields, and propagate by Maxwell's self-sustaining method.

Bingo, Now you see my problem. When I saw the penning trap example I began to see the electron movement relevant to the chamber of a vacuum capacitor. Only, once I saw it's construction and using the why it is constructed that way.

Ratchet, Sorry about that, I am follow some vain idea; just because I see waveforms existing everywhere I look.

Edit: I understand the principle of a transformer and a magnetron or cyclotron. I see the chamber of a vacuum capacitor.

 

[Mr RB]

Hello again,

The water/tanks experiment was sealed so that no air can flow. There's no displacement current. This is what i was getting at. The only communication between the water tanks is that one pipe, that's it. We can have water flow from one tank to the other without any displacement current. The flow is also constant so we have no acceleration.
...

Sorry to nitpick but if the tanks have no other openings then a flow in or out of a tank is not possible. This is no longer analogous to a capacitor.

A 2-pin capcitor is defined as a device where current can go in one side if equal current comes out the other side. And it has a defined size, so there is a finite limit to how much flows before the current stops.

Valid analogies would be 2 half-full water tanks with an air tube. Or a water tank with a flexible membrane. Or a solid container with 2 balloons inside.

... Any measurement of displacement current in the capacitor has to rely on the field. We already know that the Electric flux change causes what we call a displacement current, we know that long time ago, when we first learned this stuff. Brownout keeps repeating this like it's new information which doesnt make sense.
...

Are fields that critical to this concept? It seems to me that an electrolytic capacitor is still a capacitor by definition and still behaves as such, but it's ability to store is increased per plate area because of additional electrochemical action inside the capacitor. Fields are less responsible for the "amount of capacitance" of the device. And taken to an extreme is a lead acid battery, of higher storage still per plate area and fields are almost irrelevant to its "capacitance".

 

[bryan1]

OK Guys,
What seems like 200 posts ago I said I used caps in serial to increase the CURRENT out of my F&P wind generator. Now the wind generator is a CURRENT source depending on rpm and will deliver wild AC in a 3 phase arrangement. By placing 2 off 400 volt 470uf electro caps back to back to 1/2 the capacitance, then placing one cap set on each of the three phases in series I was getting a marked increase in CURRENT after rectification then into my batterybank. The F&P is an iron cored motor turned generator and when caps are installed the low end CURRENT performance is much better, in higher winds the caps aren't needed.

Rather than wind on & on & on & on step back and read what I said above. If you guys still don't believe me try it out for yourself.

I find it sort of funny where so-called experts can argue until the cows come home and still keep going, getting no-where, yet a mechanical guy can go and do it and get the results.......

 

[BrownOut]

Hello again,
Brownout keeps repeating this like it's new information which doesnt make sense.

Looks to me like it's making sense to everyone except you. Maybe you should look inward for the key to understanding.

Posted by MrRB: Sorry to nitpick but if the tanks have no other openings then a flow in or out of a tank is not possible. This is no longer analogous to a capacitor.

I wouldn't call it nitpicking. I'd call it just being realistic.

Fields are less responsible for the "amount of capacitance" of the device.

I agree. This is mostly just musing about physical phonmina. The displacement current can become a consideration from a EMI standpoint at very high frequencies, and understanding it can be helpful when thinking about transmission lines, but it's almost never discussed, and can almost always just be ingored.

 

[killivolt]

killivolt, I have always said that no physical charge passes through a capacitor dielectric. Capacitors work by changing their charge imbalance between their plates. This gathers charge on one plate and loses charge on the other plate for a net charge of zero. This allows a transistory current to exist in the capacitor leads. The so called displacement or virtual current is equivalent the changing electric field within the capacitor, but is is not a physical current. This changing electric field is proportional to and is caused by the imbalance of charge on the plates. This imbalance of charge is what supplies a transient current when there is no path for the charge carriers through the capacitor.Ratch

Thank you. It has increased my understanding on my part because you have.

Capacitors work by changing their charge imbalance between their plates.

To create the first charge imbalance, I would need current to move correct or not? I am just not seeing electric charge carriers moving on Plate A is not vibrating it's not moving in any way to produce a waveform in my mind. Electrons move and create Electric field energy ? I really wish I could see it.

I know you guy's have the math to back up what you see. If I see a volume in a box I can measure it down to what ever the space is, plus see it in detail that will be satisfiable. I think this is the dividing point for me.


I would need an EM field to render some sort of response from plate B, Plate A is not a Magnet or an electro magnet how am I supposed to see the transition when their is no physical mechanism to create it. Transformers will move it physically through the wire to ground with a core conversely the secondary must respond in kind with the emulated field energy into charge.