Can DC capacitor charging energy be made more efficient by adding an inductor?

crutschow

Joined Mar 14, 2008
34,283
You don't need a voltage difference for power. Only charge flow or movement. A voltage difference is just one way to get the charge to move. There are others. A voltage difference is not required.
If the charge is moving with no inductance and with no voltage drop then it has no energy or power.
If so what is the formula for the energy/power?
 

MrAl

Joined Jun 17, 2014
11,389
Hi,

A superconductor can keep a current flowing for a long time in a loop, but you cant extract any energy from it or it drops down.
I also dont see how you can have power without a voltage difference.
 

studiot

Joined Nov 9, 2007
4,998
ELE1,
As the inductor finishes charging, the energy stored in the inductor can than be released (ideally) into the capacitor toward the end of the capacitor charging process, where more energy is required to place charge on the capacitor. So, both charging and discharging the inductor helps make the capacitor charging more efficient.
So many have already put their oar in here that I hesitate to add to the confusion, but you will not resolve without abandoning some basic misconceptions.

1) We do not 'charge' inductors. No charge is separated or stored in an inductor.

2) The creation/depletion of a magnetic field is dependent on the rate of change of current. At the beginning of charging a capacitor the rate of change is very large, but this reduces as time goes on so near the end of the charging the rate of change of current is very small. This is why basic charge discharge curves for capacitors are studied in elementary physics.

3) The work required to place the first charge on and uncharged capacitor is precisely zero. When you try to add a second charge you have to overcome the repulsion provided by the first one so have so do a small amount of work. Each additional charge added requires more work than the previous one as it faces greater repulsion. The total work is the sum of each of these individual quantities. When we go from placing charges one at a time to a continuous current we move from a sum to an integral.
 

crutschow

Joined Mar 14, 2008
34,283
................................................
3) The work required to place the first charge on and uncharged capacitor is precisely zero. When you try to add a second charge you have to overcome the repulsion provided by the first one so have so do a small amount of work. .........................
I'll have to quibble with that. ;)
The first charge requires a small voltage to move it into the capacitor and cause a single charge separation, so even moving the first charge requires energy. Even a single electron stored on a capacitor has energy.
 

studiot

Joined Nov 9, 2007
4,998
Quibble away all you like, we are talking perfection here.

Placing a single charge on a perfect conductor involves zero work (do the math).

You need to calculate the work involved in bringing the charge from infinity to its position against the force of the electric field

Normally this involves many charges and an integral but for the first single charge the field is zero so the integral is zero.
 

WBahn

Joined Mar 31, 2012
29,978
Quibble away all you like, we are talking perfection here.

Placing a single charge on a perfect conductor involves zero work (do the math).

You need to calculate the work involved in bringing the charge from infinity to its position against the force of the electric field

Normally this involves many charges and an integral but for the first single charge the field is zero so the integral is zero.
But it's not. There are two ways to disprove this.

First, look at the end result. You have a capacitor that is charged with one electron which therefore has a both a charge and a voltage. Thus energy is stored and that energy came from somewhere.

Second, just imagine the simplest mechanics involved in accomplishing this. You have two plates separated by some distance that are uncharged. You then move one electron off of one plate into the gap between them just a small (differential) amount, leaving the plate positively charged. There is thus an electric field between the electron and the plate trying to pull the electron back to the plate. Moving the electron further toward the other plate requires that work be done against this field.
 

WBahn

Joined Mar 31, 2012
29,978
other than a mental exercize, what difference is the charge efficiency of a capacitor?
In the world of small, battery-operated products if you can design a circuit economically that doesn't wasted energy from the battery in order to charge a cap, that might give you a competitive advantage. There might also be situations in which you are talking about high power (large capacitors storing lots of charge) and charging them in an energy efficient way might make a considerable difference.
 

BR-549

Joined Sep 22, 2013
4,928
The wire ring is not producing anything....it is just storing what you put in it.
If any energy is absorbed by anything external.....it will not be replaced.

The energy is not being produced or maintained........it is just not being opposed.

Again, a voltage drop is not required for energy or power. Only charge flow.

Take an electron and put a voltmeter on it. Reference the meter to ground or a steady voltage source.

Measure the voltage at 5 degrees K. It is one electron charge. The electron is at ground state....the lowest energy level.

Now heat the electron to 5000 degrees K. Now the energy level is many magnitudes greater than the ground state.

What is the voltage now? The voltage is exactly the same.

Anytime a charge moves in any way, ac or steady dc......there is inductance and capacitance.

Voltage and current is two ways of describing the same thing.....charge.

When charge is accumulated and has potential energy, we call it voltage.

When the same accumulated charge moves, the potential energy transforms to kinetic energy.......we call that current.

You can store energy in a potential, but to charge and store.....along with using any power.....you must transform the potential to kinetic...........you must have charge movement. You must have charge flow for power.

If we take a glass ring and charge it to 1000 volts. That gives us a potential energy for the ring.
Now spin the ring at 10,000 rpm. Does the voltage on the ring change? No it doesn't.

Does the energy level of the ring change? Yes it does.

The ring is spinning now. That is charge flow. This causes a magnetic field to develop in the center of the ring due to this current. This added energy did not come from a change in voltage, it came from the momentum of the spin....converted to a magnetic field.

Now spin the ring at 100,000,000 rpm. The energy and power will increase by many magnitudes.....but the voltage is the same......whether measured with itself or any other reference.

And if we can't charge an inductor......we are in big trouble.

A capacitor stores charge as potential......an inductor stores charge as kinetic.

Just because an inductor can't hold a charge as long as a capacitor, doesn't mean it can't be charged.
There most certainly is a charge accumulation on an inductor.

An electric field is the expression of charge potential........the magnetic field is the expression of charge movement.

A capacitor stores charge in a static aligned manner on the plates. An inductor stores charge in a dynamic spinning manner on the coil.

About 30 years ago......all electric and electronic properties and interactions were thoroughly understood and verified and proved and all this was settled.

And then....some idiots....started playing with superconductors. Now...being that we knew exactly what current was.....this has great potential because of no resistance.

BUT it turned out that the SC did not preform as expected. What a surprise.

And of course...true to modern science......they assume their proven theories on regular conduction can not be wrong.........so there must be new properties and new laws that control this SC.

This happens in all branches of science.......scared to death of the fundamentals.

So now we have electron pairs, disappearing fields, dark matter and dark energy, point particles with no structure, randomness and probability controlling the universe.

I think not.

Real current is not charge flow. Current is magnetic flux flow. This is caused by a certain kind of charge flow. It has to rotate. Only when charge rotates, that you get a magnetic field. Not just movement......it has to rotate. Only rotation causes a magnetic field.

Magnetic flux flowing thru the center of a conductor is current. The electrons spinning around the surface of the conductor is what powers the M flux.

One can not use math to explain action.....it will lead you astray every time. You can only describe action, not explain it.

Example......math tells you it takes no work to put the first charge on a plate.

Why on earth would anyone believe that?

A charge(or a particle) has inertia. It will take work to move it anywhere at any distance.

If you believe in math explaining cause or state for anything,......you will never understand.

The only thing math causes, is mis-understanding. Math has not caused any action in the universe ever.
 

studiot

Joined Nov 9, 2007
4,998
BR549
You have a capacitor that is charged with one electron
This, of course, is not possible, nor what I said.

The simplest way to (theoretically) place one electron on a conductor is to add one electron to a conductor and wait until its random movement places it where you want it.

This method is to be preferred since it allows the time to sink many beers.
 

alfacliff

Joined Dec 13, 2013
2,458
but how can you tell if one electron has been added when the process of measurement will take it away?
there are many better ways to imporove efficiency than the efficiency of charging capacitors. charging inductors is even more silly, as soon as you remove the charging source, it discharges itsself. has anyone truely seen an inductor sitting by itsself with a measureable charge on it?
 

WBahn

Joined Mar 31, 2012
29,978
but how can you tell if one electron has been added when the process of measurement will take it away?
there are many better ways to imporove efficiency than the efficiency of charging capacitors. charging inductors is even more silly, as soon as you remove the charging source, it discharges itsself. has anyone truely seen an inductor sitting by itsself with a measureable charge on it?
If by "charge" you mean a current flowing in an inductor that is sitting by itself, then I have seen that many times. They are called persistent-mode superconducting magnets. A typical magnet will lose a percent or two of its initial current over the course of about six months.
 

studiot

Joined Nov 9, 2007
4,998
We have been through this before.

A capacitor has two distinct conductors.
What happens to the second conductor if you introduce a single charge (say an electron) on to the first?

That depends upon what the second conductor is connected to.

1) If the second conductor is isolated from the rest of the universe, nothing.
No work is done.
The capacitor remains 'uncharged'
No voltage difference is induced between the plates.

2) If the second conductor is connected to an electron sink

An electron is displaced from the second conductor to the sink
~Work is done
A voltage between the two plates is now established
The capacitor is now charged.

But once again work is only done when the second charge is introduced, or in this case, leaves, the system.
 
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alfacliff

Joined Dec 13, 2013
2,458
the electric field from charging only one side of the cap procuces an equal, oposite charge on the other. seen this many times in older tube stuff where higher voltages were present. you are talking about a unipolar charge, which isnt practical to measure or keep in a bottle. same as unipolar magnetic fields, existance has not been proved.
 

studiot

Joined Nov 9, 2007
4,998
It may help to think of things this way.

Most folks start counting at 1

Mathematicians and elevator manufacturers start at zero.

We are talking about the first charge of many so that stating n for our summation is mathematically zero not 1 in our summation.
 

The Electrician

Joined Oct 9, 2007
2,971
One can not use math to explain action.....it will lead you astray every time. You can only describe action, not explain it.

If you believe in math explaining cause or state for anything,......you will never understand.

The only thing math causes, is mis-understanding. Math has not caused any action in the universe ever.
What more is there to say at this point?
 

BR-549

Joined Sep 22, 2013
4,928
What happens to the second conductor if you introduce a single charge (say an electron) on to the first?

That's easy, simple and fundamental. The second plate polarizes. Work is done on second plate.

The second plate does not have to be connected to anything. Add another charge to the first plate.
The secondary plate polarizes more....more work done on second plate.

By adding one charge on the first plate.....we cause one charge separation on the second plate....without a sink connected to the second plate. We caused one electron on the second plate to move from the near surface to the far surface. That leaves one positive charge on the near surface of the second plate and a negative charge on the far side of the plate. That's polarization....it takes work. And now we have a voltage difference between the plates, and the second plate is not connected. And that is done with just one charge.

That first charge polarizes both plates.

But I must be wrong because the math says so. That first electron is a mathematical freebee........only the second charge does anything. Wait....I know....it's a quantum integral effect.

This is how charge works.

Sometimes, instead of thinking that a capacitor TRANSFERS power from the first to the second plate.......it's easier to think of a capacitor as a device that uses the power of the first plate, to CONTROL the power of the second plate.
 

crutschow

Joined Mar 14, 2008
34,283
but how can you tell if one electron has been added when the process of measurement will take it away?
.....................................
I'm still quibbling. They have fabricated one electron transistors in the lab that can turn on with one electron added to the gate.
And since that one electron adds a voltage to the gate then the gate capacitance has more stored energy than without the one electron.

Adding the first electron to a capacitor increases its voltage and since energy = 1/2 CV^2 that one electron increase the capacitor energy. Thus it takes work to add the first electron to a capacitor (do the math). :rolleyes:
 

studiot

Joined Nov 9, 2007
4,998
I'm still quibbling.
And I'm still smiling

:)

The gate is not one single isolated conductor.

and my maths tells me that 1/2CV^2 = 0 since v = 0 on an isolated conductor.

BR549.

Your proposal violates one of the most sacrosanct laws of physics.
Even more sacrosanct than the laws of conservation of energy or mass, which are subject to relativistic complications.

The law of conservation of charge.

If the second plate is not connected to anything there is nowhere for it to either draw extra charge from or dispatch charge to.

So it cannot change its charge.
 
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