Energy Stored in Inductor

In pure theory, the energy will remain there forever in electric and/or magnetic fields. In real life, unavoidable losses decay those.

Taking those losses into consideration, no energy is left unaccounted for.

A capacitor maintains its voltage as long as it can. An inductor maintain its current (tightly coupled to the energy storing magnetic field) as long as it can. In that, a long spark may result (as the voltage on the terminals is uncontrolled). The spark dissipate the stored energy mostly or completely.

An open-circuit indictor does not store energy. An open-circuit capacitor does.

A capacitor will store its energy when disconnected from the supply because that charge is stored in the form of an electrostatic potential difference between the two plates which cannot equalise due to the open circuit.

An inductor stores its energy in the form of magnetic lines of force which are developed around the coils solely by the current flowing through those coils.

When said current is removed and the ends of the coil open circuited the electromagnetic field will immediately collapse.

A spark can initiate at the breaking point of the circuit as the collapsing field induces a current in the windings which tends to have the same polarity as the original source.

If the ends of the coil were to be removed from the power source and instantaneously connected together, then the collapsing magnetic field would be slower due to the induced current tending to keep the magnetic field activated.

Either way - you cannot store energy in an inductor once it has been disconnected from supply. There may be a little residual magnetism retained if the inductor has a ferrous core, but this is generally considered to be pretty worthless.

"A capacitor will store its energy when disconnected from the supply because that charge is stored in the form of an electrostatic potential difference between the two plates which cannot equalise due to the open circuit.

An inductor stores its energy in the form of magnetic lines of force which are developed around the coils solely by the current flowing through those coils."

How does the current flow through the coil when the circuit is disconnected? For current to flow there has be a conducting material in between two points at different potentials. So are the ends of the coil at different voltages? If not how does a current flow?

I think you misunderstood my point so I will reiterate with a bit more info..

An inductor stores its energy in the form of magnetic lines of force which are developed around the coils by the current flowing through those coils, and obviously this will only occur when the coil is connected to a power source.

When the circuit is disconnected, there is now no current to sustain the magnetic field and so it collapses - there does not need to be any sort of circuit configuration for this to occur - there will be a momentary voltage appearing at the open ends of the circuit as the collapsing field attempts to maintain the current flow, but this will rapidly drop to zero - there does not need to be a circuit of any kind for this energy to be lost, and it cannot be stored once the power source is removed.

Energy stored = 1/2Li²

Voltage = L di/dt

Plug some numbers into these equations and you'll see that you can get some very large voltages across an inductor when the battery is removed.

Just to add my few few pennyworth.
Yes it can store energy... IF..

The two ends aof the coil are immediately linkled together as the original source of current is taken out of circuit AND the whole thing is at absolute zero.
The current will keep going round the inductor indefinitely.

One way of lkooking at it is. The inductor tries to maintain the current flow, if the circuit is broken then it will generate a high voltage spike in order to keep the current flowing... it will force this current to flow through anything available (and is particularly fond of humans) until the energy is dissipated.
Del

Hmmm. That pretty much flies in the face of all known facts about inductors.

Perhaps the laws of Physics are different where I come from, but linking the ends of the coil together will marginally slow the decay of the field, but it will still fall to zero as the induced current also falls to zero.

Depending on the size of the inductor, this will normally occur within milliseconds but would rarely exceed a few seconds for the very largest.

I suggest you read my post again... slowly... noting the bit about absolute zero.
They have actually done this sort of thing and maintained current flow for a long time, of course you can't extract energy from it.
Del

(grrrr ftttzzzzz hisssss)

PS.I can't be ar$ed to do an extensive search just to show I'm not daft.... but try this link. It talks about perpetual current flow around a superconducting loop.

Temperature approaching Absolute zero (AZ) has the possibility to reduce wire resistance to zero, however inductive impedance due to the changing magnetic field will remain a restrictive force that will cause the current to drop to zero in a finite time span.

There is also the problem that the more inductance that you introduce into a superconductor, the colder it has to be kept in order to retain its superconductivity, to a point where it just can't be done

Whilst it is possible at critical temperature to maintain high current flows in a loop circuit with no source voltage, this precludes the inclusion of an inductor into the circuit, as any form of magnetic field being produced above a very small critical level by the circuit will cause the super conductor to revert to its normal mode.

There is also a theory that a superconducting material will reject other magnetic fields, so this may result in a rejection of the collapsing magnetic field around the inductor which, if it doesn't cut across the coil, will not induce a current in that coil to aid the original current, and so the circuit current would drop to zero even more rapidly.

It's actually a good question. Consider the case where you have current flowing in an inductor generated say using a battery with a parallel resistor. Remove the battery just leaving the resistor. The energy will be dissipated in the resistor as the summed product of voltage times current (= power) over time until the current stops. If you increase the value of the resistor, the current stops more quickly and the inductor creates more voltage. The product summed over time still equals the stored energy, only more voltage and less resistance. In theory, if you could stop the current instantaneously (infinite resistor), you would have infinite voltage.

In practice, the air and the inductor's insulation resistance are not infinitely resistive and will provide a path for some current when the voltage becomes high enough.

When an inductor is connected to a DC supply, magnect field builds up around the coil. When supply is disconnected, magnetic field collapses and creates back emf which opposes the current causing it. Depending on the number of turns the back emf can be harmful when placed inside the circuit. Therefore placing a diode in parallel with the coil with anode connected on positive side, takes care of the back emf energy.

Actually, whilst the induced voltage from the collapsing field is of the opposite polarity to the original voltage that created the field, the resultant current flow through the coil is in the same direction as the original and therefore it tends to aid the original current rather than opposing it. If the current was in the opposite direction, we probably wouldn't need spark quench circuits at all

When placing a snubber diode across a coil, it must be reverse biased, therefore the anode will be connected to the negative not the positive.

Electricity and magnetism are the yin and yang perfect duality for the electromagnetic theory and reality.

Electricity is charges in Coulombs and measured commonly in Voltage in a phys. obiect.

Magnetism is flux in B and measured commonly in current in a physical obiect.

Maintaining electricity requires prefect open circuit.

Maintaining the flux requires perfect short circuit.

Letting electricity decay in a controlled fashion requires a (high) parallel resistance.

Letting magnetic flux decay same way requires a (low) series resistance.

The Q formula for components expresses exactly the last two sentences.

QED.

------------------------------------------------------

Other than that anybody is entitled to hang onto to their fundamentally flawed understanding. For their own use, that is.

Thanks to you all for the help.

In a nutshell, the vast majority of energy stored in the inductor is dissipated in the electric arc that occurs when disconnecting.

I would have to say that there was never really any "energy stored" in the coil in the first place. The magnetic field that collapses only existed because there was a current flowing in the first place.

Technically, the magnetic field created by the current flow through the inductor is "stored energy". When the current source is decreased, disconnected, or when the inductor is short circuited, then some or all of the "stored energy" from the inductor's magnetic field is returned to the circuit.

Yes, but its not like the energy being stored in a capacitor. Which is rather static.

Although I'm not all that experienced with this kind of stuff, I do recall warnings of shock hazards with coils. I don't know if that's because there are capacitors incorporated though. But it makes me wonder if there isn't some kind of charge left behind after a coil is disconnected. I mean if so, what's holding that there?

Energy is energy and it comes in different forms, in this case for a capacitor, when a voltage is present on the capacitor, it stores emf where for the inductor, when a current is present, it stores mmf. For the capacitor, when it comes to "storing" energy, as it returns the energy back to the circuit in the form of a voltage, the moment of disconnect from an electric circuit, it will act like a very short term battery. However it is important to note that there will always be an internal resistance that will eventually allow the capacitor to discharge. For the inductor, when it comes to "storing" energy, as it returns the energy to the circuit in the form of a current, the moment of disconnect from an electric circuit, the voltage raises very high so it will be either high enough for the air gap resistance or the insulation will break down allowing the circuit to discharge the current. leveles' comment in #15 says it best when he generally states the fundamentals.

#15 summarizes EM basics related to fundamental electricity and magnetism.

It is wonderful, having opinions beyond the basic facts.

Which are not even mine, but known for the better part of 150+ years.