Electron wrote:
> Hi,
> trying to improve my knowledge of inductors.
>
> The energy stored in an inductor is proportional to the current that is flowing
> through it in that certain moment. If the current increases, then (part of it or
> all?) gets stored as additional energy in the magnetic field, if the current
> decreases, part of the energy gets released to oppose this.
>
> I'd three questions for Your brains:
>
> 1) The "(part of it or all?)" already written above part.
>
> 2) Suppose I increase the current in an inductor till 1A, then keep it constant
>    for 1 second. What happens during this second? Do I simply waste power?
>   
If the voltage across the inductor is not changing, then "all" of the 
energy possible is stored. Assuming ideal inductor.

If it's a perfect inductor it has zero "real" resistance. Imaginary axis 
"resistance" is invisible at DC.

Thus no power is wasted. IN THE INDUCTOR. Other parts of the circuit 
will  / may dissipate power. The actual power wasted in a non ideal 
inductor for steady state current is P = I^2 x R, where R is the DC 
resistance (Real axis Resistance).


> 3) If I simply wasted power (continuing from the previous question), then I
>    suppose I will waste some power even during the "current is increasing" part.
>    Then, when current is increasing (that is, dI/dt is not zero), how much energy
>    I am storing and how much I wasting (as heat, etc..)? What is the formula?
>   
Wasted power when current changing is these main parts:
P = I^2 x R, where R is the DC resistance (Real axis Resistance). Mainly 
winding DC resistance. At high frequency the current in a conductor 
flows closer to surface. Skin effect. This makes "real" resistance 
higher even at 1MHz.  By  400MHz a flat strip will have much lower 
"real" component (lossy resistance) than a circular wire. High power RF 
coils may be wound with 4mm hollow copper, possibly silver plated as 
almost no current flows in the  core.  Polished copper with lacquer to 
avoid oxidising is lower loss than tin or tin/lead plated or gold.

Radiated RF (large air core coil is higher, on ferrite toroid is lower). 
Formula is complex and depends on frequency, construction, size
Losses in the Magnetic material if not air core.
Magnetic/Induction losses: Eddy current with in core and windings, worst 
for solid conductor, less laminated, lower insulated dust iron or 
ferrite and least on air core. Coupling to magnetic materials or other 
nearby coils.
Core Saturation
Magnetic hysterises

Losses are usually lowest with sine wave and highest with  Square wave 
due to frequency dependent eddy current loss, skin effects on 
conductors, RF emission and such.

Interwinding capacitances may not increase losses directly but affect 
self resonant  frequency and actual inductance.

> I fail to make an analogy with capacitors, as once charged they get (theoretically)
> infinite impedance. Inductors instead get (theoretical) zero impedance, and this
> may imply the "waste" problem stated above. As I said, I fail to make an analogy
> with capacitors on this particular issue.
>
>   
harder to make a "good" inductor that's millihenries. A perfect 
capacitor with DC (fixed/steady) voltage has no current. A perfect 
inductor with DC(fixed/steady) current has no voltage  across  it.

For C   P =  V x 0  =  0
For  L   P =  0 x I  =  0
no power dissipated.

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