What are the effects of eddy currents in an inductor core?

[Landru]

I've been googling around, and I can't seem to find a straight answer to this:

Do eddy currents generated within an inductor core change the inductance, the impedance, or both?

My reason for asking is to understand whether more or less eddy currents will change the resonant peak of the inductor, the Q factor, or both.

 

[Svein]

Do eddy currents generated within an inductor core change the inductance, the impedance, or both?

My understanding is that the eddy currents create a loss (RI², where I is the eddy current and R the resistance along the current flow).

 

[Averagesupernova]

Eddy currents are unwanted currents within the core. Since they encounter higher resistance in the iron core than they would with ordinary conductors the Q will be lowered. The Q will always affect the resonant peak no matter what the cause of the Q changing.

 

[Landru]

Eddy currents are unwanted currents within the core. Since they encounter higher resistance in the iron core than they would with ordinary conductors the Q will be lowered. The Q will always affect the resonant peak no matter what the cause of the Q changing.

When you say a change in Q will always effect the resonant peak, are you saying that the frequency itself will change?

My understanding is that resistance effects the Q factor, but that the frequency is independent of resistance:

So maybe my question is: do eddy currents change the value of L at all?

 

[Averagesupernova]

One way eddy currents could affect the resonant frequency is the properties of the core could change enough due to the heating. How much I do not know.

 

[marcusl]

To first order, no. This is because eddy cuurents (EC's) at the surface of the core flow in phase with the coil current while the induced emf due to inductance is out of phase. Reistive and induvtive effects are separate. That's why coil impedance is a useful concept--the real part is resistive (EC) while the imaginary part is inductive. The reason I said 'to 1st order" is that EC's deep down are shifted in phase and so could affect inductance--but they are exponentially smaller so the effect is small.