Rs raising quickly with freq. in an inductor?

I have a couple of inductors which are more or less the same in construction (P type core.). All of them are wired to be about 30 Ohms in DC. Each core is made from a different material and while testing the inductors with an LCR meter I noticed that Rs is one of them goes up very quick, much faster than the others. At 1KHz with 1V input, Rs was about twice the value of the other inductors. Any idea why is that?

Rs in the inductor equivalent circuit represents all kinds of losses (DC resistance, skin+proximity effect AC resistance, core losses, eddy current losses). In so far, you can't easily determine the nature of losses showing in increasing Rs numbers. You can probably guess about it if you know the design details and differences between individual inductors.

Thanks for the post, if I look at what makes Rs in my inductor you said:

1. DC resistance - which is the actual resistance of the wire at DC.
2. Skin effect - is a larger current density near the surface of the conductor.
3. Proximity effect - similar to skin effect but due to the magnetic field.
4. Core losses - what energy got "wasted" by the core, what turns into heat.
5. Eddy current losses - are caused by the changing magnetic field and are causing current loops inside the inductor (as far as I understand).

I have no information about the material used in the inductor where I can see the phenomena of Rs increasing very quickly.
Here is an experiment I did and perhaps it helps to rule out some factors? I made a similar inductor with the same wire and same physical dimensions that measures about the same Ls, Rs, Xs in low freq. (near DC). I added a 2nd winding with about the same number of turns on top of the main winding and I shunted that coil with a 200K resistor. At low freq. the two inductor behave the same way (because the 200K is not yet reflected to the main coil). As I go up in freq. the 200K gets reflected more and more so Rs goes up quickly, just like in the original inductor.

Does this offer any kind of clue?

can you send specification of inductor, let us analyse for you.

You didn't tell in your original post, if the observed loss behaviour is reproducable with a same design inductor. If not, it may be e.g. caused by a winding short.

I will gather all the data is an orderly fashion and will upload it today!

FvM - If you'll look at my 2nd post I wrote that I took a bobbin and wrapped two coils on it (before putting it between two commercially available P type cores). 1st coil is about the same coil as the one in the "special" inductor and on top of that another coil with about the same number of turns. I shunted the outer coil with a 200K resistor and from the LCR meter's perspective the two inductors are behaving very similar this way. Off course that with a different turns ratio a different resistor value would have caused the same effect.

Here is an Excel file with some data I gathered this morning: http://www.freefilehosting.net/inductordata

Your table shows negative R values, as this is physically impossible, it suggests a defective LCR meter or somehow usage outside the specification.

I would prefer supplementing data attached with the post (under manage attachments). Excel files can be zipped.

The meaning of some columns in the table needs explanation, e.g. Vac and Iac.

FvM - Attached the zipped file.
I know that a negative value for Rs is not possible, however this is what another meter I used shows exactly (an HP one!). Something is going on with this inductor and it is "cheating" the LCR meters. My LCR meter is also pretty good and it is fooled the same way. Vac and Iac are the voltage and current being applied to the DUT. I set the source impedance to 100 Ohm (highest) and at low freq. it will actually show a different voltage from a reason I have explanation to. When measuring other inductors I don't see these strange side effects.

The values beginning from 500 Hz look quite plausible, below completely confused. I would measure impedances with a generator, reference resistor and oscilloscope to understand what's going on.

You mean generator -> resistor of known value -> coil -> ground and measure the voltage drop on the resistor and on the generator output and calc. the impedance of the coil?
I would also like to point out that R is going up much faster than on my other inductors as the freq. goes up.

I mean any measurement setup that allows to "see" impedance phase and magnitude directly.

Yes, but that seems to me as a minor effect as long as the results can't be validated in total.

With a 50Hz Sine 8.56Vppk --> 2.2K --> L --> GND
Resistor V: 8.4V
Inductor V: 0.968V
Resistor I: 8.4/2200 = 3.818 mA
Inductor Z: 0.968 / 0.003818 = 253.5 Ohm which is double what the LCR meter said.