home made inductor

Just a guess, but could your reactance measurement method be responding to whatever method you are using to vary the (DC I presume) voltage? I'm thinking along the lines of the impedance of the voltage source changing with the output voltage and this throwing off the reactance numbers. I'll admit that it has been some decades since I've actually set out to measure such real-world values but as I recall there would be several different ways to attack the problem.

Could it be that the core losses are a major part of the equation at low voltages (and currents) and become less significant as the voltage increases.

I presume you are measuring voltages across the inductor and a series resistor and constructing a phase diagram. Make sure you select the resistor value so that the sides of the diagram are fairly equilateral, so as to minimise errors.

Inductance is not linear with applied voltage/current over such a range.

"joe" wrote in message news: snipped-for-privacy@posting.google.com...

The Permeability of iron is very non-linear as a function of the magnetizing force (amp-turns). This nonlinearity creates the familiar B-H curve of the material. The nonlinearity will cause an unstable inductor when wound as you describe because the inductance is a function of the permeability. One would have to know the particulars of the B-H curve for that particular material to correlate your measured non-linear inductance with the permeability. Furthermore, the non-linear inductance will cause distorion of the current wave form with voltage so there will be an additional error in the inductance measurement. Proper inductors are always stabilized with an air gap in the core. With an air gap, the majority of the magnetic energy is concentrated in the air gap and the permeability of the iron which is many thousands of times greater than air does not greatly effect the inductance even if it changes or is non-linear. Think of it as two resistors in series, a high conductivity low ohm resistor representing the iron in serires with a low conductivity high ohm resistor representing the air gap. It's like a 10 ohm resistor in series with a 10K resistor. If the 10 Ohm resistor is non-linear or changes in value, the series combination doesn't change much, it's sitll basically 10K regardless of the 10 ohm. So it is with an inductor with an air gap, changes in the iron permeability doesn't change the inductance much. Bob

Joe:

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James