I have a few handfuls of scavenged inductors that I really want to know the inductance of. Some of the air-core inductors I've been able to somewhat successfully (worked in filters I made with them and etc) ballpark the value using formulas and programs from electronics sites. However, that really only works with the ones I am able to figure out the wire gauge and from there the number of layers, and the inner/outer circumference of the core. Also, I have a fair number of ferrous-core inductors that I can't measure either. I don't have the money or resources currently for an oscilloscope or signal generator, although I suppose I could just put together a quick oscillator for a signal to useanyway, isn't it possible to just measure the current through the inductor (or maybe with a known value capacitor too) with 60-hertz line frequency with a known (obviously lower than line) voltage? Then calculate the combined reactance/impedance etc?
I guess theoretically you can use the 60 Hz 120 AC Volts from you home wall socket as your source, but I DO NOT RECOMMEND THAT AT ALL. You cannot just measure the current in an inductor because the inductor has reactance against current while allowing voltage to vary across it. The only thing you can try to do graphically measure out the current curve, measure the rise time and approximate the inductance keeping in mind the frequency that way. The problem is that the current is going to reach its settle point a lot quicker than you can measure it unless you have specialized equipment. My advice to you is to bite the bullet and visit your nearest community college/university with a physics/electrical engineering department and try to get a lab tech to help you. Let me know if you need any help calculating or setting up to measure the inductance. My question is why do you need inductors anyway? It is one thing if you do not have an O-scope, but no generator? What good is the inductor?
The resistor is used to sense the current.
It is theoretically possible to do what you say, but how much accuracy do you need? What purpose are you going to use this inductor for? How are you going to determine the current or volatge rating? If it is a high-frequency choke that doesn't matter or a tuned circuit, resonant circuit, etc it might. It would take so long and have not very good accuracy I would say just figure out what you need and buy it rather than mess with trying to figure out what you have there. Also are you sure it is unmarked, you might look for distinguishing features and try to determine by markings or codes? If you have the resources, just buy the one you want, unless you are in school and want to do this as an excercise in which case you need to figure it out yourself anyway! ;-)
