Unmarked Iron Core Inductors

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Thump,

Here's why I'm confused.

Your method for estimating the coil using drivers and effect is valid IF and only IF your driver ZMA files are correct.

If you can meausre a driver's impedance, you can measure a coil, which means you can derive the coil's measurements.

So this isn't making sense. If you can measure the driver Z files, then you also can measure the coil directly. IF you cannot measure the driver, then the coil estimation won't work.

Best,


Erik
 
I was thinking about this very issue. My thought was toput together a switch box to put together series RCL resonant circuits with different R and C values. The idea was to take a guess at approximate range of inductance and set up a circuit placingg a DMM across the resistor I would manually sweep a frequency generator on my phone to find the null.

2*pi*f=1/sqrt(LC)

mike
 
Having followed the previously posted links to a variety of ways to measure a coil, they all seem, at a glance, valid and require the construction of some jig to preform the task. I already had the LIMP jig to measure a drivers impedance. And yes, for those that may wonder, it is different than the one required to measure a coil.

My method suited the tools I already had to work with, and the results speak for themselves.
 
Upon your persistence, Erik, I tried hooking up my jig for the LIMP software to measure speaker T/S parameters to one of the coils I just tested with my other method. Reading more about what all the software does other than what I have always used it for (T/S parameters) it does say that it will measure inductance. All the other links previously put forth (REW, etc.) all require some jig be made to do this. One showed using "headphone out" (don't have that) and another shows it needing a capacitor of some sort (my LIMP jig doesn't have that).

Anyway, upon learning more about LIMP and what it can do, I confirmed that the LIMP software will in fact measure the inductance of a coil with no additional jig than what is used to measure speaker T/S parameters.

To bad no one said you can use LIMP like this from the outset.
 
I just tested this 100 turn 0.3mH aircore with a ferrite core in it, and as I expected, inductance went up 4 fold to 1.2mH. :cool:

598810d1486901283-unmarked-iron-core-inductors-inductance-0.3mh.jpg


I wouldn't assume that coils you buy are accurately specified. I've had some 0.2mH that turned out to be 0.3mH. Easy enough to unwind a few turns, of course.
 
I have tried a simple way of measuring inductance with only a signal generator ( 1 kHz from a CD), output amp voltage 2,828Vrms, a resistor (150R) in series with unknown inductor and it worked reasonably accurate for a 0,56mH(air) and 5,6 mH(ferrite) coils. Measure the voltage drop with a multimeter across each part and use the following formula.

L(mH)=(Vl*R)/(Vr*6,28)
Vl=voltage drop on L
Vr=voltage drop on R
 

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I have tried a simple way of measuring inductance with only a signal generator ( 1 kHz from a CD), output amp voltage 2,828Vrms, a resistor (150R) in series with unknown inductor and it worked reasonably accurate for a 0,56mH(air) and 5,6 mH(ferrite) coils. Measure the voltage drop with a multimeter across each part and use the following formula.

L(mH)=(Vl*R)/(Vr*6,28)
Vl=voltage drop on L
Vr=voltage drop on R

I think that must be exactly how an inductance meter works, as it goes. I was doing some tests on inductance with nearby ground planes and coils with a 1mH coil here.

You could hear the test-tone from the tweeter as a high pitched whine, which I estimated at 1kHz from comparing with my little sweepgen utility on the computer.

Audio Tools - from David Taylor, Edinburgh

It's quite good to have a feel for what 1kHz or 3kHz sounds like. Since we use these sort of frequencies in crossovers. There aren't many fundamental notes above 1kHz in practise with most musical instruments and voices. 3kHz is guitar higher harmonics territory. :)
 

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