Now THAT's interesting.
Please pardon the following ramble. Old guys just do that.I once devised an inductor test that seemed to work
but it gave results comparable to a much easier to use computerized inductance meter we already had in the shop.
I mention it because it's sort of similar to your "Ringing" test.
I established about an amp DC through the coil
then interrupted it and captured the 'inductive kick" in a capacitor trapping it there with a rectifier..
Connected to the capacitor i had a Fluke DMM set for peak capture.
I sized the capacitor for about a hundred volts on the coils i was measuring.
It would find coils with shorted turns but so did the little computerized inductance tester .
I do hope you build yourself some sort of tester. Just brainstorm about the properties of inductance and experiment away.Another thing i tried is Lissajous patterns on a 'scope.
Remember that sinewaves are a special math function - their derivatives have the same shape as the undifferentiated one.. That's why for a sinewave voltage you get a sine-shaped current, really cosine because either one is the derivative or integral of the other.
I built an integrator and produced the time integral of the induced voltage in the inductor. That should be a measure of the flux in the inductor because e=N
turns X dΦ/dt..
I applied that to the Y axis of my 'scope.
I measured the current through the inductor with a low ohm resistor and applied that to the X axis of my 'scope. That too should be a measure of the flux in the inductor because Φ = μNIA/L
ength.<---- observe absence of derivative
A perfect inductor should give a straight line on the 'scope because flux and current are in phase
any phase difference between the signals makes the trace more of an open circle.
I had the luxury of a second winding on my inductors which i used for a zero current "Flux detector" to measure induced voltage. You'd need either a search coil(as i had in that second winding) or a Hall sensor to get your flux signal.
A perfect inductor will give a straight line for a Lissajous pattern of ( Φ by integrating induced voltage or direct measurement ) versus (current by direct measurement).
Its open-nes approaching a circle indicates there are other currents flowing besides what you're putting through the windings yourself.
On my inductors that showed me just what lousy cores they had.
With core out i got straight lines as expected . With the core partway inserted i got ellipses. as i inserted more iron core the trace got more circular.
My cores were not laminated and had so much eddy current flowing in them they were suitable for only less than 10hz operation.
I got about 30 degree phase shift because of eddy currents. (Incidentally that explained their odd temperature coefficient - as they warmed their inductance went up because the hot core's resistivity went up, reducing eddy currents)
So I'm thinking- since you have a 'scope - and we can now buy Hall flux sensors reasonably
One of these glued to a popsicle stick should detect flux:
http://www.ti.com/lit/ds/symlink/drv5053.pdf
And the most striking thing i noticed about my inductors was their phase shift when extra current flowed...
And since power tools have a laminated core, eddy currents should be low,
meaning more than a teeny bit of phase shift between measured current and measured flux should be a decent indicator of shorted turns.
.......................
I envision a source of line frequency AC current an amp or less, a current measuring resistor, and a Hall flux detector probe.
Readout could be either a 'scope, or an analog meter indicating phase shift in degrees.
Just squaring up and AND'ing two sines gives a PWM proportional to phase difference... a DC meter reporting average value of that PWM would work.
...
You'd soon either become skilled at its use or figure out what's wrong with the idea.
And if you said it worked i'd buy one.
old jim