Measuring Filter Reactor - Value vs. Load?? How to...

[WBear2GCR]

It's likely out there on the web... or yoohootoobe.

BUT, if you have an unknown Hy value choke, and you want to know the value
unloaded and LOADED (maybe intermediate levels too), what methods can be used??


              _-_-bear

EDIT: I was thinking that unloaded one can take a known capacitor and create a
parallel or series resonant circuit, sweep it, and from the resonant freq, drop that
into the formula and find the L value... but under load? (Load = DC)

[WBear2GCR]

One answer set is here:
http://amfone.net/Amforum/index.php?topic=6909.0

[Tom WA3KLR]

I thought I made a post many years ago on coming up with choke's inductance under load but can't find it.  I did find this posting I did under a separate thread describing my technique.

"You have an ohmmeter and inductance meter I assume.  The square-wave drive-digital auto-ranging ohmmeters go wacko on an inductor sometimes. This is a niche where the old VOMs come in handy for inductor dc resistance.

For exploring some inductors one time, I put together a Variac, transformer, diode bridge, inductor under test, known capacitor, load resistor(s) in a choke input L-C circuit.  I measured the peak-to-peak ripple voltage on a scope and ran simulations with LTSpice with the known values and adjusted the simulated inductor value and ripple results until it matched the measured breadboarded ripple value.  I ran different load currents and was able to make a plot of the inductance over a wide range of currents. (This gives you actual inductance under load!)
 
From experience with other chokes/data you have on hand/used, lead wire size, resistance,  along with the dive in the S-curve of inductance vs. dc load current, you should be able to come up with a ball-park current rating."

Have a good model with the ac secondary voltage and resistance, dc resistance in the choke, accurate filter capacitor value, accurate measured ripple peak-to-peak value.

[Tom WA3KLR]

Should one do the lab bench and simulation deal above, one caveat is to avoid 120 Hz resonance with the L-C filter.
Avoid this region, where L(H) X C (uF) = 1.759

With the transformer i was using for the test, I ran around 100 to 140 Vdc I think and various load resistor values to cover perhaps 10 mA to 400 mA.  I was testing receiver chokes at the time.
 I haven't looked for my old plots of the chokes.

[ae7db]

Attached is the circuit for measuring choke inductance in the presence of dc from Terman's Radio Engineering Handbook, in case it is of interest.

Dean

[WBear2GCR]

Dean,

Thanks!

My copy of Terman is at my other QTH... somewhere... Mmmmm...

Anyhow Terman's method is more or less what I was envisioning. Creating a resonant circuit.
He answers the question of the effect of the series R... although, I expect with
a high enough R, the Q is greatly reduced, which was my concern. But I also expect
that at practical values, it's not a big problem at all.

Think I will go with this sort of idea... I think making a full wave supply to create 120Hz
ripple will be about right...

                        _-_-