Correction:
Make that a voltage dip, not spike, sorry.
I was thinking of series resonance in a normal circuit, not as wired on
the bench. In any case, where the meter does something interesting is
the resonant frequency...
73,
Jim N7CXI
On 3/9/2012 11:34 AM, Jim Barber wrote:
> You could determine the light-current inductance by hooking it in series
> with a suitable capacitor, then using an audio generator and a scope to
> find resonance.
>
> It's most likely they are indeed swinging chokes. If not, they'd again
> most likely be wired up to resonate with a fairly small capacitance,
> something like 0.1uf. (that makes a resonant choke filter at 159hz, a
> little above the 120hz ripple frequency as cussed and discussed on this
> list)
>
> So:
>
> . Find a decent-quality 0.1uf capacitor. (electrolytic will work, but
> not my first choice)
>
> . Hook the cap up in series with the choke
>
> . Set your audio generator to 40hz or so to start with
>
> . Put your audio generator and scope (or AC voltmeter) across the pair
>
> . Slowly increase the frequency of the generator until you see the
> voltage "spike", then tune the generator for maximum voltage.
>
> The resonant freq is then 1 / (2 * PI * SQR(L * C))
>
> Where:
> "SQR" means Square Root
>
> PI = 3.141592654 or thereabouts
>
> and L and C are in equivalent units. Farads and Henries, microFarads and
> Microhenries, etc. Doing a little algebra will derive the inductance
> given the other two, *or* here's a list of approximations for 0.1uf:
>
> 159hz 10 Henries
> 225hz 5 Henries
> 355hz 2 Henries
> 500hz 1 Henry
>
> Note:
> The only way to know the saturation current inductance of a swinging
> choke (that I know of) is to saturate it, sorry.
>
> Online resonance calculator:
> http://www.deephaven.co.uk/lc.html
>
> My .02, adjust for your local currency as appropriate.
>
> 73,
> Jim N7CXI
>
>
> On 3/9/2012 10:55 AM, Mike Lucas wrote:
>> I'm trying to characterize two filter chokes from 4x1 amps, other
>> than big and heavy. Can someone
>> suggest a procedure, literature, or visual methods to identify what I
>> have? Am I safe in assuming that
>> they are swinging chokes? Originally from W4GD supplies, weight is about
>> 25 Lbs each, although they
>> are of different construction.
>>
>> Thanks, Mike W5CHR Memphis
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>
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