[Milsurplus] Triad Choke

[Richard Brunner]

More:  Measuring a power filter choke on an inductance meter is not
useful because the inductance goes down substantially when dc passes
through, as in service.

Measuring choke characteristics is easily done.  Use most any power
transformer with full wave rectification and no filtering.  Connect the
test choke in series with a resistor R of several thousand Ohms, and a
milliammeter from + to the transformer center tap.  Varying input
voltage, measure ac voltage across the choke, and resistor, and dc
current.  Then:

L = (Echoke x R) / (Eresistor x 2 x pi x f)

For 60 cycle input with full-wave rectification, 2 pi f becomes 2 x 3.14
x 120, or 754  
Now L = (Echoke x R) / (Eresistor x 754)

Measure ac voltage with an average reading (VOM) meter.  Use a blocking
capacitor to keep dc off the meter.

As you increase the current you will see the voltage increase levelling
off, indicating you are getting into saturation, and is approximately
the useful current limit.

References:
"Measuring Inductance of DC Loaded Chokes," J. H. Ellison, W6AOI, QST,
Feb. 1963 pp16, 17.
"Know Your Filter Choke Coils," Harold Reed, W3EJP, CQ, Nov. 1959, pp
50, 51.

Richard, AA1P




On Sun, 2010-12-26 at 13:08 -0500, n2lxm at juno.com wrote:
> Good Afternoon All,
> 
>         While looking through the supply closet for a project on the
> bench I found a Triad choke I can't ID. The only markings on it is 30L4.
> I guess I had measured it on a LC Meter at one time, as there's a note on
> the bottom of 11 Hy. Can Anyone ID this choke, I really just need to know
> the current rating. Thanks, and I hope everyone had a Merry Christmas.
> 
> 
>                                 Jeff N2LXM
>                   AMATEUR RADIO OPERATOR
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