[Boatanchors] Measuring Swinging Choke values

[mac]

Mark,

As I'm sure you know, the inductance value of a "swinging" choke  
changes in value,  decreasing with increasing DC current levels  
flowing through it.  "Smoothing" chokes do this as well but but the  
change range is much smaller.  Don't know what kind of a DVM you have  
but suspect the DC current level involved when making measurements  
with it would be very small. Concomitantly, the inductance of a large  
choke designed to be of the swinging type could be VERY large when  
passing essentially no current, perhaps outside the range of your  
instrument.

All of which raises the interesting question of how to measure the  
inductance of an unknown choke passing currents in a range normally  
associated with a practical power supply.  One way might be to measure  
the percent of ripple for a given current, say 200ma. and a known  
filter cap value using a scope and the formula:    L = 100/(%ripple)C

Dennis D. W7QHO
Glendale, CA



On Jul 21, 2010, at 5:12 PM, Mark K3MSB wrote:

> I'm trying to measure the inductance of a swinging choke that's come  
> into my
> possession.
>
> I don't have a DVM that will measure into the Henry range,  so I use  
> my
> restored IT-28 with an external Inductance standard to measure large  
> chokes.
>
> Using several different known inductors as standards,  my IT-28  
> gives me
> correct readings for other known inductors.
>
> However,  for any swinging choke I try to test,  the IT-28 gives me no
> reading at all.
>
> What am I doing wrong here?
>
> 73 Mark K3MSB
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