Re: Help with a inductor problem

To: tesla-at-pupman-dot-com
Subject: Re: Help with a inductor problem
From: "Lee Marsh" <lmm-at-flash-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Fri, 01 Oct 1999 17:39:35 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Thanks a lot  I'didnt want this baby to get away        Lee     this was a
great help

----- Original Message -----
From: Tesla List <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, September 30, 1999 1:49 PM
Subject: Re: Help with a inductor problem


> Original Poster: "Eric Davidson" <edavidson-at-icva.gov>
>
> Lee,
>
> IMO you sent it back prematurely.  You will NOT be able to measure the
> resistance with a high input impedance ohmmeter like the Flukes, Beckmans
> etc. A 60's vintage Simpson may do the job.  The huge inductance of the
> choke causes it to buck when the ohmmeter tries to measure the resistance.
> The counter emf generated by the inductance opposes the voltage from the
> meter.  Your resistance reading will likely fluctuate wildly and never
> stabilize.  The fix is easy.  Simply place a 100 ohm 1/2 W resistor (or
any
> known resistance under say, 10 kohms)  in PARALLEL with the choke and
> measure the resistance of the two in parallel.  Calculate the resistance
of
> the choke.  The resistor will damp the inductive kick of the choke and
your
> resistance reading will be rock stable and very accurate.  I've used this
> method to measure the DC resistance of the control coil on my saturable
> reactor, it works great.  Hope this helps.
>
> Eric
> edavidson-at-icva.gov
>
> PS  I'd try to get that choke back...sounds like a nice find..just my
> opinion.
>
>
>
> > Original Poster: "Lee Marsh" <lmm-at-flash-dot-net>
> >
> > Hi All    I found an old Radar modulator charging inductor.  On the can
it
> > has a list of specs.
> > as follows:   15 Henrys,  17.5 kvrms,   0.110 A ,     DC res  nom.   296
> > ohms.  A diagram
> > on the can indicates that it is a simple Iron core choke.  When I use my
> > DVM to measure
> > the resistance it tells me that it is over one meg ohm. Does this make
> > sense? The guy I
> > got it from says you cant measure it with on simple ohm meter that it
> takes
> > a high voltage
> > to do it  (like  HV diodes) and he FAXed me a diagram of how to measure
it
> > This consists
> > of   a 100W  200000 ohm resistor and another 1 ohm in series with a
1570dc
> > supply.
> > When  he measure  across the 1 ohm resistor he obtains a reading of
7.9mv
> > or .0079 A
> > then  he adds the inductor and measurs again  this time he gets 6.9mv or
> > .0069 A which
> > if true tells me that that the choke resistance isn't in the meg ohms
> > range. But its still pretty high more than 296 ohms listed on the can.
> >
> > I sent it back.  Did I do the right thing?
> >
> >
>
>
>