Re: Inductor question . . . permeability vs. AC flux

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: robert & june heidlebaugh <rheidlebaugh-at-desertgate-dot-com> 

If you are watching the wave spape on a scope you should also see the AC
tends to be of one polerity like it is rectified by a magnetic amplifier
action. If you bias the choke with a perminate magnet you will see the same
action.
      Robert   H
-- 


 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > Date: Fri, 20 Feb 2004 21:33:58 -0700
 > To: tesla-at-pupman-dot-com
 > Subject: Inductor question . . . permeability vs. AC flux
 > Resent-From: tesla-at-pupman-dot-com
 > Resent-Date: Fri, 20 Feb 2004 21:45:45 -0700
 >
 > Original poster: dhmccauley-at-spacecatlighting-dot-com
 >
 > When designing a DC filter inductor the other day, I noticed something
 > interesting.
 >
 > The first thing was expected.  With an iron powder (distributed air gap)
 > core, as you increase the amount of DC bias on the core, the permeabililty
 > of the core decreases.
 > So for example, an inductor with zero bias might read 50uH but with 20A DC
 > bias on it, its down to about 10uH.  Okay, pretty normal.
 >
 > Now, the second interesting phenomenon is that if you have a core with some
 > DC bias on it, and now you have some AC ripple on that bias, it turns out
 > the more
 > AC ripple (or AC flux) there is on the core at that point, the permeability
 > starts increasing dramatically again.
 > So my particular core is almost saturated with 20A of DC current and
 > permeability is about 20% of nominal at this point on the B-H curve.
 > However, if there happens to
 > be 10A ripple current (which there is) riding on this 20A of DC current, the
 > permeability increases by over 250%.
 >
 > Can anyone explain this phenomenon and what is causing it?
 >
 >