Re: Current Limiting and Impedence

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Mark Dunn" <mdunn@xxxxxxxxxxxx>


Steve, Gerry, Jim, Paul, et all:

When I started this thread it was to discuss issues with current
limiting and has now progressed into Charging Reactor Design.  That's
OK, but we need to keep straight what we are talking about.

Right now I am returning to the original current limiter issue and will
come back to Jim's charging reactor in later post.

As you know, my current limiter was saturating.  It was very interesting
to follow the discussion between Gerry and Steve, because what they
discussed was exactly what I was running into.  I needed many turns to
get the B(Core Flux Density) low enough, but the high turns drove the
inductance through the roof and demanded a huge gap to get it back down.

Last week I began analyzing a "bad" MOT(coincidently a destroyed
charging reactor)  I have to see if I could use it for a current
limiter.  A similar "good" MOT had a primary inductance of ~300 mH(sec
open).  I measured Ve & Ae and calculated Le & C.  Then back figured
~AL.  Preliminary analysis suggested B would be around 500 mT which
should be OK for steel.

I cut the "bad" MOT unit apart and was surprised to find that all the
E-core laminations were in the same section.   All the I-core
laminations were in the other section.  This meant I could easily gap
this device.  (Note: I sawed it apart right at the weld on either side.
I ran a weld bead parallel, and above and below, each original weld so
that the laminations would not fall apart before I sawed through it.)

I made a 60 turn coil(R=0.2 Ohms) and placed it on the E-core, clamped
the I-core on top, measured V,I and computed Z & L with no gap.  L = 38
mH.  This gave me an AL = 10555 nH.  Does this make sense for steel?
I then measured L for a number of gap spacers up to about .070"(note
this means total gap of .140") when I reached ~4 mH.  My theoretical
math suggests that I should be around .070" total gap or .035" spacers.
Are gapping calculations highly accurate or do they just give an
approximation?  B will be around 620 mT which is good for steel.
(Another data point of interest was .009" spacer for .018" total gap and
L = ~15 mH.  This would meet the criteria of my original current
limiting requirements.)

Pls comment about this design.  Like to delve into the math issues with
you guys if your willing to work with me.  I think my issues are in the
Ui, Ue, Ur area.

Thanks.
Mark

Mark