Re: Current Limiting and Impedence

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Paul Benham" <paulb@xxxxxxxxxxxxxxxxxxxx>

Hi Mark,

Cutting off the I's on MOT's and bolting them back together with plastic
spacers is exactly what I do.  I have run 4 in series on a 2" coil and on my
14" coil I have two in series and another two in parallel.

After extended running one of the MOT's insulation broke down, but I do have
up to 10kV across each of the two MOT's so they are being pushed quite hard.
I need to go to three in series and more in parallel.  It is becoming a bit
of a joke, carting around so many MOT's but they came at the right price and
do work.

Cheers,

Paul.

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, May 10, 2005 5:44 PM
Subject: Re: Current Limiting and Impedence


> 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
>
>