Re: Current Limiting and Impedence

["Tesla list" <tesla@xxxxxxxxxx>]

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

Hi Mark,

I use two MOT's in series as a HV transformer for the power supply providing
approx +-5kV once fed through a voltage doubler arrangement.  These have the
shunts removed, but are not gapped, they are working as transformers.

I also have a HV charging inductor that uses the secondaries of 4 MOT's, two
in series, two sets in parallel.  These have the air gap introduced with
primary, heater winding and shunts removed.

This then charges the capacitor to approx 20kV through resonant rise.  I am
sure it never gets there in operation as the power supply sags under load.
I keep meaning to build remote sensing so I can scope the tank voltage and
charging current waveform from the power supply but it has not happened yet.

Cheers,

Paul.

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, May 11, 2005 7:46 PM
Subject: RE: Current Limiting and Impedence


> Original poster: "Mark Dunn" <mdunn@xxxxxxxxxxxx>
>
>
> Paul(Benham):
>
> Are you using the MOT's for HV Transformers or Inductors?
>
> Thanks.
> Mark
>
>
> 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  >  >
>
>
>
>
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