Re: MOT leakage

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

Original poster: "Hydrogen18" <hydrogen18-at-bellsouth-dot-net> 

You say "only twice", how much do reccomend over designing something?

---Eric
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, November 09, 2004 6:21 PM
Subject: Re: MOT leakage


 > Original poster: "robert heidlebaugh" <rheidlebaugh-at-desertgate-dot-com>
 >
 > Borislav: The microwave transforrmer is made to supply a lot of power in a
 > small space usualy 1 amp at 2100 volts.  This makes it  noisy, If you use
 > plastic or aluminum to mount it this will reduce the noise. Steel will
make
 > noise. Some list members mount the transformer in an oil filled can. This
 > reduces the noise but may be messy. You may find the 1N4007 a little low
in
 > current so a 3 amp diode may be a better choice to withstand your surge
 > current in a 400 ma supply. Your diode is rated at 1 amp. That is only
twice
 > your expected load.
 >     Robert   H
 > --
 >
 >
 >  > From: "Tesla list" <tesla-at-pupman-dot-com>
 >  > Date: Mon, 08 Nov 2004 08:10:28 -0700
 >  > To: tesla-at-pupman-dot-com
 >  > Subject: MOT leakage
 >  > Resent-From: tesla-at-pupman-dot-com
 >  > Resent-Date: Mon, 8 Nov 2004 08:13:35 -0700
 >  >
 >  > Original poster: "Borislav Trifonov" <bdt-at-shaw.ca>
 >  >
 >  > I assume subscribers to this list are familiar with microwave oven
 >  > transformers, and that is why I ask my question here, even though I'm
not
 >  > constructing a tesla coil.
 >  >
 >  > I'm working with plasma and I need a DC supply at about 3 kV and 400
 >  > mA.   In order to save money I got a large MOT with 2100 VAC secondary.
The
 >  > thing was quite noisy and heating was a problem, so I rebuilt the core.
I
 >  > grinded out the weldings and took apart the laminations.  The secondary
had
 >  > one end grounded to the core since insulation between the inner part of
the
 >  > winding and the core was minimal.  I stuffed extra insulation (mica) so
I
 >  > could safely unground that end of the winding (I'm bridge rectifying it
 >  > with chains of 8x the usual 1N4007s into a CLCRC filter).  I put the
core
 >  > laminations back together with nail polish, as I have no shellac.
 >  >
 >  > Now the transformer is very quiet, except when I put it in the chassis
(3u
 >  > format, steel, earthed) the chassis resonates very loudly.  At first I
 >  > thought the problem was mechanical vibration transmission, but
 >  > foam/rubber/springs didn't help, and I even made a pneumatic isolator
with
 >  > a pump -- nothing.  Turns out the hum was being induced into the
chassis
 >  > electromagnetically.  All my tests were with an unloaded secondary as
the
 >  > load has not yet been built.  The noise is so loud that I cannot leave
it
 >  > as it is.
 >  >
 >  > I have two questions:
 >  > Will the induced hum get worse/better/same when the transformer is
loaded?
 >  > What are my best magnetic shielding options?  Mu-metal foils are
expensive,
 >  > hard to find, and I'm guessing too thin and will saturate and be
 >  > ineffective; a silicon steel enclosure will buzz defeating the purpose
of
 >  > shielding and present a cooling problem.  I'm going to go crazy trying
to
 >  > figure out how to get rid of the noise.
 >  >
 >  >
 >
 >


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