Re: MOTs & Thoughts

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Ken,

On 22 Jul 2002, at 19:08, Tesla list wrote:

> Original poster: "Crow Leader by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<tesla-at-lists.symmetric-dot-net>
> 
> I want to see the voltage and current waveforms of these so called
> "saturated" transformers. Show me clipped output voltage waveforms at no
> load.
> 
> do these "saturated" transformers dissipate 600 watts of heat?
> 
> KEN

To see it for yourself, you can stick a 0.1 Ohm current sense 
resistor in series with the primary and see the waveform across it 
with an isolated scope. Here is roughly what I saw when I looked:

          *
         * *
        *   *
       *     *
    *           *
*                   * * 
                          *            *
                             *      *
                               *   *
                                * *
                                 *

A crude depiction but you get the idea. The primary current in the 
transformer I tested peaked at around 20A on each half cycle. The 
primary voltage was sinusoidal of course. I don't recall the phase 
relationships but I do remember that adding some capacitance across 
the primary didn't alter them much if at all. Since I have posted 
this picture several times, there may be a reference to it in one of 
my old archived posts.

     Re the heating - I've never run one of these for long enough to 
determine the amount of heating but might set this up again to check 
the unknowns out of curiosity if time permits. None of the 
transformers I've come across has used self-fluxing wire but I have 
seen a number which have cooked their windings in normal use 
regardless.

     All the microwave ovens I've come across emit a lamination 
rattle when they are first powered up despite the welded core seams 
which is quite a telling indication.

Regards,
malcolm

> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Monday, July 22, 2002 5:38 PM
> Subject: Re: MOTs & Thoughts
> 
> 
> > Original poster: "Marry Krutsch by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <u236-at-earthlink-dot-net>
> >
> > Hi Tim, all,
> >
> > I'm not sure about your MOT, but all of mine are partially saturated at
> > 120 volts.  They start to vibrate, and the primary no-load current goes
> > up to between 2 and 4 amps, depending on the unit being tested.  I have
> > graphed the no-load current vs input voltage, and the graph stays linear
> > until 90 volts, then begins rising exponentially after that.  I have 5
> > MOTs, each differing in size/output, and they all begin to saturate with
> > 90 volts in.  The input current really begins to take off at 100 volts
> > in.  I wish I had a transformer like yours :-).
> >
> > Peace,
> > Winston K.
> >
> > PS- If anyone is interested (let me know), I can send you a copy of my
> > measurements, complete with graphs (they look cool :-)).  It's done in
> > Excel.
> >
> > "Marry Krutsch" <u236-at-earthlink-dot-net>
> >
> >
> >
> > Tesla list wrote:
> > >
> > > Original poster: "Tim J by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <digital_raven45-at-hotmail-dot-com>
> > >
> > > I have to agree with KEN on this one!
> > >
> > > MOT's DON'T saturate at 120VAC...it wouldn't make sense if they did.
> > > Personally, I've done tests to 160 VAC on a 120 VAC rated MOT, and that
> was
> > > the absolute max I could push the transformer before I started hearing a
> > > loud buzz...peak output voltage/ current began to drop off like crazy.
> Now
> > > that was a classic case of saturation. This did not happen at 120 VAC or
> 140
> > > VAC...I can assure you.
> >
> >
> >
> >
> 
> 
> 
>