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Re: MOT Experiment

Hi Greg,

	Mine also measures 2400mA!  I also notice that when I flip the on switch,
the AC wiring "jerks" do to the inrush current.  The input current with the
output shorted is about 22 amps (hard to measure because the lights go out
:-)) .  The shorted output current is 1.4 amps.  Open load output is 1860
VAC.  These things are very dangerous!!

	Apparently, the designers play tricks to match these transformers to their
single intended use.  They are not just plain old universal current limited
transformers.  The large input capacitor supplied with these transformers
no doubt helps to match these things somewhat to the intended load.

	The 2400mA is not magnetic loss.  It is due to the apparent inductance of
the input windings across the AC line.  The voltage and current are almost
90 degrees out of phase so there is not much real power dissipated.  You
will notice that the transformer does not get very warm despite the 253 VA
going into it.  I = 115 / (377 x L)  so  2.4 = 115 / (377 x L).  Lprimary =
127mH.  Since the ratio of input to output voltage squared is proportional
to the ratio of primary and secondary inductances, the secondary must have
an inductance of (1860/115)^2 x 0.127 = 33.2H.  The current limiting is a
factor dependant on the input to output coupling which cannot be easily
found (needs computer model and these numbers to find).  This is the
general approach used to model these transformers along with the DC
resistances of the windings.  I should note that small inductance meters do
not have enough current drive to accurately measure big iron core
transformer inductances.  You really need to run full AC into them to get
accurate measurements.

Hope this was enlightening and not just confusing...

	Terry





At 10:29 AM 10/24/98 +-100, you wrote:
>The other day I wired a DMM set on AC Amps function in series with a 115V
600W MOT and measured its magnetizing current.  To my surprise, the thing
drew 2200ma with no load!  Core CCA is about 2.4 square inches, and based
on the turns-per-volt of the low voltage filament winding, I calculated its
primary turns at 132.  I'm no EE, but over 2 amps of magnetizing current
seems excessive.  If I use four of these to achieve 8KV, they will draw
almost 9 amps of current with no load.  I like to tinker with MOTs because
they are cheap and plentiful.  Unfortunately, they also appear to be on the
very edge of saturation!  I'd still like to try to make a Tesla coil power
supply with MOTs, even if they are wasteful.
>
>Greg
>
>