Re: Microwave Oven Transformers (MOTs)

Hi!  MOTs must be ballasted, because unlike NST's or OBIT's, they
don't have current-limiting shunts that keep the core from
saturating and dumping as much current as it can till either the
wires burn up, the breaker/fuse goes, or someting else blows up
(read "Your Cap!")
   The "shunts" are simply laminates that are separated physically
from the rest of he laminations by a non-conductive, non-magnetic
material (usually plastic). When the AC current energizes the wire
of the MOT primary, it magnetizes the core, and forces a current
into the wires of the secondary as the magnetic field rises and
collapses.  The core is said to saturate when you keep pushing more
current through it, and try to create more flux (magnetic force)
than the core can hold, so the extra energy is dissapated as heat
(and a bit as noise!).  A MOT has shunts in it, but it's
current-limiting is pretty much diddley-squat (as I've found, it
keeps tripping my power-board breaker unless I ballast it with a
100 watt bulb, another MOT with the leades shorted, or a heating
element.  Removing shunts from an NST is a way to increase it's
current, because it allows the core to push more flux across the

  MOTs are lower voltage than NST's usually are, (mot is
~1.5-2.5kv, NST is 4-15kv), but where a NST only puts out 30-120ma,
the MOT can put out around 500ma to 1 amp in extreme cases.  Very
lethal man.  They'll knock you into the middle of next month and
then some.  I am messing with them currently to learn more about
these little beasties.  The low voltage means a static gap *must*
have air across it to quench, and the high current will make your
copper-pipe electrodes get really hot in short order if quenching
doesn't happen.  These things are also pretty hard on caps...Lots
of current brings the BPS up to a high number, 'cause it charges
the caps *really* fast.  If you want to use MOT's, I'd recomment an
MMC for sure.

Hope I cleared itup some :)  Keep it safe man.  These little
beasties are *very* deadly.  Think of them as a low-voltage
Pole-Pig.  And above all, be afraid.  Be Very afraid :)


If I've messed this up, everybody, feel free to correct me, but
this is how "i" understand it.
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Monday, May 01, 2000 10:13 PM
Subject: Re: Microwave Oven Transformers (MOTs)

>Original Poster: Fucian-at-aol-dot-com
>Then why must they (MOTs) be ballasted?