[Amps] Microwave Transformers?

[ToddRoberts2001 at aol.com]

In a message dated 3/11/2009 3:50:21 A.M.  Eastern Daylight Time, 
g8gsq at eltac.co.uk writes:
Microwave oven transformers  can be very different one from 
another, even when the original appliance had  the same nominal rating.

A lot have quite high resistance windings for  the power rating, so 
will give poor regulation and run hot on continuous  load. Most 
also have too few turns on the primary for continuous  
energisation, and get very hot from that (in most ovens they are 
fan  cooled, even though on for only short periods). You can add 
extra primary  turns in the space from the heater winding and 
shunts to help with this, but  that increases the resistance. 
Measure some and use the Duncan Amps PSU  Designer to see what 
performance they will give.

All I've toyed with  can be used with the secondary disconnected 
from the frame - one out of  eight or nine needed a bit of kapton 
tape for insulation on a hipot  test.

Steve
_______________________________________________________

Dittos  from all I have learned about MOTs about the only thing they will
do  correctly  is run a microwave oven. They have too few turns in the  
primary
so the transformer runs hot and lossy, the magnetic shunts limit  output 
current
and the welds along the edges of the laminations act like a  big shorted turn,
so the transformer runs hot and lossy. The transformer  pulls several
hundred watts just idling with no load. Did I mention they run  hot and lossy?
They were built with one thing in mind - maximum  cheapness.

It is a shame because they look so tempting to use. But for  all the work
and aggravation of trying to rebuild them, grinding off the  welds across the 
laminations, knocking out the magnetic shunts, possibly  adding turns to the 
primary, you might be much better off to just buy some  laminations and 
build your own transformer. Plus you will learn something by  building
your own transformer and it is fun!

73 Todd WD4NGG  

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