WTB: Tower case for IBM model 80, 60 or 65 (PS/2) - test-drb@ccmp.vtda.org

22 Sep 2005

Hi
 Another option on the auto transformer is to use
the primary of a transformer that was designed to
be configured for both voltages. You just ignore
the output leads. The transformer in this case only
needs to be rated for 1/2 the power that you are
sending to the final device. It should be noted that
in der Mouse's diagram, each transformer needs to
be rated for 1/2 the power.
Dwight

...
 From: "der Mouse" <mouse at
rodents.montreal.qc.ca>

  A crude method is to find three biggish AC power
transformers all the
 same.  Hook all three secondaries together in parallel, then use one
 of the primaries as the primary and hook the other two secondaries
 series-aiding to make the 220 volt 'secondary.' 
Just watch your phasing; get the leads swapped to one of the "other
two" transformers and you'll get (nominal) zero voltage instead of
double voltage.

Indeed, you can do something autotransformerish with only two
transformers:

   ---------------------.
IN                      |
   --------+------------|-------------------------------
           |            +----+                           OUT
           |            |    |            +-------------
           |            |    |            |
           |_()()()()()_|    |_()()()()()_|
            _==========_      _==========_
           | ()()()()() |    | ()()()()() |
           |            |    |            |
           +------------|----+            |
                        +-----------------+

Of course, the three-transformer version produces double voltage that's
isolated from the input, whereas the above doesn't.  Also, you still
have to watch the phasing; get a winding's leads swapped and you get
zero voltage instead of doubled voltage.

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