Haven't paid much attention to this thread (sorry), but
had saved this link for a rainy day, and thought it might
be useful to whoever asked...
 http://members.tripod.com/~schematics/xform/xformer1.htm

Cheers,
-Neil.



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Morgan Olsson
Sent: Thursday, June 20, 2002 1:13 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: Custom transformer source anyone?


>I need to convert a 7805 based supply from a 230VAC line to 277V

Downconvert using a small additional transformer:


Use a small trafo specified as, say,  230V prim, 35V secondary

Connect the windings in serial, feed 277V across both windings, get 230V
across the 230V winding.

You will be *feeding* the winding labeled "secondary", instead of loading
it, so it4s voltage will be higher than specified for normal use, as this is
a small trafo (high loss) it will be significantly higher, say 47V.

So, you feed it 230+47V=277V, and you take out 230V to your original
tansformer across the 230V winding.

Note also that this downconvertng transformer can have a lot lower VA rating
than the main transformer.  The output current is the originally specified
current in each (prim and sec) windings *added*, then multiply by 230Volts
and you get the new VA.

/Morgan

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