Re: How do you increase voltage using a transformer

A transformer "changes" voltage and current for only for alternating 
current (AC).  You can think of a transformer as two coupled 
electromagnets.  When you pass the current through the "input" side, you 
generate a magnetic field.  If this field "crosses" another conductor (in 
the case of the transformmer, the "output" side), voltage and current are 
induced this conductor as a function of the "rate of change" of the 
magnetic field.  The amount of voltage and current is a function of 
the "turns ratio" of the transformer, that is the ratio of the turns on 
the input coil to the output coil.  If the number of turns are equal, then 
the induced voltage and current are equal to that on the input side.  If 
the output side has twice as many turns, the output current is half of the 
input current but the output voltage is double the input.  (In reality it 
will be a bit less due to losses.)

The operation of a transformer is described by "Maxwell's Laws".  You 
should find a more detailed discussion of this in any basic physics 
textbook.

Modifying the power supply is another story.  You can't just put a 
transformer on the DC output of the power supply because, other than a 
transient spike, you won't generate any voltage or current.

Without knowing the details of the design of the power supply, I couldn't 
tell you how to modify.  If you don't need a very "smooth" DC output, it 
would probably be easiest to build the power supply from scratch.  You 
should be able to find a book with detailed instructions in a library, 
bookstore, or electronic hobbiest shop.

Good luck, and warn you roommates when you're ready to cause a brown-out!

Christopher Seaman
Alcoa Technical Center