Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!rutgers!ub!boulder!weverka
From: weverka@boulder.colorado.edu (Robert T. Weverka)
Newsgroups: sci.electronics
Subject: AC-DC at wall current voltage
Message-ID: <27666@boulder.Colorado.EDU>
Date: 6 Oct 90 15:45:08 GMT
Sender: news@boulder.Colorado.EDU
Reply-To: weverka@sashimi.Colorado.EDU (Robert T. Weverka)
Organization: University of Colorado, Boulder
Lines: 29


Looking for assistance
I want to convert an AC electric blanket to DC.
The controller is a bimettalic thermastat that makes contact when cold.
When contact is made the 60 Hz wall voltage is dropped accross the blanket
resistance of 100 ohms heating the bed, and the same 60 Hz wall voltage is
dropped accross a 47000 ohm resistor in the controller (presumably to heat the
controller).
  I think I have to keep the voltage up so that the blanket still runs at
about 100 Watts.  This means I need moderate efficiency and can't use a step
down transformer.
  My thought was to put an AC-DC converter between the controller and the
blanket.  I can get the full wave bridge, but a 10,000 microfarad capacitor
with a rating of 200 Volts (recall 110 volt is the RMS wall current) is hard
to find and may be bigger than I'm bargaining for.  Is it dangerous to rectify
wall current without a transformer for isolation?  If so, is it possible to
find a one to one transformer ratio?
  In addition to the above questions I would appreciate advice on either:
     1) where do I get the capacitor of 10,000 microF 200 V rating  or
     2) an alternate means of efficient wall current to DC conversion.
My electrical background consists of repeated browsing of Horowitz and Hill
yet I can't find what I want there.

Thanks in advance,  -Ted            email  weverka@boulder.colorado.edu

PS.  Yes the desire to convert the blanket is motivated by the cancer scare
of 60Hz magnetic fields.  Yes I know that the evidence is not conclusive 
(for a review see 9/90 IEEE Spectrum), but this is a better safe than sorry
type situation to be installed in my kid's bed.