Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!unmvax!ariel!hydra.unm.edu!ee5391aa
From: ee5391aa@hydra.unm.edu (Duke McMullan n5gax)
Newsgroups: sci.electronics
Subject: Re: 100V Japanese products on 120V US lines
Keywords: power conversion, burning toast smell
Message-ID: <1201@ariel.unm.edu>
Date: 30 Dec 89 01:39:28 GMT
References: <3215@uceng.UC.EDU>
Sender: news@ariel.unm.edu
Reply-To: ee5391aa@hydra.unm.edu.UUCP (Duke McMullan n5gax)
Organization: University of New Mexico, Albuquerque, NM
Lines: 58

In article <3215@uceng.UC.EDU> cradens@uceng.UC.EDU (carl radens) writes:
>What is a good technique for running 100V Japanese products (audio) on
>a 120V US power line ? Apparently, some units have a selection switch
>in the back, or at the power supply section; but if not, what to do ?

Let's assume you don't want to dedicate a variable autotransformer (that's
what a Variac (TM) really is) forever to this task.

OK, go to your junk box, and pull out an old 24 volt transformer. You DO have
an old 24V xformer in you junk box, DON'T YOU?

Sigh. OK, buy one at Radio Schlock if you must. Just come up with an ap-
propriate transformer. Wire as follows:



     o__________ ||
	  |	)||
	  |	(|| _________________________________o
	  |	)||(
	  |	(||)    24v secondary
	  |	)||(_____________
	  |	(||		|
	__)_____)||		|
	| |	 ||		|
     o--| |			|
	| |			|
	|_)_____________________|
	  |
	  |__________________________________________o

Now, here's what's happening: The 110v (or 115v, or 120v, let's not quibble)
on the primary generates about 24v at the secondary. This 24v is wired IN
SERIES with the 110v line. The 110v is applied to the left-hand pair of
terminals. You need to look at the voltage across the right-hand terminals now.
A meter isn't necessary; a regular 110v light bulb will do the trick. (Just in
case, use a bulb you don't mind losing.) 

The phase (like polarity, only AC) of the secondary is critical to this working
properly. Wire one way, this will ADD the secondary voltage to the line, giving
about 150v (VERY bright bulb); the other way, the voltages subtract, giving you
a dim bulb at a little under 100v. Wire appropriately; don't exceed the current
rating of the secondary (primary current won't be a problem).

1) I hope the picture survives. If your tabs=8 spaces, we're probably OK.
2) This circuit IS NOT an isolation transformer.
3) I trust you aren't offended by the detail and low-tech description. I know
	nothing of your electronics background, so I assumed VERY little.
4) For the record, when you wire the thing this way, it is an autotransformer.
5) Don't try this trick with a neon-sign transformer. ;^)

						Here's hoping it helps,
								d


	"You should never threaten a man you are not going to fight,
   and if war is your intention, it is best to get on with it." -- F.J. Lovret
      Duke McMullan n5gax nss13429r phon505-255-4642 ee5391aa@hydra.unm.edu