On Monday, 29 July 2019 03:47:49 UTC+1, John Larkin  wrote:   
   > On Sun, 28 Jul 2019 19:56:47 -0400, Bob Engelhardt   
   >  wrote:   
   >    
   > >I was looking for a 120-120 isolation transformer on eBay and I kept    
   > >finding 120-240/480 transformers.  There are 2 secondaries on these    
   > >(connect in parallel or series).  It occurred to me that I could use one    
   > >of these as a 120-120 by using one secondary as input and the other    
   > >secondary as output.  I know that this is theoretically possible, but    
   > >are there practical reasons why it wouldn't work?   
   > >   
   > >Also: if one of these 120-240/480 transformers is rated 500VA, that    
   > >means 1 amp on the secondary, right?  I.e., 1A at 480v.   
   > >   
   > >Thanks,   
   > >Bob   
   >    
   > You can use a 120/240-to-anything transformer as a 120-120 isolation   
   > tranny. Connect one half of the official primary to the line and use   
   > the other half as the isolated output. Ignore the "secondary". The   
   > power rating will be a bit less than specified because you're not   
   > using all the copper.   
      
   Sort of. Vout will be a little low under load due to copper resistance. That   
   could be solved by putting eg a 12v secondary in series with the output,   
   connected right way round. But the big issue is that you won't have a level of   
   isolation that's    
   considered safe for many applications. For some jobs it's adequate, for many   
   not.   
      
      
   NT   
      
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