[TCML] Transformer Sources

[jimlux]

FIFTYGUY at aol.com wrote:
>  
>  
> In a message dated 3/13/09 6:42:25 P.M. Eastern Standard Time,  
> bunnikillr at cox.net writes:
> 
>> Lost  me on this set up...  where can I find some schematics on this type  
>> of wiring?  Im still trying to understand how a 400VA trannie can  handle 
>> 2.5KW load...
>> Is the low voltage trannie added to the  line voltage for 140V?
> 
>     It's a standard application for an autotransformer.  "Buck/boost" is the 
> industry term.

Buck boost connection can be an autotransfomer, but often isn't: the 
usual transformers I've used have totally separate windings; while I use 
autotransformer to refer to things like a variac, where it's one 
continuous tapped winding.  Yes, they're electrically about the same.

> 
>     Most buck/boost transformers are used on 120, 208,  or 240 VAC circuits 
> where the voltage isn't where it should be for one reason or  another. A common 
> application might be bringing a 208V circuit closer to  240V so a 240V device 
> can run better. Or compensating for the voltage drop from  a heavy load.
>     Also, buck/boost transformers are *used* as  auto-transformers, but they 
> are *built* as standard isolating transformers to  allow many connection 
> options. We've used buck/boost transformers as  high-current sources (up to 1500 
> Amps). The secondary windings tend to be  terminated in lugs that stick out of 
> the potting resin, and require bolted lugs  for cable connections.

There's also often a higher insulation between pri and sec on the 
buck/boost than on an autotransformer.