# [TCML] Transformer Sources

FIFTYGUY at aol.com FIFTYGUY at aol.com
Fri Mar 13 18:36:20 MST 2009

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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
>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.

_http://en.wikipedia.org/wiki/Buck-boost_transformer_
(http://en.wikipedia.org/wiki/Buck-boost_transformer)

_http://www.squared.com/us/products/transformers.nsf/unid/C82FCAA16A8A5A0285256A5D006A234A/\$file/buckandboost.htm_
(http://www.squared.com/us/products/transformers.nsf/unid/C82FCAA16A8A5A0285256A5D006A234A/\$file/buckandboost.htm)

Note the trick is that the low voltage secondary  (secondary volts is the
amount of the "buck" or "boost") has to carry the same  current as the load.
The secondary could be 24VAC at 16.7 Amps, for 400 VA. This  will give 24Volts
of boost to a circuit with up to 16.7 Amps of current. The  buck/boost
transformer's primary voltage rating puts the limit on the type of  circuit you
apply it to.
Theoretically, if you had a transformer that had  a primary rating of
1,000,000 Volts you could use it to "boost" the  voltage of a 1,000,000 Volt
circuit to 1,000,024 VAC. So long as the circuit  current was limit to 16.7 Amps,
you would be perfectly OK using that 400 VA  transformer on a 16,700,000 VA
circuit.
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.

-Phil LaBudde

Center for the Advanced Study of Ballistic  Improbabilities
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