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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Xformer sources needed
Summary: Try "buck-boost" transformers
Message-ID: <4342@kitty.UUCP>
Date: 24 Jan 91 03:10:16 GMT
References: <36148@netnews.upenn.edu>
Distribution: usa
Organization: Recognition Research Corp., Clarence, NY
Lines: 36

In article <36148@netnews.upenn.edu>, depolo@eniac.seas.upenn.edu (Jeff DePolo) writes:
> I've been running in circles trying to find a source for high-current 
> transformers for a 120 AC to 13.8 DC supply.  The prices for most of
> the commercial supplies around (Astron, et. al.) seem ridiculously high.
> I'm hoping to find a transformer that will handle a solid 35A.
> Any info would be greatly appreciated (except suggestions to roll my own) :-)

	Consider a "buck-boost" transformer used in electrical power
distribution applications to adjust line voltage by a fixed amount.

	A common transformer style has 120/240 primary (split winding
for series or parallel connection) and 12/24 volt secondary (also a
split winding).  These transformers are available in ratings from
250 VA to 5 KVA (i.e., approximately 10 amps to 200 amps on the secondary
side at 24 volts, with twice that current at 12 volts).  These
transformers are all of NEMA-1 construction, and their dimensions are
"reasonable" for power supply usage.  A 12/24 volt secondary with
split windings can obviously be wired to provide 12 volts center-tapped.

	My guess is that you want a 750 VA, or possibly a 1 KVA transformer
for your application (based upon my conservative thinking, 500 VA for a 35
ampere @ 12 volt DC load is too close to rating). 

	I would also guess that a 750 VA buck-boost transformer as described
above could be purchased for less than $ 100.00 from a wholesale industrial
electrical supply distributor.  You may find this transformer for quite
a bit less money at a dealer in used industrial equipment.

	One word of caution:  Most buck-boost transformers have isolated
secondary windings, but some models use an autotransformer approach with
a common connection between primary and secondary.  Obviously, one does
not wish to use the latter style for this application.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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