larry@kitty.UUCP (Larry Lippman) (01/24/91)
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?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 [note: ub=acsu.buffalo.edu] uunet!/ \aerion!larry
k3tx@wells.UUCP (Dave Heller) (01/24/91)
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) :-) > > --- Jeff > -- > -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- > Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 > depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) > University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104 What's wrong with a roll-your-own job? You're talking about something in the 500+ watt range, which is *heavy* and to buy new could be on the expensive side. But there are plenty of *big* transformers around practicallyl for the taking --- usually with 120 v in, but sometimes with 240 v primaries, which would be better. So you find a roll of #12 or #10 insulated wire, start putting turns on the core where they can be fit, and before long you have enough volts coming out --- then four (4) big but cheap diodes bridged and you have what you wanted in the first place. A *big* surplus condenser across the output and the ripple isn't too big, maybe. Or maybe find a transformer from a junked welder or industrial battery charger and you have it made. Carrying the thing could pose a problem. *heavy*. Or another wild but actually practical suggestion: I've seen *many* junked computers and major components thereof in scrap yards, and many of these have multiple transformers in the range you note. Those possessing them have no idea what they are and emphatically don't want to know and are very happay to sell by the pound. Or, if you want a pig, I have one for the taking, which with 120 on the secondary might give you what you want on the primary. Free for the taking on condition I don't get it back. In summary, you ask for what can be very expensive if *bought* but can be very *cheap* if scrounged. Take your pick. K3TX
strong@tc.fluke.COM (Norm Strong) (02/05/91)
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) :-) What do you think you ought to pay for one? Then we'll discuss the best way to go. -- Norm Strong (strong@tc.fluke.com) 2528 31st S. Seattle WA 98144
keating@motcid.UUCP (Edward Keating) (02/06/91)
In article <1991Feb4.163039.28658@tc.fluke.COM>, strong@tc.fluke.COM (Norm Strong) 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. You might want to try the DC power supplies used for RV's. I've seen them rated at 40A @ 14.4v and 70A @ 12v. These are usually CV transformers with simple diode rectification. (no filtering, they are used to charge and float batteries). -- Never ascribe to malice that which can adequately be explained by stupidity.
dmturne@PacBell.COM (Dave Turner) (02/07/91)
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. I just got the latest Signal catalog. They list a part no. 36-20 which with secondaries in parallel will produce 18.0 VAC @ 40 Amps. I haven't worked out all the design equations given in the back of the catalog but it looks like you might be able to use it for a 13.8 VDC supply as long as the input voltage stays above about 100 VAC. They list many other transformers. I have no idea what these things cost new although I have bought several Signal transformers from various Silicon Valley surplus stores. Their address is: Signal Inwood, New York (516) 239-5777 -- Dave Turner 415/823-2001 {att,bellcore,sun,ames,decwrl}!pacbell!dmturne
wb8foz@mthvax.cs.miami.edu (David Lesher) (02/10/91)
>In article <1991Feb4.163039.28658@tc.fluke.COM>, strong@tc.fluke.COM (Norm Strong) 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. Try Electronic Surplus Inc. 216 621-1052 -- A host is a host from coast to coast.....wb8foz@mthvax.cs.miami.edu & no one will talk to a host that's close............(305) 255-RTFM Unless the host (that isn't close)......................pob 570-335 is busy, hung or dead....................................33257-0335