Path: utzoo!utgpu!watmath!clyde!att!rutgers!mcnc!ecsvax!dukeac!sgt
From: sgt@dukeac.UUCP (Stephen G. Tell)
Newsgroups: sci.electronics
Subject: Re: DC to DC powersupplys
Summary: Commercial unit; not cheap but good
Keywords: power supply switching
Message-ID: <1113@dukeac.UUCP>
Date: 20 Nov 88 07:39:16 GMT
References: <500@unocss.UUCP>
Reply-To: sgt@dukeac.UUCP (Stephen G. Tell)
Organization: Academic Computing, Duke University, Durham, NC
Lines: 42

In article <500@unocss.UUCP> ca063@unocss.UUCP (Thomas Davis) writes:
>    The system needs +5V @ 5amps, +12V @ 1amp, and -12V @ 100mAs.  The +5
>and +12 are no problem, it's the -12.  Like, it's just not available
>on a normal 12v car batttery system.  So, any ideas?  I have no desire
>or time to sit down and design an +12V dc to -12V dc convertor.  Is there
>a commercial power supply available that can be feed +13.8 volts, (car
>battery), with outputs close to those listed?

I have used some switching power supplies from Converter Concepts, Inc.,
and noticed that they have some that run on a DC input of 10-40 volts.
(I used the models that ran on 100-380VDC or 90-265VAC, and liked them.)

Their VT/VX-50 (50-watt) series has one that can take 10 to 40 volts
DC input and produce that following outputs:
+5 @ 1.2 to 6 amps
+12 @ 0.05 to 1 amps
-12 @ 0.05 to 1 amps

as for input current; the requirements
you specified of 5(5)+1(12)+.1(12) = 38.2 watts; call it 40.
They specify efficiency of typicaly 70%, so input power is 57 watts, or just
under 5 amps at 12 volts.  The other 17 watts comes out as heat, which
doesn't look too bad.

I paid somthing like $160 for a single-output, 100 to 380V input one of these
last year, so while they aren't cheap (and a multi-output is probably a bit
more) that is probably less than a good inverter.

I would caution against connecting too directly to the vehicle's battery
(say using that 13.8 as the +12 supply directly.)  The regulation
won't be good enough, and automotive electrical systems have lots of
noise of all kinds.  A switching regulator of this sort will help
insulate you from a lot of that.

My only connection with these guys is as a satisfied customer:
Converter Concepts Inc.
Industrial Parkway, Pardeeville WI, 53954
800-253-5227  or  608-429-2144
-- 
Steve Tell:  senior, Duke University school of Engineering (please hire me).
Former Chief Engineer, Cable 13 / Duke Union Community Television.
sgt@dukeac.ac.duke.edu;     !mcnc!ecsgate!dukeac!sgt