Looking for advice on power distribution

[gstopp at fibermux.com]

     Not mundane at all!
     
     From an engineering point of view, it's probably better to distrubute 
     raw D.C. and regulate it at the destination, rather than distributing 
     regulated D.C. in a large system. We had all kinds of problems with 
     the 930's in Emerson's Moog, mostly due to age and vibration, and 
     those problems were propigated to all modules on the particular power 
     supply. Boy did that suck.
     
     A word of caution about this, however. Since the modules will probably 
     have some kind of connector for power, that means that there will 
     probably be lots of connectors, and therefore lots of opportunity for 
     connector failure, loose contacts, pluggin/unplugging with power on 
     (whether intentionally or by mistake), etc. If regulated D.C. is 
     distributed, no problem - any screw-ups will be protected by the 
     regulators. If raw un-regulated D.C. is distributed, any screw-ups may 
     cause big sparks or smoking wires or even fire which is always 
     entertaining to your onlooking friends. BTDT.
     
     So if you do distribute raw D.C., it's probably a good idea to put 
     some current-limiting devices in line. Fuses would be good, and if you 
     want to get fancy you can install some of those resettable positive 
     temperature coefficient thingeys (PTC's) which you don't have to 
     replace when they blow (you just let them cool off).
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Looking for advice on power distribution
Author:  Bob Zimmer <bzimmer at voicenet.com> at ccrelayout
Date:    4/12/96 9:48 AM


I remember there had been a discussion on power distribution, but didn't 
catch all of the messages.
     
In designing a fair size modular system of 30 or so modules, it has occurred 
to me that there are two ways to distribute power to the separate modules.
     
First, a large linear or switched supply (3A or so) sending power down buss 
lines that are connected to the modules.
     
Second, a large rectified supply (3 to 5 amp xfmr, bridge rectifier, main 
filter cap) sending power down buss lines that are connected to the modules 
and then having separate small regulators (78L15, 79L15, 78L05 etc) with 
small caps surrounding them on each board.  This would add about $1.50 to 
each module, but if it would be a better and safer approach, it would be 
worth it.
     
Any comments on which would be the best approach?
I realize that this is mundane to EE's, but for those of us who aren't ...