Power supply recommendations

[David Bandel]

On Thu, 25 Nov 2004 10:06:00 -0600, Alma J Wetzker <almaw at ieee.org> wrote:
> Kurt Wall wrote:
> 
> 
> > On Tue, Nov 23, 2004 at 03:08:24PM -0500, dep took 23 lines to write:
> >
> >>quoth Kurt Wall:
> >>
> >>| On a similar note, if a PC has a 250 watt power supply, is it
> >>| acceptable to replace it with a quieter, say, 300 watt power supply?
> >>
> >>yes. other options include a louder one, a much louder one, a really
> >>screechingly louder one, and one that makes just about the same amount
> >>of noise.
> >
> >
> > We're definitely going in the wrong direction here. ;-) But, it's nice to
> > see you back, dep. I, at least, have missed your wit.
> >
> >
> >>(the more juice the power supply can deliver, the better -- it don't
> >>force extra electrons down your device's wires.)
> >
> >
> > That's really the question I was hoping to get answered. My ignorance
> > of the fundamentals of things electric and electronic is both broad
> > and deep. In fact, to remedy this deficiency, I start taking a series
> > of electonics engineering courses at the local community college next
> > semester.
> >
> > Thanks for the information.
> >
> > Kurt
> 
> Don't feel too bad about not getting it.  I have about eight classes to
> compleat my EE degree.  I took a late Junior level lab and one of the students
> on my team thought that if we had a 1W power supply that it would force 1W
> through our system that was only rated to handle about .45W.  The simple magic
> circle(*) to remember is Ohm's Law (V=IR).

Ohms law (last time I checked) was: E=I*R (E=volts where volts is
electromotive force, thus the E), I is amps, R is resistance (simply).
 Resistance takes many forms, but for this formula we just want the
equivalent resistance as if the circuit were a resistor translating
reactance (either inductive or capacitive) to resistance.

Now, more to the point for this conversation: P=I*E, where E is volts,
I is amps, and P is power (watts).

Since what we normally use is 110v, a 250w power supply will draw up
to 2.3 amps.  If you add several SCSI drives which run at 12v @ 1 amp,
you'll use 12w for each drive.  All your components, including your
motherboard have a rating in either volts and amps, or in watts.


> 
> As for noise, it takes an autistic to hear the electronic switching of a power
> supply.  The noise comes from the fan.  Quiet fans are expensive.  Moving air
> through confined spaces is noisy.  Keeping the air path clear inside is the
> designers problem.  Keeping the air path clear outside is your problem.
> Things like round cables and not putting CD's right next to the PS go a long
> way toward keeping noise down.
> 
> Final note:  (expensive fan != quality PS)  Many people bet that way and it is
> generally true.  But, it does not have to be.  (Statement:  A quality PS
> includes an expensive (quiet) fan.  A implies B does not mean that B implies A.)
> 
>      -- Alma
> 
> (*)  [For those who don't know about magic circles, you draw a circle and put
> the V in the top half and the I and R in the bottom half, side by side.  

Maybe I learned too long ago, but I know the HAM test still talks
about electromotive force (E) not volts (V).  Is this new?

I can recommend the ARRL Handbook for Radio Communications (available
from www.arrl.org) for good discussions on all the above theory and
_much_ more.

You
> cover the letter that you want to find and you have either multiplication of
> division of the other two.]

Ciao,

David A. Bandel
-- 
Focus on the dream, not the competition.
            - Nemesis Air Racing Team motto