Power Supply Requirements

Can anyone help me figure out
1. Tell me if a specific system I have in mind would work without problems
with a 350 watt power supply.
2. What happens if you use too low of a power supply with a system.
3. How to measure or determine the right power supply for a given system.
Details follow.

1. Basically, I'm trying to get a new system for myself (while keeping
costs as low as possible). The current place I'm considering buying from
offers me a 350 Watt Power Supply by default. I'd love to get it to 420
watts, however, the way this place is set up, I'd have to change the case to
get which raises the price by almost $50 which I rather not do unless I have
to. The system is Athlon 2800 XP with 3 case fans (or 2 LED case fans if
that matters). 2 hard drives. 1 DVD-ROM. 1 Flash Media Card Reader.
Quite possibly also 1 CD-RW (I can leave this off as I have another system
with a CD-RW I can use to burn CDs with). The case doesn't come with all
the glowing neon lights everywhere...but considering it's only a few
dollars, I might add some in IF it won't boost my power supply requirements
by any noticeable amount. It will of course have video card (GeForce5600),
fax/modem, etc. as well. So, with this system, am I safe with a 350 watt
power supply (remember the CD-RW and any LED lights are optional for me if
they present a problem)? Or must I have a 420 or higher watt power supply?

2. So what happens, generally speaking, if you use a power supply that is
too low for all your system needs? Will it still turn on? Does it have any
possible chance of causing damage? Will the system perform at 100%
functionality and if not, how will it be reduced?

3. I vaguely remember there being some sort of rule of thumb for
determining how big of a power supply is needed based on type or number of
devices as well as a more exact way of measuring how much power your devices
will take and buying the corresponding power supply to match it. If my
vague memories are right, you also have take into account about the extra
power the devices might draw at boot up as well as their normal drain.
Unfortunately, it's all vague and been a while. Can someone tell me exactly
how it all works for both the rule of thumb version as well as the more
exact version? If the exact version requires, though, knowing the exact
power each device draws, it won't help as I haven't bought the system in
question.

Thanks!

Joe

"Joe" <> wrote in message
news:NyVEb.159674$_M.741229@attbi_s54...

answers in line.

> Can anyone help me figure out
> 1. Tell me if a specific system I have in mind would work without
problems
> with a 350 watt power supply.
> 2. What happens if you use too low of a power supply with a system.
> 3. How to measure or determine the right power supply for a given
system.
> Details follow.
>
> 1. Basically, I'm trying to get a new system for myself (while
keeping
> costs as low as possible). The current place I'm considering buying
from
> offers me a 350 Watt Power Supply by default. I'd love to get it to
420
> watts, however, the way this place is set up, I'd have to change the
case to
> get which raises the price by almost $50 which I rather not do
unless I have
> to. The system is Athlon 2800 XP with 3 case fans (or 2 LED case
fans if
> that matters). 2 hard drives. 1 DVD-ROM. 1 Flash Media Card
Reader.
> Quite possibly also 1 CD-RW (I can leave this off as I have another
system
> with a CD-RW I can use to burn CDs with). The case doesn't come
with all
> the glowing neon lights everywhere...but considering it's only a few
> dollars, I might add some in IF it won't boost my power supply
requirements
> by any noticeable amount. It will of course have video card
(GeForce5600),
> fax/modem, etc. as well. So, with this system, am I safe with a 350
watt
> power supply (remember the CD-RW and any LED lights are optional for
me if
> they present a problem)? Or must I have a 420 or higher watt power
supply?

It sounds like 350 watts is plenty for that system. Including a cd
burner.

> 2. So what happens, generally speaking, if you use a power supply
that is
> too low for all your system needs? Will it still turn on? Does it
have any
> possible chance of causing damage? Will the system perform at 100%
> functionality and if not, how will it be reduced?

Things go awry. Strange days ensue. You become perplexed and the
problem of troubleshooting takes on a whole new dimension, until you
finally figure it out. More specifically, all kinds of things happen.
Failures to start. Spontaneous reboots. Memory errors, processor
errors. Bad data writes. Freezes. Often, if the PS is almost strong
enough, it'll start up okay and seem fine until you try to use two
devices at once that draw a lot of power, like copying from hd to hd
or to CD. Then crashes and reboots and possible lost data. So that
kind of damage is possible. Electronically inclined people will also
tell you that prolonged underpower will damage certain devices, but
you may well have figured out you have a problem before that happens.

> 3. I vaguely remember there being some sort of rule of thumb for
> determining how big of a power supply is needed based on type or
number of
> devices as well as a more exact way of measuring how much power your
devices
> will take and buying the corresponding power supply to match it. If
my
> vague memories are right, you also have take into account about the
extra
> power the devices might draw at boot up as well as their normal
drain.
> Unfortunately, it's all vague and been a while. Can someone tell me
exactly
> how it all works for both the rule of thumb version as well as the
more
> exact version? If the exact version requires, though, knowing the
exact
> power each device draws, it won't help as I haven't bought the
system in
> question.
>

You discover the current drawn by each device in your system and
compare it to the current provided by the power supply. Example, I'm
looking at an old, dsyfunctional 250 watt PS. Under each voltage
+5,+12,-5,-12, it shows the maximum current available in that line.
In amps. Amperage. or A. So under 12 volts it shows a max of 10 A.
To find out if the PS is adequate, you add up all the current draws of
your 12 Volt devices, mainly the motors in the computer, drives, fans,
etc. if the total is 9 or less (less than 10 percent less than ten),
you can feel sure you're okay. And then your 5 volt devices, 3.3 volt
devices and so on. You do not need to think about the negative
voltages.

And that is how you do it, and yes, you can do it without having the
computer, because many manufacturers list the current draws of their
devices on their websites where you can look it up, AND there are also
lists of typical draws by device on various websites. I don't have
any links handy or I'd give you one. Go to google and look it up. As
to the various formulas, the only one I remember consistently is Watts
over Volts = Amps. Reason I remember it is that 2000 watts over 120
volts equals 16.6 amps, usually enough to blow the fuse in an older
house; so when you're lighting a movie scene and you want 2000 or more
watts of light for the scene(which you usually do), you need to be
careful to put your lamps on separate circuits. That's the one I
learned the hard way, so that's the one I remember - (but the rest
are equally simple).

You should be okay with 350. Good luck.
> Thanks!
That'll be $75.00, please.
Just kidding.

MF