"Jorgen [2400]" said:
for example, im looking at these cases
AOpen H 340H = 200 watts
Antec LifeStyle Minuet = 220 Watts
AOpen H 360A = 250 Watts
but I've had one bad experience with a PSU burning out on my previous
system.
- jorgen
It takes a lot of work to engineer a small system. The smaller the case,
the harder it is to balance power dissipation, noise, and performance.
In terms of raw power, 250 watts of power is enough to power a pretty
impressive system. The trick is, the power has to be in the right place,
to prevent overloading any one output. A P4 system powers the processor
from +12V, as do some of the current Athlon64 class systems. Boards
with AthlonXP (socket 462) tend to draw power from +5V, rather than +12V.
One hint of this, is the presence of the 2x2 ATX12V power connector.
Since the ATX 20pin power connector has only one +12V pin, and a pin
is limited to 6 amps of current, 72W at 80% efficiency, or 57.2W isn't
enough power for a lot of processors. That is why, either a 2x2 connector
is used, with two more +12V pins, or the designers use +5V and its
multiple
pins, to draw the power.
What this means, is you should be shopping for a different 250W supply,
depending on whether the motherboard seeks its power from +5 or +12.
Also, if you insist on using a high end video card, ATI9800/FX5900 class
cards draw 5V@10A and 12V@2A while doing 3D gaming. So, that is also a
major consumer of power, and has to be accounted for.
Power numbers are hard to get, as I discovered when I visited the
Shuttle web site. Shuttle makes small systems that are suited for
what you want to do, but I couldn't find specs for the power supply
used in the AMD and P4 systems. Both of the example systems below have
250W power supplies, but it is possible they have different limits on
their 3.3, 5.0, and +12V outputs. Here are the example systems:
http://www.shuttle.com/hq/product/product_b_intel.asp
http://www.shuttle.com/hq/product/product_b_amd.asp
ftp://ftp.shuttle.com/Manuals/en/fb61/fb61v3en.zip (P4/865 graphics)
ftp://ftp.shuttle.com/Manuals/en/fn41/fn41v3en.zip (AthlonXP/Nforce2 IGP)
I don't see a video output on those machines, so a cheap low end video
card would be a minimum extra purchase.
The systems intended for multimedia use, generally have power
specs, and make it easier to engineer. That Ibase system based
on the ATI RS300 chipset, has numbers like:
Power Consumption
Pentium 4 2.4GHz (512KB) with 256MB DDR memory
+5V: 3.29A; +12V: 4.83A
Pentium 4 3.06GHz (512KB) with 512MB DDR memory
+5V: 3.17A; +12V: 7.14A
If you use a decent size case, like a mid sized ATX, you can stick a
bigger power supply in it, or add case fans, and you have room to work.
The smaller the case, the harder it is to work in there, there are
fewer powering options (like the 250W limit), power budgeting must
be done more precisely, and so on. Even then, a small case solution
may be noisier than you expected. There are limits as to how much power
should be dissipated in a small volume, and many users complain about
overheating or noise on their small systems.
You could shop for Mobile processors, as the Athlon comes in a mobile
version, as do some Pentiums. The problem here is, certain ingredients
may be missing from a desktop chipset/motherboard that would make it
easier to work with them. For example, "LarsJ" just finished modding
an A7V8X, so the voltage regulator VID pins could be programmed for
the lower voltage of a Mobile Athlon. This was needed, because Asus
has a policy of not allowing undervolting in their products (why,
escapes me, because if a board didn't start with a low setting, you
could always clear CMOS and try again). Many Athlon boards are adjustable
from 1.65 to 1.85, and to get the cool benefits of a Mobile processor,
requires lower voltages than that. LarsJ used the relatively safe
mod, of programming the five VID pins on the regulator with wires, to
get what he wanted.
Similarly, there can be multiplier issues with certain chipsets
or motherboard implementations, that would require bridge painting
or socket modding for a Mobile Athlon (only if you want to adjust
the multiplier). So, to get the range of features you want, can
sometimes mean doing some modding.
I spent about a month of spare time, trying to plan for such a
small system, and in the end, I gave up, simply because the project
was becoming too expensive. (The vendors of such small systems tend
to charge a premium for them, all sorts of hidden costs, like the
fee they tried to charge me for shipping.) I think it is easier to
go with a standard sized PC and hide it in the room somewhere. If things
go wrong, it is easier to buy replacement parts to fix it up. On a
small system, one mistake might mean buying another case/motherboard
etc.
HTH,
Paul
