Timothy Murphy wrote:
ed@xxxxxxxxxx wrote:
Also, match the power supply to the load. If you only need 50 watts,
do not buy a 400 watt power supply. I think I have a 150 or 200 watt
power supply in my VIA C3 computer, LPX form factor.
While you don't need a huge supply, one bigger than your current needs
gives you more room to play with later on, if you have to add something,
or the power supply gets a bit sick. The wattage is the capacity of
what it can deliver, not that it's always going to draw 400 Watts from
the mains and be a drain on your electricity bill.
You are correct, that at 400 watt power supply does not always draw 400
watts from the wall. But the efficiancy of the power supply is less when
how running at full power. Take this article for example:
http://www.silentpcreview.com/article263-page4.html
The 300 watt power supply leaks 12 watts when the computer only needs 40
watts.
Probably an ignorant question,
but if one is talking about a mini-ITX system,
will a cheap external AC power adaptor do the job,
like those incorporated into a power plug, eg
<http://www.mini-box.com/60w-12v-5A-AC-DC-Power-Adapter_2?sc=8&category=13>?
I'm an EE and I know that every power supply made today for computers is one of the switching types. They ALL have a device designed to switch any AC voltage from about 90 to 240 VAC.
The switched waveform is very fast. We use 60 Hz here and this power
supply switches at 16,000 Hz. Some nice things happen at that high
frequency, like transformers get small. So you can make a transformer
that puts out the proper voltage to make plus 5 volts and plus 12 volts
and others that are regulated.
If you measure the power input to a switcher with no load you will
discover it's quite low, like 30-40 watts. This is wasted power just to
run the power supply with no output. But if you put a computer load on
the supply it will be directly sent to the AC load but with very small loss.
So if you buy a 450 Watt power supply to run a server that does
nothing most of the time, the power supply will not draw 450 watts. It
will draw perhaps 100 Watts. This is good. The power supply is lightly
loaded and will last much longer than if it is drawing 400 watts.
So do not worry about what the power supply is rated at. It will
adjust to a smaller load.
--
Karl F. Larsen, AKA K5DI
Linux User
#450462 http://counter.li.org.
