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Real Watts???

E

East-of-lake

Jan 1, 1970
0
Since I haven't popped the $100+ for a Watts Up meter I was wondering if
anyone could answer the following:

If I have a PC with a 350 Watt power supply will is draw 350 watts or should
I add up the draw of each piece (motherboard, floppy, CD/DVD, hard drive,
etc)? It's the etc that's particularly difficult as many peripheral cards
don't bother giving you power consumption figures.

Also I have a UPS and was wondering what it's "parasite" load is once it's
fully charged and just passing on the power to the PC.

Thanks for your help.
 
D

daestrom

Jan 1, 1970
0
East-of-lake said:
Since I haven't popped the $100+ for a Watts Up meter I was wondering if
anyone could answer the following:

I bought a 'Kill A Watt' meter for <$40
If I have a PC with a 350 Watt power supply will is draw 350 watts or should
I add up the draw of each piece (motherboard, floppy, CD/DVD, hard drive,
etc)? It's the etc that's particularly difficult as many peripheral cards
don't bother giving you power consumption figures.

The 350 Watt power supply is rated for a *maximum* of 350 Watts. I doubt
that any 'average' PC draws anything like that. My Dell draws about 80
(measured with the aforementioned Kill-A-Watt). But the monitor draws
another 70 when its on. Don't forget about that. And cable modem, network
hub, whatever else you might want to use ;-)
Also I have a UPS and was wondering what it's "parasite" load is once it's
fully charged and just passing on the power to the PC.

Sorry, can't help you here.

daestrom
 
W

William P.N. Smith

Jan 1, 1970
0
East-of-lake said:
Since I haven't popped the $100+ for a Watts Up meter I was wondering if
anyone could answer the following:

Well, _my_ wife loves me, so I got one for Xmas! 8*)
If I have a PC with a 350 Watt power supply will is draw 350 watts or should

No, it'll be much lower than that, unless you are near or at the limit
of the supply, in which case it may draw slightly more than that...
I add up the draw of each piece (motherboard, floppy, CD/DVD, hard drive,
etc)? It's the etc that's particularly difficult as many peripheral cards
don't bother giving you power consumption figures.

Well, that's a good starting point (except as you note the number is
hard to come by), but then you need to divide by the efficiency of the
power supply, which will give you a slightly higher number.
Also I have a UPS and was wondering what it's "parasite" load is once it's
fully charged and just passing on the power to the PC.

My system, with an Antec True 380S
P4-2.4/800
1G memory
GigaByte GA-8KNXP motherboard
2 35G Raptor drives
Radeon 9800 Pro
Floppy, dual optical drives, fans, etc

draws about 3W in "off" mode,
hits a startup surge of 457W,
stays pretty much under 200W while booting,
sits idle at about 135W
sits barely under 200W when playing HalfLife
is about 4W when in S3 (suspend to RAM) mode

My APCC BackUPS Pro 650 draws about 11W by itself while in
float-charge mode.
 
R

Redmondite

Jan 1, 1970
0
"Watts" the difference between the Watts Up and the Kill a Watt?
 
S

steve

Jan 1, 1970
0
Load drawn by the computer power supply is dependent upon the power
demands of the cards in it plus some overhead due to less than 100%
efficiency of the power supply.

Typical computer power supplies are around 90% efficient, so at most,
with a full 350 watt load your computer power supply would draw 350/.9
or 389 watts. It will be less because the cards inside the computer are
not likely to draw all 350 watts.

The ups will draw only slightly more power than the power drawn out of
it -- UPS efficiencies are higher than 90% at full load.

So assuming a 90% efficient ups (at 389 watts output load) the total
would be 389/.9 or about 432 watts.

Don't forget the monitor and other peripherals too.

Yes, the manufacturers of the cards inside your PC don't do a very good
job of reporting the power required most of the time. You may find the
current required on each power supply voltage if you look carefully. I
have found that hard drive manufacturers often do a good job of
reporting total power required.

Steve
 
W

William P.N. Smith

Jan 1, 1970
0
steve said:
The ups will draw only slightly more power than the power drawn out of
it -- UPS efficiencies are higher than 90% at full load.

Actually, when the power is on, the UPS isn't drawing any power except
what it takes to float charge the batteries.
Yes, the manufacturers of the cards inside your PC don't do a very good
job of reporting the power required most of the time. You may find the
current required on each power supply voltage if you look carefully. I
have found that hard drive manufacturers often do a good job of
reporting total power required.

Plus their numbers are probably the maximum power consumption of the
card, not what it'll do under real-world conditions. Hard drives will
draw a lot less when just spinning than they will when starting or
working hard...
 
W

William P.N. Smith

Jan 1, 1970
0
Redmondite said:
"Watts" the difference between the Watts Up and the Kill a Watt?

I got the Watts Up Pro, which has a small (1K points) data memory and
a serial connection for downloading data logs. Good box for the
price, though a bit kludgey in the software department, which reminds
me, I've got to get the latest software... [Nope, still doesn't save
graph background or landscape print settings, oh well...]

Watts Up will lose it's data if unplugged or the power fails (though
the Pro will keep it's data log), and it has a cord instead of
plugging into the wall directly.

Essentially the Watts Up is a little nicer and more expensive.
Imagine, you get what you pay for! 8*)
 
R

Redmondite

Jan 1, 1970
0
wolfhedd said:
they pretty much explained it, but to put it a little more clear, a
powersupply has two rating, its draw, and its supply. any thing that uses
electricity has a draw, but not necessarily a supply. something specific as
a "powersupply" is made to supply power so you need to know just how much it
can supply, thats 350 watts max in your case. another example, look at a
duracell, its "supply" is 300mA, it doesnt have a draw.
components draw electricity, and we look at their specifications to find
this. add all current draw ratings up to get total theoretical current
draw. Heat is a big factor factor as components overheat like when they are
real dusty variances change altering the current draw.
dont forget to add the current DRAW of your power supply if you want to
figure draw all the way to the wall outlet of your PC.
wolfhedd
Well my original question is pretty much answered. But I've realized that
there's a second question that the answers raise:

If (for example) the components of a system (PC, stereo, whatever) draw 170
watts are you better off using a 200 watt power supply running near it's
rated load or a 350 watt supply loafing along? What about the power
supply's life expectancy?

The question's not theoretical since I have to upgrade my PC and had been
planning on a new case/PS because the current one is a 200 watt box. I'll
be running MB, FD, HD, CD/DVD
 
W

William P.N. Smith

Jan 1, 1970
0
Redmondite said:
If (for example) the components of a system (PC, stereo, whatever) draw 170
watts are you better off using a 200 watt power supply running near it's
rated load or a 350 watt supply loafing along? What about the power
supply's life expectancy?

Well, there's a tradeoff here. From an efficiency standpoint you are
better off matching your power supply capability to your load, but
many supplies are (ahem) agressively rated, and every supply will have
a significantly longer lifespan if run at a fraction of its' rating.
RUnning close to the rating also means you'll have trouble adding
peripherals afterwards. I'd load a power supply at about 1/2 to 3/4
if I were to plan ahead. [I didn't, but ended up at about 1/2
anyway!]
 
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