Power Supplt Watts help


G

Gabriel Knight

Hi all

Ive got a mobo - intel D915GAG/D915PSY , E210882 , I have the manual from
the net from somwhere sorry I cant supply a link but it dosnt say anything
about the power supplys wattage. I need to know if a 450 watt PSU will be ok
for it or dose it need to be higher? It will run a PCIE video card much
later when I sell it but for now it will use onboard video.

Thanks all
GK
 
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P

Paul

Gabriel said:
Hi all

Ive got a mobo - intel D915GAG/D915PSY , E210882 , I have the manual from
the net from somwhere sorry I cant supply a link but it dosnt say anything
about the power supplys wattage. I need to know if a 450 watt PSU will be ok
for it or dose it need to be higher? It will run a PCIE video card much
later when I sell it but for now it will use onboard video.

Thanks all
GK

It makes it easier, if you make an inventory list of what will be inside
the computer. If you want the power supply to run some video card
at some future date, then try and guess what that card will be.
You probably have a good idea whether it is a $100 card
or a $600 card. The processor and video card are major
consumers, but if you have enough disk drives, that
makes a difference too.

Paul
 
G

Gabriel Knight

It makes it easier, if you make an inventory list of what will be inside
the computer. If you want the power supply to run some video card
at some future date, then try and guess what that card will be.
You probably have a good idea whether it is a $100 card
or a $600 card. The processor and video card are major
consumers, but if you have enough disk drives, that
makes a difference too.

Paul

Ok thats true Paul but for now it will only run a single 80gig ide hdd,
onboard video and an ide dvd rom drive.
The cpu is a P4 3.0GHz dual core, other than all that will a 450 watt psu
work ok?

Thanks
GK
 
C

Charlie Hoffpauir

Ok thats true Paul but for now it will only run a single 80gig ide hdd,
onboard video and an ide dvd rom drive.
The cpu is a P4 3.0GHz dual core, other than all that will a 450 watt psu
work ok?

Thanks
GK

Of course, a lot depends also on the quality of the PS, but my guess
is that a 450 will be more than adequate. I base that on the fact that
my computer uses 4 hard drives, has 8 GB ram, and has a 450 watt PS,
and my wife's has one HD, 1 GB ram, on-board video and a 250 watt PS.
(both have DVD writers)

To get an accurate idea what you need, enter alll the information
about your system...

http://www.enermax.outervision.com/index.jsp

and their PS calculator will tell you just what you need.
 
L

larry moe 'n curly

Gabriel said:
The cpu is a P4 3.0GHz dual core, other than all that will a 450 watt psu
work ok?

2.8GHz P4 Dell GX270 Optiplex computers come from the factory with
just 250W PSUs, so 450W should be more than adequate, even with a
fairly high (but not very highest) performance graphics card. I'm
assuming the 450W rating is honest because with the typical $19.95 no-
name bargain PSU it's greatly exaggerated.
 
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P

Paul

Gabriel said:
Ok thats true Paul but for now it will only run a single 80gig ide hdd,
onboard video and an ide dvd rom drive.
The cpu is a P4 3.0GHz dual core, other than all that will a 450 watt psu
work ok?

Thanks
GK

I didn't expect the 450W would be a problem for you, but I like to work
with an inventory list, to show you how you can figure this out for yourself.
With no list, the details of the calculation can't be shown in any detail.

Your P4 is roughly an 89W processor. 89W/12V * (1/0.90) = 8.24 amps feeding
the Vcore circuit on the motherboard from the 12V rail. 0.6A for a hard drive.
0.5A for cooling fans. 1.5A for CDROM drive (only when media is in the tray).
So far, the 12V is 10.84A. You don't have much load in the PC right now, besides
your processor, so as the others have said, the 450W supply will be fine.
Check the label on the side, and see if it has 12V @ 15A minimum.

If the supply is a dual rail type, with 12V1 and 12V2, then 12V2 loading
right now is the 8.24 amps of the processor. The other loads, including
your future video card, if it needs 12V, will come from 12V1. Again,
check the label on the side of your 450W supply, and see if there is
enough amps rating on there.

To give some idea of other rails, on my S478 motherboard with a P4 in it,
it used 3.3V at 14 amps (I measured it while benchmarking). That is because
both the chipset and the DDR RAM were powered from that rail. As a result,
in terms of basic ratings on modern systems, I recommend 3.3V @ 20A and 5V @ 20A.
Only the most anemic of the high efficiency (80%+) type supplies, fail to
meet that. Most others will have sufficient rating printed on the label
of the supply.

In summary, these are basic ratings for something like you're building.
I can't calculate all the rails, and for the 3.3V and 5V, rely on a few
measurements I've made here, to bound the requirements.

3.3V @ 20A, 5V @ 20A, 12V @ 15A, plus have total power in watts sufficient for everything

For total power on your system, I have 89W * (1/0.90) + 12W + 25.5W + 6W + 10W
+ 50W = 196W. If you throw in a 60W video card, you're still in good
shape. (That previous calc is CPU + HDD + ODD + fans + standby_or_USB
+ motherboard_and_ram for 196W total.) As long as the current limits on
the individual rails are sufficient, as well as the total power is OK, then
you're fine.

I've seen one "bargain" 500W supply in the past, with a 12V @ 10A output
limit, and your loading even without a video card is 10.84A. So you can
see that the power number (500W) is not sufficient vetting of the product.
That bargain supply would fail to meet your requirements. That is why
I work out load current values for people, so they avoid inappropriate
junk. All the numbers printed on the power supply label are important.

Paul
 
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