Sizing a power supply

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MikeB

Hi all,
I'm planning on building a new computer as a bit of a pastime. One of
the interesting obstacles that I came across is that I can't find any
guidance on how to size the power supply.

I'm planning on an Intel Core 2 Duo E6700, an Intel DB975XBX
motherboard, possibly 2G of Ram, 2 SATA drives, a video card (not
high-end, I'm not into gaming - just good enough to run Vista Aero
interface) and a wireless PCI card.

I have no idea how to adequately size the power supply. The intel specs
for the Mobo says that the max power consumption of the mobo fully
loaded (with all the USB ports drawing power, etc.) is 750 watt! The
minimum is 300w.

I also know that the CPU will use max of 65w (per specs), but I assume
this (or a larger factor for the older Pentium models) is included in
the above consumption levels. I've not yet looked at the draw for the
memory, but again, I assumed that would be included (up to the max 8GB)
in the board specs. Also allowed in the spec is 2Amp per PCI slot,
which is adequate.

So all that is left is to figure how much over the 300w I need to shoot
to support the CPU running at full load, with the drives added.

Any advice? Thanks!
 
My advice is not to get too wrapped around the axle over power
consumption details. If it were me, I'd probably wave my arms around a
bit a pick a number depending on budget...

You're not getting SLI which would present a substantial additional
power drain (If you were I'd recommend 750W.) and the rest of it seems
pretty normal. Depending on your budget, accept no less that 500W and
take a serious look at 650W.
 
MikeB said:
Hi all,
I'm planning on building a new computer as a bit of a pastime. One of
the interesting obstacles that I came across is that I can't find any
guidance on how to size the power supply.

I'm planning on an Intel Core 2 Duo E6700, an Intel DB975XBX
motherboard, possibly 2G of Ram, 2 SATA drives, a video card (not
high-end, I'm not into gaming - just good enough to run Vista Aero
interface) and a wireless PCI card.

I have no idea how to adequately size the power supply. The intel specs
for the Mobo says that the max power consumption of the mobo fully
loaded (with all the USB ports drawing power, etc.) is 750 watt! The
minimum is 300w.

I also know that the CPU will use max of 65w (per specs), but I assume
this (or a larger factor for the older Pentium models) is included in
the above consumption levels. I've not yet looked at the draw for the
memory, but again, I assumed that would be included (up to the max 8GB)
in the board specs. Also allowed in the spec is 2Amp per PCI slot,
which is adequate.

So all that is left is to figure how much over the 300w I need to shoot
to support the CPU running at full load, with the drives added.

Any advice? Thanks!
Click to expand...

You're not asking the right question. A good 300W power supply might be OK,
whereas a cheap 600W will beg for mercy. It's not the WATT level that
counts, its the amps per rail. And even if the amps per rail look OK, how
long will the power supply last? (good name brand helps here)

You know that X is greater than 300W. That's not very helpful. Choose your
video card next, see what it says you need. Specifically, look for +12V
rail requirement, listed in AMPS. Also see what connectors are required for
both the mainboard AND video card.

Then you'll be a lot closer. Let's say the video card recommends 450W
minimum and 30A minimum on 12V rail. Now you're getting somewhere. Find a
power supply with all the right connectors that is 450W minimum, has 30A or
more (combined) on all +12V rails, and is a good name brand (enermax,
seasonic, fortron) and you've got a winner.

Note that recommendations by video card manufacturers include a generous
fudge factor to account for other system components (mainboard, cpu, drives,
RAM, etc.). So the minimum or "suggested" power supply specs. for the video
card is a pretty good indicator of exactly what you will need. -Dave
 
MikeB said:
Hi all,
I'm planning on building a new computer as a bit of a pastime. One of
the interesting obstacles that I came across is that I can't find any
guidance on how to size the power supply.

I'm planning on an Intel Core 2 Duo E6700, an Intel DB975XBX
motherboard, possibly 2G of Ram, 2 SATA drives, a video card (not
high-end, I'm not into gaming - just good enough to run Vista Aero
interface) and a wireless PCI card.

I have no idea how to adequately size the power supply. The intel specs
for the Mobo says that the max power consumption of the mobo fully
loaded (with all the USB ports drawing power, etc.) is 750 watt! The
minimum is 300w.

I also know that the CPU will use max of 65w (per specs), but I assume
this (or a larger factor for the older Pentium models) is included in
the above consumption levels. I've not yet looked at the draw for the
memory, but again, I assumed that would be included (up to the max 8GB)
in the board specs. Also allowed in the spec is 2Amp per PCI slot,
which is adequate.

So all that is left is to figure how much over the 300w I need to shoot
to support the CPU running at full load, with the drives added.

Any advice? Thanks!
Click to expand...

The 65W processor would be 65W/12V * (1/0.90) = 5.4 amps from 12V2, at
an assumed 90% conversion efficiency by the motherboard Vcore converter.

You could allocate 0.5A for fans. A hard drive draws 0.5A at idle.
A CD/DVD draws a max of 1.5A.

Low to mid range video cards might be 30W. Xbitlabs has a number of
articles, where they measure the power. Even if we allocate 3A for
video, the system power is not very high.

Everything except the processor is on the 12V1 rail. Assuming you
buy a power supply with dual rail output and a 24 pin connector
to match your 24 pin powered motherboard.

The total current in the above minimal system
= 5.4 + 0.5 + 0.5 + 1.5 + 3A = 10.9A

Current for 12V2 is 5.4A, and 0.5 + 0.5 + 1.5 + 3A = 5.5A for 12V1.

Even a modest supply with a 15A total output would work in this case.
That would typically be in the range of a 350W supply.

Let's study a cheap supply for a moment. This supply is decent for
a cheapy, with the only limitation of units like this being the
cables aren't long enough.

http://images10.newegg.com/NeweggImage/productimage/17-104-951-03.JPG

3.3V @ 20A 5V @ 20A 12V1 @ 16A 12V2 @ 16A +5VSB @ 2A -12V @ 0.6A
3.3V & 5V to 120W maximum. 12V1 & 12V2 to 254W maximum. (And unit is
a 300W supply, which is a limitation of all outputs together.)

If the 5V draws 20 amps, that leaves only 20W limitation for the 3.3V,
which would be 6 amps for 3.3V. Thus, the overall power rating has
more influence there, than the max current rating. Since it is pretty
hard to estimate 3.3V and 5V consumption, all we can use is extrapolation
from previous systems. I've measured two systems, and one draws 50W
on 3.3V and 5V, the other draws 100W (but that system powers an AthlonXP
processor from 5V). The 120W limit above would seem to be enough to
run a minimal system, even with a few more watts wasted running a
bunch of PCI Express lanes.

The 254W limit (if I read that number from the image correctly), would
seem to limit 12V1 and 12V2 to about 10amps output each. The minimal
system calculation above, was 5.4A for 12V2, and 5.5A for 12V1. We
still seem to be in good shape.

Even if we estimate 100W for 3.3/5V consumption, and 130W for the
12V loads, that is still only 230W. And like a pessimistic estimate
at that.

The Intel BadAxe motherboard is capable of holding a boatload of
high power hardware. That is where the extraordinarily high power
rating comes from. You should stuff a P4 Netburst dual core processor
on there, which would draw twice the power of your Conroe/Allendale.
Video cards now range up to 120W a piece. So those are the kinds
of components that raise the power to astronomical levels.

Your system is a modest one, and it is even possible the power supply
that comes with a computer case, could run it. My personal preference,
is to select a brand name supply at the price of $50 or more, to
get something better than bargain basement quality. What you
buy is your choice of course. It doesn't look to me like the power
level would be too much of an issue.

This doesn't look too bad and is $42. The reviews look good. Other
name brands are Enermax, Antec, Seasonic etc. There are a
ton of other brands I would not touch, and new brands pop up
every day, trying to sell the cheap stuff.

FSP Group (Fortron Source) AX400-PN, RoHS, 12cm FAN, version 2.0
2 SATA, 20+ 4 pin, PCI Express, 400W Power Supply - Retail

http://www.newegg.com/Product/Product.asp?Item=N82E16817104953

Paul
 
MikeB said:
Hi all,
I'm planning on building a new computer as a bit of a pastime. One of
the interesting obstacles that I came across is that I can't find any
guidance on how to size the power supply.

I'm planning on an Intel Core 2 Duo E6700, an Intel DB975XBX
motherboard, possibly 2G of Ram, 2 SATA drives, a video card (not
high-end, I'm not into gaming - just good enough to run Vista Aero
interface) and a wireless PCI card.

I have no idea how to adequately size the power supply. The intel specs
for the Mobo says that the max power consumption of the mobo fully
loaded (with all the USB ports drawing power, etc.) is 750 watt! The
minimum is 300w.

I also know that the CPU will use max of 65w (per specs), but I assume
this (or a larger factor for the older Pentium models) is included in
the above consumption levels. I've not yet looked at the draw for the
memory, but again, I assumed that would be included (up to the max 8GB)
in the board specs. Also allowed in the spec is 2Amp per PCI slot,
which is adequate.

So all that is left is to figure how much over the 300w I need to shoot
to support the CPU running at full load, with the drives added.

Any advice? Thanks!
Click to expand...

Here are some online calculators that might help...
http://www.journeysystems.com/power_supply_calculator.php
http://www.extreme.outervision.com/psucalculator.jsp
 
Get the biggest you can afford but certainly not less than 500 watts. Or
you'll be putting up another post wondering why nothings working like lots
of other posters here. Its a no brainer. Ge the biggest and no more worries
for many many upgrades. Stick to Antec, Enermax, PC Power and Cooling, OCZ,
not the cheapoes as so many claim work just as good.

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A64 3500+, Gigabyte GA-K8NSC-939,AIW 9800 128mb
MSI 550 Pro, X-Fi, Pioneer 110D, 111D
Antec 550 watt,Thermaltake Lanfire,2 Gb Dual Channel OCZ
2XSATA 320gb Raid Edition, PATA 120Gb
XP MCE2005, 19in Viewsonic,BenchMark 2001 SE- 19074
Games I'm Playing- Falcon 4, winSPWW2, winSPMBT
 
So all that is left is to figure how much over the 300w I need to shoot
to support the CPU running at full load, with the drives added.

Any advice? Thanks!
Click to expand...

I haven't seen anyone except idiots recommend anything under 500
watts in a LONG time.

If you're using a modern cpu, the manufacturers tell you to start at
500 watts and go up depending on your video cards.
 
OK, all the responses have been really helpful and I now know a lot
more about PSUs than I did before. I am, however, no nearer to making
up my mind, so I'd like to tap the collective wisdom of the ng some
more.

Case: I'm interested in some bling, so I'd like a case with a side
window. I'm planning on getting one of these from Aspire (now known as
Apevia): http://tinyurl.com/yakyma . I have one into which I
transferred the innards of an older PC when I thought that PC's problem
was overheating, so I really like the case, even though I hardly ever
see it mentioned on the web or in reviews.

Power supply: Aspire also have some PSUs and I kinda like this one
(http://tinyurl.com/ymob6x), but I'd also rather have modular power
connectors to cut down on cable clutter, so I'm thinking the Antec
NeoHE 500 or even the 430 (http://tinyurl.com/g5cy6). Also on my
shortlist is the Seasonic S12 Energy Plus series
(http://www.seasonicusa.com/s12plus.htm), but I can't quite figure out
whether it has modular cabling. If not, I'd probably spring for the M12
series that does have modular cabling.

Video card: Here I'm completely at sea. All I know is that I'd like one
that is able to support Aero in Windows Vista and is HDMI compliant
(whatever that means). I think the two big names are Nvidia or Radeon,
but I've heard mention of ATI as well. I'm not a gamer, so all I need
is for the video card to support a display up to 1600x1200 and be able
to perhaps at some point in time output some HDTV if I get around to
installing a TV tuner card or some interface/intercept of my satellite
TV system. So I guess I need something in the 128-256M memory range,
but further than that I can't go, the options and numbers are just too
confusing for a neophyte. The video card in my other system is an
nVidia, so I guess I have some sort of preference for that since I've
not had trouble with it (but it's an older system and the card only has
32M on it).
 
MikeB said:
OK, all the responses have been really helpful and I now know a lot
more about PSUs than I did before. I am, however, no nearer to making
up my mind, so I'd like to tap the collective wisdom of the ng some
more.

Case: I'm interested in some bling, so I'd like a case with a side
window. I'm planning on getting one of these from Aspire (now known as
Apevia): http://tinyurl.com/yakyma . I have one into which I
transferred the innards of an older PC when I thought that PC's problem
was overheating, so I really like the case, even though I hardly ever
see it mentioned on the web or in reviews.
Click to expand...

Looks good.
Power supply: Aspire also have some PSUs and I kinda like this one
(http://tinyurl.com/ymob6x),
Click to expand...

Not only no, but HELL NO
but I'd also rather have modular power
connectors to cut down on cable clutter, so I'm thinking the Antec
NeoHE 500 or even the 430 (http://tinyurl.com/g5cy6). Also on my
shortlist is the Seasonic S12 Energy Plus series
(http://www.seasonicusa.com/s12plus.htm), but I can't quite figure out
whether it has modular cabling. If not, I'd probably spring for the M12
series that does have modular cabling.
Click to expand...

All good ideas. No, S12 is not modular, but it is by far the best of the
ones you mentioned.
Video card: Here I'm completely at sea. All I know is that I'd like one
that is able to support Aero in Windows Vista and is HDMI compliant
(whatever that means). I think the two big names are Nvidia or Radeon,
but I've heard mention of ATI as well. I'm not a gamer, so all I need
is for the video card to support a display up to 1600x1200 and be able
to perhaps at some point in time output some HDTV if I get around to
installing a TV tuner card or some interface/intercept of my satellite
TV system. So I guess I need something in the 128-256M memory range,
but further than that I can't go, the options and numbers are just too
confusing for a neophyte. The video card in my other system is an
nVidia, so I guess I have some sort of preference for that since I've
not had trouble with it (but it's an older system and the card only has
32M on it).
Click to expand...

Just about any current card will support Aero. HDMI is a new type of
connector, used for High-def displays. I don't know why you'd need this
connector specifically. Most current video cards will drive a HDTV, just
not with an HDMI connector. The HDMI includes other information that
wouldn't be processed by a video card anyway. Radeon is a model name of ATI
card. Not to confuse you, but ATI (who makes the radeon line) is now owned
by AMD, the CPU manufacturer. I'd recommend the following. No HDMI, but I
think you'd be really happy with it, assuming your mainboard has PCI-Express
X16 slot:

http://www.newegg.com/Product/Product.asp?Item=N82E16814130062

If you ever need an HDMI connector on a PC, you'd be more likely to connect
HDMI equipment to an optional expansion card, like a TV tuner or DVD
hardware decoder or something like that. -Dave
 
MikeB said:
Hi all,
I'm planning on building a new computer as a bit of a pastime. One of
the interesting obstacles that I came across is that I can't find any
guidance on how to size the power supply.

I'm planning on an Intel Core 2 Duo E6700, an Intel DB975XBX
motherboard, possibly 2G of Ram, 2 SATA drives, a video card (not
high-end, I'm not into gaming - just good enough to run Vista Aero
interface) and a wireless PCI card.
Click to expand...

Your power needs seem to be rather ordinary. I would buy a PSU/case
combo to save $30 to $50. Check newegg for reviews of namebrand combos
(e.g. Antec). Look at the models with a lot of reviews from the past
year (read: newer, more popular models). Choose from those one whose
power output is near the top of the range (or at least average) for
those models. Above all, do not buy a cheapo supply even if it has a
high power rating.
 
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