Re: Power supply sizing for a new Athlon X2 2700 system

On Thu, 05 Feb 2009 20:34:45 -0500, Paul <nospam@xxxxxxxxxx> wrote:

Al Dykes wrote:
I haven't built a system from scratch for years. I want a "better"
desktop system for Photoshop and to run VMware VMs for servers that
are modest by today's hardware speeds. No games, no heavy 3d. I know
that 4GB memory is enough for what I do.

In addition to the mobo, I plan on
up to 3 SATA drives,
a Blue-Ray
a CD/DVD burner.
A couple fans.

Is this an approprate PSU? Any other comments are welcome.

PSU: Antec earthwatts EA500 500W ATX12V v2.0 SLI Certified CrossFire Ready
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371007&Tpk=Earthwatts%20500W

CPU: AMD Athlon 64 X2 7750 Kuma 2.7GHz 2 x 512KB L2 Cache 2MB L3 Cache Socket AM2+ 95W
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103300

MOBO: ASUS M3A78-T AM2+/AM2 AMD 790GX HDMI ATX AMD Motherboard - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131331

MEMORY Memory (4 GB total)
OCZ OCZ2RPR10662GK 2gb kit (1gb x 2) pc2-8500 1066mhz 5-5-5-15 240-pin ddr2

VIDEO: on-board video with option to put one mid-range Video card in
without stressing the PSU.


Thanks.


High end video would be 265W. A mid range card (55nm technology), might be
about 80W or so. So what you eventually decide to buy will make a difference.

3 SATA drives 5V @ 1A + 12V @ 0.6A, roughly 36W

For Bluray, I found a picture of the label on the product, and I
think it says 5V @ 1.9A and 12V @ 3A. A previous number I had in
mind was 12V @ 2.5A.

http://www.cdrlabs.com/Reviews/lg-ggw-h20l-super-multi-blue-blu-ray-disc-rewriter-hd-dvd-rom/All-Pages.html

For CD/DVD, I use 5V @ 1.5A and 12V @ 1.5A. I've measured my
CDRW at 12V @ 1A with media inserted and spinning.

For fans, I allocate 12V @ 0.5A, but you can read the numbers off
the fan hub to be sure.

For motherboard and memory combined, I allocate 50W, coming from the
lower voltage rails (3.3V or 5V). Usually the 3.3V and 5V rails on the
supply are not a limiting factor.

*******
12V2 - powers the CPU. 95W/0.90 = 105.6W, 105.6W/12V = 8.8A of 17A available.
(The 0.9 factor is 90% conversion efficiency on Vcore.)

12V1 - powers everything else 12V related. I set the CD/DVD to 0.0A
in the following, because if you're using the Blu-ray, then
the CD/DVD tray is probably empty.

80W_video/12V + 3*0.6A + 3A + 0.0A + 0.5A = 6.7+1.8+3.0+1.5+0.5= 12.0A of 17A available

System power estimate (includes the 5V things not counted yet, includes
5V @ 2A for 5VSB standby).

(all 12V loads) 12V * (8.8A + 12.0A) = 249.6W
mobo+RAM 50W 50.0W
SATA_5V 3*5W = 15.0W
Blu-ray_5V 5V*1.9A = 9.5W
CD/DVD_5V 5V*1.5A = 7.5W
+5VSB (USB/WOL) 10W = 10.0W
--------------- ------
Total 341.6W

So your new supply looks good. Even with my bloated estimates.
You supply passes on the 12V1 and 12V2 calculation, and also on
total power. And your 3.3V/5V are not likely to tax the supply
limits - I cannot provide a precise way of working that out,
and my 50W estimate is based on measuring a couple motherboards
here. That is the best I can do.

Some power supply estimator sites give double my estimates. Which
is why I try to do them myself. I've seen outrageous numbers
like 25W for RAM, when you can get real numbers much smaller in
size. This is some RAM I bought today - 2W per 2GB module. The
power numbers quoted for RAM, are usually based on the "standard
industry cycle mix". RAM gets hotter doing some things, than
others. The 2W number is representative.

http://www.valueram.com/datasheets/KVR800D2N5K2_4G.pdf

Paul

Great information, Paul. Thanks!

NRJ - just butting in...
.