scully said:
hi
what do we need as far as a psu for this machine?
computer spec:
Case COOL MASTER ELITE 330
Motherboards Gigabyte P35-DS3L ATX
Processor INTEL CORE 2 DUO E6850
Memory 4 gigabytes ddr 667
Hard Disks SAM 500GB SATAII HDD x3 units
CD/DVD DVD WRITER DUAL x2 units
Sound SoundBlaster Xfi elite pro
Video Gigabyte 8800GTX 768 meg
Keyboard ms key mouse wireless desktop 6000
Monitor Samsung 24 wide 244T
Card reader Generic
OS XP HOME SP2+
usb port up to total 12 Generic - integrated
thanks
scul
12V @ 1.5A, 5V @ 1.5A Estimate for an optical drive.
http://sony.storagesupport.com/dvdrw/downloads/dru720a/DRU720A_UG.pdf
Hard drive 12V @ 0.6, 5V @ 1A (had to make this one up - web sites are crappy)
Hard drive peak startup current 12V @ 2.5A for first 10 seconds (Seagate)
Samsung - no specs.
E6850 - 65W / 12V * (1 / 0.90) = 12V2_current = 6.02A at 90% Vcore efficiency
http://processorfinder.intel.com/details.aspx?sSpec=SLA9U
RAM 3.4W per stick, 13.6W total
http://www.valueram.com/datasheets/KHX5400D2_1G.pdf
Motherboard - adjusted to make a total of 50W for mobo and RAM, so 36.4W
Hard to get numbers for this.
Gigabyte 8800GTX - three sources totals 127.6W / 12V = 10.6A
http://www.xbitlabs.com/images/video/msi8800gts-640/8800gtx_full.gif
Soundblaster - allocate 5W
Add them up.
Two opticals (12V @ 1.5A)x2 (5V @ 1.5A)x2 Total 12V1 @ 3.0A plus 15W for lower rails
Three HDD (12V @ 0.6A)x3 (5V @ 1A)x3 Total 12V1 @ 1.8A plus 15W for lower rails
Fans 12V @ 0.5A estimated Total 12V1 @ 0.5A (for three small fans)
RAM 13.6W for lower rails
Motherboard 36.4W for lower rails
Soundblaster 5 W for lower rails
Processor 12V @ 6.02A Total 12V2 @ 6.02A
8800GTX 12V @ 10.6A (3.3V @ ~1A) Total 12V1 @ 10.6A 3W for lower rails
Standby 5VSB 5W for lower rails
Grand total: 12V2 @ 6.02A \_ 263W + 93W = 356W total power
12V1 @ 15.9A /
93W for lower rails
The above assumes:
1) Both optical drives burning at the same time. Not really likely. Could drop motor
power from one unit for a more realistic estimate. Say gaming with key disk loaded
into one of the drives.
2) Estimate is developed, assuming a gaming situation, with maxed 3D and processor.
3) A second test case, is the first 10 seconds of operation. The three hard drives
could draw up to 2.5A starting current each. But, at idle, the video card drops by
5 amps, and the processor current is also much lower. So in this case, there
is no point doing a second calculation of startup current levels. It will be
less than the gaming test case.
What does "lower rails" mean ?
3.3V and 5V are examples of lower rails. The motherboard designer could use either.
Usually, the two of them have a combined power rating in watts, and each output has
an ampere limit. By the time you buy a big enough supply to run the video card,
usually the "lower rails" are big enough to do the job. My cutoff for them, is
at about 3.3V @ 20A, and 5V @ 20A. In the case of this build, the 93W number
makes me want to aim a bit higher. 25A to 30A would probably cover it, in the
sense that then, I no longer care which rail it all comes from. I've measured
a couple motherboards, and in fact, designs can vary wildly (one used 3.3V and
the other leaned on 5V).
The 12V rails are not "balanced" in any sense. In terms of value for money,
a power supply with a single rail, makes better use of the amperage capability.
The 12V1 at 16 amps, means you might get a supply with 12V1 @ 16A and 12V2 @ 16A
and the 12V2 is hardly loaded at all. If you had a 130W processor, the balance
would be a bit better, and an ATX 2.0+ type supply wouldn't seem like such a
stupid purchase.
In this case, the connectors also play a role. We need a pair of 2x3 PCI Express
connectors, judging by pictures of 8800GTX on Newegg.
OK, now to analyse a supply for acceptable characteristics.
ENERMAX EG495AX-VE FMA ATX12V Ver 2.2 485W Power Supply $80 (and there is a rebate)
+3.3V@32A,+5V@32A,+12V1@22A,+12V2@22A,
[email protected], +5VSB@3A
170W max on 3.3/5 384W max on 12V1/12V2 485W max for full supply.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817194015
The 3.3V and 5V peak ratings are excellent, and even if the entire 93W of
the lower rails came from either output, it would be handled with ease.
Similarly, the 170W max is greater than the 93W load.
On 12V, our total power is 263W. This is less than the 384W limit. Using
about 2/3rds of the capacity here. 12V1 is rated 22A, and the load is 15.9A,
so that one is OK.
Total system power is 356W and that is less than 485W. The supply is
basically running at 75% of total capacity, which is high, but would be
OK if the unit was a quality design (i.e. a $20 500W supply would pop if
you did this).
The only concern I might have, is the second reviewer (running an 8800GTS)
commented about the exhaust temp of the PSU. That supply does not have a
stated efficiency, and it could be 70%. But searching for an 80%
efficient supply, generally adds quite a bit to the price. But it is
only $80 (less after rebate).
This thing is currently $120. I picked this one, because I got tired of
looking at quad rail supplies on Newegg. This has one output rail and
is labeled as such. Other supplies cheat and you never know for sure how
they are constructed. And I'm not going to waste my time looking for a
reviewer who has opened each one up. For $40 more, you get a more
efficient supply, with perhaps a lower operating temp. If the manufacturers
of quad rail supplies would document them, there'd be more recommendations
for them.
+3.3V @ 24A +5V @ 30A +12V @ 49A -12V @ 0.8A +5VSB @ 3A 83% efficient
http://www.pcpower.com/products/viewproduct.php?show=S61EPS
http://www.pcpower.com/products/assets/S61EPS/S61EPS2.jpg
http://www.pcpower.com/prices/
HTH,
Paul
