Re: Psu - 500 Watt?
- From: nospam@xxxxxxxxxx (Paul)
- Date: Sat, 18 Feb 2006 12:42:09 GMT
In article <tink.23enyj@xxxxxxxxxxxxxxxxxxxxxxx>, tink
<tink.23enyj@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
I have a bit of a problem here.
First of all I did some more searchs for PSU calculators to find PSU
Watt requirements for my system. The results differed between 250W
&350W using different calcs. So to be safe I would think go towards the
higher end.
Anyway I read somewhere that they only do microATX PSUs up to 300W. So
doing searches I found a FSP PSU at 300W, two Athena PSUs at 350W and
450W and three SilenX PSUs at 300W, 400W and 450W.
The SilenX PSUs have S-ATA connections and I want the standard 4pin
connections so that rules them out.
I found the Athena PSUs on Newegg, however I'm in UK and they
dont ship internationally.
Which leaves me with the FSP 300W which I can get in the UK. I'm
wondering should I risk the FSP or just get a standard case and a
decent PSU? I'd rather just get the PSU because I specifically wanted
a smaller case but didn't realise PSUs would be so limited. Does anyone
know of any other microATX PSUs at 350W or over?
-- tink
<< from USENET >>
FSP Group FSP300-60GLS 300Watts P4 Micro ATX 12V with 20+4 pin B.B
http://www.newegg.com/Product/Product.asp?Item=N82E16817104904
+3.3V@18A, +5V@18A, +12V1@8A, +12V2@xxxxx, -12V@xxxx, +5VSB@2A
AFAIK, 12V2 powers only the processor. The 8A of 12V1 will be for
disk drive connectors, for the fans on the motherboard, and for
any 12V used on the motherboard.
To give you some idea on a processor, I have a 2.8GHz Northwood.
If I look that up on processorfinder.intel.com, it says 70 Watt
TDP. Using an ammeter, my 2.8Ghz draws 1.1 amps sitting idle in
Windows, and draws 6 amps doing multiple copies of Prime95 in Linux.
So the max measured was 72 watts, but on the input side to the
Vcore conversion, which would be roughly 65 watts at the processor
itself. In other words, the TDP is only an estimate - a better
crafted "CPUBurn" program might cause power consumption to exceed
TDP (thermal design power).
If I pick a 3Ghz LGA775 P4 processor, the TDP is 84W.
http://processorfinder.intel.com/scripts/details.asp?sSpec=SL7J6
84W/12V * (1/0.90) = 7.77 amps from 12V2 (90% conversion efficiency)
For your video card, the measured 12V is 4A. (See table at bottom
of page - click to enlarge.)
http://www.xbitlabs.com/articles/video/display/geforce6600gt-oc_3.html
The 4 amps flows through the pins of the video slot, and the source
will be the 12V1 output. That means you have used half the output
of 12V1.
Now, subtract from the remaining 12V1, some current for fans. This
should be less than 1 amp. The fan rating is printed on the label
of each fan.
According to Xbitlabs, the video card draws 1.5A when idle (BIOS).
Now, the hard drive analysis. To spin up a hard drive, takes 2 to 2.5
amps for the first 20 seconds. Then the current drops back to 0.5A
or so.
So, there are two points in time, to check power. First is
bootup time:
Video (1.5A) + HDD (2.5A) + fans (0.5A) = 4.5A of 8A available.
Second is run-time, say while gaming:
Video (4A) + HDD (0.5A) + fans (0.5A) = 5A of 8A available.
It looks "good to go".
A CD/DVD burner has a name plate rating of 1.5A from +12V. This
current will only flow while burning or to a lesser extent while
reading. You can see there is still enough room to run a single
optical drive.
You can see from the above analysis, that the 8 of 14.5 amps
used by the processor, means 5.5 amps of capacity are being
"wasted". The peripheral output, on the other hand, could use
the extra current. You should try to find an older Matx
supply, that doesn't split into 12V1 and 12V2.
You can use a 20 pin power plug, on a 24 pin motherboard. As
long as you are not using more than 6 amps flowing through
the 12V wire on the 20 pin connector, you would be OK. In
your case, the current would be 4 amps for video plus maybe
0.5 amps for fans, so there is current carrying capacity left.
You do not need to use an adapter cable if the power supply
has a 20 pin connector.
So, now we try a PSU with single 12V output:
FSP Group FSP270-50SNV-R P4 Micro ATX 270W (oversized - check
dimensions before buying)
http://www.newegg.com/Product/Product.asp?Item=N82E16817104905
+3.3@xxxxx,+5V@25A,+12@16A,-12V@xxxx,+5VSB@2A
In this case, 12V@16 amps is used for all loads. At boot time,
CPU will be at half power or so (BIOS is typically neither a
minimum nor a maximum power consuming state). We'll use full
power for the calculation anyway, just to be safe.
CPU (7.8) + video (1.5) + fans (0.5) + hdd_spin (2.5) = 12.3 of 16A
Then, at run-time while gaming:
CPU (7.8) + video (4) + fans (0.5) + hdd_idle (0.5) = 12.8 of 16A
Again, there is still enough room to run an optical drive.
I have not attempted to calculate +3.3 and +5V, because there isn't
enough data to do so. A hard drive uses a little more than 1 amp
from +5V, for the controller. An optical drive is rated for 1.5 amp
from +5V. But other estimates are unknowns.
On my P4C800-E motherboard (P4 S478), 3.3V max current measured is
14.4 amps. The motherboard runs the DDR memory from that supply. My
idle current on 3.3V is 8 amps or so. That was with four sticks
of 512MB memory. Both power supplies have enough 3.3V current (just
barely) to do the job. Two sticks of RAM drops the current to
11.6 amps or so on 3.3V. My motherboard has no appreciable +5V
consumption to speak of.
How the 3.3V and 5V will be used on other motherboards, will vary
from design to design. I doubt your board will be greedier than
mine. Reducing the number of memory sticks, helps a little bit.
I also have a motherboard that powers the processor from +5V (it
has no 2x2 ATX12V connector), and the +5V required could only
be met by the FSP 270W example supply above. In the Matx world,
you likely won't find "one size fits all" in power supplies.
Summary:
MicroATX and small computer cases require power budgeting
for which insufficient data is available for exact calculation.
There will always be a danger, that the supply you buy will not be
sufficient for the job. A more complete Takaman style web site
would be required to do a better job of estimation.
Paul
.
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