Adam said:
To summarize:
1) Startup current is higher than normal. Startup current
can stress the limits of the power supply. 2.0A or perhaps
2.5A from +12V is a typical number for the first 10 seconds.
2) On a desktop, the drives will be "idle" most of the time,
so an idle power estimate may be sufficient for doing
thermal estimates.
3) I've noticed a disturbing trend, to not providing real
power information. In the past, drive manufacturers have
been pretty good about providing idle, seek, read/write,
and spinup numbers. With industry maturity, comes contempt
for customers...
Another source of idle power numbers, is here. This will give
you some idea of how much they vary between brands/speeds etc.
Since these are measured, they'll bear no resemblance to my
idle estimate above
http://www.storagereview.com/comparison.html
HTH,
Paul
Hi Paul,
Thanks for a very informative reply, better than what one can get from
the Tech Support Centers from any of the disk manufacturing companies.
My reason for raising the question stems from the need to determine my
power supply needs for a system.
The system contains the following:
Motherboard MSI-7125 ATX K8N Neo4 Series
Processor: AMD Athlon(tm) 64 X2 Dual Core Processor 3800+
2.0 GHz (2 CPUs - in one unit)
Math Support: Present
BIOS: Phoenix - AwardBIOS v6.00PG Phoenix - AwardBIOS
v6.00PG, 07/21/06
Bus Type: PCI, ISA, USB
Ports: 1 Parallel, 1 Serial
Memory: 2048 MB
Floppy Disks: 1.44 MB
Hard Disks: 160 GB [SATA in RAID 0 Mirroring Array]
160 GB [SATA in RAID 0 Mirroring Array]
320 GB [SATA in RAID 1 Mirroring Array]
320 GB [SATA in RAID 1 Mirroring Array]
400 GB [PATA]
500 GB [PATA]- backup, swap / page
Multimedia: Sound, CD-ROM
DVD/RW _NEC DVD_RW ND-350A
CDROM CDWRITER IDE5232
Video: 800 x 600 in 64K Colors, NVIDIA GeForce 6200
TurboCache(TM) Ver. 6.14
Operating System
Windows: Windows 2000 Professional 5.0 (Build 2195)
Net Clients:
In an Ione SI-1 box w/ 400W power supply w/ 1-92mm fan & 1-smaller case
fan.
CRT and other peripherals, if present or required will be externally
powered.
I've tried to get an estimate of my power needs from various sources but
an alarming number seems to come from persons with a generic "bigger is
better" philosophy, without any limits or regards to "excess capacity".
Thank God!, there is, as yet no 1-MW power supply for desktop PC's.
Given the spec above what would you consider a reasonable power supply
to drive the system.
Athlon X2 3800+ Either 65W or 89W, as there are three different models,
and two models are actually available. (89W/12V) * (1/0.90) = 8.24 amps
from +12V, at 90% Vcore efficiency.
http://www.amdcompare.com/us-en/desktop/details.aspx?opn=ADA3800IAA5CU
The 6200 video card would be pretty low powered, and a lot of the
ones I see on Newegg are passively cooled. I don't have an exact number,
but the 7300GS here, uses 12V at around 1 amp and 3.3V at around 1 amp.
http://www.xbitlabs.com/articles/video/display/power-noise_7.html
You can compare the characteristics of the 7300GS and 6200 here.
http://www.techpowerup.com/gpudb/
Optical devices tend to have "boiler plate" specs printed on them,
which may not reflect their real power usage. Typical numbers are
5V @ 1.5A and 12V @ 1.5A. The 12V draw will not be close to that,
if there is no media in the drawer. 12V draw is heavy, when there is
a CD/DVD in the drive.
Six hard drives, with an allocation of 12V @ 0.6A and 5V @ 1A for
idle power.
For motherboard chipset power, I use 50W spread over 3.3V and 5V as an
estimate. That is because while I've measured a couple computers here
with my clamp-on ammeter, there isn't a way to calculate numbers for
them. The first stick of RAM on a channel, draws more power than the
second stick, so four sticks on a dual channel board does not draw
twice as much power as two sticks. Only one stick can be "active" at
a time on a channel, in terms of the most consumptive memory cycle types,
so the second stick is more like an "idle" stick.
+12V (during normal operation)
Processor - 8.24 amps (at 100% CPU on both cores)
Video - 1 amp (just to be safe)
(2) optical - 3 amps (I usually consider only one optical to be active)
(6) hdd - 3.6 amps (idle current)
(3) case fans - 0.5 amps
Total - 16.3 amps
+12V (at startup)
Processor - 8.24 amps (I'm leaving this as max, but usually it is <1/2)
Video - 0.5 amp (The Xbitlabs chart lists 6.24 watts for the 7300gs)
(2) optical - 1.5 amps (Likely to only have one optical running at boot)
(6) hdd - 15.0 amps (assume the "greedy" drive type, 6 x 2.5A for 10 sec)
(3) case fans - 0.5 amps
Total - 25.7 amps
Total power would be (12V * 25.7A) + ~50W for the first 10 seconds. Which is
about 358W. This drops to (12V * 16.3A) + ~50W once booted, or 245.6 watts
when booted. That assumes both CPU cores are at 100% in the second case.
Rather than the watts being the limiting factor on your 400W supply, it
could be that it cannot manage 12V @ 25.7 amps. To refine the figure,
you could, for example, look up each individual hard drive, and see if
they are 2A peak boot or 2.5A peak boot. I've measured my CDROM drive,
and it draws 12V @ 1.0A when a CD is spinning at the highest speed, so
the 1.5 amp figure isn't that far off. You could whittle the CPU current
down quite a bit, and that is perhaps the figure with the largest
margin for error. Since I don't have any Athlon64 products here, I
cannot give you an actual measurement of the startup current. Suffice
it to say, that allocating 8.24A at startup for that, is a mistake.
But I have no way to estimate how much less than half of that figure,
is more realistic. So we could actually be at the ~20A level for example,
during startup.
So check the label on the side of the 400W supply, and see how many
amps are available on the 12V.
Paul
