Dave Plater wrote:
Carlos E. R. wrote:
The Thursday 2008-02-14 at 21:38 +0100, Per Jessen wrote:
Carlos E. R. wrote:
I'm thinking that the power measured at the input is not important at all. The important figures are the amperage capacity on each of the DC output lines, and that's the power that has to be matched to the load, and where the measurements are important. The AC side is irrelevant, somehow.
Well, my only reason for looking at the AC side was to see what the real load was. I'm a little disaapointed that I got convinced to buy a much bigger power-supply, when my 350W would quite obviously have been enough. Still, like I said, the new one is also much quieter, which is very pleasant.
What I think is worth noting here - a somewhat highend system like this still uses barely 250W at _full_ load.
Still, I don't know if those new measurement gadgets can be trusted. I mean I don't know, not that they are bad.
Then, there is another issue.
The important thing is the power needed at each of the internal DC lines. Some one said that the MB nowdays uses power from the 12 V line, and also the video card uses it (I don't know what for). Plus the fans, the high speed drives... sum all of that. If it close to 10 Amps, and the 350W unit can supply only 10 A (for instance), then you really need a higher wattage power supply: not because you need that so much power, but because one of the lines uses much more power.
If this is the case, what the manufacturers will have to do is to change the power distribution on new PS so that they have more Amps at the 12 V line.
Its an hypothesis only, but it might be so.
Let me see... for instance, the Seagate barracuda, ST3250310AS, 250GB, a small disk nowdays (the top of the family is 750 GB, 8 heads). From the datasheet:
Table 12: DC power requirements
--long_line--------------------------------------------------------------------------------- Power dissipation (4-disc values shown) Avg (watts 25° C) Avg 5V typ amps Avg 12V typ amps Spinup 2.8 (peak) Idle* 9.30 0.611 0.520 Idle* (with offline activity) 10.40 0.719 0.567 Operating (40% r/w, 40% seek, 20% inop.) 13.00 0.772 0.762 Seeking (random, 20% idle) 12.60 0.613 0.795 Standby 0.80 0.106 0.023 Sleep 0.80 0.106 0.023
Ie, the peak power during spin up is 2.8 Amps on the 12V line, 0.8A avg maximum during seeks. The power supply must be able to handle that, and if it is true the MB uses also that line, there will be problems.
Of course, the same calculation should be done for the MB and video card.
-- Cheers, Carlos E. R.
Due to low vcore voltages for cpu and gpu and the load on the 3.3v (5v vcc is a thing of the past) they are derived from the 12v supply nowadays. The lower the operating voltage the faster the logic switches and less power is needed. That is why you have extra 12v connections on MB. Dave
Actually, I think you've got that a bit backward. Generally lower power results from lower voltage and that lower power allows faster switching. To get fastest switching from a device, ignoring power dissipation, requires higher voltage. -- Use OpenOffice.org http://www.openoffice.org -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org