kanenas@hawaii.rr.com wrote:
On Saturday 09 February 2008 09:39:13 am Randall R Schulz wrote:
On Saturday 09 February 2008 11:22, Philippe Landau wrote:
Randall R Schulz wrote:
But many power supplies are only efficient when they don't operate close to full load. This seemed counterintuitive to me, so I decided to do a little looking around. According to the graph on page 14 of "Power Supplies: A Hidden Opportunity for Energy Savings" http://standby.lbl.gov/CEC_Workshop/Docs/Ecos_FinalReport.pdf
On Saturday 09 February 2008 10:08, Philippe Landau wrote: this is not the case. It very much depends on the power supply in question. Of course.
But to go back to the original question (mine), the issue is whether highly over-rated supply is wasteful of power. It appears they are.
Randall Schulz
I disagree:
I looked at a bunch of efficiency plots from 80plus.org. They generally peak at 50% of the rated load, at around 84-85%. their low load (20%) efficiency is around 82%, the high load (100%) efficiency is around 80%.
Only for power supples that are endorsed by 80plus.org. If you had bothered to look at the PDF that Randall presented, you would see that NON-80plus.org power supplies appear to have bad to dismal efficiency at loads below 40% rating. And as suggested, those curves are in fact typical.
so, for a 400 watt load, typical i would say for today's computers, an 800 watt power supply would draw around 470 watts, as it would operate at 85% efficiency. for the same 400 watt load a 400 watt power supply would draw 500 watts, efficiency at 80%
Until it burned up. Power supplies are generally rated on how much power they consume, not how much they supply. You're demonstrating that you really don't know enough about this subject to give qualified comments on it. Perhaps if you took some electrical engineering courses, specifically a course on electric power. Impedance matching is a very big issue, as well as Q-factors and other things which all have HUGE impacts on efficiency. To get the 80+% efficiency across the board is NOT a trivial thing. It takes more components, and higher-quality ones at that -- both of which cost money -- which is why manufacturers typically haven't made them UNTIL their was an organization promoting it so that the retail buyer would understand the added value of these more expensive supplies.
for the same load, a 550 w power supply would draw around 488 watts, efficiencyaround 82% for the typical efficiency curve shown on this site, the same 400 watt load, supplied by a 2000 watt power supply , would draw 488 watts, as at 20% load the efficiency is at 82%.
so, it is better to get a power supply at least twice as big as the load. Even when the rating is way greater, say 4 times the requirement, the efficiency is better than using a power supply at over 75% of it's capacity.
the SUV syndrome fails when applied to power supplies:) d.
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