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# True power, power unit

Posted on 2007-03-25
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what is the different of True power (power unit) and normal power unit. My friend told me that the true power unit example 400W, when it is on low load or  high load will draw all the full power 400W. is this true. show me some prove  (Antec 480W True PSU)
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Question by:kianhow
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nobus earned 1500 total points
ID: 18787858
This is NOT true.
Each power supply has an efficiency ratio, varying from 60% for really bad ones, to up to in the 90-ies for good ones
BTW Antec  and Enermax are well rated ones
http://www.gillware.com/
http://www.tomshardware.com/2004/01/22/getting_the_right_power/

to answer your Q : it will draw a tiny percent + actual load - the percent depends on the efficiency
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ID: 18787859
i forgot : get a new friend (who verifies his facts before telling them)
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ID: 18788266
The PSU will put out 400w when it is at maximum output, if the computer needs 200w it will output 200w. The efficiency has less to do with it as it is already incorporated into the amount of Watts the PSU can output.
If you have a 70% efficiency the PSU will output say 400watts at max but the power draw into the PSU from the wall outlet will be 571w. the 30% loss is generated as heat from the PSU(heat is energy too) thats why they have heatsinks in them.
There are PSU's that are more efficient than others, seasonic for example rate their PSU's at 80% efficiency but have been known to be capable of 95% under ideal conditions.

Now onto the question at hand.
Does a PSU constantly output the 400W its rated for-->NO and here is the link that shows how each component fron CPU to cd drive and everything inbetween changes its electrical draw under different situations, from idle to maximum.
http://www.silentpcreview.com/article265-page1.html

No need to get a new friend, just slam him with the facts next time you see him. Much more fun than just getting rid of him.
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Expert Comment

ID: 18788330
what's the difference , sparkmaker  ? (quite fitting for power supplies :-))   )
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LVL 32

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ID: 18788392
Can't humiliate a PSU, but a friend, definately.
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