Does "x watt" PSU really draw x watts from the wall?

nbarb99

Senior member
Mar 14, 2003
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... or does it draw as much as required at the time? Doing a little bit of energy calculations:

Running a 60W light bulb 24/7 costs approximately $32 per year in my area. A 300W power draw would theoretically cost $1576 per year.

I seem to remember that "switching" power supplies draw by demand; i.e. if you don't have many devices drawing power, not much is drawn from the wall. Is this the case, or am I confused?
 

EeyoreX

Platinum Member
Oct 27, 2002
2,864
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That is correct. The PSU will only draw what power is needed. A 300W PSu is capable of supplying 300W to your components, it doesn't draw 300W all the time.

\Dan
 

DaveSimmons

Elite Member
Aug 12, 2001
40,730
670
126
Good articles on this at www.SilentPCReview.com -- short answer no, but you should choose the PSU carefully as they waste different percentages of what they draw and some are much more efficient / less wasteful than others.
 

tallman45

Golden Member
May 27, 2003
1,463
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Most power supplies are at best 70% efficient, so if you have a 300watt power supply and system draws 200watts then your wall current draw is approx 280 watts.
 

Zinn2b

Banned
Jan 9, 2004
361
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0
It is plain here that many people here haven't a clue as to how electral mechanical force works even thow there are differances how wasteful a P/S supply may or may not be,you want to look it in this way, power consumption kinda works like this let me use a car for an example, fuel system supply well be the voltage ok the engine well be the wattage ok and the road well be the demand on the P/S now you are cruising along getting great milage , nice flat road everthing is great right consumption of fuel is great, now you come to a down grade man milage is great consumption is low you are idling ok, now you come to a hill and you have to small of a motor in your car, now fuel consumption goes way up now its costing you mileage the motor is working hard , now the grade gets stipper your motor starts heating up your fuel supply is at its limits than suddenly bang your motor blows because you put to great of a strain on it, now if you had the perfectly sized motor in your car there would not have been a problem going upgrade there would have been a fuel consumption increase but thats ok cause your motor is running cool going down hill your idling again and on flat you are cruising the differance in motor size may or may not effect effiency of fuel supply, now to big of a motor is ok but that well effect fuel consumption and thats the just of it ,to small of a P/S can cost you way to much to run +it does't allow everthing to work correctly very wasteful and harmful the perfectly matched P/S is effientant and reliable and well run for years to large of P/S well do everthing that a perfectly matched P/S well do and last for years but may consum more power please excuse the poor spelling and grammer your friend Zinn2b
 

bjc112

Lifer
Dec 23, 2000
11,460
0
76
Originally posted by: Zinn2b
It is plain here that many people here haven't a clue as to how electral mechanical force works even thow there are differances how wasteful a P/S supply may or may not be,you want to look it in this way, power consumption kinda works like this let me use a car for an example, fuel system supply well be the voltage ok the engine well be the wattage ok and the road well be the demand on the P/S now you are cruising along getting great milage , nice flat road everthing is great right consumption of fuel is great, now you come to a down grade man milage is great consumption is low you are idling ok, now you come to a hill and you have to small of a motor in your car, now fuel consumption goes way up now its costing you mileage the motor is working hard , now the grade gets stipper your motor starts heating up your fuel supply is at its limits than suddenly bang your motor blows because you put to great of a strain on it, now if you had the perfectly sized motor in your car there would not have been a problem going upgrade there would have been a fuel consumption increase but thats ok cause your motor is running cool going down hill your idling again and on flat you are cruising the differance in motor size may or may not effect effiency of fuel supply, now to big of a motor is ok but that well effect fuel consumption and thats the just of it ,to small of a P/S can cost you way to much to run +it does't allow everthing to work correctly very wasteful and harmful the perfectly matched P/S is effientant and reliable and well run for years to large of P/S well do everthing that a perfectly matched P/S well do and last for years but may consum more power please excuse the poor spelling and grammer your friend Zinn2b


Paragraphs my friend..

:)
 

Barnaby W. Füi

Elite Member
Aug 14, 2001
12,343
0
0
Originally posted by: bjc112
Originally posted by: Zinn2b
It is plain here that many people here haven't a clue as to how electral mechanical force works even thow there are differances how wasteful a P/S supply may or may not be,you want to look it in this way, power consumption kinda works like this let me use a car for an example, fuel system supply well be the voltage ok the engine well be the wattage ok and the road well be the demand on the P/S now you are cruising along getting great milage , nice flat road everthing is great right consumption of fuel is great, now you come to a down grade man milage is great consumption is low you are idling ok, now you come to a hill and you have to small of a motor in your car, now fuel consumption goes way up now its costing you mileage the motor is working hard , now the grade gets stipper your motor starts heating up your fuel supply is at its limits than suddenly bang your motor blows because you put to great of a strain on it, now if you had the perfectly sized motor in your car there would not have been a problem going upgrade there would have been a fuel consumption increase but thats ok cause your motor is running cool going down hill your idling again and on flat you are cruising the differance in motor size may or may not effect effiency of fuel supply, now to big of a motor is ok but that well effect fuel consumption and thats the just of it ,to small of a P/S can cost you way to much to run +it does't allow everthing to work correctly very wasteful and harmful the perfectly matched P/S is effientant and reliable and well run for years to large of P/S well do everthing that a perfectly matched P/S well do and last for years but may consum more power please excuse the poor spelling and grammer your friend Zinn2b


Paragraphs my friend..

:)

I can handle paragraphs that big, but only when it's divided into more than one run-on sentence...
 

Jeff7

Lifer
Jan 4, 2001
41,596
20
81
Originally posted by: nbarb99
... or does it draw as much as required at the time? Doing a little bit of energy calculations:

Running a 60W light bulb 24/7 costs approximately $32 per year in my area. A 300W power draw would theoretically cost $1576 per year.

I seem to remember that "switching" power supplies draw by demand; i.e. if you don't have many devices drawing power, not much is drawn from the wall. Is this the case, or am I confused?

Wait a sec, 60W bulb costs $32 a year. 300W is 5x more.
5 * $32 = $160.




Originally posted by: Zinn2b
It is plain here that many people here haven't a clue as to how electral mechanical force works even thow there are differances how wasteful a P/S supply may or may not be,you want to look it in this way, power consumption kinda works like this let me use a car for an example, fuel system supply well be the voltage ok the engine well be the wattage ok and the road well be the demand on the P/S now you are cruising along getting great milage , nice flat road everthing is great right consumption of fuel is great, now you come to a down grade man milage is great consumption is low you are idling ok, now you come to a hill and you have to small of a motor in your car, now fuel consumption goes way up now its costing you mileage the motor is working hard , now the grade gets stipper your motor starts heating up your fuel supply is at its limits than suddenly bang your motor blows because you put to great of a strain on it, now if you had the perfectly sized motor in your car there would not have been a problem going upgrade there would have been a fuel consumption increase but thats ok cause your motor is running cool going down hill your idling again and on flat you are cruising the differance in motor size may or may not effect effiency of fuel supply, now to big of a motor is ok but that well effect fuel consumption and thats the just of it ,to small of a P/S can cost you way to much to run +it does't allow everthing to work correctly very wasteful and harmful the perfectly matched P/S is effientant and reliable and well run for years to large of P/S well do everthing that a perfectly matched P/S well do and last for years but may consum more power please excuse the poor spelling and grammer your friend Zinn2b

I'll take "Periods and other punctuation" for $300, Alex.:)
 

CZroe

Lifer
Jun 24, 2001
24,195
857
126
It's called a "switching" power supply because it can vary it's draw and output according to the load.
 

Bleep

Diamond Member
Oct 9, 1999
3,972
0
0
It's called a "switching" power supply because it can vary it's draw and output according to the load
I think you should read up a little on power supplies. here

Bleep
 

nbarb99

Senior member
Mar 14, 2003
581
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0
Thanks everone for the explanations, and for the example Zinn2b :)

Wait a sec, 60W bulb costs $32 a year. 300W is 5x more.
Oops, I must have calculated that wrong :eek:
 

merlocka

Platinum Member
Nov 24, 1999
2,832
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0
Originally posted by: Zinn2b
EXCUSE me for breathing

Breathing is OK, in fact, if you woulda breathed between sentances that paragraph woulda been easier to read.

 

Zinn2b

Banned
Jan 9, 2004
361
0
0
In the future I promise to take more time. OK? Dam feel like I am back in school and the teacher quality is about the same.......................
 

Mday

Lifer
Oct 14, 1999
18,647
1
81
No, it does not. What it can do is draw up to that wattage without fuses being blown or the specifications no longer fitting. Your powersupply will draw whatever is necessary to support the powered components. Don't forget the efficiencies, so it draws more than the sum of the components attached to it. After a certain limit, which is typically the wattage labeled, the current draw will cause the fuses to be blown, wires to overheat, etc. Before that happens, the output voltages can vary out of spec.
 

Zepper

Elite Member
May 1, 2001
18,998
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0
. The simple answer is that switching PSUs use more energy than they put out - at least 1.4 times (as about 72% efficient is tops) as much (but are more efficient and lighter in weight than most other types of PS) and their outputs vary depending on the load.
. They are called switching PSUs because they use fast state switching electronics to chop the 60Hz AC sine wave power into a high frequency square wave and thence into the various DC rails voltages.
.bh.
 

buleyb

Golden Member
Aug 12, 2002
1,301
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0
Originally posted by: Zinn2b
In the future I promise to take more time. OK? Dam feel like I am back in school and the teacher quality is about the same.......................

Not to beat a dead horse, but we use paragraphs and punctuation in the real world too, not just in school.

 

martind1

Senior member
Jul 3, 2003
777
0
0
Originally posted by: Zinn2b
In the future I promise to take more time. OK? Dam feel like I am back in school and the teacher quality is about the same.......................

you had plenty of time to break that up into sentences. maybe instead of ending every sentence with "ok, " you can try using this key combo ". " that would save you 2 key strokes per sentence ok, in this case saving you quite a bit of time ok, that would help everyone reading it ok, also breakign a huge paragraph would help ok, so like when you went to your car analogy that shoudl've been anotehr paragraph ok, maybe when you are out of school you will understand how to communicate ok,.