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Question about PSU Wattage
- Thread starter yuriz43
- Start date
BillParrish
Supreme [H]ardness
- Joined
- Aug 25, 2006
- Messages
- 7,519
The power supply only delivers what the rest of the computer demands/needs. The 700W is a maximum rating not what it puts out all the time. Hope that helps.
If worried about electric bills, look for the supplies efficiency rating, 80% or better is very good. less than 80% so so and some are as bad a 65%. Lots of power supply reviews on the main Hard page. What the the efficiency means is lets say the supply is 75% efficient (not bad but could be better) for every 100W it pulls out of the wall as AC and you pay for, it converts into 75W for your computer. Its a fact of life that you lose stuff in the conversion process.
If worried about electric bills, look for the supplies efficiency rating, 80% or better is very good. less than 80% so so and some are as bad a 65%. Lots of power supply reviews on the main Hard page. What the the efficiency means is lets say the supply is 75% efficient (not bad but could be better) for every 100W it pulls out of the wall as AC and you pay for, it converts into 75W for your computer. Its a fact of life that you lose stuff in the conversion process.
silent-circuit
[H]F Junkie
- Joined
- Sep 18, 2005
- Messages
- 16,132
To expand a bit on what Bill said, hopefully clarifying:
No, it doesn't draw the same amount all the time. Draw from the wall is determined by what you have in the case. A quad core will draw more than a dual or single of the same architecture, an 8800 GTX will draw more than a X600, 3 HDDs pull more than 1, etc.
Also as he said, higher efficiency = lower power bill. It's a bit more complex than that, though; all PSUs have an efficiency curve. They usually advertise their max efficiency, but this only happens over a fairly small range of wattages drawn. The curve tends to be a "bell curve" or modified bell curve -- it goes up from the left, plateaus, then goes down toward the right. You want (in order to get highest efficiency) to keep load in the range at the plateau, which tends to be anywhere from 40% of rated maximum load to 75%. Somewhere between 1/2 and 2/3rds is a good guess in most cases
This is the main reason you don't want to buy a PSU that either won't be loaded at all by your system, like a 1200 watt unit running your grandparents' Dell, or a PSU that will be loaded very heavily all the time, like a 500 watt PSU running a quad core and 8800GTX's in SLI with a bunch of HDDs. In the first scenario you're just paying more per watt, there's no major drawback. In the second, the PSU is stressed and running hot as a result, because lower efficiency also means more energy lost as heat during conversion, and thusly more fan noise. More importantly hotter running components tend to be shorter lived, especially capacitors.
No, it doesn't draw the same amount all the time. Draw from the wall is determined by what you have in the case. A quad core will draw more than a dual or single of the same architecture, an 8800 GTX will draw more than a X600, 3 HDDs pull more than 1, etc.
Also as he said, higher efficiency = lower power bill. It's a bit more complex than that, though; all PSUs have an efficiency curve. They usually advertise their max efficiency, but this only happens over a fairly small range of wattages drawn. The curve tends to be a "bell curve" or modified bell curve -- it goes up from the left, plateaus, then goes down toward the right. You want (in order to get highest efficiency) to keep load in the range at the plateau, which tends to be anywhere from 40% of rated maximum load to 75%. Somewhere between 1/2 and 2/3rds is a good guess in most cases
This is the main reason you don't want to buy a PSU that either won't be loaded at all by your system, like a 1200 watt unit running your grandparents' Dell, or a PSU that will be loaded very heavily all the time, like a 500 watt PSU running a quad core and 8800GTX's in SLI with a bunch of HDDs. In the first scenario you're just paying more per watt, there's no major drawback. In the second, the PSU is stressed and running hot as a result, because lower efficiency also means more energy lost as heat during conversion, and thusly more fan noise. More importantly hotter running components tend to be shorter lived, especially capacitors.
Ok, so with the following components, do you think im atleast at 1/2 of 700watts?
I
MSI p35 platinum
C2D E6420 OC'd to 3.2ghz ( that should bring up some power usage)
Geforce 8800 320 No-OC
2g Ram @ 800mhz
SATAII HD
DVD-ROM
Case Fans
The reason im asking is because I have a 500watt(Xclio) PSU and a 700watt(OCZ GamerXstream) PSU. The 500watt dosen't have the EPS12v 8pin connector which is why I got the 700.. really im just wondering if I should return my 700 if its going to end up costing me more per watt..
I
MSI p35 platinum
C2D E6420 OC'd to 3.2ghz ( that should bring up some power usage)
Geforce 8800 320 No-OC
2g Ram @ 800mhz
SATAII HD
DVD-ROM
Case Fans
The reason im asking is because I have a 500watt(Xclio) PSU and a 700watt(OCZ GamerXstream) PSU. The 500watt dosen't have the EPS12v 8pin connector which is why I got the 700.. really im just wondering if I should return my 700 if its going to end up costing me more per watt..
silent-circuit
[H]F Junkie
- Joined
- Sep 18, 2005
- Messages
- 16,132
Ok, so with the following components, do you think im atleast at 1/2 of 700watts?
I
MSI p35 platinum
C2D E6420 OC'd to 3.2ghz ( that should bring up some power usage)
Geforce 8800 320 No-OC
2g Ram @ 800mhz
SATAII HD
DVD-ROM
Case Fans
The reason im asking is because I have a 500watt(Xclio) PSU and a 700watt(OCZ GamerXstream) PSU. The 500watt dosen't have the EPS12v 8pin connector which is why I got the 700.. really im just wondering if I should return my 700 if its going to end up costing me more per watt..
Return the Gamexstream if you can -- it has bad 12v rail ripple, I would not use it. You can get a nice Silverstone Zeus 650watt for $100 or so at Newegg right now, but the Xclio should be plenty.
My system at full load (STALKER seems to load it the most right now) sits at around 360watts at the wall, which is 288 watts true internal load, assuming 80% efficiency. In most cases you don't need the 8 pin EPS12v, you can just plug the 4 pin in to the 8 pin port (motherboard manual should have specifics). So figuring 30ish watts less for the 8800GTS as opposed to my GTX, and maybe 12 watts less for the single as opposed to dual DVDRWs, you're looking at full load around 250 watts. But that's just in STALKER, highest numbers I've seen thus far, and newer stuff will no doubt push things harder. I'd say assuming a 300 watt load for your system is reasonable at /full/ load, so the 500 watt is really your (and my, ironically, at least for now) sweet spot.