Do I have enough watts in my PSU?

Grant56810

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Here's my computer: http://pcpartpicker.com/user/Grant56810/saved/ZHcNnQ Does my PC have at least about 100W more than I need? Please give answers based on you actually checking the product's parts' wattages instead of pcpartpicker.com's recommended wattage. Please reply ASAP. Thank you very much!
 
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it won't wear out faster but you may run into undervolt issues. at idle and low power tasks you will be using so little of the psu that it will have trouble supplying it. think about trying to drive 25 mph in a 1200 hp bugati veyron. the engine will be sputtering and close to stalling. too powerful of a psu can have the same issues. it just won't know how to "only" supply 120 w or so at idle and low power things like web surfing. they are rated from 25% and up which is 250 watts minimum it wants to put out.

this is really the issue you may run into. i have never done it myself but this is the theory anyway. either way i am jealous of the system you're building :) gonna be a beast.

Aaayron

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Fine, I did my research and PCPartPicker's not far from the actual wattage use. Not sure if you know but the GTX 970 uses VERY LITTLE power while still being very powerful. So even with 2 of them you can run your system on a good 750W PSU. (Not kidding. A lot of people already do.)

So your current PSU choice is RIDICULOUSLY overkill and would actually lower its efficiency because of that. The sweet spot for this build IMHO is a 750W.
 

Grant56810

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Power requirement: 550W (with one 6-pin and one 8-pin external power connectors)
Is this an overall power requirement or does it add up? That's what it says on the 970. Please answer ASAP as well. Thanks!
 

Aaayron

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Where'd you get that information? Is it on the box? It even says on the official Geforce website that one GTX 970 has a power consumption of just 145W
http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-970/specifications. So having 2 should only really need 290W total...

The one you mentioned might be the overall power requirement but even so it still seems very large...
 

Grant56810

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If you go to the Gigabyte Gaming G1 version (http://www.newegg.com/Product/Product.aspx?Item=N82E16814125684) then if you scroll down it says that that power requirement is 550W (in the specs page). Maybe it's because this is the only one with 3 fans on it?
 

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ok so math to the rescue. each of those 970's needs about 160w and the rest of your system needs about 200w. so 160+160+200 = 520w. the important number here is not watts but amps. 520w/12v = 43.3 amps needed. to stay in the safe operating range of 80-85%, a psu for this system will need at least 51-54 amps. the psu you picked has 83 amps and will run into undervolting issues due to being MASSIVELY overpowered.

any of these 3 psu's will easily work http://pcpartpicker.com/parts/compare/evga-power-supply-110b20750vr%2Cevga-power-supply-120g10650xr%2Cevga-power-supply-120g10750xr/

save yourself some cash and lower that psu some. and since you are going to ask, the manufacturer overstates the needed wattage to compensate for all the crappy psu's out there. many "750w" psu's will have less 12v amps than a quality 450w one!! the amps is what is important and not the stated wattage.
 

Grant56810

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GeForce GTX 970 or 980 in 2-way SLI - On your average system the cards require you to have an 800 Watt power supply unit as minimum.
Source: http://www.guru3d.com/articles-pages/gigabyte-geforce-gtx-970-g1-gaming-review,7.html
 

Math Geek

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they are right an "average" psu will have to be higher to work. the math does not change the amp requirements however and a "quality" psu, such as i have recommended, will be fine.

again, watts is not what's important but the 12v amps that really tells what the psu is capable of. i have seen a "850w" psu with 26 amps on the 12v rail. should this one be used in this system since it has enough "watts"??
 

Math Geek

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alright so here goes. amps = watts/volts. this is the formula governing what we are talking about. watts is potential power and amps is actual used power. (simplified explanation). a psu is designed to supply so many amps on each of the 3 voltage rails, 3.3v, 5v and 12v. the main power of the system comes from the 12v rail. most of the power given to the 3.3v and 5v is unused while the 12v rail is leaned on heavily. A cheap psu will give a lot of power to the 3.3 and 5v rails to claim a lot of wattage. it may all add up to the stated watts but 30 amps on the 3.3v rail (or 99w) will never be used. the psu make will still add this into the total wattage.

in the end the supplied amps to the 12v rail is very low when they do this as they cheated by adding lots of watts to the low volt rails you won't be using. for instance, 25 12v amps = 300w but 40 12v amps = 480w. both of these may be on "500w" psu's but the 40 amps actually supplies more to the system than the 25 amps.

manufacturer's know this so they overestimate what is required to compensate. so they may say "800w minimum" so that a crap 800w psu will have enough power, despite the fact that a quality 600w psu does the job fine.

an analogy of this would be if you bought a car with a 700 hp engine that only gets 450 hp to the tires. another car has 600 hp but gets 580 hp to the tires. which is the better performing car? same goes for watts. it's all about what gets to the system not what sits unused in the power supply.
 

Grant56810

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Ah, I see. Do the PSUs you recommended to me have more power going to the 12V rail then my 1000W current PSU? If not, then I think I'll stick with my current PSU. If so, I might switch. Thanks!
 

Grant56810

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Obviously I care about my budget but a hundred dollars alone doesn't matter that much to me. If I get the 1000W PSU, Will there be any other downsides other than my power bill (for example, maybe the PSU would wear out shorter)? Thanks!
 

Math Geek

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it won't wear out faster but you may run into undervolt issues. at idle and low power tasks you will be using so little of the psu that it will have trouble supplying it. think about trying to drive 25 mph in a 1200 hp bugati veyron. the engine will be sputtering and close to stalling. too powerful of a psu can have the same issues. it just won't know how to "only" supply 120 w or so at idle and low power things like web surfing. they are rated from 25% and up which is 250 watts minimum it wants to put out.

this is really the issue you may run into. i have never done it myself but this is the theory anyway. either way i am jealous of the system you're building :) gonna be a beast.
 
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