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Minimum Power Supply

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  • Homebuilt
  • Power Supplies
  • Systems
Last response: in Systems
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May 3, 2012 2:19:52 PM

Hello,
TH techies! This is my first forum question so go easy on me!
I plan on building a new computer in late summer and I was a little confused on how power works.
I'm just confused on what the minimum should be, and I know there have been multiple threads already, but I'm still a little confused. I'm not giving real examples cause I'm having problem conceptually understanding so if you have the time to explain I'd really appreciate it!

Mythical GPU - min. 500 w
Mythical processor - min. 200 w
Total Minimal Wattage = 700 w

Now assuming I don't do anything fancy like overclocking and disregarding additional parts, would a PSU of 700 be sufficient to run this machine? And if not, how do you know the range for the upper limits?

Thanks a lot for your answers and your time!

More about : minimum power supply

a c 118 B Homebuilt system
May 3, 2012 2:37:02 PM

There is no one answer to this question, how much power is needed depends on many factors, as the link jtmunn pointed out it can give you a general idea. But not all power supplies are created equal, there are quality issues that are a matter of concern, generally the old adage applies "you get what you pay for".

As far as general things, typically the video card you choose is going to dictate how much power you need as they again typically by far the most significant power drawing component in your computer.
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a b B Homebuilt system
a b ) Power supply
May 3, 2012 2:53:22 PM

I do Not use the PSU calculators, Primarilly because I do NOT recommend PSUs that fall below wath is called tier II.

What I do do is google a Review of the GPU that I intend to use, and look at what they say total system power is Under a heavy Load then add 100 Watts for Min and 200 Watts for recocommended.

For ex my I5-2500L OCed to 4.2 GHz and with a AMD 6870 (Also I have 16 gigs Ram, 4 drives). When I look at reviews it shows around 300 -> 350 Watts under heavy load with a qualifier that this is 50 -> 100 Watts above typical. Based on that I would recommend a Good quality PSU in the range of 500 W -> 650 Watts. NO higher for a Typical system with a high end single GPU. For most systems with a Daul GPU setup in SLI/Xfire a Corsair TX750 would be a grat choice.
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a c 122 B Homebuilt system
a c 144 ) Power supply
May 3, 2012 3:34:14 PM

The size of your power supply will depend on what components you are going to use in your system.

The best thing for you to do when you get ready to build is to post a budget and the main purpose for the system. There are people here who are great at system configuration.

Like RetiredChief, I also do not use PSU caculators. I have a different method. But then, we have both been doing this for a long time.
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a b ) Power supply
May 3, 2012 3:55:24 PM

Shooting for the smallest PSU to get you by will definitely get you in trouble eventually. Personally, I try never to run a PSU at more than 50% of rated wattage. My advice is to buy the largest QUALITY PSU you can afford. Obviously, this will cost you a little more up front but IMHO it is the cheapest insurance you will ever buy for your rig as PSU issues will often show up as random unpredictable and unidentifiable events. Stressing a PSU is never a good idea.
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a b B Homebuilt system
a b ) Power supply
May 3, 2012 4:04:56 PM

In the long run, buying a low quality low watt power supply will just the amount of chances for PSU issues
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May 3, 2012 4:10:56 PM

For a single graphics card system without CPU overclocking, 550W 80 Bronze is sufficient. I wanted to have more room and found a good deal, so got 620W one, though. Here is my system. In a test for a similar system (actually a little bit more demanding), the total system power consumption is 386W, while the minimum requirement for the graphics card is 550W PSU.
http://www.hitechlegion.com/reviews/video-cards/14955-e...
You can see that the minimum requirement does not mean the actual max that your graphics card and CPU can hit. It's rather a safeguard calculated by experienced engineers to provide stable condition, assuming a single graphic card system with safety headroom. So it's safe to follow the minimum requirement power number provided by the graphics card manufacturer.

i5 2400 (40W-98W)
Coolermaster Hyper 212 CPU cooler
EVGA GTX 560 Ti 448 Classified (210W Max)
H67 Motherboard
Corsair XMS3 1333MHz 4GB x 2 RAM
Samsung F3 500GB HDD
LG 24X DVD-RW

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a b B Homebuilt system
a b ) Power supply
May 3, 2012 4:27:02 PM

ram1009 "My advice is to buy the largest QUALITY PSU you can afford." sound great on the surface. But there is a point of diminising returns. ie I can certainly afford a 1KW or 1.2KW PSU for my MAX 350 Watt system instead of the Corsair 650 I choose - Would I , NOPE.
.. Both will probably last about the same - electrolitic Caps also experence aging based on age. The 1KW or larger is a large jump in cash (if it was worth it I would, just not cost effective).
.. Then you get to throw in the Higher cost of operating of a five year period. While running at loaded wattage it should be the same. However, a lot of time is spent at idle power draw. And herein lies the added cost of the Way overkill PSU. many systems at down to a 100 watts at idle (some even lower). As you go below about 20 % eff goes down and the cost goes up - small increase per day, but multiply that by 5 years/365 days X hours at Idle could add up.

LOL - as I said, generally good advice, just not so for he (or she) with deeper pockets.
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May 3, 2012 6:10:58 PM

Awesome replies guy! Thanks for all the advice and tips so far. I understand it a little bit better now but I realize that I'm still very very inexperienced to these sorts of things. Hopefully I'll be able to learn more from you guys :D 
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