Hot!GTX 780 FTW and Power Supply Question

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Dante Rising
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2013/11/06 10:52:54 (permalink)
I'm looking to build an m-itx PC, and the Lian Li case I purchased calls for a PSU with a length of only 140mm. This drastically reduces the available choices, especially for modular PSUs. Silverstone has a 750 watt version, but the reviews are lackluster.
 
Seasonic has a very highly rated 550 watt power supply that meets the length spec, but I'm curious if you think that PSU is powerful enough (single rail, 45Amps, 550 watts, Gold certified). The Extreme Power Supply calculator says it is fine, estimating a draw 0f 431 watts under 95% load for the PC I hope to build.  But I would like other opinions. Here would be the specs:
 
Gigabyte 787N Mobo (draws 65 watts, 127 under full load)
EVGA GTX 780 FTW (apparently draws 250 watts under full load?)
8 GB DDR3 1600 1.5V
1 samsung 256GB SSD- EVO 840
i5 3570 processor (no "k" version)
2 140mm fans
 
I have no plans to overclock the CPU, and there will be no optical drive or secondary hard drives.
 
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    kubi07
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    Re: GTX 780 FTW and Power Supply Question 2013/11/06 11:00:46 (permalink)
    Yea, you should be fine. The Hadron case from EVGA come with a 500 watt power supply and that can run an i7-4770K and a Titan. Which uses more than what you have up there so you'll be good.

     
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    trabe3
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    Re: GTX 780 FTW and Power Supply Question 2013/11/06 11:45:55 (permalink)
    I agree, you should most likely be fine, but you are getting close to be out of the efficiency band.  I don't know the specific output vs. efficiency for this psu, but being Gold certified, I would think the most efficient output band would be pretty wide.  Power supplies are most efficient in the middle of their output range.  At 431W calculated of 550W rated, that is about 78% capacity.  If I had to guess, the efficiency band would be about 40-70%.  Outside those ranges, the efficiency is reduced.  Lower quality units, the efficiency might really drop off, but in the case of that one, I would think it would only drop a few percent.

    System #1
    ASUS RIV BE
    4930K 4.5GHz - Kraken X60 push/pull
    16Gb Corsair Dominator Platinum 2133MHz
    EVGA 780 Classified SLI - Pro SLI Bridge
    Corsair AX1200i
    Windows 7 Pro
    NZXT Switch 810
    ASUS PB287Q 4K
     
    System #2
    3930K @ 4.4GHz
    8Gb 1600Mhz
    XFX R9 270X (for now)
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    Dante Rising
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    Re: GTX 780 FTW and Power Supply Question 2013/11/06 12:48:52 (permalink)
    trabe3
    I agree, you should most likely be fine, but you are getting close to be out of the efficiency band.  I don't know the specific output vs. efficiency for this psu, but being Gold certified, I would think the most efficient output band would be pretty wide.  Power supplies are most efficient in the middle of their output range.  At 431W calculated of 550W rated, that is about 78% capacity.  If I had to guess, the efficiency band would be about 40-70%.  Outside those ranges, the efficiency is reduced.  Lower quality units, the efficiency might really drop off, but in the case of that one, I would think it would only drop a few percent.



    I don't know much about PSU efficiency, but after a brief glance at some online literature it appears that reduced efficiency does not equate to system instability, but rather wasted energy. Is this a correct summation?
     
    Thank you again for the replies. This is the exact PSU: (Seasonic S12G) at Seasonicusa.com
     
    As you can see, it is not modular, but the 550 watt version is the proper size (140mm) and has significantly fewer cables than the 650 watt version, or most other PSUs.
    -2 less PCI-e 8/6 pin cable
    -no CPU 8 pin cable (the 550 watt contains only 1 8/4 pin cable)
    -1 less peripheral 4 pin
    -2 less SATA
     
    I figure in a m-itx build, the reduced number of cables would enhance airflow and reduce clutter. If I don't need the extra 100 watts, it seems better to focus on heat.
     
     
    I was just nervous about system instability from an overtaxed PSU.
     
     
    Thanks again for the help.
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    trabe3
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    Re: GTX 780 FTW and Power Supply Question 2013/11/06 12:58:14 (permalink)
    No, efficiency shouldn't affect the stability of the system.  As long as the components are receiving the amount of power they need, there shouldn't be any issues.  If certain rails will be starved for power, such as an overclocked CPU or GPU (which you aren't going to do), then stability could be a concern.  But yes, inefficiency would cause extra power consumption and therefore more heat.  At extreme cases of being way outside the efficiency area, the power supply could see reduced life expectancy.
    post edited by trabe3 - 2013/11/06 15:24:56

    System #1
    ASUS RIV BE
    4930K 4.5GHz - Kraken X60 push/pull
    16Gb Corsair Dominator Platinum 2133MHz
    EVGA 780 Classified SLI - Pro SLI Bridge
    Corsair AX1200i
    Windows 7 Pro
    NZXT Switch 810
    ASUS PB287Q 4K
     
    System #2
    3930K @ 4.4GHz
    8Gb 1600Mhz
    XFX R9 270X (for now)
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    Spatalos
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    Re: GTX 780 FTW and Power Supply Question 2013/11/06 15:18:47 (permalink)
    Should be fine if you dont overclock

    MB: MSI Z77A-GD65 Gaming
    CPU: Intell I7 3770k @ 4.7Ghz, 1.16V
    GPU: 1x GTX 780 Watercooled 1x GTX 780 ACX (soon to be watercooled)
    Cooler: XSPC Raystorm
    RAM: 16GB Corsair Vengeance 1600
    HDD: 1TB 5600RPM / 64GB SSD / 128GB SSD
    PSU: Coolermaster V850
    Case: Corsair C70 Vengeance Militairy Green
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