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Do I Have Enough Power?

Hi guys, I wanted some advice for my future setup. Here are my System Specs

Asus P8Z77-V Pro
Intel i5 2500k @4.2 Ghz 1.25v
4Gb DDR3 1600 Wintec Ram
XFX ATI Radeon 5870 1GB
1TB WD HDD Green
128GB SSD Crucial M4
LG DVD Drive
XFX Core Edition PRO550W
http://www.newegg.com/Product/Product.aspx?Item=N82E16817207013&Tpk=xfx%20550


I wanted to upgrade to a 7870 and eventually crossfire with another 7870. I know my current power supply is pushing in this setup but I did use a volt meter to monitor my system wattage at what I believe is full load. My system peaks at 150W without my 5870

I wanted some insightful opinions if I can safely upgrade to a crossfire setup of 7870s in the future.

Thanks in advance
10 answers Last reply Best Answer
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  1. even crossfire 7870 will be safe

    xfx psu has good reputation
  2. g4kioN1 said:
    Hi guys, I wanted some advice for my future setup. Here are my System Specs

    Asus P8Z77-V Pro
    Intel i5 2500k @4.2 Ghz 1.25v
    4Gb DDR3 1600 Wintec Ram
    XFX ATI Radeon 5870 1GB
    1TB WD HDD Green
    128GB SSD Crucial M4
    LG DVD Drive
    XFX Core Edition PRO550W
    http://www.newegg.com/Product/Product.aspx?Item=N82E16817207013&Tpk=xfx%20550


    I wanted to upgrade to a 7870 and eventually crossfire with another 7870. I know my current power supply is pushing in this setup but I did use a volt meter to monitor my system wattage at what I believe is full load. My system peaks at 150W without my 5870

    I wanted some insightful opinions if I can safely upgrade to a crossfire setup of 7870s in the future.

    Thanks in advance


    Hi - The XFX 550w is plenty for one 7870 and is an excellent value right now at Newegg.

    I believe to CF 2 7870's you'd be ok if no or slight oc & stock cooling, but the
    550 has only 1 6pin & 1 6+2pin pci-e connectors, you will need
    dbl that to CF 7870's without adapting molex plugs, so I'd go
    a little higher on the PSU if you are going to oc 2 7870's
  3. Hi :)

    If you are going to DEFINITELY crossfire in the future, get an 850 watt...its what I use for my 7990..

    All the best Brett :)
  4. Why can't I use the molex adapter? I thought that was the reason for including them.
  5. Best answer
    g4kioN1 said:
    Why can't I use the molex adapter? I thought that was the reason for including them.

    With a 550W PSU, that should work in theory.

    For safety reasons, you want each of the molex plugs used by your molex-to-6pin to be from a separate PSU cable so if your PSU has two cables sporting molex connectors, you can safely use a single 6pin adapter. If you have three, you should still be safe with two adapters (one adapters on cables 1+2, the other on 2+3 or 1+3) since the HD7870 needs little more than PCIe slot + PCIe 6pin (75W + 75W) to meet its ~160W requirement so you can do 1x PCIe power from PSU + 1x molex-6pin adapter.

    For dual HD7870, your PC would use around 2x160W for the GPUs + 130W (likely less) for everything else so around 450W max out of 550W.
  6. Thanks, btw if I overclock the GPUs without rasing the voltage will it affect the power that is drawn?
  7. g4kioN1 said:
    Thanks, btw if I overclock the GPUs without rasing the voltage will it affect the power that is drawn?

    Yes it does.

    Worst-case CMOS logic power can be estimated as: P = C * V^2 * F
    C = bulk capacitance of switching elements within the IC (CMOS logic doing work is essentially charging/discharging gate and trace capacitances)
    V = core voltage
    F = frequency

    So power increases roughly linearly with frequency (10% higher clock = ~10% more power) and proportionally with the square of voltage. (10% higher voltage = ~21% more power)
  8. InvalidError said:
    Yes it does.

    Worst-case CMOS logic power can be estimated as: P = C * V^2 * F
    C = bulk capacitance of switching elements within the IC (CMOS logic doing work is essentially charging/discharging gate and trace capacitances)
    V = core voltage
    F = frequency

    So power increases roughly linearly with frequency (10% higher clock = ~10% more power) and proportionally with the square of voltage. (10% higher voltage = ~21% more power)



    I love this answer thanks so much!
  9. Best answer selected by g4kioN1.
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