Do I Have Enough Power?

[g4kioN1]

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

 

[AMD Radeon]

even crossfire 7870 will be safe

xfx psu has good reputation

 

[toyftw]

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

 

[Brett928S2]

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

 

[g4kioN1]

Why can't I use the molex adapter? I thought that was the reason for including them.

 

[g4kioN1]

bump

 

[InvalidError]

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.

 

[g4kioN1]

Thanks, btw if I overclock the GPUs without rasing the voltage will it affect the power that is drawn?

 

[InvalidError]

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)

 

[g4kioN1]

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!

 

[g4kioN1]

Best answer selected by g4kioN1.