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Confused. Need help...

post #1 of 8
Thread Starter 
I have a OCZ Modstream pro 700watt PSU. It has two 12v rails supporting 25amps each. During some overclocking on my 6850 today, I noticed in GPU-Z that its pulling 40amps overclocked. So I reset the clocks to see what it does stock clocks. It was pulling 35 amps stock. So heres where I get confused. If the line is rated for 25amps.... where is it getting 35 and 40? And does this mean I wont be able to crossfire two 6850s at stock speeds because they would each need 35amps?
post #2 of 8
The amperes measured by GPU monitoring software have nothing to do with the PSU.

P = VI
Power = Voltage * Current
Watts = Volts * Amperes

In your GPU, you have 40A at (vcore)V. So if your vcore is, say 1.15V (seems typical) then your GPU core is consuming 40*1.15 = 46W. Then you have additional power draw from your VRAM and ancillary circuitry on the graphics card including its power conversion circuitry, which should all total up to around 120-140W. And all but about 2-5W of that is on the +12V (the remaining couple watts are on the +3.3V).


Meanwhile, your ModXStream has 46A total +12V capacity, or 552W.


That clear things up?
Edited by Phaedrus2129 - 2/3/11 at 7:12pm
post #3 of 8
Thread Starter 
Quote:
Originally Posted by Phaedrus2129 View Post
The amperes measured by GPU monitoring software have nothing to do with the PSU.

P = VI
Power = Voltage * Current
Watts = Volts * Amperes

In your GPU, you have 40A at (vcore)V. So if your vcore is, say 1.15V (seems typical) then your GPU core is consuming 40*1.15 = 46W. Then you have additional power draw from your VRAM and ancillary circuitry on the graphics card including its power conversion circuitry, which should all total up to around 120-140W. And all but about 2-5W of that is on the +12V (the remaining couple watts are on the +3.3V).


Meanwhile, your ModXStream has 46A total +12V capacity, or 552W.


That clear things up?
Clears it up enough for me. Power calculating is way to confusing. Is there some sort of tool you can use to plug into specific power ports, like 6pin and 8pin connections to see the actual card draw? I know you can buy tools to check the total power draw from a specific power plug. But is there anything designed for actual plugs inside a PC?
post #4 of 8
Not really. There's a custom PCIe card that you can get that slots into the PCIe slot, and then the GPU slots into that and that measures draw through the slot; and then you can use ammeters to measure draw through the PCIe power connectors. But the card costs well over a thousand, and it takes some expertise to learn how to use all of this.
post #5 of 8
Thread Starter 
Quote:
Originally Posted by Phaedrus2129 View Post
Not really. There's a custom PCIe card that you can get that slots into the PCIe slot, and then the GPU slots into that and that measures draw through the slot; and then you can use ammeters to measure draw through the PCIe power connectors. But the card costs well over a thousand, and it takes some expertise to learn how to use all of this.
F. that. lol
post #6 of 8
hardware.fr is a French site that has that setup and uses it to accurately measure graphics card consumption. You should check out their lists.
post #7 of 8
Thread Starter 
116 watts full load on stock settings? that seems lower then most other sites.
post #8 of 8
Every other site (except one other, I forget who) record power at the wall, meaning that that includes the CPU and RAM and hard drives and motherboard and fans and everything, divided by the power supply's efficiency at that particular load.

Hardware.fr are the ones who are correct.
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