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Max Power Consumption of Asus P5B Deluxe Wifi-AP?

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February 5, 2011 2:22:40 AM

I have an Asus P5B Deluxe Wifi-AP motherboard and I'm wondering what its max power consumption is.

For a "three 12V rail" power supply (ATX standard) one rail supplies the CPU, one rail supplies the PCI-E connector and the other 12V supplies power to everything else (hard drives, optical drives, motherboard). The 3.3V and 5V rails power USB devices and depending on the computer power some of the motherboard and RAM.

Anyway, I'm trying to see how much power my motherboard uses at max power consumption, but I have only been able to find one site that has it listed. The website said it was a ridiculous 170 watts at load and 135 idling. This seems really high, maybe they're counting RAM and other things like that in there, I don't know.
What I'm guessing is they are including components connected to the motherboard: and
If my motherboard really does use 170 watts at max load (~14 amps) then in addition to my single DVD drive and hard drive one of my 12V rails would be (sometimes) overloaded (has a max of 18A). This doesn't seem right.

I guess it doesn't really matter if my machine has been running fine for years, but I was just curious. I was looking at all my components today and seeing what power supply I needed for my GPU upgrade and the motherboard was the only thing I didn't really know about. For the longest time I've been under the impression that motherboards don't really use much power at all, but I may be wrong.
a b V Motherboard
February 5, 2011 7:15:49 AM

Quote:
I have an Asus P5B Deluxe Wifi-AP motherboard and I'm wondering what its max power consumption is.


The ASUS P5B or any MB for that matter does not have a power consumption or power draw rating as you are suggesting. Motherboards have built in voltage regulators which create and direct the various voltages needed to power the hardware plugged in to the various headers the MB supplies. For example, the CPU will draw 12v power from the MB's CPU socket according to the CPU's voltage requirements and MB's compatibility for it's voltage regulators to supply x amount of power needed for the specific CPU. RAM slots have a voltage regulator directing the power to the slots. System BIOS can have voltage adjustments to CPU and RAM and other chips or connection headers built onto the Motherboard.

To measure how much power your system is putting out at any given time, boot up, overclocked, etc., a simple monitor like this can measure the amount of power a system is using.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
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a c 217 V Motherboard
February 5, 2011 6:47:25 PM

sgtmattbaker said:
The website said it was a ridiculous 170 watts at load and 135 idling.

Those power consumption figures are measured at the wall outlet. It's the total system power consumption including power loss due to power supply unit inefficiency.
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February 6, 2011 4:22:30 AM

Everyone understands what I'm trying to do right? I'm trying to see how much power each component hooked up to my power supply uses so I can add up the devices' total amperage and see how much current is being drawn through each rail.

Anyway, so I would measure the power at the wall, multiply that by the efficiency of my power supply, then subtract the known energy use from my other components to know the watts my motherboard uses when powering the other devices?

Thanks.
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a c 217 V Motherboard
February 6, 2011 3:39:53 PM

sgtmattbaker said:
Anyway, so I would measure the power at the wall, multiply that by the efficiency of my power supply, then subtract the known energy use from my other components to know the watts my motherboard uses when powering the other devices?

Thanks.

If it were only that easy.

Power supply efficiency is not constant, it varies with the load placed on it. Some power supplies don't even reach the efficiency stated as the manufacturers' claim.

If you want real accuracy you would use a digital DC clamp-on ammeter and measure the current flow of each of the non-black wires (i.e. +5 VDC (Red), +12 VDC (Yellow), ..., etc.) exiting the power supply unit and sum the currents for each voltage.
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February 7, 2011 1:28:08 AM

Hmm, that doesn't sound particularly safe.
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a c 217 V Motherboard
February 7, 2011 4:05:31 AM

sgtmattbaker said:
Hmm, that doesn't sound particularly safe.

I take it you've never seen or used one before.



You just clamp the sensor over one of the current carrying wires and read the amps. No need to break the circuit because it is contactless. It is much safer than using an ammeter that is inserted in-line, is less disturbing to the circuit, and much more convenient.

To do a contactless measurement with the clamp ring the ammeter uses a hall effect device to measure the axial magnetic field generated in the wire by current flowing through it. The clamp surrounds the wire, which is creating a magnetic field around it according to Ampere's Law. The magnetic field is concentrated by an iron core contained in the clamp. The magnetic field is sensed at an air gap that contains a semiconductor hall effect detector. Current flowing through the silicon chip is deflected by the magnetic field creating a voltage perpendicular to the direction of electron flow. This voltage is detected and converted to amps by the internal microprocessor and displayed on the LCD panel.

The direction of the magnetic field depends on the direction of current flow in the wire and is indicated by the plus and minus ampere readings. An arrow in the clamp ring indicates the polarity.
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