redleader
10-24-2004, 09:51 PM
Looks like someone finally built a system for recording power use in processors electrically:
http://www.goodwin.ee/sulo/Power2.htm
I made myself a modified PSU, where I measure a DC voltage drop across the DC resistance present in smoothing inductors that are already in place in the PSU. I have RC circuits to smooth out all the voltage ripple so I can just measure an DC voltage drop and would not annoy my millivoltmeter with AC components.
I then measured the DC resistance of those inductors by placing various loads on three power rails and measuring the voltage drop across the inductors. Then calculated the resistance based on a known load resistance and measured voltage drop.
After that I measured all the other important bits that would consume current from the rails that interested me most: +12V and +5V. +5V rail was only interesting with K7 boards because my K7 boards consumed the CPU power from +5V rail. In these cases I only had to measure what HDD consumed from +5V rail. As long as I didn’t have PCI cards in the system, nothing else seemed to consume anything really from +5V rails. To single out current going to CPU from a +12V rail, I also had to measure current HDD consumed from +12V rail and also that of all the fans. The fans were different and so I measured all the fans separately whenever I measured the other stuff. Just pulled out the CPU cooler fan to see how much the consumption dropped, then inserted it right back. The fan in a PSU itself I had of course measured beforehand.
After subtracting all this “other stuff” from the currents I measured from PSU rails, I also had to take into account the efficiency of CPU power regulator. I assumed it to be 84% efficient. No, I have no real experimental basis for this, only a lot of reading of a few powerregulator datasheets. I think it is quite a good guess. If the efficiency is actually higher, then my measured results should be corrected upwards slightly, but more so for load power figures.
He goes on to test a few modern processors. What was interesting was the Palomino figures. They're at least as high as most if not all of the Northwood line. Not prescott though.
http://www.goodwin.ee/sulo/Power2.htm
I made myself a modified PSU, where I measure a DC voltage drop across the DC resistance present in smoothing inductors that are already in place in the PSU. I have RC circuits to smooth out all the voltage ripple so I can just measure an DC voltage drop and would not annoy my millivoltmeter with AC components.
I then measured the DC resistance of those inductors by placing various loads on three power rails and measuring the voltage drop across the inductors. Then calculated the resistance based on a known load resistance and measured voltage drop.
After that I measured all the other important bits that would consume current from the rails that interested me most: +12V and +5V. +5V rail was only interesting with K7 boards because my K7 boards consumed the CPU power from +5V rail. In these cases I only had to measure what HDD consumed from +5V rail. As long as I didn’t have PCI cards in the system, nothing else seemed to consume anything really from +5V rails. To single out current going to CPU from a +12V rail, I also had to measure current HDD consumed from +12V rail and also that of all the fans. The fans were different and so I measured all the fans separately whenever I measured the other stuff. Just pulled out the CPU cooler fan to see how much the consumption dropped, then inserted it right back. The fan in a PSU itself I had of course measured beforehand.
After subtracting all this “other stuff” from the currents I measured from PSU rails, I also had to take into account the efficiency of CPU power regulator. I assumed it to be 84% efficient. No, I have no real experimental basis for this, only a lot of reading of a few powerregulator datasheets. I think it is quite a good guess. If the efficiency is actually higher, then my measured results should be corrected upwards slightly, but more so for load power figures.
He goes on to test a few modern processors. What was interesting was the Palomino figures. They're at least as high as most if not all of the Northwood line. Not prescott though.