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RE: Current measurements on powersupply P4 pin

hfavandepas wrote:

In some posts, I saw measurements of the current on the P4 pin of about 0.7 amp when working. And 1 amp during boot and startup. I found these mentioned currents very high. So I measured them myself.

The only reported measurements of CPU current draw on this list in recent months that I know of have been mine so I assume it's these you are referring to. If so, your report is not quite accurate. In January, I wrote:

“I repeated . . . the measurements I did of the current drawn by the E7200 chip [on the G31 motherboard]. On power up, it draws about 1.5 amps. As ‘underclocked’ BIOS settings kick in during POST, this falls to about 0.6 amps. Once the OS is loaded and while playing music (with a NOS DAC), the chip draws between 0.4 and 0.5 amps or between five and six watts."

The meter I used was an old Avometer DVM 2001 with 1000-milliamp (ma) and 10-amp ranges. For obvious reasons, I started on the 10 amp range, saw the 1.5 power-on peak and, well, left it there.

In the light of your post, I dug out my other meter, a rather newer Fluke 8060 with a 2000 ma range, making it safe for this test.

I'm using a 12 volt linear supply to drive the CPU (and a "pico-processor" à la mode GStew for the P24 line). Except that I use a USB NOS DAC (so no soundcard) and run at 140 MHz and a nominal Vcore of 0.75, I think the systems are comparable.

I repeated my tests using the Fluke on its 2000 ma scale. The current peaked soon after power-up for about 30 seconds at around 1500/1600 ma (though it went off the scale on one occasion), falling by degrees to settle at 330/340 ma when playing.music.

This figures seems much the same as yours though I confess I'm less willing than you to place confidence in figures showing tiny differences when doing this or that.

The difference between my January measurements and the ones I've just done I'd put down to

1. Using a different meter on a different scale - a 10-amp scale is always going to be rough. I was happy enough to get any data at the time as I couldn't find anything else anywhere else and all I wanted was a ball-park figure. I got one.

2. Since taking those measurements, I've changed a deal of settings and no longer recall what is different between the two setups. The measurements are broadly in line with each other, much the same as yours and adequate for purpose.

What might be of interest is that if you set Vcore to "Normal" (i.e. 1.5 volts or about double what I used above), the system settles at 1070 ma when playing the same track as above. In short, setting Vcore with care can cut the current draw by almost two-thirds – not to be sneezed at.

Best

Dave

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