CPU Current/Power

In the Intel specifications for processors, each has a thermal design power. Is this the maximum power that your processor, when heatsunk in the Intel approved way, can stand ? Does it correspond to the maximum temperature of operation ?

When your processor is consuming some power, P, it is drawing some current. It is also operating at some voltage - just one ? I will assume that it a single voltage. Then at the power P it is possible to calculate the current drawn...now I seem to remember reading that in motherboards equipped with a "P4" 4-pin square Molex connector, the processor is powered through this connector which uses 12V. To calculate the current drawn by the processor at power P do I use the operating voltage of the chip (assuming it is one voltage, typically 1.5V) or do I use the 12V voltage supplying it ? (You will have worked out that I am trying to estimate the maximum current drawn by the CPU on the PSU)

In contructing this question, I have made some assumptions about the way a CPU is powered, and I would appreciate if I were corrected if any of these are incorrect.

Dumb_Question
7.September.2012
Compaq Presario S5160UK DT261A under XP/SP3
Processor - Celeron 2.7 GHz
Motherboard - MSI MS-6577 v2.1
RAM - 1GB + 512MB (1GB +1GB max) DDR PC2700
PSU - Octigen 300W model 10270PSOTG ('upgraded' from original Bestec 250W PSU [in 2011?])
Nvidia GeForce 6200 graphics card in AGP slot.

 

Hi DQ,

I don't have schematics of any late motherboards but will make some assumptions. Those Toroids, especially near the 4 pin 12 V. connector indicate that they are probably using switching power regulators so the effeciency is great. The 12 V. is being reduced to the 1.5 V by one of those regulators. The power draw by the processor must be very great or we wouldn't need those monster sized heat sinks. Hope this helps a little.

Jim

 

hey Jim,

Thanks, you seem what you're talking about anyway. Assuming you are right, and the 12V -> 1.5V step down is 100% efficient, it doesnt matter where one measures the TDPmax. TDPmax for my processor is about 68W, hence the draw on the PSU at 12V (I assume all the power for the CPU comes through the "P4" connector) 6.7A - call it 7A. If the conversion is a pessimistic 50% efficient, that would be 14A - significant for my PSU.

Anybody know what voltages an AGP socket delivers, and what a GeForce 6200 takes ? I can't find that on the Nvidia site.



Dumb_Question
9.September.2012
Compaq Presario S5160UK DT261A under XP/SP3
Processor - Celeron 2.7 GHz
Motherboard - MSI MS-6577 v2.1
RAM - 1GB + 512MB (1GB +1GB max) DDR PC2700
PSU - Octigen 300W model 10270PSOTG ('upgraded' from original Bestec 250W PSU [in 2011?])
Nvidia GeForce 6200 graphics card in AGP slot.

 

The TDP is the maximum the amount of heat the cooling system will have to handle during normal use,as simple as that.

The maximum temperature of operation is a separate number,this number usually means the cpu will not become permanently damaged when kept under this temperature e.g 110C.

It's the debatable what the best temperature is best for a cpu to run at but in general the cooler it runs the longer it will last,under 70C during regular use is a nice number to shoot for.

At full load your CPU will draw about 7 amp's as you stated,the efficiency of the power conversion will be in the ball park of 80-98% so an actual draw of about 8amps at full load.

AGP slot can provide 48 watts,your card will run fine in an agp slot it draws little power.

Your maxumum power consumption at full load will be around the 100w mark and your power supply should handle it fine unles you have an excess of ancillary components.

 

Geforce 6200 draws 11W idle 26W under full load.

http://mark.zoomcities.com/images/gfx/GFXpowerchartby3d.png

 

26W ? that's pathetic :-D Thanks for that information.

The maximum temperature for my CPU is 67C I think. I've been up to 60C (briefly, on occasions) but now usually I run at ~40C or just under (speedfan shows some spikes that are up to 42C and I am a bit concerned that the sample misses the real peak temperature).

Thanks for info on AGP and GeForce 6200, do you know which PSU rail this is from ?

My maximum power consumption will be around 100W ? I cannot get below 300W (recommended, 250W minimum) using eXtreme Outer Vision PSU calculator, and if I put everything I can think of in, absolute worst case, I get 464W (of course I havent told you every device that's hanging off my system, but I will).

Additional bits of my system

I have 6 USB2 ports (maybe that is 4 true one ? HP have removed the spec for my PC from their website so I can't find out), so that's potentially another 6 x 0.5A @5V = 15W.

Usually I only one fan (not including the PSU fan), but at present I'm using 2, so that's another amp (at most) 1A x 12V = 12W.

I have 1 HD, a CD, a DVD and a 3.5in floppy [all c 2000 so of old, possibly inefficient design].

A 56K dial up modem resides in a PCI slot

Then there are the sundry other chips on the m/b including Northbridge [6W} (I looked it up, that's probably the biggest user as it had a h/s), Southbridge. and of course the 2 DIMMs (draw on the 3.3V ?).

Then there are the three heatsinks which are presumably on the switching transistors referred to by jlphlp, which indicate some additional power consumption (maybe that's included in the 2 -20% step down from 12V to 1.5V for the CPU)

So that's at least 130W (max) without counting drives, memory and things I've forgotten [67 x 1.1 + 26 +15 +12 + 6] (can't understand how the PSU calculator gets up to 300W let alone more - adding 'capacitor aging' makes a significant difference [upwards])

Dumb_Question
10.September.2012
Compaq Presario S5160UK DT261A under XP/SP3
Processor - Celeron 2.7 GHz
Motherboard - MSI MS-6577 v2.1
RAM - 1GB + 512MB (1GB +1GB max) DDR PC2700
PSU - Octigen 300W model 10270PSOTG ('upgraded' from original Bestec 250W PSU [in 2011?])
Nvidia GeForce 6200 graphics card in AGP slot.

 

300w is about the minimum most calculators recommend and that's the maximum power draw before failure not the maximum power draw during general use,most cheap power supply's would fail catastrophically if you draw anywhere close to that so it's better to have some headroom.

Most power is drawn from the 12V rail.

Suffice to to say your system should be fine.

 

Headroom is what I'm after really. The eXtreme Outervision PSU calculator (have you tried it ? Doubtless you have) is quite detailed [that's only the free one] and also gives a 'minimum' power and a 'recommended' power.

Most power is drawn from the 12V rail ? That's what they say, but my PC was designed in the older days when perhaps that wasn't so true. The original PSU was a 250W model, but able to draw up to 165W from the (3.3V & 5V) rails [if you believe the label]. New "good quality" power supplies are not specified to that limit on the (3.3V & 5V) rails, infact they are often labelled as being more than 25% short of it (but they are occasionally capable of exceeding specification). My thinking is "Why did they put a PSU with that spec into my PC (design into my PC) ? " There was, I suspect, some reason...I've yet to find any kind of explanation.

Dumb_Question
10.September.2012
Compaq Presario S5160UK DT261A under XP/SP3
Processor - Celeron 2.7 GHz
Motherboard - MSI MS-6577 v2.1
RAM - 1GB + 512MB (1GB +1GB max) DDR PC2700
PSU - Octigen 300W model 10270PSOTG ('upgraded' from original Bestec 250W PSU [in 2011?])
Nvidia GeForce 6200 graphics card in AGP slot.