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How do I measure How much amps my CPU uses?

post #1 of 9
Thread Starter 

I have a CP850 which has 4 12V rails. The CPU is on 12V1

 

My next PSU is one big single 12V rail.

 

I understand the CPU uses the 8pin cable to pull power from, correct me if I am wrong. is there a tester or something ? Or what tool should I use? Please give me a link

 

All I find is using a multimeter. I want to know how much my 2500K draws from my CPU


Edited by jonashendrickx - 9/26/12 at 12:17am
post #2 of 9

On the +12V, divide the wattage by 12.  So if the CPU is using about 95W under full load, then it's using about 7.91A.

 

Which PSU are you getting?

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It's a computer!
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CPUMotherboardGraphicsRAM
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post #3 of 9
simple physics,

A(in amperes)=W(in watts)/V(in volts)
so:
A=W/V

for example, I have a CPU which uses 12V rail, tdp is 125 watt, so 125/12= 10.4166 amps, this is probably wrong, becouse I don't exactly know what voltage and wattage is right in this case but, that's the formula to calculate amperes. just need the right numbers for it to work correctly thumb.gif
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post #4 of 9
Thread Starter 

So if a 2500k uses 120W while stressing with Linx it's actually using 10A at 4.5GHz?

 

I have my PSU plugged in in something like this: 

 

And at idle I fluctuate between 68W-80W

When I fire up Prime95 or Linx I get 300W at 4.3GHz

 

68-80W equals 5-15W in CPUID HWMONITOR

300W equals 112W in CPUID HWMONITOR


This is a big difference hardware vs software monitoring. I realise the method I currently use is not that accurate. But you ain't telling me software is that accurate here... The other components shouldn't be taking so much power. Let's say I don't have even a discrete GPU connected when doing this.

 

300W-70W=230W (substract load and idle)

230W/12A= 19A


I wonder which calculation sounds the most realistic :P

post #5 of 9

The reading in a monitor like that must be multiplied by the approximate efficiency of your PSU, but it's still going to be a bit approximate.  So if your PSU is 85% efficient during the reading, then let's take 68-80W and multiply it by .85:  that shows that the system is actually pulling about 57.8-68W (68 and 80 multiplied by .85).  So a 300W reading with an assumed 85% efficiency means the system is pulling about 255W from the PSU.

 

Software really isn't accurate for this sort of thing.

 

I'm curious about something:  why are you so concerned?

 

I am also still wondering: which PSU are you getting?

It's a computer!
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CPUMotherboardGraphicsRAM
i5-2500K @ 4.5GHz (1.368-1.384V fixed voltage) ASUS P8P67 EVO B3 (UEFI ver. 1850) GTX 780 ASUS DirectCU II (1228 / 6300, 1.180V) G.SKILL Ripjaws X 8GB (2 x 4GB) 1866MHz, CL9 
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It's a computer!
(19 items)
 
  
CPUMotherboardGraphicsRAM
i5-2500K @ 4.5GHz (1.368-1.384V fixed voltage) ASUS P8P67 EVO B3 (UEFI ver. 1850) GTX 780 ASUS DirectCU II (1228 / 6300, 1.180V) G.SKILL Ripjaws X 8GB (2 x 4GB) 1866MHz, CL9 
Hard DriveHard DriveHard DriveOptical Drive
250 GB Samsung 840 EVO (C:\) 250 GB Samsung 840 EVO (D:\) 150 GB WD VelociRaptor Samsung SH-S243N 24x DVD Burner 
Optical DriveCoolingOSMonitor
Samsung SH-S203N 20X DVD Burner Thermaltake Frio Win 7 Home Premium x64 SP1 Retail AOC G2460PG (24" 1920 x 1080 144Hz G-SYNC) 
KeyboardPowerCaseMouse
Filco Majestouch 104-key Cherry MX Blues w/NKRO Corsair HX650 (Bronze, ordered on 12-12-2009) CM 690 Intellimouse Optical (1.1A) 1000Hz polling rate 
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Basic, but premium round X-Fi Titanium HD Klipsch ProMedia 2.1 (with 16 AWG Monster Cable... 
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post #6 of 9
TwoCables beat me to it- you can't directly correlate wattage from the power socket with the wattage your CPU is using. PSU efficiency (AC-DC conversion), rail splitting; and yes the other components do use power (DVD drive, fans add up).
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post #7 of 9
Thread Starter 

My PSU is a CP850. It has 80% effeciency. That brings me to around 15A.

I am getting a Antec HCG650W.

Reason I am throwing away the CP850 is that I didn't feel like buying a big antec case. They were either too expensive or  something else. Another reason is that the CP850 isn't very efficient. It's already almost 4-5 years old. Now I finally will have a PSU that fit's my case with 88% effeciency. It may not be the best PSU around but it was one of the best for its price.

I won't buy a new GPU anyway. I currently have a HD6950. The integrated graphics from intel are becoming so good I won't need one for what I use it for.

So I figured 650W and a single rail is plenty for my needs.

I might jump onto Haswell bridge or Ivy Bridge-EX and get me a faster i7. Even you say a 2500k is fast enough. If you compile Android very often jumping to a i7 will at least make it one hour waiting instead of the two hours I have now.

post #8 of 9
Quote:
Originally Posted by jonashendrickx View Post

My PSU is a CP850. It has 80% effeciency. That brings me to around 15A.

I am getting a Antec HCG650W.

Reason I am throwing away the CP850 is that I didn't feel like buying a big antec case. They were either too expensive or  something else. Another reason is that the CP850 isn't very efficient. It's already almost 4-5 years old. Now I finally will have a PSU that fit's my case with 88% effeciency. It may not be the best PSU around but it was one of the best for its price.

I won't buy a new GPU anyway. I currently have a HD6950. The integrated graphics from intel are becoming so good I won't need one for what I use it for.

So I figured 650W and a single rail is plenty for my needs.

I might jump onto Haswell bridge or Ivy Bridge-EX and get me a faster i7. Even you say a 2500k is fast enough. If you compile Android very often jumping to a i7 will at least make it one hour waiting instead of the two hours I have now.

 

So, have you been wondering if the 650W High Current Gamer will be enough?  If so, then it's actually overkill because all you would really need is a quality 450W power supply because a quality 450W power supply would be able to continually deliver 450W.

 

http://www.guru3d.com/articles_pages/msi_r6950_twin_frozr_ii_oc_review,9.html

 

Their system pulled 316W from the wall outlet with one 6950 in it under full load.  The 6950 was the only thing under load, so if we add 200W in order to account for the rest of the system, then that comes to 516W.  If we assume that their PSU is 85% efficient, then that would mean the system would pull up to 438W from their PSU.  This means that a quality 450W power supply would be enough.

 

In other words, you have much more than enough for just about any CPU upgrade or video card upgrade - especially considering how each new CPU and GPU requires less power than its predecessor.


Edited by TwoCables - 9/26/12 at 1:56am
It's a computer!
(19 items)
 
  
CPUMotherboardGraphicsRAM
i5-2500K @ 4.5GHz (1.368-1.384V fixed voltage) ASUS P8P67 EVO B3 (UEFI ver. 1850) GTX 780 ASUS DirectCU II (1228 / 6300, 1.180V) G.SKILL Ripjaws X 8GB (2 x 4GB) 1866MHz, CL9 
Hard DriveHard DriveHard DriveOptical Drive
250 GB Samsung 840 EVO (C:\) 250 GB Samsung 840 EVO (D:\) 150 GB WD VelociRaptor Samsung SH-S243N 24x DVD Burner 
Optical DriveCoolingOSMonitor
Samsung SH-S203N 20X DVD Burner Thermaltake Frio Win 7 Home Premium x64 SP1 Retail AOC G2460PG (24" 1920 x 1080 144Hz G-SYNC) 
KeyboardPowerCaseMouse
Filco Majestouch 104-key Cherry MX Blues w/NKRO Corsair HX650 (Bronze, ordered on 12-12-2009) CM 690 Intellimouse Optical (1.1A) 1000Hz polling rate 
Mouse PadAudioAudio
Basic, but premium round X-Fi Titanium HD Klipsch ProMedia 2.1 (with 16 AWG Monster Cable... 
  hide details  
Reply
It's a computer!
(19 items)
 
  
CPUMotherboardGraphicsRAM
i5-2500K @ 4.5GHz (1.368-1.384V fixed voltage) ASUS P8P67 EVO B3 (UEFI ver. 1850) GTX 780 ASUS DirectCU II (1228 / 6300, 1.180V) G.SKILL Ripjaws X 8GB (2 x 4GB) 1866MHz, CL9 
Hard DriveHard DriveHard DriveOptical Drive
250 GB Samsung 840 EVO (C:\) 250 GB Samsung 840 EVO (D:\) 150 GB WD VelociRaptor Samsung SH-S243N 24x DVD Burner 
Optical DriveCoolingOSMonitor
Samsung SH-S203N 20X DVD Burner Thermaltake Frio Win 7 Home Premium x64 SP1 Retail AOC G2460PG (24" 1920 x 1080 144Hz G-SYNC) 
KeyboardPowerCaseMouse
Filco Majestouch 104-key Cherry MX Blues w/NKRO Corsair HX650 (Bronze, ordered on 12-12-2009) CM 690 Intellimouse Optical (1.1A) 1000Hz polling rate 
Mouse PadAudioAudio
Basic, but premium round X-Fi Titanium HD Klipsch ProMedia 2.1 (with 16 AWG Monster Cable... 
  hide details  
Reply
post #9 of 9
There's no simple way of doing it accurately... and it's not cheap either. The closest you can get (without spending a few thousand $) is using a quality clampmeter on the EPS/ATX CPU connector... but that's not what the CPU uses, it's what reaches the CPU VRM, so without the ability to accurately measure the VRM efficiency, you won't know what kind of power actually reaches the CPU, but it should still be a relevant number (VRM numbers won't be that far off from the actual CPU draw, so on a quality board you can estimate a ~90% VRM efficiency and go from there).
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