Is there a "Power Gauge"?

Discussion in 'Power Supplies' started by rjolin01, Aug 29, 2009.

  1. rjolin01

    rjolin01 [H]ard|Gawd

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    Is there a way to monitor how much power your psu/computer is utilizing? I know there are "adapters" that you plug into your outlet and they tell you how much wattage you are using. But I was wondering if there was a built in program in windows or a downloadable one that tells you how much you using. Kinda wanna see what I use doing various things on my pc.
     
  2. Rogue71

    Rogue71 [H]ard|Gawd

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    youd have to measure your power usage from the source....meaning the wall, to get an accurate measurement of power usage. your best bet to my knowledge is one of the "kill a watt" tools. i find it useful for almost all my electrical equipment to guage power usuage. i dont beleive it would be possible to use a program on the computer to measure true power usage of the system. you could read some voltages but the true measurement is from what your psu draws.
     
  3. rjolin01

    rjolin01 [H]ard|Gawd

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    ok thanks I just ordered a kill a watt off ebay so I am curious as to how much my pc contributes to the electric bill.
     
  4. Zero82z

    Zero82z [H]ard as it Gets

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    No, that would be impossible. And be careful with Kill-A-Watts, because they can often report incorrect power consumption numbers when used with PSUs that have active PFC.
     
  5. ryan_975

    ryan_975 [H]ardForum Junkie

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    Aren't they usually wayyyy off when that happens though (like 23 watts when you know you're drawing at least 150)?
     
  6. Zero82z

    Zero82z [H]ard as it Gets

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    No, it usually isn't that obvious. Someone who knows a decent amount about the power consumption of various components might catch it, but most people wouldn't realize. And that's the real problem.
     
  7. Rogue71

    Rogue71 [H]ard|Gawd

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    i guess im confused... how can a kill o watt be off by 23w?? regardless of a psu using a pfc or not, it records power being pulled from the wall. so by leaving it plugged in for 12 hrs should give you pretty accurate yields, unless there is somehting im not understanding. i dont care what my psu does with its power, i just want to know how much the system sucks out of the wall. id like some clarification pls.
     
  8. Dangman

    Dangman Ninja Editor SuperMod

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    And that's why I keep notes like this:

    Here's Paul Johnson's post about the inaccuracy of the Kill-A-Watt:
    http://hardforum.com/showpost.php?p=1032190998&postcount=7
     
  9. Zero82z

    Zero82z [H]ard as it Gets

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    Kill-A-Watts are wrong because measuring power with loads that aren't purely resistive is not as simple as it sounds, and when it comes to $20 devices compared to a $150 Brand power meter, you get what you pay for.
     
  10. Rogue71

    Rogue71 [H]ard|Gawd

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    i actually did quickly look this up but from what i an see no it isnt as acurate as it should be but its close. being off by 10-15w isnt that huge. ive never bothered to mesure systems at load because its a pita but the killowatt has always been pretty close with idle power usage. nice to know about the fluctuation though.
     
  11. Zero82z

    Zero82z [H]ard as it Gets

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  12. keenan

    keenan 2[H]4U

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    A PSU with PFC should give a more accurate reading, not less.
     
  13. Zero82z

    Zero82z [H]ard as it Gets

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    No, not really.
     
    Last edited: Aug 30, 2009
  14. AVT

    AVT [H]ardness Supreme

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    I'm just curious, what leads to these inaccuracies? Why can't it accurately measure it for some PSUs?
     
  15. Zero82z

    Zero82z [H]ard as it Gets

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    The specific reason is unknown. All we know is that it happens, but not why or how to predict which PSUs it will occur with. That unpredictability is why Kill-A-Watt readings are so problematic.
     
  16. keenan

    keenan 2[H]4U

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    Yes. If the power factor is 1, as PFC aims for, the load appears entirely resistive, and any dumb/slow measurement device will be accurate. Most of the measurement problems result from non-unity power factors and nonlinear waveforms. With a power factor of 1 both current and voltage should be in phase and close to pure sinusoids (since the voltage is not controlled by the device in question and is a 'pure' sine from the grid), and thus easy to measure. Certainly PFC won't make anything worse.

    With pure DC it's simple, you just measure the current and voltage and you've got a sample of instantaneous power consumption. However AC makes things a lot more complicated; the power that appears to be flowing into the load may in fact be returned to the source during a later part of the cycle (this is what the power factor represents), so it's not actually consumed in the load. This effect is made yet more complicated by loads that are nonlinear, like computer PSUs. Getting an accurate measurement is fairly difficult and requires either highspeed digital sampling and signal processing or high speed analog circuitry, neither of which is cheap or easy to design. You really need proper test gear if you want to measure this accurately.
     
  17. Oklahoma Wolf

    Oklahoma Wolf PSU Warranty Voider

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    I actually have two KAW's along with the Brand 4-1850 for reviews. The two KAW's are a fair bit apart from each other in readings... one of them is so far off I can't use it for anything. The good one is still a fair bit less accurate than the Brand is.

    When it comes to units fooling the KAW, it does happen now and then but to be honest it's been months since I last had a review sample actually do it. That said, these things have a really slow sampling rate and as such are useless for catching transient peaks. That, along with the fact that they just aren't that accurate, means I rarely ever use even my good one for data on a power supply review. They just don't get anywhere near as accurate as the Brand. The Brand can also measure far more precisely below 100W.

    FWIW - my good KAW's been off by 60+ watts on high power units. Don't ask how far off the not so good one gets, but it's significant.

    Bottom line - you get what you pay for with these things. It'll only give you a general idea what's going on most of the time. Just don't expect pinpoint accuracy from it, because you won't get it.
     
  18. Zero82z

    Zero82z [H]ard as it Gets

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    As I understand it, Kill-A-Watts and similar meters have a slow sampling rate and measure the average power transfer over a period of time, so they don't require voltage and current to be in phase in order to get accurate power readings. If they did, they would be almost entirely useless for measuring the power consumption of any device without APFC, which is the case for many consumer electronic devices. Of course, as Oklahoma Wolf pointed out, the slow sample rate also means that they are useless for catching transient spikes.

    Like I said before, the cause of the problems with Kill-A-Watt meters and APFC PSUs isn't known, but I don't think it's directly related to that. It could have something to do with the way certain manufacturers implement their PFC circuitry, or it could just be a random thing. I don't think there's enough information out there to make that determination (or if there is, nobody has gone ahead and done any testing to try and narrow it down as far as I know).
     
    Last edited: Aug 31, 2009