Can't believe how little power my system actually uses!

By Bobbyrae
Jul 15, 2012
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  1. I had been wanting to do this for long time and finally just decided to. I hooked up a Fluke ammeter to the input of my system to measure the total power consumption while running. I think most of us have no real clue how much power we are using. I know I didn't.

    Remember, the power supply is only about 80% efficient, so if the power consumption from the wall comes out to 500 watts, then the system is probably actually using 400 watts.

    Here's my system:
    Athlon XP 2000+
    1 gig DDR 3200 RAM
    SCSI card plus 3 SCSI drives
    GeForce4 MMX video
    CD burner
    DVD burner
    card reader
    5 fans

    When I bought the system, I got an Antec 480 watt PS. When it went out, I replaced it with a Seasonic 400 watt fanless PS. Now it was acting weird, so I replaced that with a PC Power and Cooling 500 watt PS. With the two PS failures, I was getting concerned about how much power I am using.

    But when I measured the power, the maximum draw was 1.2 amps! Which works out to 144 watts from the wall, and that is about 115 watts available to the system. I ran it for a while and did a bunch of things trying to work the CPU and drives as much as possible, but that was the most power draw I could see. I did not do anything with the CD or DVD drives, but how much do they pull?

    Am I missing something? All this time I was thinking maybe 400 watts wouldn't be enough, but it looks like overkill.
  2. dmill89

    dmill89 TechSpot Guru Posts: 737

    400w isn't really overkill since that system will draw around 330w under 100% load. That being said it is very rare that a system actually runs at 100% especially in a system such as that one where the drives make up a significant portion of the power draw. You would have to be running something graphically intensive, while writing to all HDDs, and using both optical drives which would likely be impossible on a single core CPU like the Athlon XP. Under normal conditions that system will likely draw around 150-200w when loaded so a good 350w PSU would likely be sufficient although a 400w would offer some extra overhead, a 500w would be slightly overkill but not excessively so especially given the minimal price difference between 400w and 500w PSUs these days. Your PSU failures are not likely caused by system loading but by the models of PSUs that were chosen. From The age of the system I'm guessing that the 480w antec was one of the older CWT built models (SmartPower,TruePower, TrueBlue,etc.) with failure prone fuhjyyu capacitors. The SeaSonic while a good unit, being fan less would likely run hot potentially reducing its capacity prematurely (all PSUs weaken over time but heat accelerates this). The PCP&C is an excellent option. While 500w may be a little overkill it should be as reliable as anything you can find (except for a server grade unit but those cost several time more than it).
  3. SNGX1275

    SNGX1275 TS Forces Special Posts: 12,489   +292

    A long time ago I posted what my system uses. It was the same system as I have now, except I had an old 8800GTS (320) rather than my 5830 that is in it now. Under heavy gaming load I was able to pull 261 from the wall. I forget what I was pulling at idle but I'm sure I said what it was when I posted it originally. So I am not surprised at your results. I used a Kill-A-Watt meter for my numbers.
  4. Marnomancer

    Marnomancer TechSpot Booster Posts: 808   +51

    Anyone heard of a Raspberry? :cool:
  5. Bobbyrae

    Bobbyrae Newcomer, in training Topic Starter Posts: 25

    OK. But remember that I said I couldn't get it to go past 115W!

    Yes, it was a TruePower. Just before it failed completely, it would shut off a few seconds after first turning the system on, then work fine for hours on the second power on.

    Actually, the Seasonic is now working just fine! Despite all my testing and being convinced it needed to be replaced, I can now save BIOS settings to CMOS. I have concluded that there must have been a small amount of corrosion on the cable contacts, and that removing and reconnecting BOTH ends fixed it. Oh well, the PPC unit is now a backup.
  6. dmill89

    dmill89 TechSpot Guru Posts: 737


    With an old single core CPU like that one it is virtually imposible to load a system to 100% power wise (the CPU may be at 100% but not every other system device would be at 100% but rather they would cycle in and off due to the CPUs inability to multi-task which can lead to lower than expected power draw at a given "load".

    Also the CD/DVD drives can draw around 15w ea. so if you are using them it might put you up around 150w or so, again the CPU may not be able to access them continiously while also preforming other tasks, again skewing the numbers.

    In general it is always a good idea to get a PSU atleast powerful enough to run a PC with all devices at 100% power draw (which all of yours were) even if few systems will ever see this, enough to run the system at 100% with a 20% overhead is usually recomended.


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