useless, but fun facts.. effect of overclocking on power use - Page 2
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Thread: useless, but fun facts.. effect of overclocking on power use

  1. #16
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    I've wanted to see such a thread for a while now. Great work Jerboi.

    I hope this dispells so many misconceptions about PSU requirements. This also says to me that new PSUs need to be developed. The new CPU use increasingly small core voltages but consume a fair current.

    As for the magic 1.1:

    Pure resistive load,

    Full bridge rectified (no cap) has Idc=2Ipk/pi
    Irms supply = Ipk/sqrt(2) => Irms= Idc * pi/2 *1/sqrt(2) = 1.1

    There is your relationship between average & RMS and hence the scewed scales on multimeters.

    For my studies I have 1 year for research and will be looking at resonant voltage regulators and EMC compliance. It will be interesting to see if they would be viable for multirail computer supplies.



    More magic numbers:

    Idc = output current Irms=supply current

    Half bridge: Irms=1.57Idc (resistive) 1.41Idc (inductive)

    Full bridge: Irms=1.1Idc (resistive) 1.0Idc(inductive)
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  2. #17
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    Originally posted by SexyMF
    I've wanted to see such a thread for a while now. Great work Jerboi.

    I hope this dispells so many misconceptions about PSU requirements. This also says to me that new PSUs need to be developed. The new CPU use increasingly small core voltages but consume a fair current.
    Unfortunately marketing will continue to push 500W and such PSU. A PSU with properly balanced output in each bus and designed with low enough ripple will work just fine. 180W of power properly distributed is more than adequate.

    You should have 42% extra power than necessary, so PSU is only loaded to 70% the rated power. Even then, 250W PSU is more than adequate for most consumer computers.
    My web machine
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    It's very quiet.

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  3. #18
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    Cool

    Yes, I agree about the power supply ratings turning into a bit of a marketing numbers game. I did my power measurements about a year ago (and posted the results in the cpu forum here). I was trying to dispel the myth that typical home computers actually use all the 300+ Watts that the PSU’s are rated for. Generally it is true that the higher rated your PSU then the larger the main capacitors and the more resilient it will be to load dump transients and the like, so bigger generally is better. But just the same I also firmly concur with Jerboi that a properly designed 200Watt PSU could (if one was specifically designed to ) handle just about any home PC in use today.

    I sometimes think of the PSU ratings “numbers game” as being a bit like the old audio power ratings fiasco. You know when you’re buying and audio amplifier (or even a set of amplified computer speakers) and you see all those ratings like 1000 Watt PMPO or even 2000 Watt PMPO (peak music power output). Just as with computer PSU ratings this no doubt gives people the false impression that many hundred or even thousands of Watts are need to provide a reasonable sound level in the average living room. This is of course nonsense as it really only takes about 5 to 10 Watts (with reasonably efficient speakers) to do this. Hehe, I even pulled one of my friends “1000 Watt PMPO” amplified computer speakers apart the other day to show him that the actual driver (speaker) was rated at only 10 Watts, LOL. As many people know, when you go shopping for a stereo amplifier that a unit rated at something like “20 Watts RMS per channel at 0.005% THD” is often way better (louder and cleaner) than one rated “1000 Watt PMPO). Just another marketing numbers game LOL.

    Power factor is down to 0.64 due to harmonic distortion. 1.5A+1.5A+1.5A+1.5A will be less than 6A, because harmonics from multiple computers tends to cancel out the distortion and increase the power factor. The resultant current is what really counts when you're trying to squeeze in many computers on the same circuit.
    Sorry but I have to nit-pick the above just a little. Sure it is true in general that if multiple different types of load are connected in parallel that some of the current harmonics are likely to cancel out giving a results current with a somewhat lower RMS value than the sum of the individual RMS currents. You’re correct, indeed it’s a mathematically provable fact that the RMS of the sum of the currents can be no larger (only equal or less) than the sum of the individual RMS currents (triangle inequality). Unfortunately however if you connect multiple computers then they will all have very similar shaped waveforms on the input line current. In particular they will all tend to pull a positive/negative spike of current right at about the positive/negative peak of the AC mains voltage. In reality the scope for harmonic cancellation is quite limited with multiple loads that are so similar.

    BTW, It’s nice to meet some others here with interest in electrical power. .
    Last edited by uart; August 19th, 2002 at 12:23 PM.

  4. #19
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    Yes, I agree about the power supply ratings turning into a bit of a marketing numbers game. I did my power measurements about a year ago (and posted the results in the cpu forum here). I was trying to dispel the myth that typical home computers actually use all the 300+ Watts that the PSU’s are rated for.
    Let's not forget that physically near identical power supply maybe rated 300W by manufacture one, but 340W by manufacture two. My power supply is supposedly 340W. The OEM manufacture limits safe load to 315W. Another seller says 340W max, but 5V+12+3.3V load shouldn't exceed 285W. One is playing more conservative.


    Generally it is true that the higher rated your PSU then the larger the main capacitors and the more resilient it will be to load dump transients and the like, so bigger generally is better.
    Larger main capacitor only means more energy stored in DC bus and it means more up-time in case of power black/brown out until UPS transfer. Large capacitor for small load means detrimental effect on input power factor. Larger the capacitor, worse it is for power factor. If you're running hundreds of computers with unnecessarily large input stage capacitors, this creates unnecessarily high neutral current on 208Y/120V distribution system.

    Sorry but I have to nit-pick the above just a little. Sure it is true in general that if multiple different types of load are connected in parallel that some of the current harmonics are likely to cancel out giving a results current with a somewhat lower RMS value than the sum of the individual RMS currents.
    No need to be sorry. This is a technical forums. I'm all happy if you can contradict my errors through technically valid arguments.

    I guess you have a point here.
    Since institutional computer facilities use multiples of identical power supplies, it is even more similar than home situation. Although, with slight difference in load, RMS current is slightly reduced.

    Loads of obviously different character difinitely influences significantly. 30W CFL on electronic ballast has PF of 0.51, two lamp 40W magnetic ballast has PF of 0.6. When you use them together on same circuit, the resulting PF is about 0.75. One is inductive. Other is rectifier load.


    Unfortunately however if you connect multiple computers then they will all have very similar shaped waveforms on the input line current. In particular they will all tend to pull a positive/negative spike of current right at about the positive/negative peak of the AC mains voltage. In reality the scope for harmonic cancellation is quite limited with multiple loads that are so similar.
    Current crest factor is used to quantify such current pattern. Pure resistive load has a crest factor of sqrt 2. Crest factor is peak current/RMS current. As to cancellation... hmm.... I dunno.. I'll have to hook 'em up to my scope and see. I won't be able to tell exact distortion content though.. I don't have a Dranez-BMI power analyzer..


    BTW, It’s nice to meet some others here with interest in electrical power. .
    ]

    I thought I was the only one.
    My web machine
    ~Econobox 60W~
    Power consumption at the plug while web browsing: 60W
    It's very quiet.

    Intel D815EEA2 Desktop board
    Intel Celeron 1.0A @ 1.0GHz w/ Intel Fan
    ATI Xpert98 8MB AGP 2x videocard
    Sound Blaster PCI 128 soundcard
    WD 40GB ATA100 7200RPM HDD (8.4GB 5400RPM ATA33 circa 1999 Maxtor decommissioned and eBay'd off)
    384MB PC100 (3 x 128MB)
    40x12x48 BTC CD-RW
    300W Enlight PSU
    100% normal looking case. Certified free of fruity, sad looking, PC rice mods.

  5. #20
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    Since institutional computer facilities use multiples of identical power supplies, it is even more similar than home situation. Although, with slight difference in load, RMS current is slightly reduced.
    I have been looking at single & 3 phase mains (230V) in the power electronics lab at my Tech. With a couple hundred computers with SMPS in them then mains waveform is clipped by about 5 voltages with the 3rd hardmonic multilating the falling edges.



    ...that a properly designed 200Watt PSU could (if one was specifically designed to ) handle just about any home PC in use today.
    To true.... and stop running peltiers off them!!! (badly at that)



    BTW, It’s nice to meet some others here with interest in electrical power. .
    These forums need such perspective.
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