Why Estimate When You Can Measure?

You’ve neglected to rate the power comsumption of your displays. I plug my computer, display and high end KVM into my APC UPS, which rates the power consuption and usually sit about 220watts.

I wouldn’t mind tracking down some of those killawatts for my other devices and such tho!

Incidently, your device (and my apc ups) measure and report AVERAGE flow, but I doubt either one can properly account for sudden, short spikes that might be required.

Then you get in to power per rail on the supply, ability to step into a sudden demand increase etc etc etc. Always buy QUALITY, but that also usually means higher wattage capactity also. Nothing wrong with that, as it gives you room to grow and spike into.

You’ve neglected to rate the power comsumption of your displays.

LCDs are about 20-40 watts, as I recall.

I doubt either one can properly account for sudden, short spikes that might be required

You can see the power spike when you power on the PC (hard drives are notorious for requiring a startup power spike). The kill-a-watt does sample a few times a second.

This got me interested…

so I just picked up a kill-a-watt, well ok something similar, a no-brand chinese gadget. In HL2, doom3, whatever the highest peak power consumption I’ve managed to have the thing display is 152 watts…

FYI specs
Sempron 2300 @ 2375mhz 1.85vcore (sisoft sandra 2007 estimates this as 90 watts)
1gig DDR500 @ 2.8v
seagate 250gb 7200
Legend 6600GT 128 AGP 600/1100
various lights and about six fans (25w total)

This is shocking, I’ve been looking to buy a 600 watt power supply for my SLI rig i’m cooking up, but this is implying for my current ageing rig I don’t even need my generic 400 watt power supply? I’ve got a old 300w somewhere that should do the job on my current system…??


That’s the advantage of measuring yourself instead of following all the hearsay on the Internet. :wink:

How much more does a Sapphire Radeon x850 XT take in watts compaired to a PowerColor Radeon 9800 PRO?

And can a 300/350 watt(not sure if its 300 or 350) PSU handle this?:

17" CRT Screen
AMD 64 3800+ 2,4Ghz Venice
Sapphire Radeon x850 XT
Asus-Socket 939 - ATX Nforce4 (A8N-E) - Gblan/Raid
Kingston HyperX 2x512MB DDR dual channel
2xMaxtor HDD
3xSeagate HDD
Zalman - CNPS-7700-CU (CPU fan)
2 x 80mm chassi fans

ok i came on here wonderin if my ‘‘old’’ 300w supply would b ok for the p4 i wanted to buy, and seems thats the answer is a defo yes :slight_smile: and id need to b a power mad crazy modder to get close to 300w

one question tho if i do some how top the 300w mark is it true that the only affect it will hav (according to sean’s post) will b blue screen?

OK, so if you lose 50% of the wall power, then when you buy a UPS and plug your PC into the UPS you are losing 50% of the UPS right there.

IOW if you designed the PC power supply such that the UPS comes AFTER the switching (so the battery is as close as possible to the motherboard) you would automatically, immediately get a 50% boost on UPS capacity.

Not to mention, the wall-to-DC circuitry can be removed from the UPS, as the computer’s power supply is now doing that.

That seems a better design to me …

Anybody know where these beasts might be available - or what they’re called so I can search for them?

I googled for “internal UPS” and got a few hits.

Why is this such a specialty item, since the design makes more sense to me, but the regular UPS design is available at every computer shop?

You’re measuring steady state operation.

What about turn-on requirements - I have 7 hard drives in one machine - all that inductance would draw TONS of power, right?

It’s low power requirement to keep the platters turning once they’re up, but could a 300W PSU provide that initial whack?

This is all very good discussion and Jeff, that device looks intriging… good find.

However, one issue was overlooked… heat.

The closer the steady watt usage is to the peak rating of the PSU, the more hot the PSU will get. If a PSU is used close to its peak rating steadily, you not only endanger your PSU, but you also add a little to the heat to the already hot system.

I understand not all areas suffer the 115F summer weather as I do but a suggestion for anyone like me who is very concious of heat (or even sound) in thier system, I would measure your average watt usage when idling and try to get a PSU that is rated for close to, if not, twice that amount. (and I reccomend a 120mm fan to account for sound as well)

I hope my input helps!

I’ve just got myself a eVga 7800GT and I feel my current Chinese/elswhere manufactured 400w power supply may succumb to a quick death if I shove it in…after searching a bit (and landing on this site) I was wondering if I could just purchase another Chinese/elswhere 400w and dedicate it to the VGA card? from what I’ve read this particular VGA card WILL suck 50w or so of power from its Pci-express slot would this still lead to an untimely demise for my current installed PSU?

My sys specs are:

  • Pentium 2.8 HT(cooled w/ Gigabyte Rocket cooler)
  • 768MB ram
  • Audigy 2 soundcard
  • VGA In-build Intel 915 Xtreme Graphics
  • Western Digital 80GB sata
  • 1 x Gigabye DVD writer, 1 x Gigabyte Combo drive

hi, i wanted to know how much power consumption my laptop does for a hour. my laptop spec are:
Intel core 2 duo.
1Gb ram.
Geforce go 7400 (256MB)
15.4" wide screen display.
lightscribe DVD writer (Double Layer burning).

could you please tell me how can i measure the power rating.

I have owned a “Kill-a-watt” device for some time. I purchased it to monitor the (60) cycles of my 2 RV generators. One MUST run @ 3600RPM to produce 60 cycles…but I digress…
My “Kill-a-watt” NEVER reads 60 cycles, even on the grid. It ALWAYS shows 59.9 cycles. Anyone else notice such an error in cycles? Makes me wonder the accuracy of the other functions.

For a detailed breakdown of AC power demand under idle and max load conditions for many different types of systems, have a look at the updated REAL SYSTEM POWER REQUIREMENTS table on page 4 of SPCR’s Power Supply Fundamentals – http://www.silentpcreview.com/article28-page4.html

Most of the systems are using high efficiency ATX PSUs; the highest one being 84~85% at the top of its efficiency curve. The max power draw of even an OC’d Pentium D950 + ATI X1950XTX system is just 256W.

I need a lil help im running 8 19" monitors. 4 off a ATI firemv 2400 pci-e, 2 off a nvidia gefore fx5200, and another 2 off a ATI radeon X600, in addition I have a 250GB WDC 7200rpm sata system hard drive, a maxtor 200gb external usb hard disk, a phillips 5.1 soundblaster pci audio, 4GB ddr SDRAM, and I also have a AMD Athlon x62 4800+. I have a 350W PSU and my CPU keeps crashing what you guys suggest I get

The reason people insist on big power supplies is because you need them for reliable operation. Components usually have surge powers that are 2-3 times larger than steady-state powers. Your hard disk uses 10W under normal operations, but 25-30W during spin-up. Same thing goes for your DVD/CD drive. How about your motherboard and other non-mechanical electronics? When you hit the power button, there’s a ton of capacitors with large in-rush currents. If your computer implements power saving (AMD Cool-n-Quiet or Intel Speedstep), it is periodically adjusting voltages on those capacitors, again, with big currents.

Beyond that, you want some safety margin. The most common system failures are either mechanical (fans and hard disks), or hot capacitors failing, typically in the power supply. If you’ve got a power supply with cooling such that it is rated at 250W pushing out 250W of power, it will be very close to the failure point of those caps. If it’s a 500W one, you’ll be halfway to room temperature. Your time to failure will go from quite low to very high.

Measuring beats guessing and calculating, but you’ve got to have basic clue about failure mechanisms, failure rates, and EE to do the measurements properly.

Surely you need a larger psu as it is the way it distributes the power to all the different components in your computer.

For example a 600w psu has a maximum output of 600w yes, but this is split between ±3v ±5v and 12v and other things. So as in your example if all your components need say 12v and need about 300w of it, you may need to have a psu that can supply “in total” 750 or 800. Each PSU is different and distributes it’s power differently… just something to mull over or prove wrong.


400W benchmark is come and gone. On old PC’s would’ve been fine with 400-500W PSU but latest ones will not work with less then 500W. My 2900Pro graphics card alone chews up 150W on standby and 350W on full load. Add a CPU (65-150W), all the ram, optical and hard drives etc, and you have whooping 600W. Throw in another graphics card and you got yourself looking for the latest(at least 85% efficient) 1000W PSU.

Someone mentioned that their computer blue screened, and they changed the power supply and that fixed it. A new power supply will have slightly different voltages outputs for 3v, 5v, 12v, and 28v; or whatever voltages it’s designed to produce. As soon as you change the DCPS, you have new voltages being applied to your various devices/loads, which changes the timing in all your circuits. In failure analysis I often felt I could solve a timing problem just by adjusting the voltages. Voltage inputs can straighten up a lot of the leading and trailing edges on your signals, and can eliminate timing problems that may contribute to blue screens.