The eXtreme Power Supply calculator mentioned above is pretty accurate now. Plus it has been updated on a regular basis with latest components. Now they have two versions: Lite (free) and Pro (small fee). Pro version has Amperage on main PSU rails, which is very useful since only Wattage is not enough to decide which PSU you need.
Highly recommended.
http://www.extreme.outervision.com/psucalculatorlite.jsp
How many watts does the Kill A Watt use?
How many watts does the Kill A Watt use?
My no-name KillAWatt copy apparently uses .67 watts.
Can anyone explain this for me -
I plugged my two monitors into the meter and it read approx 60 watts.
Then I plugged my computer in and it read approx 69 watts.
However when I plugged the double adapter that hooks up both the monitors and the computer, it read 80 watts. Shouldn’t that be closer to 130?
Is there a good explanation for this, or are my suspicions correct that the accuracy of the meter is not very good.
I did get more predictable results with the computer and monitors turned off - monitors sleeping at 14 watts, computer at 23 watts; combined through the double adapter is 38 watts.
Worth noting that leaving the computer turned off, but left on at the wall, for a year, adds up to 332kWh = 480kg greenhouse gases (using figures for my town)… or about the same as a 1800km car trip in a medium sized car.
Thanks for this great article. I’ve been wondering about my laptops power usage, and this really helps with getting some real answers.
I’m going to have to buy me one of those devices. Would be real helpful when I go looking at HDTV’s too.
wow this is amazing, i like every post of your blog keep it up,i’m looking forward on your everyday post… i enjoy reading it.
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Bhojoy
Funny enough, with the new graphics cards where you have to have a 1200W PSU to SLI, your laughter over not going to ever pull 450Watts of power in a system is more and more flawed… 
What about external USB devices?
There are a lot of them that recharge (MP3, mobile phones…) or use the computer’s power to work (portable hard disks, lights…). To know for sure how many Watts you need, you must add them too.
The calculations of how much power each component uses is completely off. At best you’re estimating the difference between idling and under load. It’s not like the CPU, hard drive or graphics card is going to not use any power at all when idling. It would be pretty hard to use 118W for just sitting there if that was the case.
The most basic element of any power using device is the power supply.
I always use the best quality unit(atx,ect.) I can find as the cheap units usually save money on their internal componets.
What sets a top quality unit apart is the quality of their capatitors,filter inductors and even the slew rates of their switching regulator chips.What I look for is very fast voltage recovery times under high instantanous current loads; still one of the best,and harshest power supply tests.
Also, in order to meet these requirements, most very high quality units come with power factor control built into their switching regulator circuits
Thanks for the article Jeff, got to see if I can get one of these Kill-a-Watt things over here in Blighty =)
I will have hours of fun measuring devices all over the house, mainly so I can tell my dad he is wasting more energy running around turning things off standby than he is saving!!
BTW, some people seem to think their display is going to affect power drawn from the PSU - this is only true for laptops though.
All desktop setups use separate power supplies for the monitor (and speakers). A few (older) PSUs have a output kettle socket that you can connect your monitor power lead to, but that is just a pass-through connector and doesn’t take power from the PSU.
Thanks for the article Jeff, I will have to see if I can get one of these Kill-a-Watt things over here in Blighty. =)
I will have hours of fun measuring devices all over the house, mainly so I can tell my dad he is wasting more energy running around turning things off standby than he is saving!!
BTW, some people seem to think their display is going to affect power drawn from the PSU - this is only true for laptops though.
All desktop setups use separate power supplies for the monitor (and speakers). A few (older) PSUs have a output kettle socket that you can connect your monitor power lead to, but that is just a pass-through connector and doesn’t take power from the PSU.
Couple of things that don’t seem to have been covered. One is that the power rating of a PSU doesn’t necessarily indicate its efficiency. This is a figure that is notably lacking from most specifications. In theory, a 500W (max) reasonably efficient PSU running a certain system (say requiring 180W between all the rails) could consume less mains power than a 300W inefficient PSU powering the same system.
The second is the thing about total energy auditing. It’s all very well to get a new machine which consumes 100 or 120 Watts less power, but how many people stop and think how many Joules of energy it took to produce that machine? What if, for example, in order to recoup the energy burnt creating the machine you would have to use it instead of your old box for 10000 hours?
No one ever stops to add it all up. The most environmentally friendly industry wide option would be to abandon Windows Vasti^HVista so that people can continue using the machines they already have, instead of junking them by the million for a bit of visual glitter and no extra usability.
Similarly for cars. IIRC the energy required to mine the necessary raw materials and build a new car amounts to about half as much as it will ever consume in its lifetime. So, replacing your old car with a new one has done half the damage it will ever do before you even take it out of the showroom. It is actually greener’ to repair your old car and continue using it for an extra five years or so than it is to scrap it and get the latest “I’m green” status symbol.
People don’t think about the energy audits, so many want to be seen to be environmentally conscious so much more than they actually want to be so.
Dave J.
dave h.
you are a genius.
i’ve considered that same argument form an automotive standpoint, but never considered it in reference to computers. (btw, i stumbled upon this thread)
i’m exiting your frame of context here, but if you were to consider a “petaFLOPS/mwatt” scenario, and you were to consider the benefits of owning a more modern, “my-computer-is-faster-than-yours” style machine, wouldn’t your theory of “doing more with less” become invalid?
also, since battery drain has become such a ‘hot button’ topic nowadays , what kind of stuff are you considering to increase battery life? lowering voltage in bios? general hardware mods? how would you get more life out of a laptop? (not that any of us are interesting in trivial things like that…)
great topic because nowadays electricity is too costly, but anyone can tell how to cut power consumption and do continuous computing.
http://www.australiawholesalers.com/australiansuppliers/Computers/11-0.html
Sorry for not reading all the comments, but I wanted to make it short and sweet.
I just purchased the Killawatt, and it’s an awesome device (Really does seperate the BS from the truth), but here is the kicker, and this is what you need to pay very close attention to.
It’s not the Wattage that typically kills the system (This is in response to Sean on August 2005, replying because it needs to be out there and I don’t know if it was said) It’s the amount of Amps on the 12v Rail that are of significant importance…
Let me give you my example… I recently purchsae a Corsair 650watt power supply. Thie 650 Watts is cute, but the important thing about this power supply (What makes it quality) is it has 52Amps on the 12v Rail.
You want to account for a majority of your devices being connected on the 12v rail. With my 1090T, 5770 (Crossfire), 4Gbx2 Gigs of Ram, 3HDD, 1 DVDRW, and a Thermal Take 760i (Plus Fans) I get about 240watt… When playing World of Warcraft, I hit 270watt… If you take the Total Watt consumption, and divide it by the volts pushing it (it’s on a 12 volt rail) You get a realistic representation of how well your Power supply fits in (FYI, if your powersupply doesn’t at least tell you how many amps on the 12v rail… It’s not a quality Power Supply) At 240, I am approximately 20Amps… At 270Watts, I’m at 22.5 Amps… If my 12v Rail supplys 52amps, then I’m in the clear as I’m not even approaching 30 yet.
If Someone wants to correct me, feel free, I like learning as well!
It’s funny reading this post 6 years later and realizing that your PS is much more efficient right now. I’ve at my side a 500W Corsair and it runs, at least, with 80% efficiency… That’s a lot!
And I have never been over 350W, that on the power meter.
Hmm…can someone archive this to where it doesn’t show up in searches this information is outdated to the point of being nearly completely useless.
What exactly is out of date about it? How can you even build a desktop computer that pulls 450 watts today?
It’s out of date in the other direction, perhaps, since several components have gotten a lot more efficient. Today’s CPUs and SSDs not only draw lower peak power than their older counterparts, but get the job done and back to idle more quickly. To be sure, the video card you used was pretty low power, both for that generation and compared to gaming graphics today. But more and more PCs today are using iGPUs which sip electricity by comparison.
The main problem continues to be the second-to-last paragraph, which is plain wrong and always has been. You can’t choose a power supply based on the readings from your Kill-a-Watt. The comments above have already touched on the reasons – the Kill-a-Watt has slow response time, so it is showing average consumption, not peak, and definitely not inrush. Which is appropriate per its design intent to help you save money on your electric bill. It also doesn’t give any information about the breakdown between the various power rails within the computer; having extra total power doesn’t help you if the +12V rail is overcurrent, which was a real concern when the power supply standards actually capped the current on a single rail, so that higher-end PSUs had to have split +12V rails.
Bottom line, the Kill-a-Watt was never designed or intended for capacity planning, and trying to use it off-label like that is going to end in disappointment. For electronics, the likely outcome is random reboots and data corruption. For other devices, tripped circuit breakers.
I’ll say it again: “Contrary to the suggestions in this blog post, you can’t choose a PC power supply based on the readings from your Kill-a-Watt.”