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What Devices Produce the Largest Power Draw in PCs?
bcboy asks: "Considering the energy situation in California, I borrowed a watt-hour meter and have been assessing my energy use, and waste. My daily use was almost exactly the California average. So far I've cut half of it, just by eliminating waste. Digital equipment was a full 20% of my usage. Idle hubs and DSL modems pull a surprising amount of power. So do idle HP scanners that conveniently lack 'off' buttons. The laptop was pulling 20 watts while 'off', 24 hours a day. The biggest lesson from this experiment has been that things that are 'off' frequently pull significant power. But my question is (now that my desktop PC is the biggest load after the electric drier and the fridge) has anyone assessed power usage inside the PC case? What's pulling the power? The fans? The hard drives? The CPU? The memory? The cards?" It's easy to determine the power draw of some devices in PCs by looking at the labels for the specs, but some devices, like memory, may not have such specs that are readily available that may draw quite a bit more of your wattage than you'd expect.
The other posts are very good. The biggest power draining devices are the ones that emit the most heat.
I'll add some more information.
When you feel those wall-warts, they are usually very hot. The reason for this is inefficiency. The cheaper a power supply is, the more inefficient it will be, in general. The reason for this requires some explanation of how power supplies work.
First, you'll usually have a transformer. They are notoriously inefficient because of how they work. They are basically two coils with differing numbers of turns next to each other. The input/output ratio is related to the ratio of turns. Basically, power is applied to the primary coil, which has a resistance. The secondary coil actually generates power from the EM field emitted by the primary. It doesn't take a genius to realise that most of the power applied to the primary is lost in the air.
So off the secondary you will have an AC voltage lower than what you put in (here in NA it's 120V RMS). You have to convert that to DC somehow. Usually it's a bridge recifier, which will drop the voltage by about 1.4V (from peak-to-peak, not RMS) for it's own operation IIRC. This isn't something to be worried about, however. Bridge rectification is the most efficient type of rectification I've ever seen. It basically takes the negative parts of the AC waves and makes them positive.
So now we almost have DC. There's one more piece. The voltage is still bumpy. Draw a sine wave and imagine taking the negative part and inverting it on the positive side. Our devices need clean, flat DC, especially if the circuit is frequency dependent, like radios, sound cards, hard drive buses, etc.
The last piece is the regulator. These are quite complex so I'll only briefly describe what they do. You want a voltage of, say, 5VDC. You get a 5V regulator, say an LM7805. Your input voltage must be, at it's lowest point, 2.3 volts higher than your intended output for it to work correctly. This means that you'll have to put in at least 8V to be somewhat comfortable. 9-12V is quite common and 40V is the maximum. The higher the voltage you put into it and the more current the load draws from it, the harder that little guy works on regulating it. Many regulators require heat sinks to dissipate all of that heat.
Oh, but wait, how complex is your average wall-wart. I've rarely seen the correct voltage come out of one. Try measuring the ouput of a Nintendo wall wart sometime. They rarely have "real" regulators in them, often a couple of transistors. At work there's a "3V" wall-wart that outputs 6V. It blew a set-top box that required 3V. We have some Elastic DSL modems that use real 5V regulated wall-warts (I was impressed). If your device says 5V or less on it, you'd better be damned sure that's what you put into it because it's highly likely that it's expecting real regulated DC on the input, or else it would have said 9V and had a regulator inside the device. See why that voltage is so popular, now? You could also put 40V into it, but I doubt the heatsink chosen for 9V-to-5V would provide proper temperature dissipation for 40V-to-5V. I don't recommend plugging a 16V into your 9v device, either.
Finally, after all of that, your device is powered, but you've wasted a lot of energy getting there. Is there a better way?
Of course, the expensive option! The good news: you're already using it. That power supply in your computer is a switching power supply. These are much more efficient but a lot more complex. Generally, they often have much more intelligence.
There's a good book at Radio Shack on power supplies that explains all this, including how to build them. There's a section on switching power supplies as well.
I've posted here before, showing my disdain for wall warts. What came out of it was a project. Basically, the plan is to eliminate wall warts altogether and distribute power to various devices from one "power server" similarly to how it's done inside your computer. The main difference is that that devices actually request the voltage they want. You will also be able to use it on almost any existing device.
Ok, that went on a little long, but, as you can see, I'm sort of passionate about the topic.
Depending of your PC :
- the screen : those things run from 70 to 150 Watts/hour depending of size, which is really huge. A flat panel will go 20 to 30 Watts.
- the CPU - if you have one of the latest beast (Athlon 1400/Pentium 4 1,7 Ghz) it can go above 50 Watts during intensive computations
- the graphic card can be a power drain - when the GeForce or Voodoo 5 arrived some motherboards had to be redesigned to provide enough power to the board.
- DVD-ROM, hard drives or sometimes fans (if you have 4 or 5 of them, it can stack up to over 10 Watts )