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Efficient Power Supply Contest
A reader writes: "In the June (paper) issue of Scientific American, there is a mini-article descibing the energy being wasted by power supplies in computers. Those things are only 60-70% efficient in converting line-voltage AC to low-voltage DC, and there are so many millions of them out there that a modest efficiency increase could trim $1billion or more from the annual energy costs of the USA. Well, various governmental agencies are seeking to get improved power-supply efficiency into the marketplace. The central "clearinghouse" site is at efficientpowersupplies.org, and details of their contest are in this PDF."
You can also check out power supply reviews on Silent PC Review. They concern themselves with efficiency since an efficient power supply can be quieter and produce less heat.
The site also has a lot of other good info.
Also one should take into consideration someone using a 500W is only getting 350 at 70% effecient. If you had a PS that was 90%, you would only need a 400W.
Now that you have a smaller PS, you might could drop a fan or two. This now decreases your power load on your new 400W.
Savings on effeciency == savings everywhere
Switching supplies can approach 90% efficiency if they are carefully built. Such supplies will cost more, naturally, but an improvement from 60% to 90% efficiency will save you the extra cost over the course of a year or so. And, of course, you can feel better that you are contributing slightly less to carbon dioxide emissions.
What if the same idea where applied to computers. Right next to the standard wall outlet would be a world standardized jack with six or eight pins for each of the required voltages.
Low voltage computer mains would make UPS systems less complicated too.
I've even heard of vendors who make telco friendly rackmount PC's that take 48v DC mains.
This is a boring sig
by switching from energy guzzling CRTs to cool power efficient flat screens. I went from a 19" CRT at 350w to a 19" flat screen at 50w quite painlessly.
I doubt you could achieve that kind of savings no matter how power efficient you made the PS.
In short, there is almost NO reason to not use those fluorescent bulbs and it would result in a far greater amount of energy savings right now...
I'm a professional engineer, and have done several designs of switchers that were better than 95% efficient. But they cost more to make, so dream on, it's not going to happen in the mainstream with out some sort of mandate. The tricks are simple, better inductors (cost more for bigger copper and more ferrite), synchronous rectification (fet and drive costs more than a diode), taking care to be clever about quiescent currents (more engineering time) and so forth.
Doug Coulter, owner
C-Lab
http://clab.mystarband.net
The space savings are significant in the computer labs especially. Students now have room to put their books out in front of them, between themselves and the screen. (we had crowded labs before, the desks are narrow and close together.).
The power savings are good. Before, students would forget to turn off the monitors when class was done. It still happens, but when those LCD's go into powersave mode, they use almost nothing.
The rooms stay sooo much cooler. Our AC was always running in the computer labs before, with 30 17" CRT's going (and PC's). but the LCD's produce so little heat that the room stays nice and cool, and the AC is off more than it is on. (lots of energy savings there).
My back is very thankfull, and every time i have to move a CRT monitor across campus, I am reminded about how thankfull my back is.
What are we going to do tonight Brain?
1) Because the whole electronics industry has already been built up on electronics based on DC supplies, all chips, the circuits learned in EE class for common functions, etc.
2) The semiconductor technology that 98% of our electronics know-how is based on operates on low voltages, so you'd have to convert the higher 120-220-400 line and transmission voltages to low voltages anyways.
3) Most electronic active components in our current technology (semiconductors, even tubes), are asymmetric with regards to polarity and do not have "friendly" characteristics with truly bipolar (AC) signals and supplies.
4) Much of electronics can be viewed as tasks in signal processing, particularly signals that vary in time. AC power is itself electrical power that varies in time (e.g. 50-60hz). Therefore using AC as a supply into circuit would inherent introduce a LARGE signal on top of any signals you were actually interested in.
5) Batteries are inherently DC sources, so making circuits that can run of both batteries and an AC power source would be more complicated if the circuit required AC to run (you'd have to build the equivalent of a DC->AC inverter which is considerably more difficult than a AC->DC power supply, and doing so would waste battery power (inefficiencies in conversion), which is much more precious in most applications than wasting power originating from an AC powerline source.
No, your question and your understanding was valid. The power rating on a power supply states what maximum power the supply can deliver to its load. The actual power consumed *from* the power supply is solely a function of the load attached to it (i.e. the "computer" components it runs). The actual power consumed *from* the wall outlet is the sum of the power consumed by the power supply's load (i.e. the computer components) plus the extra power consumed by the power supply (i.e. the waste) which is directly proportional to the power supply's efficiency.
WarriorPoet42 got it right the second time around - but this did not make your question "stupid."
BY THE WAY: Just because you have a 400W power supply in your PC does NOT mean you are consuming 400W of power from the AC outlet. If you put an older (slower) CPU/mobo with no expansion cards, and run, say, a modern low-power hard drive, etc., the LOAD presented to the 400W power supply will be much lower. Think about it. Small form factor PCs are often built with 150W power supplies. This means that the components NEVER consume more than 150W, and probably seldom if ever hit that peak.
A side-effect of this is that the power supply efficiency does not necessarily always *waste* its ratedpower-minus-(1-minus-efficiency).
(whaatt??) Let's say:
R is the power supply's rated power.
E is its efficiency expressed as a fraction of 1 (i.e. 90% efficiency is expressed as 0.9)
So, a 400W (R=400) power supply with 80% (E=0.8) efficiency will *waste* 400*(1.0 - 0.8) 80 watts of power. But ONLY if the LOAD is drawing the full 400 watts of power!
Now let's say we have a 400W power supply with 80% efficiency, but the computer components only draw 180W of power. Let's use C to represent the power draw of the computer, so C=180. Now, just substitute C for R and you get:
C*(1-E) = 180*(1.0 - 0.8) = 36W. This is what you are REALLY losing due to power supply inefficiency.
Note: A switching power supply will have some minimal losses even if there is NO load attached to it. These are small compared to the efficiency losses in normal operation, so for practical purposes may be ignored. You could add a constant (say, K) to the equations above to account for this static power loss in the power supply, but K would be small, when compared to C, so has little effect on the math....