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Is It Worth Investing In a High-Efficiency Power Supply?
MrSeb writes "If you've gone shopping for a power supply any time over the last few years, you've probably noticed the explosive proliferation of various 80 Plus ratings. As initially conceived, an 80 Plus certification was a way for PSU manufacturers to validate that their power supply units were at least 80% efficient at 25%, 50%, 75%, and 100% of full load. In the pre-80 Plus days, PSU prices normally clustered around a given wattage output. The advent of the various 80 Plus levels has created a second variable that can have a significant impact on unit price. This leads us to three important questions: How much power can you save by moving to a higher-efficiency supply, what's the premium of doing so, and how long does it take to make back your initial investment?"
new efficiency @ load % - old efficiency @ load % = delta%
integrate over time (delta%*cost kw/hr) until result = new unit cost (solve for t)
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we could probably use a computer to figure out the answers to those questions!
"National Security is the chief cause of national insecurity." - Celine's First Law
One advantage of a more efficient PSU is that it runs cooler. This is nice at least if you are going for a silent system, as less fans are then required.
http://www.extremetech.com/extreme/143029-empowered-can-high-efficiency-power-supplies-cut-your-electricity-bill/
If you reduce the brightness of an LCD screen backlight it will also lower power consumption. Mine uses 40 watts full brightness and 20 watts dark. So if you shave off 10 watts it may nearly equal the savings of a good psu but for no outlay.
Higher efficiency means less waste heat coming from the power supply, so its fan can run quieter.
Since the waste energy is converted to heat (which may increase the noise or temperature of the machine) it may well be worth the extra cash anyway.
Saving a few bucks on electricity is hardly the only reason to buy a more efficient power supply.
- Jesper
My security clearance is so high I have to kill myself if I remember I have it...
I tried to include an image of the formula using the IMG tag instead of text, but it wouldn't display. :( Any tips on how to include an image in a comment on /.?
I've never seen an image in a slashdot comment before, I think it's for our own safety.
Get your head out of your ass. Most electric heating is done with heat pumps. A heat pump pumps more heat into your house than the electric energy it consumes (that's why it's called that way). Heating by burning something is also more efficient than dissipating electric energy because you're cutting out conversion (see Carnot efficiency) and transportation losses.
And in the summer, if the AC is on, inefficient appliances make you lose double: once by consuming more electricity than they should, and a second time because the AC needs to consume energy to pump the heat out of your house.
The real embarrassment is that /. has never supported basic tags like <sup> which would allow proper math mark-up. Instead we get all manner of mangled, unreadable blobs for comments.
Slashdot gets worse every day... Pipedot: News for nerds, without the corporate slant
A PSU has a power efficiency curve that looks like this. That article also explains what I'm about to summarize:
Pick a PSU that is no more powerful than you need, to keep your system in the middle of that curve, for maximum efficiency. 100% margin is more than plenty, so if your components will use 250W max, you don't need a 900W PSU. Look for something in the 500 range, or even less if you pick a good-quality PSU.
You probably won't be able to make a cost argument for maximizing efficiency, but you can build a quieter system focusing on efficiency, and it's quite satisfying obsessing over something different.
This is why "software engineer" is a term I will never use willingly. It is an insult to real engineers. Heat pumps do in fact put more heat into their hot side than they consume in work. They take heat from a low temperature resivoir and send it to a high temperature resivoir.
That may be for the subset of "financial investment" but more generically:
an investment is something that returns more value than it costs.
By my definition, a car that depreciates is an "investment" because with it you were able to get a job and make more than the car cost, even if the car itself was a loss. The power supply is the same. If you count the added cost of an 80% efficient supply, you may never make back the difference, unless you count the air conditioning savings, and put a price on the externalities of increased electrical demand and such.
But in my case, the small difference was worth it by paying for itself back (including cost of capital, for those who would point that out) within 5 years. But then, I was only looking at the expensive supplies in the first place because I've found that the better supplies lower unidientified lockups, and help eliminate intermittent computer problems. So if you are looking for the cheapest power supply at 250W, and the 80% efficient one is a respectable brand and you find a no-name one for much cheaper, the no-name is the best financial decision, so long as you look at no other factors. The 80% one is an "investment" in reliable computing.
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Noise is also a factor. High-efficiency supplies have fans that run more slowly under load, or not at all. If you're building a quiet system, this is a big deal.
Note that the peak efficiency is usually at ~50% load, so be sure to size your power supply appropriately for best results. Newegg has a calculator to help with this.
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And you can thank goatse.cx for that. I can't imagine looking at that gaping hole a dozen times per day.
The info I got from the article at http://www.cameralabs.com/PC_Hardware_reviews/Power_supply/Choosing_a_PC_power_supply.shtml is this ---
If your computer consumes X-watts, it's advisable to fit a PSU that can pump out almost 2X the wattage.
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so it probably for 99% of the people won't make sense to upgrade a power supply just for efficiency
but if for some reason you need a new power-supply anyways finding a good quality (80+ gold ..etc) unit on sale is totally reasonable.... at this point most units worth trusting the rest of your gear to are probably 80+ anyways.
in my own case i had been using a 80+ power-supply that wasn't modular and cables where a hassle to manage ... i wanted a modular power-supply and also have no intention of risking a $200 processor and $300~ video card etc to a generic / shoddy power-supply so i found the Seasonic X750 (80+ Gold ) on sale for $100~ (which if you look at newegg is cheaper than any 700-800watt fully modular power supplies currently.
since i wanted/needed fully modular 750~ish watt power-supply finding the X750 for $99 made sense as it was cheapest meeting those requirements.... the fact is it 80+ is just bonus ... seasonic's 5year warr and generally pretty good reputation for quality power supplies drove the choice more than the 80+ gold.
actually I am happy to see you, however that is in fact a banana in my pocket.
If you're only factoring just the electricity bill as a factor. But there are also environmental reasons maybe and it's harder to put an unemotional price on that. This is sort of like the people who claim hybrid electric cars are a waste of money since they're only looking at the wallet and not the bigger picture. It's more than just saving a little electricity as well, there is also the slight increase in customer demand, which slightly increases the market forces towards creating more efficient products in general.
Perhaps the "pump" part of heat pump completely eluded you, since they do not defy the first law of thermodynamics as you seem to be implying.
Heat pumps work by having a sink source off of which they are pumping the heat from or away from. Most of the ones I know happen to be geothermal, which work because the sink which they are pumping from maintains a constant temperature year long underground. So, during the summer, the heat they can extract from that source would be cooler than the air above ground, but during the winter be hotter. They do this by extracting the heat from the source sink, rather than producing it themselves.
So in that respect, they work much like the fan does within your computer, since the air inside the case is much hotter when running than the air outside of the case. The fan can then displace that heat generated inside rather efficiently by just pushing the hotter air inside the case out, while bringing the cooler air from the room outside in without having to require an equal amount of energy to then power those fans as the equipment running inside of it, thus, like the grandparent, requiring less electric energy to power those fans than what the computer itself uses. If this were not so, then it'd make a lot more sense to completely seal computer cases, as the cooling benefit from the fans wouldn't make up for the amount of dust which they bring into the case during operation.
So the next time you're tempted to call bullshit on a well known physics principle, make sure you double check that you're not making some stupid mistake. Or else you'll end up looking rather foolish again when someone else points out how you don't know what you're talking about.
Are you saying this would make /. somehow a lesser site? (scratches head)
I would insert a picture of a naked cat looking quizzical here, but alas, no IMG tag support.
See what you're missing?
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If you look at efficiency graphs, you'll see that power supplies are typically the most efficient under moderate load: at low and high load the efficiency drops. A typical desktop or home server is idle most of the time, so idle efficiency will have a big impact on the total efficiency. If you over-dimension your power supply, your idle load might be 10% or less of the max rating, which is far from the optimum of the efficiency curve.
I'd recommend getting a power supply that can deliver a bit more than what you need, for example 450 W if you think you need 350 W max. A bit of margin is useful since you might not have found the actual worst case or you might want to add components later. Also it avoids poor efficiency at the high side of the curve when the system is under load.
Well technically the waste heat from a power supply is 100% efficient. Any inefficiencies from it producing heat are used to power the computer.
So they work well in heating a house as long as its not cold outside. Probably not so good in a real winter..
Theoretically spoken, they just need to pump against a larger gradient if it's really cold. They will still have a benefit, only less.
Now, practically spoken, there are these nasty little engineering considerations. A practical heat pump has to be built for cold climates, and the heat pump/AC combos that are popular in the warmer parts in the US aren't, and are actually capable of being slightly less efficient than a resistor if it's really really cold outside.
While GP is woefully incorrect and you're right to call him out on it, your explanation isn't right either. Heat pumps can in fact pump against a gradient, and are mostly used to pump heat from a cold to a hot place. Air-source heat pumps (ie. coupled to the outside air rather than a geothermal reservoir) are used in parts of the US to heat houses in the winter and cool them in the summer. They're also what makes a refrigerator work. A fridge pulls heat from a cold place (inside the fridge) to a warmer place (outside the fridge). The resulting decrease in entropy needs to be balanced by an equal of greater increase in entropy, which is accomplished by converting electricity to heat. Or, to avoid the thermodynamic jargon, you're pumping against a gradient, so you need to spend energy to do so. The heat produced at the back of your fridge is the sum of the heat that was pulled out of the interior of the fridge + the heat-equivalent of the electricity the fridge consumed. This is also what an A/C does. Now, if we turn the A/C inside-out, so that it pumps heat from outside to inside, then you have the kind of heat pump we use to heat our homes in the winter. The sum of the heat that was pulled from outside and the heat-equivalent of the electricity the device consumes is larger than the heat-equivalent of the electricity alone, thus the pump brings more heat into your home than a resistor using the same amount of electricity. GP suggested to generate electricity from this heat gradient, but the flaw in his thinking is that the heat pump as well as any electricity generation device he can come up with are bound by the Carnot efficiency, so you can never get more electricity out than you put in.
How about reliability? I require a PSU that I know is going to
(1.) Not die within a year of running at 50-75% load
(2.) Not take any other components of my computer with it.
Power supply problems are the most annoying to diagnose, because the symptoms usually show up in other components (like apparent RAM corruption, HDD stuttering, etc). I would pay $50 extra for a power supply that is *not* 80-plus if it has stellar reliability, because it means I only have to build my computer exactly once. On that note, the Corsair HX series power supplies have not only stellar reliability, but also pretty much silent. I refuse to buy anything else, and you can usually them 20% off if you watch slickdeals.
Efficiency saves you money, while reliability saves you time *and* money. And time is a limited resource for some of us...
Bought one Antec Earthwatts long time ago. The PSU was not much more expensive than the others (good brands) so the savings are obvious.
Another thing TFA doesn't take into account is that the 80-Plus certified supplies tend to have better components overall than non-certified supplies.
Read some of the reviews at Hardware Secrets and you'll see that it's not uncommon for a well-built "350W" power supply to be able to output 450W, while a crappy 350W supply can't even handle 300W.
I have built passive-cooled machines since 2004 (or very nearly passive, with some machines having a single, huge, slow fan). The only way to make a PSU fanless is less wasted heat, or better efficiency. I don't care about a few wasted watts, when I have over half a kilowatt of computation going on, but I can't stand the noise of typical computer fans. High efficiency gear also tends to be very high quality for obvious reasons, so they last long. (I still have my first passive PSU from 2004, a precursor to the PicoPSUs.)
Escher was the first MC and Giger invented the HR department.
In Sweden, electric heating is illegal because it's inefficient. "Even with a 100% efficient electric heater, the amount of fuel needed for a given amount of heat is more than if the fuel was burned in a furnace or boiler at the building being heated. If the same fuel could be used for space heating by a consumer, it would be more efficient overall to burn the fuel at the end user's building."
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