Power efficiency - laptop vs desktop

[Scott_Arm]

Someone told me that laptops use more power than desktop PCs and I could see how that would be true. I thought maybe inefficiency in charging the battery could lead to power loss, but the components are all low watt, so I still couldn't figure out how that would work. Any truth to this? I also wasn't sure if they meant a top of the line desktop hog vs a standard laptop, or if they were comparing a crippled Dell with integrated video vs a laptop.

I'm looking at either getting a laptop or a desktop as my next primary computer. I don't really care about taking the computer out of my house, but I thought it would be nice to have a computer I could fold up and put away, so I wouldn't need a designated desk for it. My other consideration is having a really low power consumption computer for my primary use, to try and reduce my overall energy budget.

 

[AlphaWolf]

Someone told me that laptops use more power than desktop PCs and I could see how that would be true. I thought maybe inefficiency in charging the battery could lead to power loss, but the components are all low watt, so I still couldn't figure out how that would work. Any truth to this? I also wasn't sure if they meant a top of the line desktop hog vs a standard laptop, or if they were comparing a crippled Dell with integrated video vs a laptop.

I'm looking at either getting a laptop or a desktop as my next primary computer. I don't really care about taking the computer out of my house, but I thought it would be nice to have a computer I could fold up and put away, so I wouldn't need a designated desk for it. My other consideration is having a really low power consumption computer for my primary use, to try and reduce my overall energy budget.

In general a laptop is going to use a lot less power than a desktop. The highest end laptop/portables could probably consume more than PC designed to be low power usage.

 

[Zaphod]

In general a laptop is going to use a lot less power than a desktop. The highest end laptop/portables could probably consume more than PC designed to be low power usage.

Maybe. The highest end laptops today consume ~90W when running at full tilt.

 

[Scott_Arm]

Maybe. The highest end laptops today consume ~90W when running at full tilt.

Yeah, w/ such low watt requirements, I couldn't see how that would be possible. The only thing I could think of was efficiency in charging the battery. Any idea how much power is wasted charging the battery vs running a traditional PSU?

 

[AlNom]

You would have to take the LCD into account too, right?

 

[Scott_Arm]

You would have to take the LCD into account too, right?

I have no idea. I'm assuming this person was wrong, but I wanted to see if there might be any truth. They said they read an article in some tech magazine, but couldn't remember any real details other than laptops were declared, "more power hungry," or something.

I'm assuming it was comparing an average desktop, because there's no way a laptop could draw more than a dual core beast with dual video cards or something like that. In the end, I still can't figure out how it would be true. I know if you have a high-efficiency PSU for your PC, it will be about 80% efficient. I have no idea what the efficiency is for a laptop battrey when fully charged or charging. It would have to be pretty low for it to ever make up for the disparity between desktop and laptop power requirements.

 

[Zaphod]

Any idea how much power is wasted charging the battery vs running a traditional PSU?

I believe notebook power supplies are in the efficiency range of >80-95% depending on load. AC adapters pretty much have to be good to meet regulatory standards.

Edit: And then, of course there's some loss when converting the (typ.) 11-15V DC power in the notebook battery to 12V, 5V and 3.3V, so worst case scenario I guess they might be less effective than a good desktop PSU (percentage wise) since two power conversions are worse than one.

 

[Bolloxoid]

Laptops themselves consume less power than desktop systems, but the "wall wart" AC adapters are less efficient than the switching power supplies used in desktop computers and waste power when you have your laptop plugged to the mains.

I can't give you any figures though, and I don't know whether the inefficiency is enough to offset the smaller power consumption of the laptop in terms of total power consumption.

 

[AlNom]

On a side note, does this mean a device such as a console with a power brick would be significantly less efficient than having an internal PSU?

 

[Blazkowicz]

probably.

building a low power PC looks fairly easy, from mostly low end parts. I can imagine a geforce 6100 mobo with a sempron (which underclocks/unvervolts dynamically like all CPUs nowadays, and it can probably be unvervolted a bit at stock speed, see what can be done with rmclock or such) ; 2 gigs (it's cheap), one 500GB hard disk (it's rather cheap too), a fortron green 350W PSU (ATX) and a micro ATX case (one with a handle? )

 

[ShaidarHaran]

Maybe. The highest end laptops today consume ~90W when running at full tilt.

Really? Tell it to this laptop which uses a 280W adapter (yes, 280W)

Compare to a low-power 690G AMD platform desktop here.

What's my point? Ok, obviously this is not representative of the power consumption of the average laptop nor the average desktop, but clearly laptops can consume more power than desktops/desktops can consume less power than laptops.

 

[Zaphod]

Really? Tell it to this laptop which uses a 280W adapter (yes, 280W)

That's not a laptop. It might look like one, but really, it's not. Although, perhaps I should have qualified the 90W statement to exclude dual GPU, dual disc, luggable DTRs with lots of desktop components.

What's my point? Ok, obviously this is not representative of the power consumption of the average laptop nor the average desktop, but clearly laptops can consume more power than desktops/desktops can consume less power than laptops.

But that wasn't the question, was it. The question was how power efficient they were, and that's the context in which the statement was made. I'd like to see the desktop PC that is as efficient as a laptop given similar specs and a similar load. Those power readings you refer to aren't relevant as a comparison, because (besides the vastly different specs) the 280W power brick would be chosen to handle the absolute worst case scenario for the machine (which would involve charging the battery at the same time as all components are being taxed to the maximum). Given his actual battery test, the Sager consumed 91W (assuming the Windows default shutdown @ 5% & that the battery was completely new and up to spec) doing light wireless work. Now, factor out the screen and the fact that those 91W are under some load, the Sager probably does just as well as your 690G reference when idle. And that's with RAID, SLI and a desktop CPU+Chipset.

 

[digitalwanderer]

You would have to take the LCD into account too, right?

Yup, or include the monitor's power consumption for the PC.

 

[Simon F]

Yup, or include the monitor's power consumption for the PC.

Speaking of LCD efficiency, at the "Emerging Technologies" exhibition at SIGGRAPH, Qualcomm were demonstrating a new display technology that used moving mirrors. By adjusting the distance of the mirror (presumably by 1/4 of a wavelength), they achieved constructive or destructive behaviour of the light waves, much like "oil on water" I guess. It seemed quite good, was low power, and was very bright in daylight.

 

[Rainbow Man]

You would have to take the LCD into account too, right?

A PC would have its own LCD screen of course (or worse; a CRT).

A portable's screen would likely put more stress on low power consumption for its rectifiers and other components in the backlight etc.

A nd the desktop system's LCD would have its own power supply separate from the PC itself meaning more losses than running it off of internal power.

Laptops themselves consume less power than desktop systems, but the "wall wart" AC adapters are less efficient than the switching power supplies used in desktop computers

Portables have switching power supplies too you know. Generally universal ones as well meaning they'll run at 100-240V 50/60Hz. Just any wall wart couldn't do that. You'd need one for every voltage zone you'll visit and that'd be impractical as hell..

Peace.

 

[digitalwanderer]

I don't get the bit about the laptop's power brick, could someone explain it in littler words for stupid Diggers please?

 

[Zaphod]

Just any wall wart couldn't do that.

These days, more and more of them can though. I don't have many AC adapters in use anymore that aren't specced for 100-240V and those that doesn't output too much power are bloody next to weightless. I think the combined pressure of weight, technical progress, regulatory requirements and metal cost is making the old linear transformers go away.

 

[Bolloxoid]

Portables have switching power supplies too you know.

Hmm, that seems to be the case. I was somehow under the impression that laptop power bricks were simple transformers.

 

[Simon F]

Hmm, that seems to be the case. I was somehow under the impression that laptop power bricks were simple transformers.

That would make them useless for international travel, wouldn't it?

 

[limerick]

hig end dell xps laptop whic has sli 8700gt graphic with 512 mb ram, also have large hdd disk, and high and cpu, 19.5V or it says 135W , i prefer to have this one, because, gf8800gtx uses about 280W alone it self, or hd4870 using about 300w itself, i got these numbers from many other review and forum pages, i went on ebay and look for power adaptor of xps1730,

so my friends, there is no game that you can not play with sli 8700gt and ageia ps.card and will cost you 130w or 19.5 W , so you make up whic is better,

i want to tell you one more thing , most of you knows there is power loss with laptop charging, but there power loss also with psu,s whic turns to heat, maybe you could say it is keepign us warm