Please help - work out power consumption of laptop with 'power brick'

Hi, I'm live in the UK and have a laptop that plugs into the wall socket via a 'power brick'. Basically a cord runs from the laptop into
this black brick shaped thing, which gets a little warm and another cord runs from the brick into the wall.
On the brick itself it says:
AC ADAPTER INPUT: 100-240V~ 50-60HZ 2.0A OUTPUT 20V (then there's a long dash with three shorter dashes underneath it) 6.0A.
I was hoping to work out how much power my laptop will use when plugged in.. Is it a simple case of multiplying 20V x 6.0A and getting 120Watts? is that how much power is being drawn from the socket and therefore how much I'm paying for, or could the laptop be drawing less?
If there really is no way of knowing, can anyone recommend a decent metering device that I can plug between the power brick and the wall and that will give me an accurate figure? Hopefully a not too expensive one!
Thanks.
Mark.
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snipped-for-privacy@yahoo.co.uk wrote:

The power drawn by your laptop will vary with use and with whether you are charging the batteries or not. The markings on the brick are just indicating what its maximum output capabilities are - the laptop will always be drawing less.
Maplin (www.maplin.co.uk plus branches) have a power meter on special at the moment - L61AQ     Power Monitor Socket - SAVE £12.50    3136 in Stock     £12.49
Very good to see someone caring about what power even a laptop uses - most people on a mains supply couldn't care less - it is only like leaving a light on. It is only when you have to generate those watts yourself that it "matters".
-- Sue
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snipped-for-privacy@yahoo.co.uk wrote:

I have a Fluke Multimeter with an AC current adaptor. You attach two leads to the 10 Amp. AC current input on the Fluke meter. You plug the adaptor into your wall outlet and then you plug your appliance into the other side of the adaptor. In essence, you set up a circuit to measure the current into your appliance.
With the wall wart plugged in and with no load on it, write down the current. Attach your laptop to the wall wart, write down the current. Turn your laptop on, write down the current. Boot your laptop and write down the current. Do this while the laptop is sleeping, while it is accessing a large file on disk, while the battery is charging.
If you assume a constant voltage input, you will have an idea of how much power each function of your laptop is using. If you want to more precise, monitor the AC voltage at the wall wart.
I've used this scheme with many appliances. For example, the power to the second floor of my old house is limited. I monitored the current drawn by a window mounted air conditioner under several use conditions. I then determined that the fuse would not blow if someone turned on a hair dryer while the A/C was running.
My meter does not have a surge current setting, so I can't measure that.
Good luck.
Al
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The laptop can only draw the maximum of the tranformer/brick. "INPUT: 100-240V~ 50-60HZ 2.0A" Any measurements on the secondary side are just confusing the issue. Your question was as I understand it, "how much power is being drawn from the socket" Doing the math on the secondary side will not include the transformer's losses. (heat) Other posters have been correct the power consumption varies depending on the state of the battery and how much your using the machine. Measuring at the socket would be the best bet to know for sure.

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Maplin's offer a plug-in power monitor see below that would do what you want. see http://www.maplin.co.uk/module.aspx?ModuleNo8343&doy=6m11
Plug-In Mains Power & Energy Monitor               Measures voltage (V), amps (A), watts (W), volt-amps(VA), hertz (Hz) and power factor (PF) Great for seeing how much power your appliances are using! Large clear LCD display Reverse socket prevents cables getting trapped Maximum current 15A Maximum power 3750VA
Save 50% on this Power Monitor Socket, Now only 12.49
    
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I've ordered one of these and so will find out exactly how much it IS using soon.
But in the mean time, from what you guys have said the maximum that can be drawn from the socket by the brick is 240V x 2A which is 480 Watts. Now is it common for laptops to consume this level of power? Or is it common for what's stated on the brick to rarely reflect the actual amount of power use by the laptop. ie: if the hard disk isn't whirring, the dvd drive isn't being used and there's no usb devices drawing power, it should be using maybe even less than 100W? What's your experiences with laptops? Mine's about a year old. a n AMD Athlon 3000 XP-M. It has this low power mode it drops into when you're not doing processor intensive stuff too.
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Probably less than 100W typically, maybe somewhat over a hundred watts if you are using the computer at the same time it is charging a discharged battery. Let us know what your meter tells you.
j
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Your power supply is marked with the range of input voltages and the maximum rated current when loaded to the rated output current of 6A, under the worst input voltage conditions, to meet the requirements of European Standard EN 60950-1.
AC ADAPTER INPUT: 100-240V~ 50-60HZ 2.0A OUTPUT 20VDC 6.0A.
The Rated Input Current is not necessarily the current that will be drawn during the operation of your computer; it is normally less that the RATED CURRENT. It cannot be more than and still meet the requirements of the standard. Most manufacturers use standard ranges of power supplies and use the one nearest to the power requirements of the computer, so you normally have an extra safety factor in the ratings.
Hope this helps.
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Okay just a follow-up now i have this meter.
Laptop at full charge running directly off AC on its own ticks over at 35 watts with the hard disk constantly whirring.
Laptop with all my usb devices plugged in (webcam, mouse, bluetooth dongle, cooling fan plate it sits on, printer, two external hard disks (powered externally), and my speaker system plugged in, (the laptop, speakers and each hard disk and the printer all plug into a power strip), uses 45 watts in total, which is pretty damn good I think.
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I brought one as well. My desktop with 17" monitor, 2-1 speakers, printer and my JVC hi-fi unit pulls 364W
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I didn't realise the power difference between an AC-powered laptop and a desktop maschine would be so great; though I'm told CRT monitors use quite a bit, and if you have a high wattage stereo system then that's going to draw alot isn't it.
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snipped-for-privacy@yahoo.co.uk wrote:
<snip>

FYI, The long dash with the shorter ones under it means the 20V, 6.0A max output is DC.
<snip>

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