[LINK] Blackle increases power use with small LCD monitors

[Geoffrey Ramadan]

A monitor that uses 51W will required 51W from the power supply.

Power supplies themselves have power losses (resulting in heat) as 
measured by its efficiency. A PC power supply (which uses a switching 
power supply) has a typical efficiency of 75%.

The rating on the power supply indicates the maximum continuous 
power/current the power supply can deliver to the attached connector 
(load). Thus the actual power consumption will depend on the actual load 
applied and should be less than the max rating.

In this example, assuming an efficiency of 75%, the power supply will 
consume 51/0.75 = 68Watts from the power outlet. 51W consumed by the 
Monitor and 17W consumed by the power supply itself.

On another point, assuming all power supplies have the same efficiency, 
it does not matter if you have one or many power supplies, to power all 
your devices, the same amount of power will be consumed.

Reg
Geoffrey Ramadan


Tom Worthington wrote:
> At 06:16 PM 4/12/2007, Kim Holburn wrote:
>
>> On 2007/Nov/27, at 8:14 AM, Tom Worthington wrote:
>>> ... monitor uses 51 W with an image and 7 W in standby  ...
>>
>> ... how much power do those little plug-in transformers actually 
>> draw? ...
>
> The power they supply can be calculated from what is written on the 
> unit. So for example the ASUS Eee PC has a 9.5 Volt 2.315 Amp supply. 
> So 9.5 X 2.315 = 22 Watts.
>
> The power meter I have only measures down to 1 Watt, so is not 
> sensitive enough to measure the efficiency of these plug packs, nor 
> the amount of power drawn when no device is powered from them. In any 
> case, compared to desktop computer, the power used is minimal. This is 
> a bit like worrying about how much power the radio in your V8 four 
> wheel drive truck is using.
>
> It might be interesting to see if the Chinese approach was taken, 
> where mobile phones are charged from USB plugs, if this would save 
> power. You would need just one mains adaptor to power one hub to 
> charge all you gadgets. That would save having lots of plugpacks. But 
> if that one larger supply is powered all the time, would it use more 
> electricity?
>
> ps: FOr more on IT and energy use, see:
>
> * The 'Inefficient Truth' released 3rd December 2007 in the UK on IT 
> emissions 
> <http://www.globalactionplan.org.uk/event_detail.aspx?eid=ef0cecc6-2621-4a3c-962c-e4758b8952f8>. 
>
>
> * Engineering Sustainable Solutions Program: This is a six hundred 
> page electronic textbook and 30 hours of course notes intended for 
> engineers and IT professionals, sponsored by CSIRO 
> <http://www.naturaledgeproject.net/Sustainable_Energy_Solutions_Portfolio.aspx>. 
>
>
>
>
> Tom Worthington FACS HLM tom.worthington at tomw.net.au Ph: 0419 496150
> Director, Tomw Communications Pty Ltd            ABN: 17 088 714 309
> PO Box 13, Belconnen ACT 2617                      
> http://www.tomw.net.au/
> Adjunct Senior Lecturer, ANU 
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