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Old 05-30-2012, 06:13 AM   #1
sulekha
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Question power consumption by switched off pc


Hi all,


just happened to watch this video:- http://www.youtube.com/watch?v=vdc18uTasC8

Does this means that normal pcs will draw current even when switched off but plugged into the socket, if it is so, on an average how many watts will it take ?
 
Old 05-30-2012, 06:24 AM   #2
tronayne
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Yeah, a lot of them do (at least the Dell Dimensions and Optiplexes that I have do) -- keeps the clock ticking but not much else.

Without attaching a Watt meter, can't tell you how much exactly but the UPS does show a teeny little bit, maybe 5-10 Watts... nothing much to worry about, on the order of a night light.

If it really matters to you, use a switchable power strip and turn it off or unplug it, eh?

Hope this helps some.

Last edited by tronayne; 05-30-2012 at 06:27 AM.
 
Old 05-30-2012, 06:46 AM   #3
michaelk
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Any PC that uses a momentary switch for power consumes current when powered off. The power supply generates a 5 VDC standby voltage and some motherboards have a LED that illuminates when the voltage is present which is anytime the computer is plugged in.

I do have one of those killawatt plug in meters with good intentions on adding up the "ghost" current in my house but have not got around to it yet...
 
Old 05-30-2012, 07:08 AM   #4
catkin
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I've tried using devices similar to Kill-a-watt to measure standby consumption and seen 8 W but do not have much confidence in the accuracy at such low power levels. The meter specifications were + or - a small percentage of the power reading (OK) + or - something like 5 W (next to useless at low power levels).
 
Old 05-30-2012, 07:15 AM   #5
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If you are drawing any power, you'd better hope for no power "zaps".
I had a system powered off and protected by a UPS that got destroyed. Mind you, there was a 60 ft tree in the street at the front of the block that got hit by lightning and split in half. Right next to the power feed into the house.

Made a mess of the UPS too ... and the phone answering machine, ...
 
Old 05-30-2012, 03:55 PM   #6
jefro
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The very fist computers did have a real line voltage switch on them. That switch cut all power to the system. It was later changed to an internal real line switch.

All the computers made in the last 15 years have a different way to power them on. They all consume from .5 watt or so to 5 watts. Some in different versions of standby and hibernate can draw more or less. This issue is also with the monitor and the wall warts.

I used a watt meter to test a common desktop with router, switch, speakers, usb external, common monitor and common desktop in what seemed to be power off. It was 22 watts with all the viper loss.

Never hurts to put all your computer stuff on a power strip and turn it all off when not in use.
 
Old 05-31-2012, 03:51 AM   #7
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I measured this here.
As has been pointed out, momentary(i.e. front power button) switches do leave a residue of power being consumed. PSU on/off switches largely kill usage, although there's usually a filter cap that still sucks a little. I used an ammeter on a 220V supply so your sum is amps x 220v = watts.

My PC Box:
~110ma (=0.11A) or 24.2 watts. For power calculations, that's watts per hour.

My Monitor:
~85mA (=0.085A) or 18.7 watts

Some other interesting details:
1. This applies in principle to printers, laptop power supplied, and anything with a sm-psu. All consume some power while off.

2. 'Standby' mode saves basically no power, as the main 5V line isn't switched off.

3. Full use current is APPROXIMATELY twice that for each device.

4. As you may appreciate, A.C. ammeters are not the most accurate thing on God's earth.

5. What you do with your bios 'wake on xxx' settings has an effect on off power consumption, as chips are switched from main 5V to aux 5V and more of the board is left powered. USB costs, and I have to leave it on for my motherboard so the keyboard works for grub.
 
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