How Much Power does a Computer Actually Draw?

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wirenut1980

wirenut1980

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I was wondering how much power a computer (CPU only) actually draws. The power supply may say 350 Watts on the nameplate, but I would hope that it is not loaded to the max. I'm guessing it depends how much crap you have on the machine and how high performance it is. Could I get a clamp on meter on the power cable and measure the current? :(
 
Re: How Much Power does a Computer Actually Draw?

You cannot put a clamp-on meter on a power cord and get an amperage reading as the power on the ungrounded condutor and grounded conductor cancel each other. You will need to get your meter on the ungrounded conductor only which is usually accesible in the distribution panel. This will measure the entire load on the circuit so you will need to ensure that the CPU is the only thing operating on the circuit when you make your measurement. I believe I saw a device one time that you would plug into receptacle, and then plug in the equipment you wish to test to this device. You could then connect a clamp-on meter to this devive for an accurate reading. I have never used such a device, but I believe I remember seeing one.
 
Re: How Much Power does a Computer Actually Draw?

The current will not be sinusoidal either. The computer will draw large currents for a very short time during each half cycle. So make sure what ever meter you use gives you a true RMS reading.

Steve
 
Re: How Much Power does a Computer Actually Draw?

I recently measured AC current draw on a dell gx240 tower workstation. Ratings on the back is 3A at 115v. I had cut into a power extension cord and measured ac current with a craftsman multimeter. It was always less than 1A. Usually 0.5-0.8A measured, lower when computer is idle and higher when running software. Fans were off, I'm sure that would increase current draw the most. I also have all the pci slots filled with AD/DA voltage cards, but they weren't controlling anything at the time. Figure somewhere around 30-40W power draw typical on most pc's.

[ June 08, 2005, 03:15 PM: Message edited by: ron7000 ]
 
Re: How Much Power does a Computer Actually Draw?

Thanks for the replies. I work at a military base and it is policy to not shut down computers when leaving for the day, so that patches can be loaded at any time, and I have been asked to speculate on how much dough can be saved base-wide by changing this policy and shutting down workstations at night and on weekends. So for my calculations I was thinking of using around 0.8 Amps per computer. Thanks again! :)
 
Re: How Much Power does a Computer Actually Draw?

Your monitor will actually draw more power than the computer itself. Simply turn off the monitor.
When a computer is not in use the hard drive continue to spin as will the cd drives.
Also turn off any local printers or scanners when not in use. But personally, you will spend more money trying to figure this out than the actual savings per year.
Turn off the monitor and hit the light switch on your way out.
 
Re: How Much Power does a Computer Actually Draw?

Modern computers have features that automatically turn off the monitor and put the CPU in a standby mode when not used. I doubt that turning them completely off would save much money.

Rattus
 
Re: How Much Power does a Computer Actually Draw?

But personally, you will spend more money trying to figure this out than the actual savings per year.
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Considering I have only spent a day on this, I don't think that is quite true. It only took a little bit of research.

There will not be much savings with the Monitors (I calculated about $2,000 in savings base-wide per year), because of the power saving features are set in Windows(i.e. going into sleep mode after a period of inactivity). I forgot to mention that the CPU's are not currently set up in Windows to go into any kind of hibernation/standby mode. But still, even if only the fan is blowing with minimal computer activity, when we are talking around 3,500 computers total, this could save at least $30,000 per year. This is assuming the fans and minimal computer activity draw about 0.3 Amps, and that the time period of about 5,900 hours per year that the computers are not in use during the year (i.e. weeknights, weekends, holidays, average vacation time), and we are getting a rate of about $0.04/kW-hr. :)

Dave
 
Re: How Much Power does a Computer Actually Draw?

Something else to consider is what damage is being done to the computer when it is power cycled from cold frequently and what does this cost in downtime, troubleshooting, parts, and software reinstalls. We typically lose one or two computer components after a holiday shutdown/restart out of about 30 large machines. Things like power supplies and disk drives are the most common components to fail. PC's seem to be more reliable than big computers, but that cycling from full cold to hot and back seems to take its toll on everything eventually.

You may want to consider shutting down only when the computer will be off for some time (like a weekend or even better if someone goes away for a week or more).
 
Re: How Much Power does a Computer Actually Draw?

I usually go for 400 watts per computer. That's the safest. I agree, just turn off the monitor, because that's about 300 watts itself. ;)
 
Re: How Much Power does a Computer Actually Draw?

just turn off the monitor, because that's about 300 watts itself.
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Actually, according to page 17 specs in the user guide for my home monitor, the Envision 17" EN-7100s LCD , the monitor draws only 45 Watts max. And I could not find the information in the manual, but I read somewhere that when the monitors go into sleep mode, they only consume about 1-2 Watts. :D

[ June 10, 2005, 10:54 AM: Message edited by: wirenut1980 ]
 
Re: How Much Power does a Computer Actually Draw?

I would expect LCD monitors to draw a lot less than a CRT, so a CRT probably is closer to 300W.

Steve
 
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