Hello,
I run a number of computers at home, and was wondering how much electricity each one consumes. Is there some kind of device that can be attached between the PC and the wall outlet to measure power consumption?
Kind regards, Herminio Gonzalez
About (finger in air) 200-500W (depending on the CPU spec, number of drives and monitor type) ;-)
Is there some kind of device that can be
Maplin do one ..
T i m
Thank you T i m, that's just what I was looking for!
And if you buy it in the next couple of days, it's half price!
Cheap power consumption meters are occasionally available for around £5 from supermarkets such as Lidl or Aldi and also on ebay. As a guide to consumption, a typical PC with an Athlon 2100 cpu, single HD, average graphics card takes about 75W when idle, rising to about 140W with full CPU load. You need to add-on the consumption of your monitor,this may be available from the manual or label on the monitor itself. Older PCs with 300-400Mhz (AMD K6) cpu can use on average about 50W. As the CPU power consumption is an important factor - it may be interesting to read this CPU power consumption comparison -
It's likely to be significantly (double the real reading) inaccurate, the one I got from maplin is. It works fine on simple loads like motors/heaters.
In practice, you can look up all the figures on websites.
2-300W is unlikely.I measured my server (12 drives spinning, 1.3G duron) at around 150W.
Sure, its possible to look up what one's CPU consumes, but there are several hardware and software components drawing power, and it quickly becomes difficult to know how much is really being consumed.
I'm particularly interested in the consumption of a lighlty equipped PentiumPro machine which is on all the time, no monitor. It is passively cooled, and the heatsink feels quite cool to the touch, so i am hoping it is below the 50W mark.
I also have a P4 1.8GHz machine with 2 HDDs and a 21" CRT, I'm curious to find out how much it really consumes, and how it compares to the value from manufacturer's specs.
Herminio
That's discouraging. So according to your post, there's an error of a FACTOR OF 2? How could one know what the real power consumption is... Maybe I can calibrate it somehow, using devices with known power consumptions. But I can't think of any such devices...
Unfortunately not. The meters (the cheap ones, the maplin and Lidl 6.99 ones) work out the current by measuring the voltage/current several times per cycle. Unfortunately, the lowest cost is got by reducing 'several' as much as possible.
For things like heaters, or motors, you can almost trivially get a pretty good reading of power and power-factor (amount current is leading or lagging voltage) with just 3 or 4 samples per cycle.
This is because the current they draw is a nice sine wave. Many PC (and other switched-mode PSUs) unfortunately have significant very fast variations in current. So, the meter misses these changes, and assumes that the power supply is drawing a higher current than it should.
It's basically a similar problem to trying to join up the dots. If you've got lots of dots, then you can make a nice smooth curve, without worrying about the shape of the curve you make being different from the intended one. As you reduce the number of dots, eventually you get to a stage when you're guessing.
More expensive meters should do better, unfortunately, determining how much goes into the electronics is hard.
I happen to know this one! :)
I for about a year, I ran 3 Pentium Pro 166 (overclocked to 240Mhz) motherboards, 3 hard disk drives, 3 ethernet cards on one 145W power supply.
I measured each motherboards DC usage as around 40W, with the CPU going flat out. (mp3 encoding)
None of them ever crashed in about 3 years total run-time (adding up all the motherboard times)
I bought one of the current Maplin ones, and I think that might not be too bad. I'm having trouble getting my proper true power meter back from someone I've lent it to (my boss;-), so I haven't been able to do a real check on the Maplin one.
I bought one of the older ones Maplin stocked a few years ago, and that's hopeless on non-resistive loads (out by a factor of
3 on SMPSU's -- too high, which is a puzzling way for it to be in error).My proper true power meter actually uses an analogue multiplier and integrator, so it has more than enough dots so there's no need to guess how the line goes between them ;-)
I have measured the consumption of an old machine fitted with a 400Mhz amd cpu at between 40-60W and a Cyrix "300" machine at 38W - these machines have large heatsinks with a very slow fan (at 5v) and don't produce much heat. Your cpu may take more power - maybe as much as a Duron 800-900Mhz - so may be worth checking further - see
I suspect the 21" CRT uses a lot of power too.
Dave
What's the name, I've forgotten the name of mine, IIRC began with a b, and was german.
If it does not sample fast enough, then it may well overestimate current consumption.
True. It's hard to tell how much someone knows on usenet though.
Yes, that's the crap one which is way off -- I think the model was PM230. The one Maplin stock now is a different make and I can't remember what it is (nothing well known though, but it is Asian not German).
Yes, I guess if the spike width at the voltage peaks is small compared with the sampling rate (hello Mr Nyquist;-) and the sampling is somehow always catching it (prehaps due to synching with the voltage waveform), then that would account for it.
Isn't it as much to with low power factor as anything. The cheap/simple power meters simply measure average (and I mean average, not RMS) voltage and current, then multiply the two together and apply the right factor to convert to RMS and say the product is power. It matters not one whit how fast your samples are if you do this, the answer will always be wrong.
Even the cheap ones do power factor. I'm fairly confident that most of these devices have a single channel
8 bit A/D (minimum current is typically 40mA = 13000mA/256), sampling at 400Hz or so. (or maybe 50Hz, with undersampling, I'm not sure.)Add a 4 bit micro, and an LCD, and you've got a power meter.
A 0 power factor device can have a very spiky current draw. My PC power supply draw looks like a sharks fin, with a very sharp rise, and a slow decay to a fast fall.
Typical older SMPSs with a bridge rectifier feeding a capacitor (which read correct) have a current draw that looks like the top of a sine wave.
Presumably if you measured total energy consumption over a long period, things would even themselves out. But how long, I wonder? My Maplin meter stops at 9999 kWh.
No, they don't. It consistently reads high by the same amount for hours or days.
But *how* do you measure "total energy consumption over a long period", that's the original problem! If the meter's view of instantaneous power consumption says 1kW thenit's going to consume (according to the meter) 9999kWh in 9999 hours (unless the instantaneous reading changes of course).
If the draw looks like a sharks fin, then the instantaneous reading
*will* vary won't it? Unless the sample times are synchronised to the wave form.Never mind. I'm quite happy to believe that the readings are unreliable for PC power supplies etc.
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