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| UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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Electric power consumption measuring device
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 |
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#2
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On 26 Jan 2005 06:32:13 -0800, "Herminio Gonzalez"
wrote: Hello, I run a number of computers at home, and was wondering how much electricity each one consumes. 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 attached between the PC and the wall outlet to measure power consumption? Maplin do one .. http://tinyurl.com/3l6hm All the best .. T i m |
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#3
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Thank you T i m, that's just what I was looking for!
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#4
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In an earlier contribution to this discussion,
T i m wrote: On 26 Jan 2005 06:32:13 -0800, "Herminio Gonzalez" wrote: Hello, I run a number of computers at home, and was wondering how much electricity each one consumes. 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 attached between the PC and the wall outlet to measure power consumption? Maplin do one .. http://tinyurl.com/3l6hm All the best .. T i m And if you buy it in the next couple of days, it's half price! -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
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#5
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"Herminio Gonzalez" wrote in message oups.com... 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 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 - http://www.silentpcreview.com/article31-page1.html Dave |
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#6
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Aniseed wrote:
Thank you T i m, that's just what I was looking for! 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. |
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#7
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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 |
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#8
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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... |
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#9
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Aniseed wrote:
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. |
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Aniseed wrote:
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 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) |
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#11
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In article ,
Ian Stirling writes: Aniseed wrote: 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. 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). 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. 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 ;-) -- Andrew Gabriel |
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#12
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"Aniseed" wrote in message oups.com... 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 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 http://www.geek.com/procspec/intel/pentiump.htm For the best power efficiency - consider getting a Via EPIA board (various built-in cpu options 500-1000Mhz). I suspect the 21" CRT uses a lot of power too. Dave |
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#13
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Andrew Gabriel wrote:
In article , Ian Stirling writes: Aniseed wrote: 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. 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. What's the name, I've forgotten the name of mine, IIRC began with a b, and was german. 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). If it does not sample fast enough, then it may well overestimate current consumption. 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. 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 ;-) True. It's hard to tell how much someone knows on usenet though. |
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#14
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In article ,
Ian Stirling writes: Andrew Gabriel wrote: 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. What's the name, I've forgotten the name of mine, IIRC began with a b, and was german. 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). 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). If it does not sample fast enough, then it may well overestimate current consumption. 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. -- Andrew Gabriel |
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#15
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Andrew Gabriel wrote:
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). If it does not sample fast enough, then it may well overestimate current consumption. 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. -- Chris Green |
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#17
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In uk.d-i-y, Ian Stirling wrote:
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. 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. -- Mike Barnes |
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#18
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Mike Barnes wrote:
In uk.d-i-y, Ian Stirling wrote: 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. 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. |
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#19
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Mike Barnes wrote:
In uk.d-i-y, Ian Stirling wrote: 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. 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. 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). -- Chris Green |
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#20
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In uk.d-i-y, wrote:
Mike Barnes wrote: In uk.d-i-y, Ian Stirling wrote: 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. 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. 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. -- Mike Barnes |
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#23
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In article ,
writes: Andrew Gabriel wrote: In article , writes: Andrew Gabriel wrote: 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). If it does not sample fast enough, then it may well overestimate current consumption. 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 If it did this, it would under estimate rather than 3 times over estimating. That's why I said the form of the error was puzzling. No it wouldn't. It could have lots of amps flowing at 240 volts but with (say) 10% power factor the Volts*Amps would be way more than the power. The example was a SMPSU, not a capacitive or inductive load. Averaging a SMPSU current pulse or failing to take into account it only happens when mains voltage is around 340V would give an under reading. I can't imagine what mistaken assumption they've made which results in such a load 3 times over reading. -- Andrew Gabriel |
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#24
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Andrew Gabriel wrote:
snip Averaging a SMPSU current pulse or failing to take into account it only happens when mains voltage is around 340V would give an under reading. I can't imagine what mistaken assumption they've made which results in such a load 3 times over reading. To quote from an earlier post I made on this. " A quick patch involving a 1.8 ohm resistor in the neutral lead and resistive dividers protected by zeners indicates that the current has a really odd shape. The couple of switchers I checked exhibited the expected short half-sine looking pulses at maximum voltage. The power indicated by the meter was within 20% of my eyeballing the scope. On trying it on my PC, I found a rather odder shape sort of sharks-fin like shape. The current rises to a peak of 2.2A in .4ms, then decays over the next couple of milliseconds more or less linearly to 0.6A, then drops in 0.5ms to 0. That's a total of 2.25Ams per half-cycle, at 320V, that's .721Ws per half-cycle, or 72W when idle. The meter however reads 138W. And in suspend, it's around 30W, around 10W 'off'. " It may well be assuming that the current will be either a 'normal' sine wave, with a power factor of whatever or a sharp chopped-sine pulse near the wave peak. This worked fine, until various regulations about harmonic content on power supplies came in. Then the PSU makers started working out the cheapest way to meet these directives. This ended up as very odd waveshapes. As to why. Well, let's assume that it samples at the peak of this pulse, 2.2A. Let's try 2.2A * 2ms = 4.4mAs. 4.4mAs * 320V = 1.4J * 100 cycles per second = 140J/s, or 140W. Surprisingly this works quite well. However, I suspect the real answer is that it's trying to make a nice smooth wave out of it. To get an accurate number, you're going to need to sample at better than 1Khz. Alternatively, if it's sampling at 500Hz or so, and trying to assume that the waveshapes may be symmetrical (be it intentionally, or through filters) then it may get vastly misleading answers. Especially as we're not talking about a 2000 quid scope that's had hundreds of man-years spent on the design, and verifying it's correct, but maybe a few hundred hours and checking on a few loads around the office. Anyway, hypothesising on how it fails is kind of pointless, in the face of the fact that it can't be repaired (practically) |
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#25
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Mike Barnes wrote:
In uk.d-i-y, wrote: Mike Barnes wrote: In uk.d-i-y, Ian Stirling wrote: 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.) snip 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. With my observations, it diddn't, but was consistent within a range of voltages (about +-2%) and with a 1.8 ohm resistor wired into the mains lead. Never mind. I'm quite happy to believe that the readings are unreliable for PC power supplies etc. |
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#26
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"logized" wrote:
"Aniseed" wrote in message roups.com... 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 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 http://www.geek.com/procspec/intel/pentiump.htm For the best power efficiency - consider getting a Via EPIA board (various built-in cpu options 500-1000Mhz). I suspect the 21" CRT uses a lot of power too. Hi again, Yesterday I recieved one of the Maplin Power meters in the post. It is made in Taiwan, by Prodigit Elecronics Co Ltd. Its of reasonlably good quality build, given the price. I've tried it out on stuff around the house. After much bending over plugging and unplugging things, I've acquired a list of results and a backache. If anybody is curious, here is what I found out: monospace font please Appliance: Reading: Kettle rated at 1800-2200W 1980W Desklamp with 60W bulb 58W PIII Dell Laptop 20W idle PentiumPro 200MHz, 1HDD 40W idle Athlon 1.4GHz, 1HDD 90W idle, 105W runing sims2 Pentium IV 1.8GHz, 2HDDs 75W idle, 100W running hl2 22" Iiyama CRT 5W standby, 70-100W on Lower back Light throbbing /monospace font please I can see that the device has correctly measured the kettle and desklamp, because the reading I get matches their power rating. However I don't know how accurately it is measuring the various computers and the CRT monitor. I hope it is accurate, because I was pleasantly surprised to see that the monitor consumes about 75W when displaying my windows desktop, I thought it would be higher. However: Ian Stirling wrote: 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. So it seems I can't trust the measurements from my device (yet). Would anyone know where I can learn more about switched-mode PSUs? Aniseed |
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#27
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Aniseed wrote:
Yesterday I recieved one of the Maplin Power meters in the post. It is made in Taiwan, by Prodigit Elecronics Co Ltd. Its of reasonlably good quality build, given the price. Yes, I've got one now, thanks to all the plugs (sorry) here. I think it's absolutely fantastic value for money, compared to any professional instrument (c.f. the price of RS stock no. 292-1274). I've not done any detailed checks on it yet, but all the readings on stuff around the house (like yours) seem about right. I've yet to try it though on any SMPS loads with a high current crest factor and harmonic content though... One clear limitation is a lack of resolution and the presence of offsets at the low current end of the range. Mine tends to read 10 mA and 2 W with no load connected, so the overall accuracy for powers under 10 W is going to be pretty poor. There's a table of accuracy figures on the instruction sheet, to which I'd suggest adding plus or minus 2 counts on the LSD. If I find the time I'll experiment with adding an outboard 10:1 (or even 100:1) current transformer, which should dramatically improve its performance at low power levels. I've tried it out on stuff around the house. After much bending over plugging and unplugging things, I've acquired a list of results and a backache. If anybody is curious, here is what I found out: monospace font please Appliance: Reading: Kettle rated at 1800-2200W 1980W Desklamp with 60W bulb 58W PIII Dell Laptop 20W idle PentiumPro 200MHz, 1HDD 40W idle Athlon 1.4GHz, 1HDD 90W idle, 105W runing sims2 Pentium IV 1.8GHz, 2HDDs 75W idle, 100W running hl2 22" Iiyama CRT 5W standby, 70-100W on All those figures seem quite plausible, IMO[*]. Lower back Light throbbing Display readability is not its strong point is it? But for £10.63 + VAT you can't complain! [*] Below, FYI, is a re-post of some figures I took a while ago and posted here in Sept '03. .. Power Current Earth Equipment /W /A VA PF /uA -------------------------------- ----- ------- ----- ---- ----- Old sys unit (P75) idle 30 0.185 44.4 0.68 30 Old sys unit (P75) CPU 100% 39 0.233 55.9 0.70 30 Iiyama 17in. CRT monitor 90 0.566 135.8 0.66 60 New sys unit (P4/2.8GHz) idle 100 0.505 121.2 0.83 30 New sys unit (P4/2.8GHz) CPU 100% 155 0.800 192.0 0.81 30 Dell 18 in. TFT monitor 42 0.268 64.3 0.65 40 PSU for computer speakers 4 0.048 11.5 0.35 - HP LaserJet 4 printer (warm up) 790 3.300 792.0 1.00 140 HP LaserJet 4 printer (standby) 35 0.239 57.4 0.61 140 Notes ----- Power measurements taken with a Feedback Instruments EW604 wattmeter. Current figures are true RMS, taken with a Fluke 87. VA figures are apparent power, calculated assuming Uo = 240 V (i.e. the approximate actual supply voltage, rather than the nominal 230 V). 'PF' column is power factor (W / VA). 'Earth' column shows protective conductor current (in microamps) taken on a Fluke 77 (mean responding). Note that the measured figures are far less than is commonly assumed in threads about spurious RCD trips. Figures for the monitors were with 'typical screens', not max. brightness & contrast. 'CPU 100%' figures taken with the SETI at home client running. -- Andy |
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