Never said P=VI is 100% valid for AC circuit! And I don't need Physics 101 lessons. Perhaps it is YOU who may require a refresher in English 101. Do you understand the word "adequate"?
I am the one who is looking for a way to measure power and reading 480W when it is really 336W is not "adequate" for me.
Chill out, or else, you will get old fast. lol!
I have used this kill-a-watt last year when I was trying to figure out the high electricity bill.
Specifically - I was trying to find out if putting my desktop on a standby saves significantly on energy charges. (I am a grad student, and so work on it most often). The other appliances were a Lacie External HD, and an ethernet cable modem. A fluorescent lamp, and a room heater.
I think - the Kill-a-watt is reasonably sensitive - could see the sudden changes in watt and ampere (and a slight reduction in voltage on load) when the CRT monitor came on, or the harddrive was started. I monitored the consumption for about 15 days (it was continuously put on the line) to get an average. (It shows the cumulative consumption of watt as well as the instantaneous consumption).
I will say it worked pretty well for me in planning and reducing the electricity consumption.
BTW, there are some limitations - if I remember correct - the maximum wattage it can test is around 1350 or 1450 peak watt. That is - you can't use it for heavy appliances like big fridge, or your washing machine - even though they are household, or may be a big screen CRT, as I am afraid there can be a transient very high wattage at the beginning of working cycle. That might destroy this meter, and void the warranty.
For your purpose of comparing consumption of small electronic appliances - I guess it will work if you have patience enough to measure it for say at least half an hour or so - specially if the difference is not that high. ... For me - I definitely noticed a difference in the numbers (realtime measure or measurement at a point of time) when the [harddrive was] on vs [when the hard drive was on+the processor was working]. Whether the absolute values are accurate like the costlier electrometers, I don't know, but it was sensitive for sure.
Hope that helps.
Specifically - I was trying to find out if putting my desktop on a standby saves significantly on energy charges. (I am a grad student, and so work on it most often). The other appliances were a Lacie External HD, and an ethernet cable modem. A fluorescent lamp, and a room heater.
I think - the Kill-a-watt is reasonably sensitive - could see the sudden changes in watt and ampere (and a slight reduction in voltage on load) when the CRT monitor came on, or the harddrive was started. I monitored the consumption for about 15 days (it was continuously put on the line) to get an average. (It shows the cumulative consumption of watt as well as the instantaneous consumption).
I will say it worked pretty well for me in planning and reducing the electricity consumption.
BTW, there are some limitations - if I remember correct - the maximum wattage it can test is around 1350 or 1450 peak watt. That is - you can't use it for heavy appliances like big fridge, or your washing machine - even though they are household, or may be a big screen CRT, as I am afraid there can be a transient very high wattage at the beginning of working cycle. That might destroy this meter, and void the warranty.
For your purpose of comparing consumption of small electronic appliances - I guess it will work if you have patience enough to measure it for say at least half an hour or so - specially if the difference is not that high. ... For me - I definitely noticed a difference in the numbers (realtime measure or measurement at a point of time) when the [harddrive was] on vs [when the hard drive was on+the processor was working]. Whether the absolute values are accurate like the costlier electrometers, I don't know, but it was sensitive for sure.
Hope that helps.
Why would there be power factor correction in a meter?
The meter installed at your residence measures instantaneous current multiplied by instantaneous voltage. The point is that cannot be done with a regular handheld multimeter.
If you have to use a regular multimeter, since it measures RMS voltage and RMS current, you will need to somehow also measure the power factor and multiply the three to come up with real power.
Correct me if I'm wrong, but isn't connecting an ammeter to your computer a big no-no? As in.... fry your computer no-no?
[Though the Kill-A-Watt is fine]
Remember reading about it somewhere... not sure :|
[Though the Kill-A-Watt is fine]
Remember reading about it somewhere... not sure :|
Again, US RESIDENCES are not charged extra for wasted power (power factor less than unity). European PSUs are required by law to incorporate a power factor correction circuit. Often, this circuit will DECREASE the efficiency of the PSU. There ain't no free lunch.
I'm not an EE, but a computer power supply is somewhat capacitive, isn't it? The Seasonic power measuring device listed above does measure power factor, I'd imagine the Kill-A-Watt device does, as well. Measuring all four quadrants of real power isn't difficult at all. I forgot the name of it but there's a type of a bridge circuit that uses optoisolators to measure each quadrant and add them up.
Edit: Kill-A-Watt also measures power factor.
Edit: Kill-A-Watt also measures power factor.
You don't actually measure PF, it is a calculated number using trig functions. This can be done manually, but it's much easier to just use % efficiency. Most appliances will come with documentation that gives the % efficiency. Using this number*V*I will give you the ~ actual power being used for that particular appliance.
As for the meter installed by the power company, it takes the average of the power*voltage because home users are only charges for actual power used rather than a peak demand charge. Since there is no peak demand charge, that is why the Kill-a-watt meter works.
I still don't understand why you are saying that a DMM won't work though. True, it can't measure PF, but but you could measure it exactly if you wanted to get the readings, determine the kind of load (Inductive, capactive, reactive) so you know if the current is leading or lagging, then go thru the actual calculation using trig. Using the %efficiency would be much, much easier.
As for the meter installed by the power company, it takes the average of the power*voltage because home users are only charges for actual power used rather than a peak demand charge. Since there is no peak demand charge, that is why the Kill-a-watt meter works.
I still don't understand why you are saying that a DMM won't work though. True, it can't measure PF, but but you could measure it exactly if you wanted to get the readings, determine the kind of load (Inductive, capactive, reactive) so you know if the current is leading or lagging, then go thru the actual calculation using trig. Using the %efficiency would be much, much easier.
If you want the BEST method of measuring power, then get an oscilloscope to simultaneously display graphs of voltage and current, then calculate the average power or instantaneous power. For most home users, the formula P=VI (with a DMM) is more than adequate. 0.7 to 0.8 is the norm for most PSUs. Simply de-rate the power by 25% and you will have a very good GUESS-TIMATE of the actual load. One can use capacitors to bring the power factor closer to unity. However, this is not necessary for US households.
If the phase is 0, there is no reactive component and power factor is 1. If the phase is 30 degrees, power factor is 0.87. If the phase is 60 degrees, power factor is 0.5. If the phase is 90 degrees, power factor is 0.
If you measure 120V for the voltage and 4A for the current, you will have 480W for a phase of 0. But, only 240W for a phase of 60 degrees. That is a big difference!
How do you know what value to use for the phase in your calculation?
Just because we know that the load is inductive does not mean that we know what the phase is!
But, this has nothing to do with efficiency. Efficiency is about loss in the power supply. it is about the resistance of the wires that ideally would have a 0-Ohm resistance but they don't.
You can have a 100% efficient device that still has a power factor of 0.5 instead of 1. Or you can have a device with a power factor of 1 (voltage and current in phase) but with a poor efficiency of 50% (badly designed regulators that heat up a lot and waste power as heat).
Power factor tells you what percentage of the power a device takes is used (real power) versus the power that the device sends back to the grid (reactive power).
Efficiency tells you what percentage of the real power given to a device is used versus the power that is wasted in it as heat.
In most areas in the world, domestic customers don't pay for 'reactive power' only for 'real power'.
What the OP was asking was whether the kill-a-watt device is the best? If by 'best' you mean most accurate and flexible then it isn't: there are better options - in the form of specialist industrial power analsyers. However, if by 'best' you mean 'best value for home use' then, it is probably one of the best options on the market. There are a few clones around (of which I have one) - but there's little to choose between the different products. They all use a relatively standard power meter chipset - similar to the ones used on digital electricity meters - so all have relatively similar performance.
Yes, it is. It measures instantaneous voltage and current - and calculates the power - in exactly the same way as does the meter installed by the electricity company. As a bonus, it will also measure rms current and rms voltage, 'apparent power' (real and reactive power combined) and the phase shift.
Yes, a dual channel oscilloscope with power quality software would be better.
But when you can get a kill-a-watt for $35 which has an accuracy of better than 1%, why bother connecting up DMMs or oscilloscopes? The kill-a-watt is plug and play - no need for splicing into live cables, or splitting the cores in a multicore cable so that you can use a clamp meter.
From a safety point of view, for the home user, a plug-in type power meter is far preferable to any cobbled together system using DMMs.
And the fact that it can actually measure the power factor (which can be highly variable between domestic appliances - especially motorised equipment e.g. AC, refrigeration) - instead of relying of guestimates which may not even be in the ball park (Not all PSUs are non-PFC corrected, some are passive PFC which can correct to about 95% - and many all new PSUs are active PFC, because it allows a much more efficient overall design).
It's a bit more complicated - the rectifier comes before the diodes, so the overall result is that the PSU is 'non-linear' rather than simply capacitative. The current waveform is distorted, rather than phase shifted. In particular, the current waveform contains lots of odd harmonics (3rd, 5th, 7th, etc. == 180 Hz, 300 Hz, 420 Hz, etc.). It's for this reason that the simple equation PF = Cos phi is misleading.
Harmonic power factor is a problem, because it can't be completely corrected with inductors or capacitors - although a circuit with multiple inductors and capacitors can provide partial correction. It also causes problems on 3 phase circuits - while 'fundamental' currents cancel in the neutral wire, harmonic currents sum.
All I know for sure is that the electricians at the plant here where I work tell me that using a DMM is a perfectably way of measuring power being used.
Since I'm not EE or anything, I just can't explain it any better than I've already tried.
Since I'm not EE or anything, I just can't explain it any better than I've already tried.
Close enough for hand grenades. A good multimeter can also measure current down to microA. No need to waste more $ on power measuring device.
0roo0roo
No Lifer
- Sep 21, 2002
- 64,795
- 84
- 91
lacie? i've heard some external hd units don't sleep ever. power waste + shortened lifespan for drive
i know there are other kill a watt type units. i forget the name
either consumer reports or some other pc mag had a review of three long ago. kill a watt has the most easy name to remember though lolFor small measurements, the only thing better than Kill-A-Watt is the actual KWH meter feeding your house. Unless, you really, really want to be accurate up to the last cent of power consumption.
Jeff7
Lifer
- Jan 4, 2001
- 41,596
- 19
- 81
Accuracy of the Kill-A-Watt, as reported on its website is 0.2%.
Probably won't get much better than that for an inexpensive consumer product.
Probably won't get much better than that for an inexpensive consumer product.
well learn to read and all will be well!!
Furbali never gets old and his advice is usally pretty right on.
so here is an article....on PFC
PFC decoded
Originally published 2003 in Atomic: Maximum Power Computing
Last updated 26/02/06.
Companies that make PC Power Supply Units (PSUs) find it difficult to make their products stand out from the crowd. On top of the increasingly outrageous wattage ratings (a quality 300 watt PSU is enough to run practically every PC out there, but lots of people buy something with a much higher rating just for the heck of it), there are multiple fans, funky cables, gold-plated connectors, little lights...
...and Power Factor Correction (PFC).
A PC PSU doesn't have to have PFC, but practically all of them do these days, because many countries have regulations that require some kind of PFC. Most PSUs have passive PFC; fancier models have active PFC.
Active PFC, your friendly shiny-suited PC salesman will explain, is more efficient. He may or may not also say that it'll save you money on your electricity bill.
Either way, he's full of crap.
Power factor correction (PFC) is, essentially, what you do to complex AC loads (such as PC switchmode power supplies) to make them act more like simple loads (such as toasters).
Alternating current oscillates continuously. 50 times a second, here in Australia and in most other 220/240 volt countries; 60 times a second, everywhere else (people living in East Elbonia and using 153 volt DC mains and four pin plugs need not e-mail me to complain about this generalisation).
If you plot voltage versus current drawn for a simple ("resistive") load in an AC circuit, the current will neatly follow the voltage, perfectly in sync. At the points in the AC cycle when there's the maximum voltage across the load, the maximum current will flow. And when the voltage reverses during each oscillation, so does the current. This is all very simple and sensible; it's what you'd expect AC to do, by applying the volts equals amps times ohms rule you learned for direct current circuits in high school physics. Or should have learned, anyway.
If you multiply the root-mean-square (RMS) voltage by the RMS current of a simple AC circuit like this, you get its power in watts. Again, this all works like DC electricity.
Complex AC loads are not this simple. Their current draw doesn't follow the voltage; it's out of sync. This is because the load is capacitive or inductive - "reactive". Reactive loads can even be both capacitive and inductive, in different mixtures over time.
If you think of a resistive load as just a length of hose, that needs a certain constant pressure to get a certain constant amount of water flow, then a reactive load is a contraption involving buckets and water balloons. Things are filling up and emptying at their own rates, in response to the water that's being pumped in.
The more complex a load is, the more out of sync the current can be with the voltage, and the worse the device's "power factor" will be. The current waveform doesn't even have to look like the voltage waveform; it can be all sorts of funny shapes. The worse the power factor, the more apparent AC power you'll need to run the device.
Multiplying a reactive load's RMS voltage and RMS current will give you the circuit's "volt-amps" (VA, which you may remember seeing on the spec sheets for uninterruptible power supplies) rating. This is its apparent power, but not its real power. Power equals VA times power factor, and power factor is the cosine of the phase angle between voltage and current.
(You're allowed to not spend time thinking about this bit. I won't be asking questions later. The phase angle thing can end up very difficult to calculate, anyway, when a load's current waveform is a funny shape, and not just a nice constant sine wave like the voltage waveform.)
A device that draws an apparent power of 1000VA and has a 0.5 power factor is consuming 500 watts of power. Not 1000. Put that device in a thermally insulated room and measure the temperature rise and it'll be the same as if you put a nice resistive 500 watt heater in there.
The VA rating is how much power the device seems to be consuming, if you don't look at the volts-versus-amps graph. But it's actually storing some power in its reactance during one portion of each AC oscillation, and returning it in the next. All of this current flow looks like real power consumption to someone who's just hooked up a couple of multimeters.
Actually, it's even more confusing than this, because the current waveform is unlikely to be sinusoidal, so it can't really be said to have a phase relationship with the voltage waveform, and frequency analysis and other evils are called for. Handwave, handwave; this stuff needn't detain us here.
Proper power meters, like the induction wheel meters that the electricity company uses to figure out how much money household power customers owe them, are meant to measure true power, not apparent power. They're supposed to compensate for differences in phase between voltage and current. How well they do that is a topic for animated discussion among people who seldom have anything better to do on a Saturday night, but the meters do more or less get it right.
So it doesn't matter much how bad the aggregate power factor of your various appliances is, at least as far as a domestic electricity bill goes.
Devices with low power factors, however, pollute the mains. Their odd current draw shifts the mains voltage around in similarly odd ways.
Consider a device with a power factor of zero. That'd be a perfect inductor - a thing that can only exist in physics-experiment-land - but it serves to illustrate what's going on here.
Feed AC through a perfect inductor and you'll be able to measure a current flow, perfectly out of phase with the mains supply (a "90 degree phase angle"). This means no actual power will be consumed; the inductor will draw current on one quarter of the cycle and deliver it back again on the next.
The AC supplier won't be happy with this, though, because it'll have to deliver current one half of the time, and handle that same current coming back again the other half of the time. This current doesn't indicate real power consumption, but it is real current. And the more of this real current the mains grid has to handle, the thicker the wires have to be, the bigger the distribution transformers have to be, the more power will be wasted thanks to cable resistance, and so on.
Lots and lots of reactive loads - an office full of PCs, say, or various other gear - can leave the mains waveform looking very weird indeed. This may be bad for other devices trying to run from mains power, and is annoying to the electricity company, for the abovementioned reasons.
Industrial power customers are, for these reasons, commonly billed according to their equipment's power factor, as well as its power consumption. The more of a mess they make of the mains, the more they pay.
Well, that's the theory, anyway; the formulae used to figure this stuff out can be baroquely complex. If you want mystifying equations, always look to accountancy before physics.
And so, Power Factor Correction (PFC) is used. PFC makes reactive loads look more like resistive ones, from the outside.
Passive PFC is just compensatory capacitance or inductance across inductive or capacitive loads; it tries to iron out the oddities with passive components.
Active PFC is an actual second circuit. It sucks power from the mains in a resistive way, and feeds it to the low power factor circuit on the other side, isolating the mains from whatever that circuit is doing. Active PFC can iron out lousy power factor better, but it's less efficient, not more; an active PFC circuit will waste some power (at least 10%, in this case) as heat, just like every other circuit in the world.
This can still work out as a good deal for industrial customers, because improving the power factor of componentry reduces the amount of power generation and distribution infrastructure needed to support it. Thinner wires, smaller transformers, smaller generators, et cetera.
But if you're not being billed by power factor - and if you're a home or small business, you're probably not - then an Active PFC PSU, or any other kind of power factor corrected hardware, isn't going to consume any less real power than cheaper gear without PFC. It'll actually probably consume a little bit more, and that little bit more will be noticed by your electricity meter, though the cost per year of this extra is unlikely to be more than you can find down the side of the couch.
If you want to do your part to clean up the mains, then PFC PSUs are a good idea. This might also qualify as enlightened self-interest, because the rate that domestic power consumers are charged per kilowatt-hour is no doubt influenced by their overall power factor. Everyone who swaps out low-power-factor gear for PFC gear lightens the load on the grid, and this may delay power price rises (or, if you live in Happy Land, actually cause the price per kilowatt-hour to drop).
Active PFC PSUs may also deal with lousy mains power better than passive PFC units, but PC PSUs generally handle spikes and surges and dropouts pretty well already, and a proper outboard power conditioner is a better solution to that problem, anyway.
So by all means, buy an Active-PFC-equipped PSU if you like; they do no harm, and they're generally high quality in other respects as well. But don't think that PFC of any kind is going to save you any money, if you're using ordinary domestic power.
The difference between car salesmen and computer salesman is that car salesmen know when they're lying, so someone who tells you Active PFC makes a PSU more efficient is not necessarily trying to pull the wool over your eyes. You'd still probably do well to buy from someone else, though
PFC decoded
Originally published 2003 in Atomic: Maximum Power Computing
Last updated 26/02/06.
Companies that make PC Power Supply Units (PSUs) find it difficult to make their products stand out from the crowd. On top of the increasingly outrageous wattage ratings (a quality 300 watt PSU is enough to run practically every PC out there, but lots of people buy something with a much higher rating just for the heck of it), there are multiple fans, funky cables, gold-plated connectors, little lights...
...and Power Factor Correction (PFC).
A PC PSU doesn't have to have PFC, but practically all of them do these days, because many countries have regulations that require some kind of PFC. Most PSUs have passive PFC; fancier models have active PFC.
Active PFC, your friendly shiny-suited PC salesman will explain, is more efficient. He may or may not also say that it'll save you money on your electricity bill.
Either way, he's full of crap.
Power factor correction (PFC) is, essentially, what you do to complex AC loads (such as PC switchmode power supplies) to make them act more like simple loads (such as toasters).
Alternating current oscillates continuously. 50 times a second, here in Australia and in most other 220/240 volt countries; 60 times a second, everywhere else (people living in East Elbonia and using 153 volt DC mains and four pin plugs need not e-mail me to complain about this generalisation).
If you plot voltage versus current drawn for a simple ("resistive") load in an AC circuit, the current will neatly follow the voltage, perfectly in sync. At the points in the AC cycle when there's the maximum voltage across the load, the maximum current will flow. And when the voltage reverses during each oscillation, so does the current. This is all very simple and sensible; it's what you'd expect AC to do, by applying the volts equals amps times ohms rule you learned for direct current circuits in high school physics. Or should have learned, anyway.
If you multiply the root-mean-square (RMS) voltage by the RMS current of a simple AC circuit like this, you get its power in watts. Again, this all works like DC electricity.
Complex AC loads are not this simple. Their current draw doesn't follow the voltage; it's out of sync. This is because the load is capacitive or inductive - "reactive". Reactive loads can even be both capacitive and inductive, in different mixtures over time.
If you think of a resistive load as just a length of hose, that needs a certain constant pressure to get a certain constant amount of water flow, then a reactive load is a contraption involving buckets and water balloons. Things are filling up and emptying at their own rates, in response to the water that's being pumped in.
The more complex a load is, the more out of sync the current can be with the voltage, and the worse the device's "power factor" will be. The current waveform doesn't even have to look like the voltage waveform; it can be all sorts of funny shapes. The worse the power factor, the more apparent AC power you'll need to run the device.
Multiplying a reactive load's RMS voltage and RMS current will give you the circuit's "volt-amps" (VA, which you may remember seeing on the spec sheets for uninterruptible power supplies) rating. This is its apparent power, but not its real power. Power equals VA times power factor, and power factor is the cosine of the phase angle between voltage and current.
(You're allowed to not spend time thinking about this bit. I won't be asking questions later. The phase angle thing can end up very difficult to calculate, anyway, when a load's current waveform is a funny shape, and not just a nice constant sine wave like the voltage waveform.)
A device that draws an apparent power of 1000VA and has a 0.5 power factor is consuming 500 watts of power. Not 1000. Put that device in a thermally insulated room and measure the temperature rise and it'll be the same as if you put a nice resistive 500 watt heater in there.
The VA rating is how much power the device seems to be consuming, if you don't look at the volts-versus-amps graph. But it's actually storing some power in its reactance during one portion of each AC oscillation, and returning it in the next. All of this current flow looks like real power consumption to someone who's just hooked up a couple of multimeters.
Actually, it's even more confusing than this, because the current waveform is unlikely to be sinusoidal, so it can't really be said to have a phase relationship with the voltage waveform, and frequency analysis and other evils are called for. Handwave, handwave; this stuff needn't detain us here.
Proper power meters, like the induction wheel meters that the electricity company uses to figure out how much money household power customers owe them, are meant to measure true power, not apparent power. They're supposed to compensate for differences in phase between voltage and current. How well they do that is a topic for animated discussion among people who seldom have anything better to do on a Saturday night, but the meters do more or less get it right.
So it doesn't matter much how bad the aggregate power factor of your various appliances is, at least as far as a domestic electricity bill goes.
Devices with low power factors, however, pollute the mains. Their odd current draw shifts the mains voltage around in similarly odd ways.
Consider a device with a power factor of zero. That'd be a perfect inductor - a thing that can only exist in physics-experiment-land - but it serves to illustrate what's going on here.
Feed AC through a perfect inductor and you'll be able to measure a current flow, perfectly out of phase with the mains supply (a "90 degree phase angle"). This means no actual power will be consumed; the inductor will draw current on one quarter of the cycle and deliver it back again on the next.
The AC supplier won't be happy with this, though, because it'll have to deliver current one half of the time, and handle that same current coming back again the other half of the time. This current doesn't indicate real power consumption, but it is real current. And the more of this real current the mains grid has to handle, the thicker the wires have to be, the bigger the distribution transformers have to be, the more power will be wasted thanks to cable resistance, and so on.
Lots and lots of reactive loads - an office full of PCs, say, or various other gear - can leave the mains waveform looking very weird indeed. This may be bad for other devices trying to run from mains power, and is annoying to the electricity company, for the abovementioned reasons.
Industrial power customers are, for these reasons, commonly billed according to their equipment's power factor, as well as its power consumption. The more of a mess they make of the mains, the more they pay.
Well, that's the theory, anyway; the formulae used to figure this stuff out can be baroquely complex. If you want mystifying equations, always look to accountancy before physics.
And so, Power Factor Correction (PFC) is used. PFC makes reactive loads look more like resistive ones, from the outside.
Passive PFC is just compensatory capacitance or inductance across inductive or capacitive loads; it tries to iron out the oddities with passive components.
Active PFC is an actual second circuit. It sucks power from the mains in a resistive way, and feeds it to the low power factor circuit on the other side, isolating the mains from whatever that circuit is doing. Active PFC can iron out lousy power factor better, but it's less efficient, not more; an active PFC circuit will waste some power (at least 10%, in this case) as heat, just like every other circuit in the world.
This can still work out as a good deal for industrial customers, because improving the power factor of componentry reduces the amount of power generation and distribution infrastructure needed to support it. Thinner wires, smaller transformers, smaller generators, et cetera.
But if you're not being billed by power factor - and if you're a home or small business, you're probably not - then an Active PFC PSU, or any other kind of power factor corrected hardware, isn't going to consume any less real power than cheaper gear without PFC. It'll actually probably consume a little bit more, and that little bit more will be noticed by your electricity meter, though the cost per year of this extra is unlikely to be more than you can find down the side of the couch.
If you want to do your part to clean up the mains, then PFC PSUs are a good idea. This might also qualify as enlightened self-interest, because the rate that domestic power consumers are charged per kilowatt-hour is no doubt influenced by their overall power factor. Everyone who swaps out low-power-factor gear for PFC gear lightens the load on the grid, and this may delay power price rises (or, if you live in Happy Land, actually cause the price per kilowatt-hour to drop).
Active PFC PSUs may also deal with lousy mains power better than passive PFC units, but PC PSUs generally handle spikes and surges and dropouts pretty well already, and a proper outboard power conditioner is a better solution to that problem, anyway.
So by all means, buy an Active-PFC-equipped PSU if you like; they do no harm, and they're generally high quality in other respects as well. But don't think that PFC of any kind is going to save you any money, if you're using ordinary domestic power.
The difference between car salesmen and computer salesman is that car salesmen know when they're lying, so someone who tells you Active PFC makes a PSU more efficient is not necessarily trying to pull the wool over your eyes. You'd still probably do well to buy from someone else, though
Most of what that article says is right - but there are some errors.
In particular, it says that active PFC may be less efficient. This is not always true. It is true that the PFC circuit needs a little power to operate - and the first generation of active PFC PSUs may have been slightly less efficient because of this.
However, adding active PFC to a PSU allows several straight-forward optimizations to be made to the rest of the PSU. The result is a significant increase in overall efficiency - from low 70s% to mid 80s%. No active PFC - no optimisation, so you're stuck using an inefficient old design.
So, if you want a PSU that will save energy - then if it doesn't say Active PFC it won't be much better than the crowd - if it does, then it's probably will save energy (as long as it's not one of the first generation designs).
Googer
Lifer
- Nov 11, 2004
- 12,576
- 7
- 81
By turning off all the lights in your home, the water heater, Air Conditioning, refridgerator, micorwave, alarm clocks, fans, washer/dryer, etc and then with only the computer running go out to the electrical meter and read it. It will tell you how much energy you are using.
The best and easiest way to disable everything is to plug the PC in to an out let on a lone circuit, then turn off all the breakers in the house except for the one the computer is using.
The method described above is cheap and requires no special tools.
If you want something serious a Fluke Clamp Meter will tell you the number of AMPS being drawn through a wire. The best way to find out total system usage including the monitor is to plug them in to an extension cord and put the clamp meter aroun the (short 3 prong) extension cord.
You will also need a multimeter to measure the voltage too. In order to get a fairly accurate measurement, you will need to take the readings from both devices simultaniously.
Multiply the AMP x Volt = the wattage being consumed.
Do not assume that a perfect 120 volts is coming out of your outlet. A slight dip in voltage will throw your calculations off but a considerable margin. That is why a Voltmeter (aka Multimeter) is important.
Do not assume that a perfect 120 volts is coming out of your outlet. A slight dip in voltage will throw your calculations off but a considerable margin.
http://store.yahoo.com/webtronics/flukclammetf4.html
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