Is Kill-a-Watt the best electricity measuring tool?
- Thread starter Kaido
- Start date
I have no answer for your question.
I would just like to suggest that you use the phrase "Power measurement" instead of "electricity measurement" to be more accurate. Electricity has many parameters. Electrical power is one of those.
It's definitely not the best method, but most likely the cheapest and most convienent for reading the power useage at any time.
The unit for power is the Watt (W), which is the consumption of 1 joule in one second.
The unit for electricity consumed is kWh.
1 kWh = 3,600,000 Joules.
This is adequate for domestic use.
In more industrial situations especially where you are generating your own power you want to use the unit kVA (kilo Volt Amps), as this takes into account the nature of the loading. (reactance and reluctance).
The unit for electricity consumed is kWh.
1 kWh = 3,600,000 Joules.
This is adequate for domestic use.
In more industrial situations especially where you are generating your own power you want to use the unit kVA (kilo Volt Amps), as this takes into account the nature of the loading. (reactance and reluctance).
Watts are a decent measurement of power, provided we have other givens:
- we assume voltage to be constant for static measuring purposes (12, 5, 15, etc.)
- voltage is not bouncing all over the place under high loads
Personally I think it's time to do away with conventional transformer power supply designs and move to full digital output stages. The later is much more stable.
- we assume voltage to be constant for static measuring purposes (12, 5, 15, etc.)
- voltage is not bouncing all over the place under high loads
Personally I think it's time to do away with conventional transformer power supply designs and move to full digital output stages. The later is much more stable.
I think you totally misunderstood what the OP was asking. He wasn't asking about kiloWatts. He was asking about Kill-A-Watt.
I suspect this device uses a hall-effect device to measure the AC current. A more accurate method is to connect an ammeter to the circuit.
You guys need to learn to read into what the OP is asking for
Back on topic, no it is not the best. It is good, however, for the money.
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What would you suggest? I'm going to be doing various projects with different PSUs and modifications this year and just want something based to measure watts and whatnot. I don't need a fancy bells-and-whistles device, but I don't want a piece of junk that stops working after a month either. Just something that will hold up and tell me basic electrical information like watts and volts and whatnot over time.
No. This device measures both instantaneous voltage and current directly. It then performs an all-quadrant multiplication before calculating average power, and total energy.
This is far more accurate than estimating AC power, by measuring the current alone.
The kill-a-watt device is likely to be more than adequate for most home and office-type situations. If you want a quality, calibrated, industrial meter then you need to pay big bucks.
Several people have mentioned, in this thread, that this (Kill-A-Watt) is not the best way for measurement. But, no one has explained what would be better!
I do not have any equipment for power measurement. But, I am looking to get one.
Do you mean this device has a 1% error and there are other equipment that can make the measurement at 0.1% accuracy?
Or, do you mean that this device has a 20% error and there are equipment that can make the measurement more accurately?
I could not care less about 1 to 5% error. But, still I would be interested to see what your other alternative is and how much it is going to cost.
I do not have any equipment for power measurement. But, I am looking to get one.
Do you mean this device has a 1% error and there are other equipment that can make the measurement at 0.1% accuracy?
Or, do you mean that this device has a 20% error and there are equipment that can make the measurement more accurately?
I could not care less about 1 to 5% error. But, still I would be interested to see what your other alternative is and how much it is going to cost.
Wihtout having to purchase an industrial piece of equipment that will cost thousands of $$ (kinds they use in electrical power plants for instance), the most accurate way is to use a digital MM that is the clamp style for measuring amperage.
You hook the clamp around the main power wire to measure the real time amperage, while constantly measuring the incoming voltage as it will jump around slightly. Then do a calculation to find power. This is not very convient though.
Power = voltage * amps
Of course, as previously stated, using a kill-a-watt meter is much easier and cheaper. It works basically the same way, but does the calculations for you. It's only problem is that it's not as accurate as a nice digital MM. But for home users, it's just fine IMO.
You hook the clamp around the main power wire to measure the real time amperage, while constantly measuring the incoming voltage as it will jump around slightly. Then do a calculation to find power. This is not very convient though.
Power = voltage * amps
Of course, as previously stated, using a kill-a-watt meter is much easier and cheaper. It works basically the same way, but does the calculations for you. It's only problem is that it's not as accurate as a nice digital MM. But for home users, it's just fine IMO.
Real Power = Voltage * Current * Cos(Theta), where Theta is the phase between the current and voltage.
Real power is what the power company charges you for.
If you just multiply the voltage by current, what you get is Apparent power.
If you want to know how much power your PC uses in order to choose a UPS or in order to make sure your PSU is not overloaded, you need to measure Real Power.
You can read about this here.
I don't see why it would be any less accurate than a digital multi meter. In fact, you cannot measure the phase relationship between the voltage and current with a simple multi meter, which is necessary for power factor measurement.
This is the product on the manufacturer's site. It claims a 0.2% accuracy.
I don't think there is anything wrong with Kill-A-Watt. It will measure Real power as well as the power factor etc.
This isn't EE here. I was guessing that you just wanted an accurate way to measure the wattage a particular appliance uses. The Kill-a-watt meter is plenty accurate for home users as I stated, but it's not going to have the pure accuracy of a DMM that are normally ~+/-0.025%, which is in theory 10x more accurate than the KAW meter you linked.
I do!
Except that a DMM cannot measure power! Neither can you calculate power using measured voltage and current unless it is DC. For AC, you will need a third parameter as well, which a regular DMM cannot measure.
When I saw posts here that Kill-A-Watt was not the best, I assumed there was data or experience that there was something very wrong with it.
That is why I posted and enquired about it since I would be interested in such data.
P=VI (instantaneous power) is adequate for US residence. No need to worry about power factor since the home consumer is not charged for the phase shift.
At least here in the US, voltage * current is a perfectly acceptable way to calculate power for household items.
If you honestly think that a $30 Kill-a-watt meter can measure the phase, you're kidding yourself. I have no doubt it gives out a reading in watts by using P=VI.
The AC voltage and current that a digital meter measures are not instantaneous. They are Root Mean Square (RMS). Therefore, VI, in this case, is not going to be instantaneous either. It is called Apparent Power.
Please read the link posted before.
Power for an AC circuit is almost always less than VI for an AC circuit.
Let me give you an example. Let's say your PSU draws 4 Amps from the wall, which is 120 Volts and let's say the PSU has a 0.7 power factor.
You may think that the power the PSU is drawing is 120V * 4A = 480W. You would be wrong!
The power it takes is 120V * 4A * 0.7 = 336W.
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