1

I just got one of these; I love it and it seems accurate. But I would like to check its accuracy.

Can anyone think of an appliance with very predictable constant power consumption that I could use to test it?

If not, can anyone think of other ways to test it? I was thinking I could get a second one, and either test them side-by-side with similar appliances or plug one into the other and see how close they are. Or maybe I could hook it to a large appliance and compare the power use to the increase in power consumption on my main meter. Not sure....

Edit: h/t @Harper - Reinstate Monica maybe I can use this method: https://youtu.be/xCVnW_Ou470?t=107

Thanks!


Update: I tested my Kill-a-Watt with the following devices:

18W portable fan with single setting - Kill-a-Watt says 17.6 120V 8A portable drill, trigger all the way down running in the air - Kill-a-Watt says much less than 960 1500W electric kettle - Kill-a-Watt says 1487

The drill is the outlier. Based on the comments this seems normal for electric motors not encountering much resistance.

  • 1
    They work. No need to go out of your way questioning it. – Ecnerwal Sep 15 at 15:06
  • 2
  • 1
    do you want to measure apparent power or real power? (there's different methods for both). Some meters are pretty accurate for VA, but not W. That said, I would just use a DMM to verify some of the meter's measurements and trust the rest. – dandavis Sep 15 at 19:30
  • 2
    We get voltage from the wall, not power, which comes from consuming the voltage to generate a current. If you want agreement with your utility meter, go for real power (for now), if you're running a generator, watch out for apparent power to avoid over-load. A high-precision and accurate way of measuring dc-equiv consumption is to briefly power a 1000 ohm 50-watt ceramic power resistor from the wall, and measure the voltage across it with a true RMS DMM. Where v is the reading, watts will be (v/1000)*v, so compare that to the usage monitor. Oh; measure the resistance and sub that for 1000. – dandavis Sep 15 at 20:11
  • 1
    Regarding your edit, it's expected that a drill will not use its full power just spinning in the air. Higher power draw will occur when it encounters a lot of resistance to turning, such as when drilling through a difficult material. This is true of all electric motors. – Nate S. Sep 17 at 20:24
2

How about a portable resistance heater?

enter image description here

| improve this answer | |
  • 1
    power draw depends on voltage though, which fluctuates throughout the day, limiting the accuracy of this test. – dandavis Sep 15 at 19:28
  • 1
    @dandavis, voltage should not fluctuate much throughout the day in most developed countries -- there's people working very hard to make sure of that. And you can always measure the voltage at the same time, and correct for any differences. – Nate S. Sep 15 at 19:59
  • 2
    @NateS. I'd like to consider my area "developed", but I measure several volts of variation ~(117-124), enough to obscure potential errors and prevent validating the 0.2% claim of the kill-a-watt. Yes, V can be measured alongside, but the KAW's accumulation and W screen won't do that when used intuitively. – dandavis Sep 15 at 20:20
  • 2
    @dandavis, fair enough, yeah, if you want to measure to an accuracy of under a percent, using a resistor of a known value like you mentioned in the comments would be the way to go, since I very much doubt the nameplate rating of a heater like this is any more accurate than that. If you turn that into an answer, I'll +1 it. – Nate S. Sep 15 at 20:27
  • 1
    The KAW is constantly making the measurments of actual voltage and actual amperage and the time (thus phase) relationship between them, and the results at the VA, W and kWh screens all reflect that to a degree of accuracy that's outstanding for the price. When I've had everything running through a KAW (early construction, small enough loads that could be the case) and a smart meter, they agree quite nicely. Either accept that it works, or go get $3000 worth of power analyzer to validate your $20 KAW. – Ecnerwal Sep 15 at 22:19
2

Since it's only good for 1875 watts, I'd be plugging in my toaster oven or a 1400 watt hair dryer. Both of those appliances will state the watts or amperage and you could compare it to your readout. Make sure you read your display before the appliances start cycling on and off... set them on high.

| improve this answer | |
  • 3
    Set them on high and give them a minute or two to reach steady state. You could use an infrared or instant-read thermometer to monitor this. – LShaver Sep 15 at 16:17
  • 2
    listed current is rarely exact, usually it's a worse-case scenario. – dandavis Sep 15 at 19:27
  • 2
    @dandavis it often assumes 125V. – Harper - Reinstate Monica Sep 15 at 21:31
  • 1
    @dandavis No meters are exact either. The line voltage from the power company changes constantly so the amps would too. – JACK Sep 15 at 21:39
  • 1
    I could just as easily have set this as the answer, thanks!! – capet Sep 17 at 18:54
1

try it with an incandescent lightbulb 100W if you have one...

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.