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Kill-A-Watt device disagrees with power Formula Watts = Amps x Volts

OnTheRoadAgain

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I'm checking a Mini Fridge AC Compressor power consumption

Amps = Watts / Voltage

Example - 34Watts, 110v, AC

AC Amps = 34Watts / 110v = .31

BUT.....

Kill-A-Watt is showing AC - 34 Watts and .61 Amps ? (Power formula say it should be 0.31 amps.)
That's nearly twice the expected result. PF (Power Factor) ?
Then again, Kill-A-Watt is known to be very inaccurate at low power

How do YOU get your "accurate" results when checking things like this? Clamp on Meter?

Cheers
 
Your fridge is not pure resistive load, if you look at fridge sticker it may show 120V 6A (my fridge), that will be 720VA not 720W due to power factor because the fridge is reactive load.
Just look hit the VA button to see the VA being consumed, then hit the W button to see the W which is the working power which will show lower number than VA.
 
My "Genuine" Kill-A-Watt (there are several brands) was fooled, or rather fooled me too.
When looking at a Label, they usually indicate X amps with start surge, It does not necessarily stay there.
BUT there's the gotcha... You are calculating at 110V, yet my system puts out 119V and the kill-a-watt sees that voltage. So look at your Real & Actual Voltage to start with.

A "GOOD" Clamp meter can devine the amperage going through the wires but it is "fiddly" especially with dual mode clamps (AC & DC), I have a DVOM with Dual Mode Clamp and it can be a PITA but it works. I should'a spent more & bought a Klein or similar.
 
Your fridge is not pure resistive load, if you look at fridge sticker it may show 120V 6A (my fridge), that will be 720VA not 720W due to power factor because the fridge is reactive load.
Just look hit the VA button to see the VA being consumed, then hit the W button to see the W which is the working power which will show lower number than VA.

VA = 33
My KAW doesn't have a 'W" button....it has "Watts" ?
Watts right now = 0
Amps = 0.30

Only in a KAW does 1/3 an amp = zero watts
 
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Using just the clamp on meter to read the current draw reactive load and calculate the Watt will not be correct unless you know what the PF of the load is.
My unit has:
Watt/VA button that you toggle to select what you want to read.
Volt button
Amp button
HZ/PF button that you toggle to select what you want to read.
KWH/Hour button that you toggle to select what you want to read.
Right now my fridge is in standby (compressor is not on, just the small fan running)
V reading is 121VAC
Amp reading is 0.06A
VA reading is 07VA (121VAC * 0.06A = 7.26VA, but meter does not have resolution that can show xx.xxVA)
Watt reading is 01W (7.26VA * 0.20PF = 1.45W, but meter does not have resolution that can show xx.xxw)
PF 0.20
As you can see, the math copmes out right from Kill-A-Watt.
BTW KWH (Kilo Watt Hour) is the accumulated power consumption over time.

"Only in a KAW does 1/3 an amp - zero watts" KAW? Can I see the picture of your unit?
 
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Using just the clamp on meter to read the current draw reactive load and calculate the Watt will not be correct unless you know what the PF of the load is.
My unit has:
Watt/VA button that you toggle to select what you want to read.
Volt button
Amp button
HZ/PF button that you toggle to select what you want to read.
KWH/Hour button that you toggle to select what you want to read.
Right now my fridge is in standby (compressor is not on, just the small fan running)
V reading is 121VAC
Amp reading is 0.06A
VA reading is 07VA (121VAC * 0.06A = 7.26VA, but meter does not have resolution that can show xx.xxVA)
Watt reading is 01W (7.26VA * 0.20PF = 1.45W, but meter does not have resolution that can show xx.xxw)
PF 0.20
As you can see, the math copmes out right from Kill-A-Watt.
BTW KWH (Kilo Watt Hour) is the accumulated power consumption over time.

"Only in a KAW does 1/3 an amp - zero watts" KAW? Can I see the picture of your unit?

KAW - Kill A Watt

killawatt3.jpg
 
It's ok for crude measurements but low amperage measurements are known to be off.

I'm looking for a more accurate (but not at professional cost) way to get AC energy usage measurements that will store the data.

May be wishful thinking.
 
Well the low Amp reading as you can see on my meter, it aboe to show in xx.xxA (00.06A in my case) and it matched my clamp on meters.
I have no idea what kind of accuratecy and display resolution you are looking for,
Do you have clamp on meter to verify to compare the readings? And as I indicate, when you try to verify the power reading of the reactive load, the amp meter is not going to give you that unless you have the way to verify the PF of the load.
BTW, how low of the AC Amp reading are you trying to measure?
 
As others have said, don't assume 110V. Most utilities ship electricity at somewhere between 115-119V. There's room for variance depending on distance from substations, transformers, etc. I've NEVER measured 110V in ANY home I've had. I don't know where the 110V comes from, except as half 220V. And my main panel is 240V, so 120V split.
 
As others have said, don't assume 110V. Most utilities ship electricity at somewhere between 115-119V. There's room for variance depending on distance from substations, transformers, etc. I've NEVER measured 110V in ANY home I've had. I don't know where the 110V comes from, except as half 220V. And my main panel is 240V, so 120V split.
History, mostly. Prior to the 1930s, the US standard was 110/220. Went to 115/230 till around 1970 when 120/240 became the standard.
 
I'm checking a Mini Fridge AC Compressor power consumption

Amps = Watts / Voltage

Example - 34Watts, 110v, AC

AC Amps = 34Watts / 110v = .31

BUT.....

Kill-A-Watt is showing AC - 34 Watts and .61 Amps ? (Power formula say it should be 0.31 amps.)
That's nearly twice the expected result. PF (Power Factor) ?
Then again, Kill-A-Watt is known to be very inaccurate at low power

How do YOU get your "accurate" results when checking things like this? Clamp on Meter?

Cheers
If you have 110v.... you have more issues. Standard American voltage is 120v.
 
@OnTheRoadAgain - "I'm looking for a more accurate (but not at professional cost)". You, me, and the rest of the world. :)

You have to remember that name plate numbers are a generic sample that best describes the thousands of units produced.
Some in actuality might be higher, some lower. The purpose of which is just numerical comparison to other similar units for sale.

For example: The wall wart for my water fountain says 120V/9W on the name plate. (which should be 0.075A)
My Kill-A-Watt shows: 124.5V, .03A, 2.8W, 4.4VA, .62PF

Somewhere along the testing line, the highest they got 9 watts so that's the safe bet for a name plate.
Do you know how many returns they would have gotten if the data plate said 120V/3W like I actually got.

If your using the Kill-A-Watt for load calculations, I would stick to VA readings. It takes into account PF.
Everything is an estimation. Use your readings as just that. If you don't, you're gonna get gray hair.
 
Direct Current and Alternating current are measured differently. quite simply, in the world of alternating current volts times amps does NOT equal watts. That is to say in AC KW does not equal KvA........Google the term "Root Mean Square" --- (measure peak to peak voltage by .7071)
 
Direct Current and Alternating current are measured differently. quite simply, in the world of alternating current volts times amps does NOT equal watts. That is to say in AC KW does not equal KvA........Google the term "Root Mean Square" --- (measure peak to peak voltage by .7071)
1V RMS = 1 V DC
1A RMS = 1A DC

120V RMS = 169.68V Peak. (120V RMS x 1.414 = 169.68V Peak)
169.68V Peak x 0.707 = 120V RMS
120VRMS = 338.4V Peak-to-Peak. (120V RMS x 2.82 = 338.4V Peak to Peak)

VA rating used when the load is not pure resistive load, this where PF come into play.

 
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