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Old 09-13-2014, 01:04 PM   #1
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Kill-a-watt reading over voltage?

My Kill a watt meter reads 149-150 volts,,, when I know that's not right... I have varified the voltage with a digital volt ohm meter and it comes up right,, around 110 volts +- .. This is in my shop so voltage is a little lower than the house... Anyway, my question is why does the kill a watt meter read so high ??? Are there batteries to replace in that thing ? Thanks,,, Monkey PS,, voltage in the house 122+- , kill a watt 150 volts... ???
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Old 09-13-2014, 02:10 PM   #2
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The Kill a watt meter is measuring peak voltage and your meter is measuring RMS
voltage.(root mean sq)
The difference is 1.414 X RMS = Peak voltage
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Old 09-13-2014, 02:21 PM   #3
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Nope, not true.

http://www.p3international.com/manuals/p4400_manual.pdf

The Kill-O-Watt reads RMS Voltage and Amps.

I would say your unit is defective. I have one and it reads within a few volts of my DVOM.

No batteries needed as it runs off of 120 VAC power.

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Old 09-13-2014, 03:10 PM   #4
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Quote:
Originally Posted by Dr4Film View Post
Nope, not true.

http://www.p3international.com/manuals/p4400_manual.pdf

The Kill-O-Watt reads RMS Voltage and Amps.

I would say your unit is defective. I have one and it reads within a few volts of my DVOM.

No batteries needed as it runs off of 120 VAC power.

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Not wrong, if the op reads 110 volts on his mult meter and 150 or so volts
on his kill o watt meter the kill o watt meter is reading peak voltage.
As to it being defective that maybe the case.
But that is the reason for the different readings.
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Old 09-13-2014, 03:32 PM   #5
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Well, I guess that I read the Kill-O-Watt manual wrong then, sorry.

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Old 09-13-2014, 03:38 PM   #6
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Quote:
Originally Posted by Dr4Film View Post
The Kill-O-Watt reads RMS Voltage and Amps.

I would say your unit is defective.

No batteries needed as it runs off of 120 VAC power.

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I agree
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Old 09-13-2014, 03:44 PM   #7
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Well, I guess that I read the Kill-O-Watt manual wrong then, sorry.

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No you read the manual right however the op asked why the difference in
readings.
The reason for it showing peak and not the normal rms the most common might indicate a defective meter or his meter is a peak reading meter.
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Old 09-13-2014, 03:55 PM   #8
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Brings up a question for me. I put a multimeter on a plug in my RV that is from the Deminsions inverter. The inexpensive multimeter gave wide reads very low 85 volts to 145 volts. I pulled the manual for the inverter and it said to use only a true RMS meter for checking the voltage. I don't have a RMS meter and none appear to be availble in the rural area where I live. I do have a killowatt (if I can find it) but the killowatt is not true RMS so am I wasting my time if I measure it with a killowatt?
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Old 09-13-2014, 03:59 PM   #9
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Quote:
Originally Posted by wb7auk View Post
Not wrong, if the op reads 110 volts on his mult meter and 150 or so volts on his kill o watt meter the kill o watt meter is reading peak voltage.
As to it being defective that maybe the case.
But that is the reason for the different readings.
wb7auk
A Kill-A-Watt meter is supposed to read RMS voltage.
See #2 of this pdf: http://www.p3international.com/manuals/p4400_manual.pdf
I guess that means you are right about "peak voltage".....and that his Kill-A-Watt is defective.
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Old 09-13-2014, 04:03 PM   #10
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Originally Posted by 1ciderdog View Post
but the killowatt is not true RMS so am I wasting my time if I measure it with a killowatt?
1ciderdog
See #2 here:
http://www.p3international.com/manuals/p4400_manual.pdf
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Old 09-13-2014, 04:07 PM   #11
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Quote:
Originally Posted by 1ciderdog View Post
Brings up a question for me. I put a multimeter on a plug in my RV that is from the Deminsions inverter. The inexpensive multimeter gave wide reads very low 85 volts to 145 volts. I pulled the manual for the inverter and it said to use only a true RMS meter for checking the voltage. I don't have a RMS meter and none appear to be availble in the rural area where I live. I do have a killowatt (if I can find it) but the killowatt is not true RMS so am I wasting my time if I measure it with a killowatt?
Sounds like your Deminsions inverter is a MSW, that being the case the
85 volts is what you would see on a RMS meter but the Peak voltage
will be 120 volts.
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Old 09-13-2014, 07:13 PM   #12
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Quote:
Originally Posted by wb7auk View Post
The Kill a watt meter is measuring peak voltage and your meter is measuring RMS
voltage.(root mean sq)
The difference is 1.414 X RMS = Peak voltage
I do not know if the Kill-a-watt is a peak reading meter which will often give false readings on an MSW inverter circuit or a true RMS meter which should give the proper voltage.

BUT this I do know.. The O/P said "IN MY SHOP". which strongly suggests it is reading line voltage which is sine wave so no matter which way it reads it should agree with th DVM (Digital Volt meter).

Fact: Any device made by man is subject to failure.. It is possible the O/Ps Kill-a-watt has failed and is giving false readings.

Mine .. still agrees with the other two analog meters I have on line and with my assorted DVM's. (I have a bunch of those, one is still on the bubble card).

To the O/P, no internal batteries, it is line powered.

Recommendation is to either replace it or simply do not use it for VOLTS. check the frequency reading.

Also, I'd not trust it for any reading needing volts, (V-A, Watts, KWH) power factor should be ok, though since that is a ratio of two things and the error should be consistant.
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Old 09-13-2014, 07:51 PM   #13
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I go back to my original post where I stated that the Kill-O-Watt is supposed to be a RMS meter, not a Peak Voltage meter or any other type of meter for that matter.

Therefore, his Kill-O-Watt is defective. Common sense says it should be replaced.

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Old 09-13-2014, 07:55 PM   #14
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Quote:
Originally Posted by wa8yxm View Post
I do not know if the Kill-a-watt is a peak reading meter which will often give false readings on an MSW inverter circuit or a true RMS meter which should give the proper voltage.

BUT this I do know.. The O/P said "IN MY SHOP". which strongly suggests it is reading line voltage which is sine wave so no matter which way it reads it should agree with th DVM (Digital Volt meter).

Fact: Any device made by man is subject to failure.. It is possible the O/Ps Kill-a-watt has failed and is giving false readings.

Mine .. still agrees with the other two analog meters I have on line and with my assorted DVM's. (I have a bunch of those, one is still on the bubble card).

To the O/P, no internal batteries, it is line powered.

Recommendation is to either replace it or simply do not use it for VOLTS. check the frequency reading.

Also, I'd not trust it for any reading needing volts, (V-A, Watts, KWH) power factor should be ok, though since that is a ratio of two things and the error should be consistant.
I will try once again:
The op's kill o watt appears to be showing peak volts and not rms voltage.
What has gone away in the circuit is hard to say, I pulled up the diagram and there are a couple of things that could cause this if it is the one that several have posted the manual on.
The op wanted to know why he was showing two different readings with different meters and I stated the reason why it could occur.
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