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Old 10-10-2016, 07:04 PM   #15
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Quote:
Originally Posted by twinboat View Post
An electric mixer
X2. Or, something like a pancake air compressor.
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Old 10-10-2016, 07:19 PM   #16
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I don't have either. Would a drill work?
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Old 10-10-2016, 07:35 PM   #17
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A variable speed drill uses an electronic circuit that may well affect draw on a MSW. An old-fashioned single speed drill would work. A small vacuum cleaner should also be a simple motor circuit.

FWIW, I did tests on a K-A-W, an old Fluke DMM without True RMS, and a newer Fluke with True RMS. As expected, the old fluke read about 100 VAC, the New Fluke read 120 VAC, and the K-A-W also read 120 VAC. That is only volts - I do not know how the K-A-W does on amps.
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Old 10-10-2016, 07:46 PM   #18
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Try the AC on fan only, if you can.
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Old 10-10-2016, 07:52 PM   #19
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The AC fan will not operate on the inverter. Also, I have no way to wire in the Kill A Watt. What about a simple fan? We have one of those.
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Old 10-10-2016, 08:30 PM   #20
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As a test, a fan could work. Not much load though.

With the AC fan, dog bone the power cord to 15 amps, shut off all, but the AC breaker and bring the cord in the door and plug it in an inverter outlet.

Crazy idea, I know.
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Old 10-10-2016, 09:03 PM   #21
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I am not sure I understand? Why canít I just plug the fan into the Kill A Watt on an inverter outlet (like the refrigerator is now), record the amps reading while on the inverter. Then, turn on that 120 supply (the inverter has pass through), and record that reading?

Then, I have exactly what I have now, except I am replacing the refrigerator with the fan.
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Old 10-10-2016, 09:21 PM   #22
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I am not sure I understand? Why can’t I just plug the fan into the Kill A Watt on an inverter outlet (like the refrigerator is now), record the amps reading while on the inverter. Then, turn on that 120 supply (the inverter has pass through), and record that reading?

Then, I have exactly what I have now, except I am replacing the refrigerator with the fan.
Should work, run it on high to max out the load. Another thing might be to use a vacuum cleaner it would generate a bigger load than a residential fan will.

Since you said you could tell DC amps drawn by the inverter I still think you would be better off telling the actual watts being used while on the inverter by the DC current draw, converting to watts by multiplying amps by voltage. This will be slightly high because the inverter is not 100 % efficient. The actual AC watts used by the AC load will be 5 to 20 watts less than the DC watts due to the power consumed internally inside the inverter and the fact it is not 100% efficient.
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Old 10-10-2016, 09:32 PM   #23
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Yes, I will run the fan on high. I also will look at both amps and watts because the Kill A Watt displays both.

And, I will absolutely measure the DC side of things with my Tri-Metric tomorrow. I am guessing that all will be fine, and the Kill A Watt is giving me some erroneous readings on the actual power consumption on the fridge when on the MSW inverter.

You are correct, the DC draw is actually what I should be concerned with most.

Thanks for all the suggestions.
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Old 10-11-2016, 07:44 AM   #24
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While its true that inductive loads are different than resistive loads, I don't think you care if the purpose is to validate the KOW measurement technique. A toaster uses amps, and what you are seeking to learn is whether the KOW measures MSW amps the same as PSW amps. Doesn't make any difference how many amps - just how the KOW reacts to MSW vs PSW (shore power).
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Old 10-11-2016, 07:57 AM   #25
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While its true that inductive loads are different than resistive loads, I don't think you care if the purpose is to validate the KOW measurement technique. A toaster uses amps, and what you are seeking to learn is whether the KOW measures MSW amps the same as PSW amps. Doesn't make any difference how many amps - just how the KOW reacts to MSW vs PSW (shore power).
Inductive and capacitive loads change the phase relationship between the current and the voltage applied. That is why places with large motor loads (inductive) also put large capacitor banks on their lines to correct the phase shift.

The change in phase can effect both the measured output and the wave shape on any inverter.

The input current required is the significant issue with supplying an inverter but the output measured current will be different with different inverters because of the efficiency factor for each one.
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Old 10-11-2016, 02:34 PM   #26
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Just in case someone can shed some light on this problem for me, I have included the results of a few tests using the Kill A Watt meter.

Testing MSW Power Readings Using Kill A Watt and a small electric fan.

1) Plug fan into inverter outlet with AC on.
2) Record amps and watts
3) Turn off 50 amp breaker, so circuit is on inverter.
4) Record amps and watts.
5) Compare results.

Results: Sorry, I couldn't get the formatting right.

............ Amps Watts
Inverter 0.43 51.4
AC Power 0.53 63.6

This seems with reason to me, although approximately a 20% loss through the inverter.

Here are the results doing the same test with the refrigerator replacing the fan.

Results:
............ Amps Watts
Inverter 2.07 149
AC Power 0.92 108

This seems way out of line from what I was expecting. Also, the watts do not track? There is over 100% increase in amps, while less than a 50% increase in Watts. Very strange readings that I donít understand.

DC Power Draw Measured with the Tri-Metric while on the inverter.
13.2 Amps @ 12.5 volts = 165 Watts

This almost tracks with the 149 Watts measured with inverter using the Kill A Watt, but is way out of line for what I hoped for. If, and only IF the Kill A Watt is correct, then my conclusion is that my MSW inverter is wasting a ton of power, and I need to get a PSW inverter for the fridge. This fridge is rated at 350 KWH per year, or say, 1 KWH per day. And it does, when on shore power. But it is using more than twice that much on the inverter. Do my conclusions make sense?

If there are other explanations, please toss them into the mix for me.
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Old 10-11-2016, 02:57 PM   #27
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I recently did an inventory of the DC/AC power used and I seem to remember where a few of the readings on my Trimetric meter didn't match up with the kill-a-watt reading. (after converting)
Unfortunately I just did a reset on my phone and lost the excel file. If I'm at the RV again this week I'll do a couple of quick checks.
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Old 10-12-2016, 07:52 AM   #28
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I think you are getting caught up in the non sinusoidal wave form coming out of the MSW Inverter. I will go back to my first post, put a True RMS Amp meter in series with the power cord. Most DMM's will do 10 A so that should not be more than a bit of wiring to make a way to connect the meter. Put it in a small box if you are worried.
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