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Old 11-04-2010
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JackandLiz JackandLiz is offline
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Question PURE SINE WAVE INVERTER?

Howdy, WOGers.
I recently read an article about an RVer changing out his RV type frig for a residential frig. One of the first things he did was to install a pure sine-wave inverter for better performance. So I asked my resident electronic expert as to why this inverter was better. He said, "why is it better to use for this residential frig."? And of course, I DON"T KNOW.

So-o-o-o, does a pure sine-wave inverter give better performance with appliances such as a residential refrigerator? And if so, why?

TIA,
Liz Pearce

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  #2  
Old 11-04-2010
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A good example would be something akin to:

The difference between driving down a logging road at 60 mph (in a pre 1980 FC) verses driving down a freshly paved freeway. Both can be done but one is much harder on equipment than the other...

Ya, ya, I know someone is gonna come along and spank me on this but the example still stands.
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Last edited by Turbokitty; 11-04-2010 at 09:45 PM.
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Old 11-04-2010
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My understanding is that if the fridge has electronic controls, they do mot like modified sine wave current. That is why people use a pure sine wave. It is likely better for the compressor motor as well. It will likely run cooler, better etc.
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Old 11-04-2010
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Ryan hit it right on the head. Smooth current flow is much easier on components than the modified sine waves. Picture this- you are lying in a canoe and someone is gently rocking it back and forth 60 times an hour. (I know- Hz is seconds- but stay with me) Your friend is in a canoe and someone is banging the side of it 60 times per hour with a 10 pound sledgehammer. Who's going to enjoy the canoe ride better?
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  #5  
Old 11-04-2010
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Anything with an AC motor is likely to do much better on pure sine wave. I didn't appreciate that until I experienced microwave ovens in two prior coaches with modified sine wave, and the current one with pure sine wave. Actually you can hear it when you run the microwave on modified, then run it on shore power.

The residential fridge has a motor (compressor).
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  #6  
Old 11-04-2010
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Harmonics. Non-sinusoidal but periodic waveforms as generated by modified sine-wave inverters actually consist of a summation of sinusoids as shown in the wave form's Fourier Series. These harmonic sinusoids produce eddie currents in the magnetic cores of electric motors. The eddie currents heat up the core and shorten the life of the motor. Some multiples of the fundamental frequency can make the motor run particularly rough. Think beat frequencies, dissonant notes...
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Old 11-04-2010
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Quote:
Originally Posted by davidmbrady View Post
Harmonics. Non-sinusoidal but periodic waveforms as generated by modified sine-wave inverters actually consist of a summation of sinusoids as shown in the wave form's Fourier Series. These harmonic sinusoids produce eddie currents in the magnetic cores of electric motors. The eddie currents heat up the core and shorten the life of the motor.
Thanks, David.
O.K. Now, would the life of the motor be shortened by 1%, 10%, 100%?

TIA,
Jack and Liz
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Jack and Liz Pearce
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Old 11-04-2010
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Ya

What David said, That's what I meant.
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Old 11-04-2010
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It may not be the motor that fails. The roughness of the motor may translate into failure of a drive gear, belt, clutch, or compressor itself. A high quality motor running at less than it's full capacity may not experience any appreciable shortness of life. A low quality motor may fail early on.

As Don said, I can hear the difference the noise my microwave makes on inverter vs shore power. It doesn't sound healthy. I hate running my microwave on the inverter, but of course I do run it out of necessity.
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Old 11-04-2010
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Quote:
Originally Posted by JackandLiz View Post
Thanks, David.
O.K. Now, would the life of the motor be shortened by 1%, 10%, 100%?

TIA,
Jack and Liz
The answer can also be translated into the size of motor as well as the quality... If you do buy a cheap frig or an expensive sinewave unit. My money would be on the sinewave unit.
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