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Old 05-20-2015, 08:37 AM   #29
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'Proper household line voltage is 120 V RMS @ 60 Hz. The key is the "RMS" which stands for Root Mean Square, which is a fancy term for saying "average" voltage. (There's a little more to it because of the voltage going positive and negative, but that's not really important to this discussion.) Normal line voltage is a sine wave, with a peak voltage of about 170 Volts. The thing is that it doesn't stay at that value but is constantly rising and falling. Over a full cycle, the average voltage is 120 Volts RMS."

Full of misinformation.

The D’Arsonval movement commonly used in multimeters is a DC movement. To measure AC the signal is rectified and filtered yielding a peak reading unless the AC is at a very low frequency as in less than a Hz. The meter scale is calibrated to indicate the equivalent for a pure sine wave input signal.

The actual Average value of a full cycle of AC is zero. Equal excursions positive and negative. The Average value of a 1/2 cycle peak as in a rectified signal is ~0.637 x the peak value.

RMS voltage is the equivalent to a DC voltage that would produce the same power usually as heat. It is a function of the sq root of 2 or ~0.707 x the peak value. Measuring it before microprocessors became common was usually done by heating a resistor and matching the DC power needed to do it. Processors used to calculate it slice the wave form into many samples and do the math on the sample values.

It still comes down to if the refrigerator is running OK then there is no problem with it. The problem is in perception. If they refer is not running OK it cannot tolerate the extra power in part of the cycle and needs a pure sine inverter. The voltage reading is not correctly representing what is going on.
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Old 05-20-2015, 09:00 AM   #30
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Quote:
Originally Posted by jerichorick View Post
Bottom line? The meter may not be capable of reading the voltage correctly but the available power source is still the true problem for the OP.

I respect your disagreement but I still disagree with you respectfully.
I agree that the net results of our arguments are the same: the OP's refrigerator probably will be happier with a pure sine wave inverter. It's the path leading to the conclusion where we respectfully agree to disagree.

(Yes, it's mostly a matter of semantics, but this could be an interesting and thought provoking campfire discussion.)

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Please give Magnum a call about that inverter. I think it has a genset start feature but I could be wrong.
The inverter does not control the genset directly. But their ME-AGS-N plugs in to the inverter and communicates with the remote control to provide the genset integration. I have it, and it works well. The only complaint is that it starts the generator strictly on voltage, and then runs the generator for a set time. If you have a temporary heavy load (like running the microwave on the inverter for a few seconds, or taking a shower while running the water pump) it can lower the battery voltage enough that it thinks the battery state of charge is much lower than it really is. That will start the generator, which will then run for the set time, even if the battery is done recharging before then (because it wasn't really that low to begin with.) Still, it's a good system and I use it a lot.

It can be improved by adding the ME-BMK which puts a shunt in the battery line to monitor power in/out of the battery and give a much more accurate indication of the actual state of charge. In that case, the AGS will start the generator based on the actual state of charge and not be fooled by temporary dips in voltage. It also stops the generator when the battery has reached the desired state of charge. It is easily added to an existing system, and it's on my to-do list, it just hasn't gotten done yet...

Quote:
It even assists when I am on 30A service by kicking in to take up the loads it is connected to when the 30A is maxed out. I have seen as much as 18A donation from it during these times.
Interesting. I don't see this feature in that model's manual, and my Magnum (a different but similar model) doesn't do that. The only way I can do something that is by turning off the breaker feeding the inverter/charger. That makes it think the shore power is lost so it takes over feeding certain loads from the inverter.

Do you have a load management system that cuts off certain AC loads if the shore power isn't sufficient? If so, is the power to the Magnum run through that system? If so, that could explain it. Mine isn't wired that way: the only loads that are controlled are the water heater, two A/C units, and the washer/dryer.
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Old 05-20-2015, 09:19 AM   #31
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Originally Posted by nothermark View Post
The D’Arsonval movement commonly used in multimeters is a DC movement. To measure AC the signal is rectified and filtered yielding a peak reading
I stand corrected. Of course the signal is rectified, but not having used a D'Arsonval meter for more than 30 years, I apparently forgot some details.

Quote:
The actual Average value of a full cycle of AC is zero. Equal excursions positive and negative. [...] RMS voltage is the equivalent to a DC voltage that would produce the same power usually as heat. It is a function of the sq root of 2 or ~0.707 x the peak value.
Like I said, there's more to it than what I was saying, I was trying to keep the complex discussion a bit simpler.

Quote:
Processors used to calculate it slice the wave form into many samples and do the math on the sample values.
That's what I was trying to explain for True RMS meters. Cheaper ones, like the OP's (and a couple of my smaller meters) just take the filtered peak reading and apply .707 to it.

Quote:
The problem is in perception. [...] The voltage reading is not correctly representing what is going on.
Precisely.
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Old 05-21-2015, 07:35 AM   #32
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It had been a while so I had to go look up a few things the first time I got into one of these discussions. At least we know what to go look for. ;-))

What troubles me is all the folks selling him on a "true sine inverter" when no one knows if there is any problem other than his meter does not read what he would like it to. If I understand the Samsung correctly the reason it works on anything is that it converts the AC to DC then uses that to run the motor. Pretty much independent of the power source noise and wave shape as long as it gets above a minimum threshold long enough. I wonder how many other new designs are doing the same thing.
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Old 05-21-2015, 09:38 AM   #33
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What troubles me is all the folks selling him on a "true sine inverter" when no one knows if there is any problem other than his meter does not read what he would like it to.
True, it is all assumptions, but I think they are reasonable.

Looking at the information so far:
  • He has a meter that isn't giving the expected RMS value, but that's expected since the meter does not read true RMS
  • The reading he gets with his digital meter is the reading you would expect with such a meter and a MSW inverter
  • It is not uncommon for some appliances to have trouble with MSW power
It all points to the MSW waveform being the culprit. But other than swapping out the inverter and trying it, the only reasonable definitive test I can think of trying before swapping out the inverter is what I mentioned in post #19: park next to a rig with a true sine wave inverter and try to run the fridge off of that.

The only other test I can think of (and one I would do if I had access to the coach) is to put an oscilloscope on the MSW output and see if it is as expected. The problem with that method is that very few people have an oscilloscope, and probably even fewer know exactly what the MSW waveform is supposed to look like (peak voltages, pulse widths, rise/fall times, harmonics, etc.)
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Old 05-21-2015, 11:33 AM   #34
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Originally Posted by nothermark View Post
It had been a while so I had to go look up a few things the first time I got into one of these discussions. At least we know what to go look for. ;-))

What troubles me is all the folks selling him on a "true sine inverter" when no one knows if there is any problem other than his meter does not read what he would like it to. If I understand the Samsung correctly the reason it works on anything is that it converts the AC to DC then uses that to run the motor. Pretty much independent of the power source noise and wave shape as long as it gets above a minimum threshold long enough. I wonder how many other new designs are doing the same thing.
You are exactly right. Many newer appliances with motors, (refrigerator, washers, dishwashers, etc.) have switched to DC motors to save energy and improve operating characteristics. We don't know the exact model of Kenmore refrigerator and what the OP meant by "doesn't run well on inverter." I find all this side discussion of meters and wave theory impressive but not germane to the OP's question.
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Old 05-21-2015, 12:24 PM   #35
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My credentials: Associates in Electronics, Wentworth Institute, 1966. 4 years in electronics in the Army, 32 years with the phone company and divestitures including emergency power work. I have forgotten way more than I wish to admit. But, with this experience, MSW inverters are limited as to what can use them BECAUSE they only simulate commercial power kind of the way a Rolex knock-off simulates a true Rolex. They both tell time but one does it more efficiently and is a better product than the other. I wonder which is the better watch??

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Old 05-21-2015, 04:39 PM   #36
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They both tell time but one does it more efficiently and is a better product than the other.
Well said!

Quote:
I wonder which is the better watch??
That's an easy question to answer, the better one is the one that's on your wrist! If you can't afford a Rolex, having the knock-off on your wrist is better than never knowing what time it is!

Not everybody needs a pure sine wave inverter, in fact I'm very happy with my MSW Magnum -- although I don't try to run a residential refrigerator with it. I see no need to spend the money to swap out a perfectly good inverter that works for me. But some people do need pure sine wave, however, and it looks like the OP might be one of them.
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Old 05-21-2015, 11:03 PM   #37
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"If you have a temporary heavy load (like running the microwave on the inverter for a few seconds, or taking a shower while running the water pump) it can lower the battery voltage enough that it thinks the battery state of charge is much lower than it really is. That will start the generator, which will then run for the set time, even if the battery is done recharging before then (because it wasn't really that low to begin with."

IIRC, you can set the time allowed before the AGS takes affect and starts the generator. This allows for the momentary dip in voltage caused by a short period draw.
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Old 05-22-2015, 01:37 AM   #38
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The inverter will run at a lower voltage to save battery until needed. add a load like an iron then check the voltage.
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Old 05-22-2015, 08:14 AM   #39
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IIRC, you can set the time allowed before the AGS takes affect and starts the generator. This allows for the momentary dip in voltage caused by a short period draw.
I have no such option on my remote. However, there is a new version of the remote that has a lot more capabilities. Perhaps that is one of the new features they added?
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Old 05-22-2015, 08:55 AM   #40
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Nobody is telling him to buy a PSw. If ex wants to run his fridge on inverter then he will have to. I have been through this 2 years ago I installed a LG fridge and would not work. Interestingly I just installed a 10 year old fridge in my friends cabin on a MSW and it woks perfect. It would be a fridgidair model
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Old 05-22-2015, 09:16 AM   #41
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Nobody is telling him to buy a PSw. If ex wants to run his fridge on inverter then he will have to. I have been through this 2 years ago I installed a LG fridge and would not work. Interestingly I just installed a 10 year old fridge in my friends cabin on a MSW and it woks perfect. It would be a fridgidair model
Not quite. You went through it with your LG probably because it has a 120 VAC line voltage to power the motor for the compressor. As you pointed out your friend has a Frigidaire that works on an MSW converter. All we know about the OP is that he measured the voltage and it read low but that is an issue with his meter. He has never said he has a problem other than that.
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Old 05-22-2015, 09:32 AM   #42
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The inverter will run at a lower voltage to save battery until needed. add a load like an iron then check the voltage.
I've seen inverters that shut down when battery voltage drops below a set point, but never seen one that adjusts output AC by determining load. I'd guess if they worked that way, more malfunctioning AC items would be reported.
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