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Old 05-29-2013, 11:58 AM   #1
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Modified Sinewave Inverter Question

I have a modified sine wave inverter connected to a wall receptacle in my 5th wheel. I am wanting to use it to operate a small thermal electric wine fridge while traveling. I have read that this type of inverter will not run a standard type fridge. Any thoughts?
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Old 05-29-2013, 12:03 PM   #2
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It may and it may not. No way for us to tell since we don't know the make and model of either the refer of inverter.
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Old 05-29-2013, 12:05 PM   #3
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Hold on a minute.....
You have an inverter and your back feeding your electrical? Did I understand you correctly? I sure hope that I am wrong, otherwise you just looking for big trouble.
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Old 05-29-2013, 12:08 PM   #4
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You describe the fridge as a "thermal electric"; if what you actually mean is "thermo-electric" then it is a device that uses electronics rather than a mechanical compressor, similar to how some electric coolers work. Many such devices have a power cord that includes a "power brick" very similar to those found with laptop computers. My experience is that most power bricks worked fine when we had a MSW inverter. Even if your fridge is directly connected and doesn't have a visible power brick, it almost certainly converts AC power to DC inside since that is what the electronics will need to operate from. Most such devices worked fine with the MSW; there were a few that didn't but we did no harm by connecting and trying them (for a moment or two).
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Old 05-29-2013, 02:34 PM   #5
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Hold on a minute.....You have an inverter and your back feeding your electrical? Did I understand you correctly? I sure hope that I am wrong, otherwise you just looking for big trouble.
Sorry for the confusion. I have one dedicated receptacle that I installed inside my RV, that is powered from the inverter.

Quote:
You describe the fridge as a "thermal electric"; if what you actually mean is "thermo-electric" then it is a device that uses electronics rather than a mechanical compressor, similar to how some electric coolers work. Many such devices have a power cord that includes a "power brick" very similar to those found with laptop computers. My experience is that most power bricks worked fine when we had a MSW inverter. Even if your fridge is directly connected and doesn't have a visible power brick, it almost certainly converts AC power to DC inside since that is what the electronics will need to operate from. Most such devices worked fine with the MSW; there were a few that didn't but we did no harm by connecting and trying them (for a moment or two).
You are correct, it is thermo-electric. That makes sense because I read somewhere of a particular brand of home fridge that converts and runs off off 12V, and works very well with a MSW. I guess the only way to find out is to plug it in and give it a try.
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Old 05-30-2013, 11:15 AM   #6
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Peltier(thermoelectric) coolers are DC. In principle they won't create a temperature difference in AC because it requires a constant flow of electricity in a single direction. Most are designed to operate at 12v. If yours has an AC plug, then it most likely has a power brick as described before or there's an electronic module inside the cooler which converts AC to DC.

I would see if it has a power brick and check the voltage into the fridge, then go from there. It's far more efficient to run directly from 12v, then to go from 12v to a 120v inverter, back to 12v DC in the cooler. You can assume a roughly 10% loss in electricity with each conversion(wasted as heat).
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Old 05-30-2013, 07:16 PM   #7
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Peltier(thermoelectric) coolers are DC. In principle they won't create a temperature difference in AC because it requires a constant flow of electricity in a single direction. Most are designed to operate at 12v. If yours has an AC plug, then it most likely has a power brick as described before or there's an electronic module inside the cooler which converts AC to DC.

I would see if it has a power brick and check the voltage into the fridge, then go from there. It's far more efficient to run directly from 12v, then to go from 12v to a 120v inverter, back to 12v DC in the cooler. You can assume a roughly 10% loss in electricity with each conversion(wasted as heat).
Interesting indeed. I will investigate.
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Old 05-30-2013, 07:33 PM   #8
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Interesting indeed. I will investigate.
The only concern with this approach is that the voltage in an RV varies from ~12.0-14.5 V depending on what part of the charging cycle the charger is in. Most devices won't mind this variation, but some might.
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Old 05-30-2013, 07:46 PM   #9
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This thread caught my attention and I am interested.

I live off the grid, my food is kept cold with propane RV fridges, but if I can use an electric unit with my solar panels, I could save a herd of money instead of using propane.

I am using a modified sine wave inverter, have been for six years now, and despite what some say, I have had no trouble with "sensitive" electronics such as my laptop and desktop computers. That said, I killed TWO standard house type fridges using MSW, each lasted less than a week on non pure sine wave power. The thermo electric unit sounds like it might be a possibility for me to consider.

Can you please keep the site updated with how this works out for you, and post what unit you are using ?

Thanks !!

Kev
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Old 05-30-2013, 08:58 PM   #10
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Originally Posted by mtnmankev View Post
I am using a modified sine wave inverter, have been for six years now, and despite what some say, I have had no trouble with "sensitive" electronics such as my laptop and desktop computers. That said, I killed TWO standard house type fridges using MSW, each lasted less than a week on non pure sine wave power. The thermo electric unit sounds like it might be a possibility for me to consider.
Are you aware that Samsung is, to my knowledge, the only major refrigerator manufacturer that has publicly stated, in writing, that its refrigerators will run fine on MSW inverters? Samsung has been a "hit" in the RV community because of this. Our Samsung worked fine for 2 years with our MSW unit until we replaced it with a PSW one.

Here's a link to Samsung's statement: http://answers.us.samsung.com/answer.../questions.htm
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Old 05-30-2013, 10:52 PM   #11
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Can you please keep the site updated with how this works out for you, and post what unit you are using ?
Plugged it in tonight and everything appeared to be working properly. Loaded it up with previously chilled bottles. We will see how it does for the next few days before we head out next week. Label on back shows it to use 1.4A AC
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Old 05-31-2013, 07:47 AM   #12
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Originally Posted by mtnmankev View Post
This thread caught my attention and I am interested.

I live off the grid, my food is kept cold with propane RV fridges, but if I can use an electric unit with my solar panels, I could save a herd of money instead of using propane.

I am using a modified sine wave inverter, have been for six years now, and despite what some say, I have had no trouble with "sensitive" electronics such as my laptop and desktop computers. That said, I killed TWO standard house type fridges using MSW, each lasted less than a week on non pure sine wave power. The thermo electric unit sounds like it might be a possibility for me to consider.

Can you please keep the site updated with how this works out for you, and post what unit you are using ?

Thanks !!

Kev
You know they make 3 way RV refrigerators now.... They can select between gas LP, AC power, or 12v power. I think that's the best way to go when using solar panels. I think they also make automatic energy selection ones, so if your batteries get too low, it'll probably switch to LP automatically. I'm not sure on that, you'd have to consult the manufacturer.
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Old 05-31-2013, 07:49 AM   #13
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The only concern with this approach is that the voltage in an RV varies from ~12.0-14.5 V depending on what part of the charging cycle the charger is in. Most devices won't mind this variation, but some might.
Peltier cooler probably won't have a problem with the extra current caused by the extra voltage, but the accompanying electronics might.
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Old 05-31-2013, 07:55 AM   #14
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Plugged it in tonight and everything appeared to be working properly. Loaded it up with previously chilled bottles. We will see how it does for the next few days before we head out next week. Label on back shows it to use 1.4A AC
Since the electronics are enclosed into the unit, i probably wouldn't go hacking inside and bypassing the AC transformer components unless you know what you're doing.

Keep in mind that you should always go by watts. Even though the unit is only drawing 1.4A AC, your inverter is drawing roughly 13 amps at 12.8V. 13amps will drain your batteries quick. Obviously the refridgerator cycles, so it's only drawing that when it's cooling. So it's hard to say how long your batteries will last without knowing the duty cycle of the fridge, and that also changes with ambient room temperatures as well. If your driving the whole time with the vehicles 12v system connected to the RV, you'll be fine.
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