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Old 11-24-2012, 07:51 PM   #1
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Inverter/Fridge

I recently purchased my 1992 32' Damon Challenger. One of the perks was the new Magic Chef fridge the previous owner had just installed. Well tonight in the midst of my thanksgiving bordem around the family i was reading the fridge manual and realized that it is a "household only" model and "not intended to be used with inverter." It has worked fine off 110 outlet with genny/shore power. However I bought an 800 watt inverter to run from 12V Marine coach battery while going down road. Does anyone have any thoughts on this setup? Am I on borrowed time if I ignore warnings? Im not sure i understand the difference between RV fridge/house fridge. Could someone fill me in? Also if I did use fridge, any kinda estimate on watts it would draw?
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Old 11-24-2012, 08:15 PM   #2
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Originally Posted by Damon92 View Post
I recently purchased my 1992 32' Damon Challenger. One of the perks was the new Magic Chef fridge the previous owner had just installed. Well tonight in the midst of my thanksgiving bordem around the family i was reading the fridge manual and realized that it is a "household only" model and "not intended to be used with inverter." It has worked fine off 110 outlet with genny/shore power. However I bought an 800 watt inverter to run from 12V Marine coach battery while going down road. Does anyone have any thoughts on this setup? Am I on borrowed time if I ignore warnings? Im not sure i understand the difference between RV fridge/house fridge. Could someone fill me in? Also if I did use fridge, any kinda estimate on watts it would draw?
Thanks
Brandon
My residential reefer runs just fine on a Modified Sine Wave (MSW) inverter. There is also a Pure Sine Wave inverter that most likely would run your reefer. So, if the inverter you bought is not a PSW type I am thinking you are headed for a problem if you run the reefer on it. MSW is a less expensive inverter but a PSW unit mimics grid power. That's my understanding of the difference.
As far as your setup goes excepting the MSW - PSW issue I would think that an 800 watt inverter (if it's continuous) would be a decent size for the reefer. But, having said that; do you know the amp draw for your reefer? That would be the determining factor. Look on the reefer data plate for the info.
As far as a single 12v battery you will not have much ability to invert without a constant recharge. And as far as keeping the battery charged while your engine is operating you should make sure your alternator is sized properly. I can't advise you on "proper" alternator size but my guess is that your current one is not sized for running the coach and it's requirements plus the inverter.
Hope all this helps you
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Old 11-24-2012, 08:21 PM   #3
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Thanks for reply. I just bought a new 180 AMP alt and had my 100 AMP rebuilt for a spare so I should be good as far as keeping my single 12V charged. As far as inverters, the one I bought is a Stanley Modified 800Watts. My father in law has a 1000 Watt pure sine that he offered to give me so I may take him up on that. I wouldn't plan to run fridge on battery during boondock just while traveling. Thanks for your input.
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Old 11-24-2012, 08:28 PM   #4
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Thanks for reply. I just bought a new 180 AMP alt and had my 100 AMP rebuilt for a spare so I should be good as far as keeping my single 12V charged. As far as inverters, the one I bought is a Stanley Modified 800Watts. My father in law has a 1000 Watt pure sine that he offered to give me so I may take him up on that. I wouldn't plan to run fridge on battery during boondock just while traveling. Thanks for your input.
I would pose the question in another thread......"PSW and MSW difference" and hopefully someone with more specific knowledge will reply.
But, if you don't want the 1000watt PSW I'll take it.
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Old 11-24-2012, 10:32 PM   #5
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My father in law has a 1000 Watt pure sine that he offered to give me so I may take him up on that. I wouldn't plan to run fridge on battery during boondock just while traveling. Thanks for your input.
Definitely take your father in law up on the pure sine wave inverter. Hook it up with the recommended wire (probably 1/0 or 2/0 awg) directly to your house battery.

Also I'd make sure your wiring from the alternator to the coach battery is up-to-par, both the plus and the ground side. The alternator may be able to put out 160A but it won't if your wiring to the battery is too small or fused at 60A like our old coach was. I rewired it with appropriate sized wire from the alternator stud through a new 200A fuse, the isolator solenoid all the way to the battery, then found I had to rebuild the ground wiring because there was too much voltage drop from the wire to the chassis, I had .25V drop across just one lug!

The fridge probably only takes a couple hundred watts when running but may take ten times that for a couple of cycles to start. The 800W MSW may not have enough uumph to start it, the 1000W PSW would have a much better chance of working.

Keep in mind that a watt is approximately an amp at 12V, so a 200W load will draw 200A from your battery/alternator combo. Most coaches that have residential fridges have at least 400A/H of batteries so the fridge can be powered overnight while boondocking without running the genny. Since you only have one battery it's good you don't plan on running it on inverter overnight.
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Old 11-25-2012, 06:09 AM   #6
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Originally Posted by Damon92 View Post
I recently purchased my 1992 32' Damon Challenger. One of the perks was the new Magic Chef fridge the previous owner had just installed. Well tonight in the midst of my thanksgiving bordem around the family i was reading the fridge manual and realized that it is a "household only" model and "not intended to be used with inverter." It has worked fine off 110 outlet with genny/shore power. However I bought an 800 watt inverter to run from 12V Marine coach battery while going down road. Does anyone have any thoughts on this setup? Am I on borrowed time if I ignore warnings? Im not sure i understand the difference between RV fridge/house fridge. Could someone fill me in? Also if I did use fridge, any kinda estimate on watts it would draw?
Thanks
Brandon
Some residential refrigerators will run on MSW and some will not. Sometimes it is the motor that is the problem, and sometimes it is the electronics in the control circuit. If the manual says not intended to be run on an inverter, it is probably MSW that is the problem since this is the most common type of inverter. It should be fine on PSW.

Although Samsung says our 18 cu ft refrigerator could draw as much as 11 amps (about 1300 watts) on startup, I have never seen it draw more than about 4 amps. This was a momentary spike during compressor start observed on a Kill-A-Watt meter. Normally, it draws only 1 to 3 amps (120 to 360 watts) when the compressor is running. It may use slightly more power during the defrost cycle, but I have never monitored it during defrost.
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Old 11-25-2012, 06:15 AM   #7
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Two thoughts, first, if you are not traveling great distances in a given day, just keep the fridge closed. It won't keep ice cream frozen for hours but will hold the cold for a day of travel. Second, if you have a genny, you can run it while you travel. Either option will relieve your inverter. I run quite frequently without power to the fridge, just to save propane, as long as I don't have any ice cream in the freezer.
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Old 11-25-2012, 06:46 AM   #8
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Good input from KIX and others.

Your fridge may kick up to 600w-800w on start-up but probably less than 300w while running so either the 800w or the 1000w will be ample. I've worked on a few TT's that had household fridges and a small invertor hooked to the 2 house batteries solely for the purpose of keeping food cool during transit. Check to see if your alternator charges house batteries while driving (some do) and if not, you'll have 2 choices. One is to hook the invertor to the chassis (my suggestion) and the other is to install a battery isolator that allows charging both house/chassis. You may already have one of these. It's easy to tell .... hook a volt meter to the house (while unplugged from shore) and read voltage. Probably 12.4-12.6. Then start the coach and see if it jumps to 13.4-14.0.
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Old 11-25-2012, 10:06 AM   #9
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Sounds good. I know my house is charged by alt. I will keep you updated.
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Old 11-25-2012, 01:44 PM   #10
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Do you know if your refrigerator is a conventional refrig, with a start relay and capacitor, or one of the newer ones with a circuit board, LED digital displays and all the whistles? We're running a high end Kitchen Aid 2 door 21 cu ft refrig I put in about a year ago with a modified sine wave box and it works fine. We don't have a circuit board. As long as the circuit board in a new one works and doesn't overheat, you should be fine. Some of the MSW inverters cause compressor motors to run somewhat hotter than a PSW one, and perhaps be a bit less efficient but on ours runs the refer just fine. AC clocks running on MSW inverters generally don't keep exact time. A circuit board may have a clock in it to time defrost cycles or some displays.
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Old 11-25-2012, 07:33 PM   #11
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Quote:
Originally Posted by paz
Some residential refrigerators will run on MSW and some will not. Sometimes it is the motor that is the problem, and sometimes it is the electronics in the control circuit. If the manual says not intended to be run on an inverter, it is probably MSW that is the problem since this is the most common type of inverter. It should be fine on PSW.

Although Samsung says our 18 cu ft refrigerator could draw as much as 11 amps (about 1300 watts) on startup, I have never seen it draw more than about 4 amps. This was a momentary spike during compressor start observed on a Kill-A-Watt meter. Normally, it draws only 1 to 3 amps (120 to 360 watts) when the compressor is running. It may use slightly more power during the defrost cycle, but I have never monitored it during defrost.
Is it possible to turn the defrost cycle off, or "manage it"?
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