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Old 03-30-2011, 07:43 PM   #1
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Using an inverter to power the fridge

I would like to use an inverter to power the fridge ONLY WHILE driving, the alternator should carry most or some of the load. The main reason is that I have to shut the gas fridge off while refueling and sometimes I forget to turn it back on. Plus i have to lay on the floor to see the flame burning and my knees don't like that when i get up. I am not so worried about it because i stay where there are hookups anyway, very little dry camping.

How many watts or amps does a fridge use on electric?

Would any inverter of the correct size work or does it take the full wave kind?

I already know the inverter should be as close to the battery as possible and use huge cables, No one on RV.net had anything to say other than suck it up and turn ther gas off then back on and don't you know your battery will wear out using it that way. That is a silly idea and so on. and did i mention use huge cables and plenty of voltage charts to check.

Only one guy said he wanted to that also he did send me a diagram of his idea, sort of a ATS using relays. It is good idea and i may try it one day but he wasn't sure how big an inverter was needed either.

After this long winded note, any ideas?
Richard
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Old 03-30-2011, 08:17 PM   #2
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Richard, my now MH has a residential Whirlpool fridge and it only has the 120 V option. Going down the highway my alternator is charging the batteries and the batteries are running the inverter for power. I have a very large 280 amp alternator and eight batteries but I believe that large alternator is to recharge those batteries fast after being stopped and running the fridge just from the batteries. What make a model fridge do you have. If you tell me that I can probably tell you how much power it draws. My guess is not very much. On my previous MH I installed by own 2000 watt inverter and we used it all the time while driving. I had it in the bottom of a closet right over the batteries and then ran an extension cord to power what I needed to power. I didn't wire it into the MH's AC circuit because I felt that I would always have to remember to throw a disconnect switch before I started the generator or plugged into shore power. It was not a full wave inverter and never had any problems with any devices plugged into it.
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Old 03-30-2011, 08:39 PM   #3
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I am putting a desk top size fridge in my basement storage compartment by the door. My fridge draws .9 amps running, but 5 to 7 times that starting. I have test run it on a 750 watt modified sign wave inverter and it runs well. I know this is smaller than your fridge but it may give you some idea of the draw.
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Old 03-30-2011, 08:46 PM   #4
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Spooky, When we had a 4 door Norcold we used a 2000 watt inverter to we havepower it. The reefer we had utilized two 110 volt heaters.......each heater used a little less than 2 amps AC. The inverter was a modified sine wave inverter with built-in ATS. Our coach battery was (and still is) three 12 volt deep cycles. The alternator is a 160 amp unit. It was no problem running the reefer while underway. It would use a lot of battery amps if the engine was off. We have since switched to a residential reefer. Only wish I had switched long ago.
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Old 03-31-2011, 11:23 AM   #5
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After posting I thought i should found out what kind of fridge it was. it was made for Winnegabgo? by Howa Sangyo in Japan, and uses 1.7 amps. I looked on my formula wheel and ... 1.7 amps X 120V = 204 watts. I think the 400 watt inverter i have should work that purpose.

but will an ordinary (square wave) inverter work for a fridge or does the fridge need a full sine wave to operate properly?

I have a 76 itasca, i think it is the original fridge and it is 120/gas. no compressor at all. i did hook it up to the inverter for a few minutes one day and no alarms came on but i though it is my luck to screw it up till i find out more about it. After your kind replies i think i will go ahead and do it, my knees and back will like it anyway!!

Thanks and be well
Richard
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Old 03-31-2011, 11:28 AM   #6
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A square wave will work just great. The heater element doesn't care and the electronics convert it to DC anyhow. I think some fridges still use the 12 volts for the electronics and just switch to the AC for the heating element.
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Old 03-31-2011, 11:30 AM   #7
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It's just resistance heating. Doesn't care how it gets it.
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Old 03-31-2011, 03:26 PM   #8
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Quote:
Originally Posted by spooky67 View Post
After posting I thought i should found out what kind of fridge it was. it was made for Winnegabgo? by Howa Sangyo in Japan, and uses 1.7 amps. I looked on my formula wheel and ... 1.7 amps X 120V = 204 watts. I think the 400 watt inverter i have should work that purpose.

Thanks and be well
Richard
Also of importance is how many amps at 12 volts this the refer will draw. In your case it will be 17 amps + what it takes to run the inverter. There are two issues:

1. You will need to wire the inverter directly to the battery with 12 guage or larger wire. A cigarette lighter is limited to 10 amps.

2. This is an additional load on the alternator (and the engine, but we knew that). Is the current alternator large enough to run the lights (headlights on high beam, running lights, etc) at night, charge the engine battery, charge the house batteries, and run the refrigerator.

If the current alternator is tired (1976) it may fail at some odd time and inconvenient place. If you have any doubt, an upgrade might be in order. I have done this on several vehicles (Suburban and Jeep) and have been happy with products from Wrangler NW - Power Products (no affiliation).

Even if you don't see your info on their web site, call them, they are very helpful.
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Old 03-31-2011, 03:57 PM   #9
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Back a few years ago All the (MOST) of the frigs; Were 3 way Gas;;.12 Volt DC;; ,and 120 Volt AC ;; There was a heating strip you could clamp on the Frig; And you were good to go;; The 12 DC drew about 10 amps. And was only for running down the road.. What was happening was the IDIOTS that did not change it back off dc When parked. ran there battery down to 00== Dead; Then they blamed the fridge; for the problem. So the manufactures quit making them. You can still get a strip and clamp it on the 110 volt Tube and you'll be good to go;; Just Don't forget to shut it off when you get to the campground;;
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Old 03-31-2011, 09:25 PM   #10
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BIG wires. on my old pace arrow i hooked up an 800 watt inverter (a very cheap one. black and decker i think?) to run the tv underway. Used 8 gauge wire, 9 feet of it. It barely worked, running a 19" tube TV and vcr or video game.
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Old 04-01-2011, 10:25 AM   #11
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Well, with a fridge you have watts and Volt-Amps (not the same) and Amps and Amps.

On the ID tag for any appliance is the RUNNING wattage or the running Volt Amps, if both are listed use volt-amps because that's what the inverter has to supply. To calculate inverter size multiply by five to ten I've tried 4.5 and that was not enough.

To figure amps, DC (Which is the figure you really need when you are looking at the alternator load) simply divide volt-amps by 10, This is not exact, but when you factor in the losses, Including wire loss (resistance in the wire) Inverter (conversion) loss and other losses,, it comes out very very close.

So a 1,000 watt Fridge needs about 100 amps at 12 volt to power it. and about a kilowatt inverter to start it. TRUE SINE WAVE PLEASE.

NOW... That said...... That is a fairly large load on the ALternator, it's not designed to provide that kind of load for a long time so you run the risk of alternator-us, Burnout-amus (To do the Road Runner cartoon thing to the words)

A 140 amp GM alternator will set you back over 250 dollars last time I bought one (years ago) likely 350-400 now days, PLUS install.
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Old 04-01-2011, 03:21 PM   #12
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NOTE: on my previous post. Someone pointed out an assumption I made which may be wrong

If that is an RV type fridge then instead of sucking about 1,000 watts it takes 300-400 watts on AC, and it does not care (usually) if it's MSW or True sine,

That works out to 30-40 amps, well within the ability of a 100 amp plus alternator to run safely

Thanks to the person to pointed out my assumption to me.. And yes, I know how to spell assume -u-
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Old 04-01-2011, 04:31 PM   #13
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I have never turned off my refrigerator because I was fueling my motorhome. It's not necessary. I can't even remember the last time I pumped gasoline without the station sucking off the gasoline vapors with the nozzle.

I've been using gas/elec refrigerators for a long time. Are you sure there's no little reflection window for you to see the flame is lit? You don't have to see the flame directly. If it doesn't use a mirror to save your knees.
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Old 04-01-2011, 06:07 PM   #14
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There are not many states that actually have nozzles that suck off fumes. I know that California does. I do not know of any other state but I am sure there are some. I know the gas stations in the Southeast don't vacuum off the fumes. So what would happen if your nozzle or the guy filling next to you did not shut off when full or fell on the ground and kept going. I have had one fall out of my car and keep pumping at gas and I have had them not shut off when full. Depending on the air temp and wind that would be scary knowing somebody had a open flame.
I would not be as concerned pumping diesel but wow with gasoline.

What do you do when you fill with propane and the tank is venting? Is your fridge flame still going?.
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