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Old 03-19-2007, 09:14 AM   #1
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Refrigerator on Invertor

The refrigerator in my Safari runs on either 110 volt shore power of LP gas. I am trying to figure out a way to run the refrigerator while underway without using LP gas.

I have read that an RV regrigerator uses 4 amps of shore power to run.

I install a 600 watt (5 amp) power invertor or larger.

This invertor is run by the TT batteries which are being charged by the the TV while underway.

I plug the refrigerator into the power invertor while underway.

The refrigerator continues to operate without switching over to LP gas.

Will this system work??????????????
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Old 03-19-2007, 09:32 AM   #2
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I wanna know this too.

Moosetag:

If we don’t get replies let’s re-run your item under

ELECTRICALLY ASTUTE MEMBERS, please help..

Sergei
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Old 03-19-2007, 10:18 AM   #3
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Is the refrigerator the standard RV ammonia cycle type?

Freon based units current surge on start-up can be 3 times that a compressor in running mode.

From an efficiency perspective your TV alternator will likely not appreciate the added loads - especially if you have a less then fully charged trailer battery when connecting up. 12VDC does not like thin or long wire runs and figuring lengths from TV nose to battery to inverter and adding inefficiencies of inverter it may leverage the TV alternator into early retirement.
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Old 03-19-2007, 10:41 AM   #4
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Quote:
Originally Posted by moosetags
The refrigerator in my Safari runs on either 110 volt shore power of LP gas. I am trying to figure out a way to run the refrigerator while underway without using LP gas.

I have read that an RV regrigerator uses 4 amps of shore power to run.

I install a 600 watt (5 amp) power invertor or larger.

This invertor is run by the TT batteries which are being charged by the the TV while underway.

I plug the refrigerator into the power invertor while underway.

The refrigerator continues to operate without switching over to LP gas.

Will this system work??????????????

The answer is a qualified....maybe... The charge line from your tow vehicle is the constrictor in the equation. Once you find out what the number of amps it is putting down line is you can fill in a few blanks. A 4 amp 110 volt load is going to be closer to 50 amps at 12 volts, enough to pull a battery down in a matter of a couple of hours. Most charge lines from TV to trailer I have seen are at best a #10 wire and the 50 amp load is going to be maxing that out. Most of my RV fridges have been 3 way where you could run them on 12 volt, but they didn't draw 50 amps either. Unless you are parked in the desert or driving for 14 hours the fridge should stay plenty cold enough if you have it on for the night. Putting a couple frozen gallons of water in the fridge compartment helps too.

Aaron
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Old 03-19-2007, 10:50 AM   #5
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Quote:
Originally Posted by moosetags
The refrigerator in my Safari runs on either 110 volt shore power of LP gas. I am trying to figure out a way to run the refrigerator while underway without using LP gas.

I have read that an RV regrigerator uses 4 amps of shore power to run.

I install a 600 watt (5 amp) power invertor or larger.

This invertor is run by the TT batteries which are being charged by the the TV while underway.

I plug the refrigerator into the power invertor while underway.

The refrigerator continues to operate without switching over to LP gas.

Will this system work??????????????
I think the first thing I would do in answering your question is by asking you a question; why would you not want to run your ref. on LP while towing?
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Old 03-19-2007, 12:18 PM   #6
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no for all the reasons mentioned plus the 50% loss in the inverter.

we use inverters to run power tools at work, just drilling up a utility pole will kill 2 batteries in a F 550 in about 15 min.

you may want to look into converting your fridge to a 3 way, when i rebuilt mine last summer i noticed an extra slot in the cooling unit to add a 12v heating element.

getting the control circuit worked out is what prevented me from pursuing this farther.

a call to dometic might be in order.

or just run it on gas.

john
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Old 03-20-2007, 04:21 PM   #7
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The 'fridge in my Airstream is one from Lowe's... all-electric, auto defrost, etc. I have an inverter in my tow vehicle and run a power cord back to the trailer's 30 amp connector. Runs the fridge just fine going down the road, plus TV, etc, if I want that.

I have found the 12 volts from the tow vehicle is anything but 12 volts by the time it enters the trailer. Check the wire size... very poor (small). Also note that you do not have 12 volts to the brakes because of small wire (voltage drop). Need to check voltages under load, of course.

I find no voltage drop using the inverter - 120 volts in the trailer at all times.

Brian, I see no reason your system would not work.

Just my observation.
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Old 03-20-2007, 09:40 PM   #8
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You seem to be doing what I want to do ....

Don in E Texas,

Very interesting. You seem to be doing what I want to do in my rebuild.

I will have a domestic model LG 9 cubic foot, 110v fridge in the galley.

I have already re-wired the trailer and relocated the 30-amp MARINCO inlet to the FRONT of the trailer.

My Sprinter Cab and Chassis tow vehicle has a 200 Amp alternator and the optional High Idle Function (with the emergency brake on and with the push of a button, the Mercedes diesel will stay at a constant 2000 rpm).

My plan is to carry two VERY LARGE glass mat batteries – 400 to 600 amp hours - in a possum belly on the truck. AND PUT AN INVERTER IN THERE TOO.

It seems to me that with such a set up I could have the fridge running on 110 while moving and have a decent source of SILENT STORED power for overnight stops as well.

Don, I hope you are out there to confirm my understanding of what you have done.

Sergei
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Old 03-21-2007, 12:00 AM   #9
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you will deplete your TT batteries faster than your vehicle can charge them.
why do you want to do this? there may be another answer.
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Old 03-21-2007, 08:52 AM   #10
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Michelle, maybe you are asking Moosetag?

Don in E Texas seems to be making this idea work. The secret appears to be in having the inverter ON THE TOW VEHICLE.

Aaron, others: is there a way to run a SUBSTANTIAL cable from the truck alternator to the trailer battery, one that wouldn’t result in line drop, or whatever the problem is that results from the wires in the harness being too small?

Sergei
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Old 03-21-2007, 09:41 AM   #11
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The reason that I am looking into this is that I have been running the refer on LP while underway. I am just looking for way to "build a better mousetrap".
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Old 03-21-2007, 09:55 AM   #12
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American Wire Gauge table and AWG Electrical Current Load Limits

DC wire runs are straightforward enough, with 12VDC one needs beefy cable.

The 4 amps of shore power is 480~ watts of power - and one needs 40 (+ losses) amps of DC to achieve that. Figuring eighteen feet of wire on the tow vehicle and eighteen feet to span the hitch and get routed to battery locker, and limiting acceptable loses to 5% means using copper conductors of 3awg or less - thats 1/4" diameter copper. You would need fine stranded copper for flexibility, and well armored insulation so lets consider marine grade wiring - $2.50 a foot with seventy-two feet cable required!! And then lugs, conduit, quick disconnects at hitch for dedicated 12V main... Expect to spend $400 if thats the route you want to go...
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Old 03-21-2007, 09:58 AM   #13
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I think the reason they no longer have three way LP/DC/AC refers is the DC drew too much current. Stick with the LP. Get bigger tanks if yo have to.
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Old 03-21-2007, 10:53 AM   #14
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Moosetags,

Many Airstreams seem to ignore it but having open LP on the highways is ill advised and illegal in many places.

I don’t like PROPANE. My “better mousetrap” was to design and build a DIESEL powered trailer.

Details here:

http://www.airforums.com/forum...ler-23048.html

Don in E Texas has an interesting way of addressing your inverter question.

Sergei
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Old 03-21-2007, 11:18 AM   #15
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Rather than trying to run on an inverter and having the necessary battery storage or alternator capacity, how about one of these: Tundra Refrigerators for Boats

I am planning on installing one of them in my Liner. Besides running on 12/120V, since it is compresser driven and not ammonia absorption it will run up to 30 degrees off level.

Bill
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Old 03-21-2007, 11:38 AM   #16
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hi moosetags...

i understand the 'better mouse trap' urge...

keep in mind the proverb...

'perfect is the enemy of good' often restated 'the enemy of good is better'

i've learnt' it several times and will again...

the classic mohos had 3 way fridges and 12v duty worked fine...

for keeping a cold box cool. not for the initial cooling or long duty or really hot days...

mine was used regularly and without issues, but only while driving....

and not when the drivetrain was needed for uphills, wind or other demanding conditions...

having 12v available for tunnels, ferry crossings and other specific "no flammables" situations is great,

but no doubt increases the cost of rv fridges and warranty issues...

cheer
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Old 03-21-2007, 03:24 PM   #17
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That Tundra two-door unit looks sharp - 53" tall and dedicated icebox from a AC 115W or 4.5 amps DC supply - 130lbs weight... only six google hits for the model number and prices of $1600.... oh well...
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Old 03-21-2007, 03:59 PM   #18
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That Tundra two-door unit looks sharp - 53" tall and dedicated icebox from a AC 115W or 4.5 amps DC supply - 130lbs weight... only six google hits for the model number and prices of $1600.... oh well...
I agree, it is not cheap, but neither is a ammonia absorption model of the same size. Too bad that the discount suppliers don't handle that model. But if you are replacing an existing refrig and need the non propane or off level capacity, it may be worth it.

Bill
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Old 03-21-2007, 04:01 PM   #19
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Another things to consider if you are going to go the 120V/inverter route is to be sure your alternator is sized to supply the DC amperage that will be required.

I put several alternators in my MH before I realized I needed a much higher capacity alternator.
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Old 03-21-2007, 04:17 PM   #20
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Factor in the duty cycle

We use a medium size dorm style fridge. When running on the inverter the defrost heaters are taken out of the circuit. Average amps the compressor draws when on is 1.2 (120volts)...that translates to about 16 amps at 12 volts drawn by the inverter. HOWEVER on a hot day the duty cycle is about 25% on time, and the average is only 10-15%. Any inverter operating at 50% efficiency should be thrown out. 80-90% efficient inverters are not expensive. Your idea will work on small, efficient, electric fridges.
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