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Old 06-09-2012, 03:04 PM   #1
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Refrigerator question?

Will this work or not? When traveling with your refrigerator using the gas option, couldn't you install one of these instead of using the gas; if you had a way to power it. All you would have to do is plug it into the inverter. I was just thinking about this:

The Cobra CPI 880 800-Watt Power Inverter converts battery power to 120 volts AC. You can power your laptop, cell phone chargers, CD and DVD players, TV sets, and other household appliances with this USB output inverter. You don't have to worry about the safety of your devices as this power inverter offers protection from current overload, short circuit, low voltage, and over heating. This Cobra power inverter comes with direct battery-to-battery cables.
Cobra CPI 880 800-Watt Power Inverter:800 watts continuous/1600 watts surge
Cigarette lighter plug
Direct to battery cable included
USB output
Dual AC outlet
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Old 06-09-2012, 03:30 PM   #2
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Sounds like a great idea until you run the numbers.

When running on AC (shore power) the smaller DM2652 uses a wire heater similar to a toaster to provide heat to run the evaporator. It draws about 5 amps of AC.

5 times 120 volts = 600 watts (required power).

600 watts (required) / 12 volts = 50 amps from your truck's alternator and camper battery.

As you use the battery up the voltage will drop up'ing the current required AND at the same time reducing the batteries ability to provide current (reduced capacity available). (see attached discharge curve).

At 11 volts the current required climbs to 55 amps.

Your truck is fused at 40 amps to protect the alternator and trailer wiring.
The battery can not supply that for very long and will be dead on arrival even with the truck running.

A typical 75AH battery supplemented by your alternator (which may trip its fuses) supplying 50-55 amps of power will last an hour or two tops (at which point the trucks fuse WILL blow.


Your ice cream will be running on the floor.
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Old 06-09-2012, 09:28 PM   #3
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Lou,

Thanks for running the numbers...saved me from buying an inverter trying it out. I sure wouldn't want my ice cream and beverages to melt down. My dw told me to quit messing with the TT. The refrigerator in the POP I owned worked on AC, Propane or the DC mode when traveling but it didn't have the larger unit. Maybe one day someone will come up a with solution to the the problem.
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Old 06-10-2012, 12:43 AM   #4
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If you travel one hour per week, every week of the year, that's 52 hours. Assume the refer is on 1/4 of the time. That is 13 hours per year. Propane burn of 1 gallon per hour, (high estimate), equals 13 gallons.1 gallon equals 4 pounds so that is just over 3 gallons. I just filled a 20 pound, (5 gallon) tank yesterday and paid $17.00. How much are you willing to spend to save nothing?

In case there are those that didn't follow this through, refer cost on propane while traveling in this picture is less than $15.00 per year.

Also, for those that want to know, the electricity provided by an alternator in a vehicle is not free. the more amps you draw from the alternator the harder it it is to turn, thus requiring horsepower from the engine to turn it, and costing fuel. even if it it is .01 mile per gallon drop in mileage, that is an extra gallon every 100 miles. Right now, a gallon is $3.35. So in 1000 miles of towing, that is $33.50, trying to run the refer on electric instead of propane.

Disclaimer. All of these are estimates, I don't have any real numbers, but hope you get the idea. Propane ain't that expensive, at least not here.
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Old 06-10-2012, 04:04 AM   #5
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I pay $12.00 for a 20 lber... Just run the LP and buy a wireless outdoor thermometer and put in fridge or freezer and receiving unit in truck that way you know the temp of the fridge or freezer without having to go into the trailer. if putting in freezer use lithium batteries in sending unit they will last longer.
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Old 06-18-2012, 10:59 PM   #6
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Ha! We don't even have our Roo 21ss yet, and I am working on the refrigerator problem. I am not a big fan or running on propane while on the road, so I am looking at alternatives. The one I came up with, if I can easily access the AC plug for the fridge (assuming there IS one...like we have on our pop-up) is to plug the fridge into this power pack:

Extreme Explorer Kit: Portable Solar Power Supply | See Goal Zero

Can someone more well-versed in these issues give me an opinion as to whether or not it is sufficient to run a 5A fridge while on the road for 4-6 hours? It's a 33Ah capacity battery pack, and surely the fridge doesn't run for more than 25-50% of the time while traveling...Also, anyone know if the AC plug is easily accessible?

The nice part about this solution (if it is one) is that once you reach camp, you simply plug the power pack into the solar panels, and 6 hours later -- in Sunny Colorado anyway -- you are fully recharged! (You can get a trickle charger, too, to keep the TT batteries topped off...)
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Old 06-19-2012, 07:07 AM   #7
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I have nothing to add to post number two about what is needed for your fridge. If a 75AH battery will only last about 90 minutes; then a 33 AH battery should make about 45 minutes providing 600 watts of power.

For anyone wanting to learn more about 12 volt DC systems and their care and feeding, I highly recommend Harold Barre's book, "How to Upgrade, Operate, and Troubleshoot 12 volt Electrical Systems."

There is a whole chapter on why using a car's alternator to charge deep discharge batteries is a "bad idea." Short answer is that a car's alternator is a constant voltage single stage DC voltage provider designed to run the DC items in your car and at the same time quickly replace the 5% capacity starting the car requires.

It will never completely (100% of capacity) recharge a deep discharge battery that has been discharged in any significant way due to the amperage reduction as the voltage increases.

Long answer:

Worse yet, without a full isolator like a motor home has, connecting a low voltage Deep Discharge (DD) type battery in parallel to a fully charged car battery will show the alternator the average voltage across it's terminals.

The single stage regulator will "see" a low voltage condition on both batteries as if it was one battery and provide the appropriate amps for that charge (chart on page 64) and can approach 60-80 amps of DC initially if the camper's battery is severely discharged. When in parallel with a charged starting battery, the amps won't be that high but will still be too high for the health of the car battery (boiling) and you won't get a complete charge to the camper's battery because as the voltage of the system rapidly increases the charging current will drop quickly to less than an amp (charts on page 65 and 67). This will happen because the car battery's voltage will mask the still low DD battery (capacity requirement) and while the DD battery needs hundreds of amps replaced, the car's battery is full so the alternator is only providing trickle or very low amperage based on the "near full" voltage of the two battery system.
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Old 06-20-2012, 07:21 PM   #8
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Why is everyone so "afraid" to run propane on the road. I have been traveling over 20 years in various rigs and haven't had a single problem with the propane. In fact the refrigerator runs more effective (cooler) on propane than electric.
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Old 06-20-2012, 07:28 PM   #9
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Some people want to make RVing more complicated than it is. I've always run the fridge on propane when traveling and (everyone gasp here) even while fueling up my previous truck which had a gasoline engine.
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Old 06-20-2012, 07:48 PM   #10
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Quote:
Originally Posted by Oakman
Some people want to make RVing more complicated than it is. I've always run the fridge on propane when traveling and (everyone gasp here) even while fueling up my previous truck which had a gasoline engine.
Filled my truck up with gas to while running.
Never gave it a thought. I guess I was to busy watching the guy fill his 911 Porsche while smoking!
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Old 06-20-2012, 09:52 PM   #11
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One time they made me stop and shut it off while traveling thru the Chesapeake Bay Tunnel but the next time down that way they didn't. I ran into a fellow this past weekend camping that didnt have a propane option on his refer, it was a house unit whirlpool inside of a Forest River Cross Country Edition fiver, about 40 foot long with 4 slides. It runs off his 4 dc batteries up to two days before he has to fire his generator up to charge the batteries back up otherwise he is on electric all the time with a unit that size. I had an old truck camper once that was 3 way with a DC option. Those units are expensive these days so you rarely see them.
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