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Old 04-18-2018, 06:08 PM   #21
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I'm an engineer, I understand everyone making the calculations, but there is also real world experience. I have travelled 8-10 hours with my residential fridge running only on 2 deep cycle batteries. Batteries were still 13-14 volts when we got to the campground. Truck is a 2016 Silverado Duramax, it was already wired for charging from the factory, no idea what size wire it is.
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Old 04-18-2018, 07:56 PM   #22
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Okay so with all of the above info then how do motor homes do this. Do they have bigger batteries or is the assumption that people will run the generator while driving? Or do they run with propane with the potential accident dangers
One significant difference between a motorhome and a trailer is that motorhomes don't have to worry about feeding charging power from a tow vehicle alternator, run it back to the hitch area, then through a connector, and eventually to the trailer's battery bank. My chassis alternator can supply significant amperage directly to the batteries through a very large conductor. So those motorhomes that have an inverter feeding AC current to their refrigerators (either residential with a compressor or an absorption with a heating element) can much more easily maintain their batteries when the chassis engine is running.

My inverter does not feed my absorption refrigerator, so I do run it on propane when I drive. But I keep the fridge on "Auto" so if I am running the generator on hot days for AC the fridge switches over and then is operating on the AC heater in the fridge. I am on my third motorhome, have always run them on propane except where prohibited in tunnels. No issues so far.
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Old 04-19-2018, 08:39 AM   #23
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Think about how the rated consumption of a residential fridge is calculated where the fridge is in a controlled environment at a constant 68-degrees. the unit only runs when the interior thermostat calls for cooling when the temperature rises above the set-point. Now where the typical RV Fridge is installed right against an outside wall with limited insulation, in a hot environment inside a closed up trailer w/o any AC running. Will the duty cycle be the same under these different conditions? Not with the heat-load being much higher in a RV.

Also note that the 4.5AH rating is at 120vAC - that equals 540W. An inverter will draw more than 45A from the batteries at 12vDC to power that same load. I have never seen a TT or 5er that has a charging cable big enough to handle that load from the tow vehicle. Also consider that we have not even factored in a defrost cycle or cabinet heaters into the equation.
The link I provided was a residential fridge in an RV and they measured 11.8 amps per hour. This is only 140 watts not 540. This would be a 12 amp draw on the DC side and only 1.2 amps on the AC side. True that doesn't account for inverter losses but that won't add a whole lot.
Even if you assume 15 amps total and the truck charging system is supplying at least 10 amps (not unreasonable, I have measured 7amps from our truck while idling on a fairly full battery, 10-15 amps while driving is not a stretch).

Your batteries only need to supply 5amp hours. Even a cheap 12 volt can sustain that for at least 5 or 6 hours. This is assuming you are starting with a fully charged battery.

Not to mention the two people in this thread who have done it and don't notice their battery discharging significantly while driving.

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Old 04-19-2018, 09:07 AM   #24
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Regarding the so-called charge wire from a truck to a trailer: keep in mind the truck's battery is right up there under the hood very close to the alternator. And is connected with heavy gauge wire. In other words, it's the truck's battery that determines what voltage the truck's alternator puts out. Because of the distance and typical 10 gauge wire back to the trailer's battery, the trailer's battery is never going to get anything but a token charge voltage.
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Old 04-19-2018, 09:45 AM   #25
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There are more things drawing power from the alternator than just the truck’s battery/batteries, so to say the output of the alternator is determined by the trucks battery/batteries incorrect.
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Old 04-19-2018, 09:50 AM   #26
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I read the article you supplied ... the most compelling comments are here:

The minimum power for running solely the residential fridge for 24 hours is six AGM batteries totaling 600 amp hours (300 ah usable). PLUS you need 600 watts of solar power on the roof to replenish the batteries during the daylight hours. Remember that is just for the fridge and it doesn’t include other devices you may use in your RV such as kitchen appliances, computers, TVs, Radio, Lights, etc.

I'm done responding... I agree with the Gone with the Wynns assesment in the article - a good read with some factual supporting detail to support the conclusion.
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Old 04-19-2018, 09:55 AM   #27
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Very true - but technically it's the truck's regulator that determines the alternator's output. My point was something 25-30 feet away connected by inadequate sized wire isn't going to have much effect on what the truck thinks it needs to do.
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Old 04-19-2018, 10:02 AM   #28
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I read the article you supplied ... the most compelling comments are here:

The minimum power for running solely the residential fridge for 24 hours is six AGM batteries totaling 600 amp hours (300 ah usable). PLUS you need 600 watts of solar power on the roof to replenish the batteries during the daylight hours. Remember that is just for the fridge and it doesn’t include other devices you may use in your RV such as kitchen appliances, computers, TVs, Radio, Lights, etc.

I'm done responding... I agree with the Gone with the Wynns assesment in the article - a good read with some factual supporting detail to support the conclusion.

The OP is looking to run the fridge while travelling. Maybe 4-6 hours and probably from shore power to shore power. Not full timing without hookups as the Wynn's were in their RV. Totally different scenario.

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Old 04-19-2018, 01:21 PM   #29
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I have an Eagle fifth wheel with the residential refrigerator. Camper came with a 1000 watt inverter from the factory. I have had very good luck with this setup. I have driven 8-10 hours and the batteries were still perfectly charged, showed over 14 volts. I do have 2 deep cycle batteries, my truck was wired from the factory for charging, I have no idea what size the wire is. I also tested the system not hooked to my truck, went 6 hours and never lowered the voltage on the batteries either.
The OP has a propane/electric frig.

The "duty-cycle" (or total current drain) with be significantly less with a residential frig vs. the 120 vac heating element on a propane frig. It's not uncommon, especially during the summer, for the heating element on a propane frig to be on, non-stop. A typical residential frig's compressor will cycle off and on a considerable number of times under the same conditions.
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Old 04-19-2018, 02:03 PM   #30
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So probably not a bad idea to shut it off before fueling and don’t drive through any restricted tunnels with it on but otherwise it’s fine. We towed our 15 27dsrl for 20k miles with the propane on without an issue.
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Old 04-19-2018, 05:10 PM   #31
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As did my father in law but I get worried about having the propane on if in an accident or maybe a tire blew out ruptures the line. I can’t see the line sine I have an enclosed belly so I have no way of knowing if it is copper, iron, or something like pex
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Old 04-19-2018, 08:03 PM   #32
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You can engineer it any way you want but this is my experience. I've only had this rv with the residential fridge for 7 months. Before that I ran my last 5 rv's on gas and never had a problem. I have the two 12v batteries that came with the rv and two 12v batteries in my F-350. My two longest trips have been 7hr's and 6hr's. When I left home my fridge was -6 and 34 and the voltage was 13.6 or 13.8 can't remember. When arriving at campground my fridge read -6 and 34 and voltage was 13.4
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Old 04-19-2018, 08:54 PM   #33
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Run the propane when driving. Run 120V when at the camp site. It’s funny this thread went so long.
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Old 04-19-2018, 09:57 PM   #34
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As did my father in law but I get worried about having the propane on if in an accident or maybe a tire blew out ruptures the line. I can’t see the line sine I have an enclosed belly so I have no way of knowing if it is copper, iron, or something like pex
Propane is not gasoline. Propane only burns with an air to gas mixture of between about 2 to 9%.. And less it won't burn, any more air it won't burn. It's not easy to ignite propane because of this limitation. Literally millions of RV are driven with propane on and fires from propane leaks are very few...maybe even less than electrical shorts.

Also if a catastrophic release of propane your regulator will cut the flow off.
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