Question about running the fridge on battery

[Jim Bennett]

I have always driven with the propane on and turn it off on ferries or driving through tunnels that require it off. Yeas ago when we had this debate here I took it upon myself to check with every provincial and the federal highways groups about the legality of it, and every one said it is legal to do.

I installed 240W of solar on my roof which quickly charges the batteries almost every day, so thought I would give the DC a go on a long highway trip in the sun. We kept the fridge temperature reader with us in the truck to monitor the temperatures, and slowly watched it rise during the day to the point of being too high. I went and turned the fridge back to propane and read the batteries voltage, I can't remember exactly what it was, but it had been drawn down a lot. I am guessing that given the weather conditions the 12V was incapable of maintaining the fridge temperature and the solar could not keep up the battery charge level. I was going to try this again but still haven't, as propane always seems to work great, even in higher temperatures.

[Bcescapist]

Thanks for all the info/opinions, especially from people who have used the d/c setting with solar. Certainly sound less than satisfactory although i'm surprised the car battery doesn't kick in and keep the trailer batteries charged. You can likely tell i don't understand the electric system. Anyway, ongoing debate in our house about the propane while travelling. We agreed to abide by the opinion of Sean and Kristy, our favourite youtube RV people. Will probably just leave the fridge off unless we have icecream in the freezer. We would never remember to turn it off at the gas station for sure. Will definately leave it off on the 7 hour ferry trip to Haida Gwaii!

https://www.youtube.com/watch?v=o91vm9M9Ll0

[John in Santa Cruz]

the reason the car alternator can't keep the trailer battery charged when the fridge is running on DC is that the fridge is drawing 12 amps or so, and the wiring from the car alternator to the trailer connector to the trailer battery has about a 2 volt drop(*) at that current because its not heavy enough gauge... so the car alternator will keep the fridge running, but it won't also keep the trailer battery charged as that requires at least 13.6V.

if you could replace the whole run in the vehicle and the trailer with 8 AWG wiring, it would probably work.


(*) like everything else electrical, this is driven by Ohm's Law. voltage = amps*resistance. there's probably 30+ feet of wire one way between the vehicle alternator and your trailer battery, assuming its in the back like in an Escape or Casita.... and then another 30+ feet for the ground return path back to the alternator. at 12 amps current draw by the fridge, if that wire combined is even 0.1 ohms, it will drop 0.1 * 12 == 1.2 volts... 13.8V at teh alternator - 1.2 == 12.6, which is not enough to charge the trailer battery. if the resistance is any higher, then the trailer battery will discharge rather than charge.

[cpaharley2008]

I have seen some motor configurations with dual alternators, one specifically for the tow vehicle and one for the trailer....

[MikeS]

Originally Posted by cpaharley2008

I have seen some motor configurations with dual alternators, one specifically for the tow vehicle and one for the trailer....

I wish this would get more focus from auto makers, maybe even make it part of a tow package.

[MyronL]

Because you never know, no trip to the sticks should be taken without bringing along your own food. When propane failure becomes the problem, in my personal world experience here's the perfect back-up plan.

[MikeS]

Originally Posted by MyronL

Because you never know, no trip to the sticks should be taken without bringing along your own food. When propane failure becomes the problem, in my personal world experience here's the perfect back-up plan.

Also keep in mind whiskey requires no refrigeration. You have to wash down the chunks with something.

[cpaharley2008]

Spam is my backup....but Myron's option looks better

[sclifrickson]

Originally Posted by MikeS

Also keep in mind whiskey requires no refrigeration. You have to wash down the chunks with something.

And can be used as a disinfectant (and anaesthetic), so does double duty as part of a comprehensive first aid kit!

[Jim Bennett]

If the propane should have a problem, we just cook on a fire, something I have done many hundreds of times before.

I used to bring a single burner white gas backpacking stove, but it just never got used, so now it stays at home awaiting the next canoeing trip.

[bdornbush]

Originally Posted by John in Santa Cruz

the reason the car alternator can't keep the trailer battery charged when the fridge is running on DC is that the fridge is drawing 12 amps or so, and the wiring from the car alternator to the trailer connector to the trailer battery has about a 2 volt drop(*) at that current because its not heavy enough gauge... so the car alternator will keep the fridge running, but it won't also keep the trailer battery charged as that requires at least 13.6V.

if you could replace the whole run in the vehicle and the trailer with 8 AWG wiring, it would probably work.

My Jeep Grand Cherokee with the trailer towing package DOES keep the batteries charged AND supplements the 150W solar enough that we arrive at camp with the batteries charged and the refrigerator cold, so it does happen. At least one of us (me) has a working solution, so it can work. Maybe Chrysler engineers have it worked out with big enough wiring. I have not checked the wire size but have no need to as it works for me.

[jennykatz]

We are in our 3rd year with 2 six volt batteries and 160 watt solar . We started a trip last week with fridge on batteries but the weather would not cooperate so we switched to propane ( we were down to 50% of battery ) and we weren't at our campsite yet .We usually can make a 8 hour trip on Solar and car charging and get to our campsite with over 50% battery or more . So it can be done if
the Sun stays shining and your trip is less then 8 hours or so .

BTW the propane works fine and we will try it again if its a longer drive then 8 hours . Jim

[Ron in BC]

Originally Posted by Bcescapist

to abide by the opinion of Sean and Kristy, our favourite youtube RV people. Will probably just leave the fridge off unless we have icecream in the freezer.

Why oh why would you degrade the quality of your food by allowing the temperature to reach unsatisfactory levels when you have the option of keeping it at food safe temperatures.

I did a propane systems check on my trailer last night preparatory to getting it ready to sell. I started with the trailer interior and fridge interior temperatures at 29* C. By bedtime the fridge was at 15* C and this morning it was at 3* C. Two hours later, after turning it off it's already up to 7*C. Well, to each his own but I can't help wondering what people with propane powered vehicles do. It's be awfully hard to drive with the propane system shut down.

Ron

[emers382]

We drive with the fridge on propane and do not worry, most of the time forget to turn off at gas stations and only ferry taken they gave me stickers to wrap around the shut off valve but didn't check to see if I'd actually shut them off.

If our 5.0TA had propane lines exposed like the long long honeymoon couple have under their Airstream I would perhaps be hesitant to tow with propane on. They have no choice to use DC, their fridge is only two way. One shot in their video shows this line!

I don't know about 17, 19, and 21 Escapes but our 5.0TA with spray foam insulation has exposed propane line only from through the foam to the outside propane hook up and it's covered with wire harness/pipe protector plastic tubing. I'm sure there's a name for that but don't know what it is It's just ahead of the door so any tire blow out would not be near it.

As to the OP's original question, I did try running the fridge on DC one time but it drew down the batteries quickly. I was driving home after picking up our new-to-us trailer and was having trouble with the propane (subsequently fixed) so switch to DC, but never again.

[Vermilye]

Originally Posted by Jim Bennett

If the propane should have a problem, we just cook on a fire, something I have done many hundreds of times before.

I used to bring a single burner white gas backpacking stove, but it just never got used, so now it stays at home awaiting the next canoeing trip.

I had one of those that was army surplus. Burned just about anything, and boiled water faster than any other stove I've used. Only problem is every third or fourth time I fired it up it generated a 1' - 2' ball of flame around it. Only lasted for a second or two, but for some reason, I eventually dumped it.

I currently carry a two burner grill (a Giantex Propane Tabletop Gas Grill Stainless Steel Two-Burner BBQ) and a 1 burner butane 8000 BTU stove.

Up to this year I cooked on a Coleman Grill/Stove, which seemed like the perfect combination for one person meals, but the grill section was terrible and had no cover that could be used while cooking, so I replaced it.

And to stick with the thread topic, I travel with the refrigerator on propane.

[Brian B-P]

Originally Posted by cpaharley2008

I have seen some motor configurations with dual alternators, one specifically for the tow vehicle and one for the trailer....

This would still be ineffective unless the charging system dedicated to the trailer was set to run at a substantially higher voltage (2 volts higher in Jon's example calculation) than the desired battery charging voltage. The problem is not charging system capacity; it is charging system voltage control.

If the trailer charging alternator were controlled with a voltage sense wire running at least to the towing receptacle, and preferably all the way to the trailer battery (such as via the towing connector's auxiliary pin), it would work well... but that's unlikely to be the way it's set up.

An easier and more effective solution, given current technology, is a DC-to-DC converter for the trailer - mounted on the trailer - as at least a couple of forum members have installed. It fixes the real problem.


A second alternator would typically be for equipment on the vehicle, rather than for a trailer. Usually a charging system upgrade is still one alternator, but with higher capacity - 200 amps isn't unusual.

[Parker]

I went to 12V for the fridge, but it takes some effort. Ours is a 2013 19' model; one of many at the time that had a lot of trouble with fridge performance while towing. There was some evidence that maybe the propane burner wasn't working well due to poor draft while towing (also a concern about overall draft for cooling the backside of the fridge, but that's a different issue). In both our old Highlander and our 2018 model, I ran a #8 charge line. As mentioned previously, the problem with running the fridge on 12DC is the high current causing a voltage drop....enough that the Escape battery won't come up to full charge. The voltage just isn't there to top off the battery by the time the current makes it to the camper. The #8 charge line pretty well overcomes that issue. We seem to get about the same fridge performance now on 12V and propane. In some windy driving conditions, we definitely do better with 12V. So for me, it's not a safety question as much as it is having the option for either power source while towing.

[Djs]

If you run the fridge on battery and forget to switch to propane when you disconnect you will run your. Batteries DEAD. Then you won't have enough power to run the solar controller. That means you will have to get some kind of charge in the batteries before the solar panels will work again. Been there done that.

[Parker]

Originally Posted by Djs

If you run the fridge on battery and forget to switch to propane when you disconnect you will run your. Batteries DEAD. Then you won't have enough power to run the solar controller. That means you will have to get some kind of charge in the batteries before the solar panels will work again. Been there done that.

I'm sorry you had that experience. Rather than trust my memory, I installed a West Marine charge relay that disconnects the charge line to the trailer when the source voltage at the tow vehicle drops as I turn off the ignition. At least we won't run tow vehicle battery down. So far, I've not forgotten switch to propane when stopped for a long period of time or disconnecting. I'm thinking the fridge probably starts alarming when the DC voltage drops enough, but maybe not.

[Vermilye]

I posted this in a different thread, but had the currents reversed, so I thought I'd correct it here.

I towed my trailer to get the bearings checked & repacked, brakes checked & the refrigerator serviced. On the way back to home I put the refrigerator on DC.

Some general info on running the refrigerator (Dometic DM2663LBX)on 12V with a 2017 21 with a 2018 Ford F 150 3.5 EcoBoost.

The refrigerator draw on 12V is 24.5 amps.

The combination of 320 watts of solar, a day with mixed clouds & truck charge line: The battery monitor showed as low as -18 amps, as high as +6 amps, the differences as I went in & out of clouds. An earlier check indicated that the truck charge line generally produced 8-9 amps through a DC to DC converter set at 14.4V.

End result - after 50 miles, on secondary roads, batteries were down 12 amp hours.