Dometic Fridge on 12 Volt while towing

[Mary Ann in NC]

We cruised on our 35-ft sailboat for 18 years. During that time we had a 12V fridge that we never turned off while cruising. We had 3 group 27 batteries for the house bank and two 55 watt solar panels. When we were plugged in at a marina, the batteries got a really good charge. Also the alternator on our engine kept the house bank charged up if we were under way but not actually sailing.

It was our experience that the fridge draw was about 1.5 amps per hour. The key is to keep it full of cold food and beverages. An empty fridge loses cool really fast.

All that said, I do not see how a fridge turned on while towing should completely draw down the trailer battery unless the ambient temp is high. The same is true for for TV battery. Our Jeep Cherokee has a 160 amp alternator and could be upgraded to 250 amp. Understand, if you are running the AC in the TV with the lights on and the stereo blasting away the load on the TV battery will be pretty significant.

I wonder whether our boating experience carries over to the RV world or should I store that memory bank offline?

[ZachO]

They relate, you just need to look at all the variables.

3 batteries. Most of us only have one. Two at most, except for the rare few. We also park in the shade. One battery running the same fridge, plus camping in shade is a significant difference.

In theory there should be no problem while driving. In practice people have found their battery dead at the end of a day of traveling. You need to find out if the power from your alternator is making it all the way back to the battery. It could 6000 amp and if there's enough voltage drop between the two, it won't do you much good.

[Mary Ann in NC]

Thanks. Those are good points to remember.

[Radar1]

Originally Posted by Mary Ann in NC

It was our experience that the fridge draw was about 1.5 amps per hour. The key is to keep it full of cold food and beverages. An empty fridge loses cool really fast.

That seems like a fairly low power usage for a DC fridge, was it the power eating absorption fridge, or a more efficient compressor fridge? The absorption fridges on DC use almost 15 amp hours.

I've always wondered how a tow vehicle is smart enough to limit charging the tow vehicle battery when it is completely charged, yet at the same time sending a bunch of amps on the same wiring system to the trailer battery that is screaming for amps.

[Carol and Mike]

Originally Posted by Steve Outlaw

Or, you could just run the fridge on Propane while going down the road like 99.99% of campers do. There is almost no reason to try to run the fridge on 12 volts. Even with dual alternators and dual batteries on our truck and 320 watts of solar on the roof, I don't even bother with it.

Agree with Steve. I have my fridge on auto so if I have shore power it runs on that and if not it goes to propane. I haven’t ever run it on 12V. A couple of times I had to pull into the designated area to turn off propane before a tunnel, but that is a rare occasion. Also, I never turn my fridge off. It’s plugged into a 20a at the storage area so cooling it down before a trip is not an issue.

[Evirk]

Thanks to all.

As usual, I received excellent and very practical advice. I admit the 110 inverter idea never occurred to me. Now that's something to think about.

I will be running a trial just to see what I can learn from it, but in the course of setting up the trial I determined that my 12 volt pin on the 7-way connector is not in fact connected to 12 volts. So, before I go very far I'm headed back to the folks who installed my hitch and plugs. At that time I'll have them run 10 gauge to the plug. Can't hurt, right?

As far as the sailboat fridge is concerned, i think we have apples and oranges. I used to install those things and they are 12 volt compressors designed to run low, slow and long. But they work great and have only a modest electrical consumption. These absorption systems are NOT modest in their demand.

Again, thanks to all who contributed. I never fail to get help when I ask.

[Civilguy]

Originally Posted by Evirk

I admit the 110 inverter idea never occurred to me. Now that's something to think about.

I will be running a trial just to see what I can learn from it, but in the course of setting up the trial I determined that my 12 volt pin on the 7-way connector is not in fact connected to 12 volts. So, before I go very far I'm headed back to the folks who installed my hitch and plugs. At that time I'll have them run 10 gauge to the plug. Can't hurt, right?

I'd be interested to hear more about the results of your trials. I was impressed by the number of people who responded that they were successfully running on 12 VDC. I tried switching our Escape's refrigerator to DC for a few minutes before we hitched and connected last week. The solar (located in the shade at the time) indicated a serious deficit, and I dropped the matter right there.

I am still in the process of closing down my business to retire while "wrapping up" a major remodel, so I haven't spent as much time as I'd like on tinkering with the trailer. But I've realized that one of the things I want to do is to learn more about basic electronics. After all, I figure I already know just enough about electrical systems to be dangerous.

[Raspy]

Originally Posted by Radar1

I've always wondered how a tow vehicle is smart enough to limit charging the tow vehicle battery when it is completely charged, yet at the same time sending a bunch of amps on the same wiring system to the trailer battery that is screaming for amps.

When the trailer battery is connected to the tow battery, they become one battery. The alternator's regulator looks at this one battery and adjusts the alternator output to bring that one battery (combination of two batteries) up to full charge.

As an example, if the tow battery is fully charged, and the trailer battery is at 50% charge, the regulator might see a battery at 75% charged when they are connected together. The tow will charge that pair until it sees a fully charged battery. The lower the state of charge in the trailer battery, the higher the charge rate from the tow alternator. The trailer battery acts as a load on the tow battery, the same as turning on your headlights with the engine not running. The regulator is only smart enough to read the voltage at the tow battery. Loads change that battery voltage reading. The load on that battery changes the apparent state of charge, and the regulator adjusts the current to bring it up to full charge.

The system does not only charge the discharged battery, it charges the combination of two batteries connected as one. It charges based on their average.

Typical running voltage in cars and truck is 14-14.5 volts. A fully charged battery, when rested and with no load, is about 12.65 volts. A battery being held in "float" sits at about 13.2 volts to keep it fully charged and prevent sulfation.

So, the charge rate from the tow is dependent on the wire size, length of that wire, and state of charge of the battery, or combination of batteries.

[Markz]

On the trailer side, I installed a relay powered off of the clearance lights.

Before I depart on my trips I switch the fridge over to 12v and turn on my lights. Turning on and off the driving lights on the tow vehicle will turn on and off the power to the camper fridge.

When I stop to go to a restaurant... I turn off the lights and hope the fridge is insulated enough to hold in the cold till we begin driving again.

This is a simple solution that works.

[Eggcentric]

Most of us leave the fridge on propane, except when we have shore power.

[Thomcat316]

Our solution has been the Dometic CF series cooler/freezer.

Very low draw, works as a refrigerator or freezer, and can be run indefinitely on TV power.

[Pdxrain]

We picked up our 2019 Scamp 13' from Backus last June, and we towed it home to Portland Oregon. After reading about the fridge issues on this forum, I tried running it on propane while towing. A few hours later, while checking over everything at a rest stop, I found the fridge warming up and the propane pilot light off. Maybe it was my error, but I decided it was not worth it to me to risk towing with the propane tank's valve open again. We reverted to what we did with our 3-way Dometic in the old popup camper: start with a cool fridge from shore power or propane, switch to 12V while towing, and switch to propane for stops over an hour. This has worked well for us.
- Vince

[Lynn Eberhardt]

The same issues and responses keep coming up. Not all tows/trailers are wired the same. Use a meter. If the trailer battery stays at 12.5V or more while traveling with the fridge on 12V, you're good to go. If not, try running on propane. Some stay lit, some don't. If yours is in the don't category, try one or more of the other ideas that have been mentioned. YMMV

[GaryM]

You don't say whether you are using the factory tow package or not. If you are, the 12 volt charging wire from the TV power source to the Bargman connector is most likely 14 gauge, or 12 at best. This wire is too small to provide sufficient current to keep the camper battery charged while running a gas absorption fridge on 12 volts. Replace or supplement the wire with a 10 gauge wire and you will be all set.


I had a new tow vehicle when I went to pick up a new camper. The TV only had a 4-wire connector. The trailer dealer installed a 7-pin connector with a 10 gauge charge wire. I towed that trailer over 60,000 miles, including a round trip to Alaska, and NEVER had the camper battery run down. I bought a new Tow Vehicle, with a factory tow package and small gauge wire. The camper battery went flat in 4 hours the first time out.


It's an easy fix. Do it and save yourself a lot of time and frustration.

[tua]

Originally Posted by Thomcat316

Our solution has been the Dometic CF series cooler/freezer.

Very low draw, works as a refrigerator or freezer, and can be run indefinitely on TV power.

Yep, love the Dometic CF! Runs on 12 volts from the battery in the trailer, and the battery in the trailer is kept charged by the sun. This is a game changer!

[GlenP]

Hi there, I ran a heavy wire from an auto-reset breaker at the Sienna’s battery to a heavy duty solenoid in the rear of the van (and then on to the 7 pin socket). I use the power to a 12 V lighter socket back there to energize the solenoid - so this 12V source at the trailer connector is only on when the van is running.

[ehoepner]

The issue concerning running the frig on 12V is whether the tow vehicle wiring is large enough. If you tow vehicle has 12 or 10 gage wiring there will be no problems. If your tow vehicle wiring is 14 gage or 16 gage, the frig will not cool and will run the camper battery dead.

[jerrybob]

Lots of info here....too much for me. Have owned a travel trailer for 30 years....have always towed with frig. on LP.....I actually leave the setting on auto....in the campground....it switches to elec. on the road...LP. Never have had a problem. Good luck.

[Perryb67]

Originally Posted by Evirk

. There are also remarks that indicate that it might work if only the towing harness is wired with #10 wire (nobody does that).

When we purchased our 2003 Honda Odyssey my best friend (who died last April from Covid) helped me install a 10g wire (it might have been 8 gauge) from the Odyssey's alternator to the converter. We bypassed the 7 pin socket and used a heavy duty Anderson Power Pole type connector to connect the Odyssey to the Scamp. We could have a nearly dead battery and in two/three hours it would be fully charged driving down the road. It would also charge in the campground on idle if needed. We pulled our Scamp for six years and our Casita for five with that Odyssey and didn't need solar or a generator.

The reason we installed the 10 g wire was the second or third time out I forgot to change the fridge switch from DC to LP. When we came back after a hike the battery was essentially dead. I've never driven down the road with the fridge on DC since, always with LP since. We camped the whole weekend with no electricity. Luckily that fridge didn't need DC when set to LP. The new fridges need DC to monitor the temperature and operate the solenoid for the LP.

Enjoy,

Perry

[computerspook]

Originally Posted by Lynn Eberhardt

Your TV battery should be fine. It's close to the alternator and has adequate wiring. The problem will be draining the trailer battery. If it's at 13V with the fridge on and the TV running, you're not drawing it down and may be charging slightly. As far as draining the TV battery while camping, you should either unplug or have a relay installed. If boondocking, run the fridge on propane. Running on 12V will take all the trailer battery's useful power in 5 hours.

Actually I can generally get almost 10 off of the frig on the trailerbattery. Yeah goofed and found out ;-) Parked and forgot to switch. I do have heavy wire to the trailer power connection on the TV. By the way remember rhe ground. That is more of the time what will get you.





I find that I can actually do well on running on 12 volts for any distance I want to drive in a day. If I had a second driver then I might have an issue. And that i safer than trying to do propane. If I am away from a camp ground I generally run a generator anyway. But yeah use the propane. If I am at a camp ground I use the AC. (I have a 3 way)

But do what works