Refrigerator Question/Discussion

[slarsen]

My refrigerator in my 2010 Mountaineer has always been a pain: alternately freezing or randomly going into the 60's. I've tried many fixes, none have worked. But my freezer works just fine. Anyway . . .

I recently put a "dorm room" sized refrigerator in my trailer, run while traveling with a battery and an 800 watt voltage inverter. I used it once so far on a 2-1/2 hour trip and it worked great! But what about longer trips?

According to my calculations, I can reasonably use this for about 5-7 hours before risking depleting the battery excessively. So I'm wondering if I couldn't tap into the 12V circuit and use the truck's power to keep the battery topped off while traveling all day.

The refrigerator draws about 11-12 amps at 12V, but of course not all the time, when the refrigerator is idle it draws very little current. The location of the battery when traveling is right by the breaker box, close to the door, where 12V should be readily available. I could add a cigarette lighter 12V receptacle for convenience. That should be a reasonable power draw on the charging circuit when driving, shouldn't it? Has anyone else done this?

[time2roll]

Connect the batteries. It will all work fine on the road and while parked(plugged in).

[RustyJC]

Stock alternator. The truck description is in my signature of my post above. It's a 2016 Ram 3500 dually with the 385 / 900 Cummins, Aisin AS69RC transmission and AAM 11.8 inch 4.10 rear axle. This is Ram's max tow package rated for 39,100 GCWR, 30,050 trailer tow, 14,000 GVWR and 9,750 RAWR.

Rusty

[ivbinconned]

Rusty. 220 amp! Was that a stock alternater? What kind of truck?

[RustyJC]

Our RV came with a residential fridge that's powered by a 1500 watt pure sine wave inverter when off of shore power. The 220 amp alternator in our truck keeps the RV batteries charged just fine when we're on the road.

Rusty

[ivbinconned]

To charge up my four six volt bats after a night boon docking with a day of driving I have jumped a cord from the 2000 watt inverter in the back of the truck that will run a charger on the Eco rpm while we drive. Works good.

[slarsen]

I have never boondocked, and don't plan to. But I've been all over the lower 48, and am on my 3rd set of tires in 7 years. Yes, as soon as we are leveled up and plugged in, I will plug the portable Refrig into the wall.

I think this will work, bpounds. Again, thanks for your input, and that of any others who have responded.

I see that Dometic just came out with a new Refrig that somewhat addresses my issues, with a section that runs on 12V. Had I known about it earlier, I might have been tempted. But despite the hassles and education process, I'm liking my solution better.

I have a freezer that works really well, a refrigerator section that works really poorly but provides somewhat cool storage space, and a refrigerator that has as much or more capacity as the built-in, which cools down to useful temps in a little over an hour, recovers from an open door in minutes, and it won't freeze my wife's lettuce and then go to 60 degrees in the same day. That's all we ever really wanted: a functional, dependable refrigerator.

[bpounds]

I take it that you don't boondock much, so your concerns are charging while driving, and the little fridge running concurrently. Then when you get to your destination, you plug into shore power, and the little fridge runs on 120v. You somehow switch the little fridge from the inverter to shore power.

I think you just need a 2 battery bank, connected together like any other RV. They can be 2 x 12v or 2 x 6v, doesn't really matter.

While driving, the little fridge may pull more current than your truck can provide, but as you said, it doesn't run all the time. Probably runs less than half time would be my guess, but of course your truck will be charging 100 percent of the time you are driving (you will lose some when you stop for gas/food). A bank of 2 batteries should handle that great, concurrent with the truck output.

Also, all inverters that I am aware of will auto-shutdown when voltage gets low. Not good for the batteries to let that happen, but at least they won't be stone dead. I don't think that is any issue though. At the current draw you've described, that won't ever happen while on the road.

Obviously, if you do boondock, you will have to remember to unplug that fridge.

[lynndiwagon]

I just got through replacing the norcold with a samsung RF18 residential. It pulls about 10Amps from the battery, through the MSW inverter, when it's running. I installed two Group 27 RV/Marine batteries in parallel to run it. They each have a reserve capacity (RC) of 180. The RC capacity is the number of minutes the battery will supply 25A of current. So 180 is 3 hours at 25A. Two of these batteries in parallel would equal about 360 minutes at 25A. Because the refrigerator only pulls 10A when it's running we can double the 360 minutes to 720 minutes of capacity. That's over 9 hours of run time even if the fridge runs constantly. I don't plan driving over 9 hours and I don't boondock so this is sufficient for me. As a precaution I installed two group 24D batteries in parallel and have them wired so that I can switch them into the circuit if needed. I keep these charged separately with an external battery charger. Hope this helps.

[slarsen]

Yeah, bpounds, that pretty much sums up my concerns, and well put.

But I can disconnect the refrigerator battery from the trailer at the end of the travel day, put it on a stand-alone 120V charger, and let the built-in inverter charge the remaining battery overnight. It's a retrofitted 3-stage charger & maintainer.

My hope is that the truck charger will be able to maintain sufficient charge to prevent the little refrigerator from running the 'dedicated' battery into the ground, to prevent damaging the battery from excessive discharge and leaving refrigerated goods to spoil. And hopefully, not damaging the trailer battery with overcharging.

I appreciate your input. My plan has been adjusting as you've been responding.

[bpounds]

Well, it is not a good plan. Chances are the 2 batteries are not matched in size, which they should be for best results, but even if they are you will be running them down at different rates. Then connecting them together to charge, so they are going to come back up at different rates too. It is not good to have such mismatched battery bank. My opinion anyway. But I do think your truck can do a fair job of charging while you drive. Not fully charging, which can take days to complete, but not useless either.

[slarsen]

Yes, a separate dedicated battery.

Why? Because wire size and length seems to be so important at 12V DC. And I don't want to run down the battery that handles the brakes, the leveling equipment and slide outs. Just wanting to be safe and responsible.

Connect it together: that's what I am asking about, what with the battery right alongside the breaker box. There are heavy-duty 12V cables running from the built-in converter, which I assume are mostly for charging the battery in the front of the trailer. So if I connect to those, I'm thinking I have a pretty good connection forward to the front battery and the truck charging system, and to the converter for when connected to 120V at a campground.

Or are those heavy 12V cables for something else?

[bpounds]

slarsen wrote:
I just looked up in the owners manual, the trailer tow battery charge circuit is fused at 25 AMPS. That seems like sufficient power, if the voltage doesn't drop too much all the way back to the breaker box.

When I'm plugged into 120V at a campground, I should be able to top off the battery overnight. I think. If the regular battery doesn't interfere with charging my refrigerator battery. Or vice-versa. This 12V to 120V ends up being surprisingly complicated.

Guess when I travel, I'd better take along a 120V battery charger, just in case?

Maybe I misunderstood. It now sounds like you have a separate battery that you dedicate just to the little fridge? Why not connect it all together and let it charge together?

My truck does a good job of charging the battery bank while on the road. I can't speak for others though.

[slarsen]

I just looked up in the owners manual, the trailer tow battery charge circuit is fused at 25 AMPS. That seems like sufficient power, if the voltage doesn't drop too much all the way back to the breaker box.

When I'm plugged into 120V at a campground, I should be able to top off the battery overnight. I think. If the regular battery doesn't interfere with charging my refrigerator battery. Or vice-versa. This 12V to 120V ends up being surprisingly complicated.

Guess when I travel, I'd better take along a 120V battery charger, just in case?

[sch911]

The truck charge lines and current flow are too little to provide a significant battery charge potential for most towed RV's. They do a decent job of maintaining the batteries though. There are many posts about enlarging the wiring to compensate. But perhaps the better alternative is to move to multiple 6V golf cart style batteries, and keep them properly charged/maintained.