8 Gauge Wire

I was under the impression that propane works much better and uses very little compared to inefficiencies of DC. Maybe one reason it is not included on all fridges, i.e. 2 way instead of 3.

I've been happy with my 4 gauge alternator to TC batteries connection. 2000 f250. If I were to power my fridge with 120V from the inverter, to keep things cheap and simple, I would merely take the shore power cord and route it to the inverter. Be sure to switch off the AC breaker and unplug your battery charger. The perpetual charging scheme has already been disproved. My inverter is only a 600 watt pure sine. A poor man's manual transfer switch if you will. My alternator is 160 amp output. The TC 4 gauge is fused with a 30 amp auto fuse which is probably costing me performance in current flow. The fuse has never blown and usually supplies 14.2 volts which drops to 13.4 after a while. I also have about 240 watts solar feeding the batteries in the TC via 6 gauge from the controller.
I'll have to actually try it sometime since I'm completely happy with running the fridge on propane.

2 guage is needed.
Here's mine --charge circuit .
Obviously, a Ford will use a different way to activate the solenoid.

Optimistic Paranoid wrote:
As to whether you can successfully charge house batteries from the alternator with heavier wires, I see different results posted in forums....

Different results for different use.
I run fridge on propane and drive long distance.
Truck system keeps my camper batteries topped up all the time.
But I don't boon-dock for more than 1 night and my batteries are never deeply discharged.
The 10 ga factory wire is limiting the current and gives voltage drop at higher amps. When it slows full recharge of camper batteries, it makes self-protection.
As I wrote above, I was considering running 2 ga cables to the camper, but vision of camper batteries discharged to 10V level and shooting 200 amp from dual alternators via heavy gauges is not passing my smart test.

work2much wrote:
If you are looking to upsize wiring and use the trucks alternator to supply power while you travel you might fine better efficiency inverting to 120V near the trucks battery and running 120v from there to the fridge.
We do run ours on 120v through the inverter/battery/solar during the day when sun is out but when this sucker dies I will going to a more efficient compressor unit.

This is what I do as well. I use the inverter in the camper to power the fridge while driving.

Here's my video:

Truck to truck camper battery charging

Brad, if your goal is to get good refrigerator performance in DC mode and still keep the camper batteries fully charged, you might want to read this topic of mine in Tech Issues. I did this after being disappointed with the camper battery charging I was seeing after running 4 AWG welding cables from the truck batteries to the camper plug in the bed of the truck. My camper is also a Lance, so the wire size then changed to 8 AWG in the umbilical.

When I had a 1995 F350, I upgraded the truck-side wires to 6 AWG, connected them directly to the alternator, and got acceptable charging performance to the camper battery. On my 2010 F450, I went to 4 AWG wires still connected directly to the alternator, and was surprised to see that the charging performance was no better than the old truck. Possibly because the camper umbilical wires were still 8 AWG, but upgrading them was going to be a huge project as you can see in the linked Tech Issues topic.

When I upgraded the charge wires on my current truck, I found that the alternator/battery charging system on the truck had changed so radically that I was very apprehensive about connecting any auxiliary loads directly to the alternator. Plus, if you have a single alternator on your truck, it’s located way down low on the driver-side of the engine, and you’d have to remove a lot of stuff to get to it. I connected my new charge wires directly to both truck batteries, which improved the charging performance over the OEM wires, but it still wasn’t as good as what I was seeing out of the older trucks. It wasn’t keeping up with the drain on the camper battery from the fridge running in AC mode through an inverter, or running in DC mode.

Without going into a long-winded explanation, the fact is the charging systems on new vehicles is so tightly controlled by the ECM that it’s nearly impossible to get decent auxiliary battery charging out of a single alternator system. I’m fairly certain that on a new truck with a single alternator, you could run 0000 cables to the camper and still not get good performance. I have no idea if the dual alternator systems work any better since I don’t have dual alternators.

I finally bit the bullet and did what I describe in the linked topic, including upgrading the camper umbilical wires to 4 AWG as well. That required removing the water heater from the camper so I could get to the area the wires enter the camper. The results have been fantastic. The refrigerator DC mode now works so much better that I no longer run the fridge in AC mode through an inverter. I believe this is due to the camper voltage always being over 14 volts thanks to the Redarc DC-DC charger. Best of all, we always arrive at camp with a fully charged camper battery.

Redarc DC-DC Battery Charger

:):)

As to whether you can successfully charge house batteries from the alternator with heavier wires, I see different results posted in forums. I suspect it has to do with the way the computer is programmed to prevent the engine battery from being overcharged and damaged. In other words, sometimes it works, and sometimes it doesn't.

Try it, and if you find it isn't working out for YOUR particular year and model, look into getting a battery to battery charger, like the marine units sold by this company:

https://www.sterling-power-usa.com/sterlingpowerusadcinputbatterytobatterycharger.aspx

burningman wrote:
They barely charge at all through the stock tiny wires and light-duty 7-pin RV plug.

Honestly, they're not really designed to keep house batteries charged. Trailers with electric brakes have a small emergency battery that will provide power to the brakes in the event of trailer separation. The RV plug and wiring is designed to provide a trickle charge to keep THAT battery topped up automatically while you drive. That's all.

I don't use the alternator for anything on the RV. Pulled that fuse.

Absorption fridges are really inefficient in any mode, 12v the worst.

If you are looking to upsize wiring and use the trucks alternator to supply power while you travel you might fine better efficiency inverting to 120V near the trucks battery and running 120v from there to the fridge. The wiring shouldn't be too hard saddled to the 7 pin with it's own quick connect.

We do run ours on 120v through the inverter/battery/solar during the day when sun is out but when this sucker dies I will going to a more efficient compressor unit.

I disagree with a few things here.
The first is, 8-gauge is still way too small. 2-gauge or larger is more like it. Especially if you plan on running your fridge on 12V. One easy and cheap way to get them that I’ve done is to buy a set of 25’ 2-garage jumper cables and cut the clamps off.
If there was a risk of blowing up the batteries with a heavier charge line, you’d see batteries blowing up when people jump start cars with dead batteries. It doesn’t happen. And you absolutely will not get anything close to 150 amps through 25 feet of 8-gauge anyway.
Generally, people are only running their fridge on 12v while driving, and that works OK.
It’s totally worth running heavy-duty camper battery charging cables even if you never use the fridge on 12V.
They barely charge at all through the stock tiny wires and light-duty 7-pin RV plug.