Truck charge camper battery?

?
Wondered when 'fear' would be thrown out there, which these posts about 12v always devolve to.
Or (per OP)
3. Conserve the propane

My guess is that this conversation was prompted by one of two things:

1. The refrigerator keeps blowing out. This is not normal and is a problem that can be addressed. Lots of discussion on this subject here.

2. An irrational fear of propane. The truth of the situation is that the conditions in the refrigerator compartment make it virtually impossible to have an explosion or even an out of control fire.

OP
Manfred you need to update your signature-appears many are responding to it and topic title and not reading post & question.

I'll further muddy the water,
I'm reading question is about powering refer between point A & B, on the road with 12v, starting with charged batteries.
Between solar and truck alternator, all it needs to do is supply at minimum what refer draws.
Biggest factor in using 12v on road IMO is never using without charge source (engine running). Turning on refer last, turning off first.
Its that draw down that system likely will have a hard time with-supply adequate charge while supplying ~16-19amps to refer.

Start with reading refrigerator sticker.
The 12V element is rated for much less power than 120V element.
I post my test somewhere on this forum about my Dometic and 120V and gas had almost the same performance. Gas run like 2 degrees colder, but that could be within error margin.
Standard truck plugs are rated for 30 amp when big fridge is rated 18 amp.
Lance idea might be overkill, but usually weak point are the plugs. They are build cheaply and often neglected, so making bigger connection is never bad idea if you want to spend time on it.
Would I make new connection, I would make it >100 amp rated so I could use my dual truck batteries for fast inverter/microwave use on the road. That also would allow me to run fridge on 120V for full output.
For me, driving in 110-120F weather now the 12V is just not giving enough cooling power.

cewillis wrote:

bighatnohorse wrote:
Unlike other camper brands, your Lance camper has a factory supplied proprietary heavy duty power supply wire built into the umbilical cord to the truck.

What does 'proprietary heavy duty' mean here?

It means an 8 gauge wire. Lance documentation specifically calls out this wire for powering the refrigerator.
See: http://manuals.adventurerv.net/Lance-6-way-wiring-schematic.pdf

bighatnohorse wrote:
Unlike other camper brands, your Lance camper has a factory supplied proprietary heavy duty power supply wire built into the umbilical cord to the truck.

What does 'proprietary heavy duty' mean here? Unless the wire is at least 4g (2g is better), the alternator output voltage is most likely reduced too much to ever fully charge the camper batteries.
The so-called 'isolator' also causes a voltage loss in some cases.

Both can be assessed by comparing output voltage at the alternator (14.2v - 14.4v) to voltage actually at the camper batteries (when the batteries actually need charging, so that there is substantial current in the wire). If charge voltage is less than 14v, trouble.

Several have posted charge circuit implementations that actually work: here's mine .

I think the answer to this question lies more specifically with the type of use you anticipate. If you are just going up to camp for a week or two a few times a year than I have to agree with HMS Beagle, run it on Propane. Not sure what type of tank setup you have but in my rig I have two of the standard BBQ tanks and I can go for easily a week if not two without needing to fill up.

That being said, if I was full timing (not sure if that is your case) I could understand why wanting to run on DC would be appealing. It's one thing to get your tanks filled up a couple of times a year, it's another to have to do it a dozens of times throughout the year.

As others have suggested, if you really need to run DC then you need to run the proper wiring to be successful. The question I don't think is dependent so much on your alternator but rather the wire used between the truck and the camper. If you get the right size wire then charging the camper from the truck shouldn't be an issue. That means a trip to the Home Depot and buying some 4, 2 or 1, AWG wire (do your research) and running it from your alternator to your camper (possibly bypassing the umbilical all together). You will of course want the charge controller to ensure the camper battery bank is being maintained properly.

The determining factor is the wire gauge from the alternator to the camper's battery. Most likely you still have factory wiring, maybe 10 gauge, possibly 12. Let's be optimistic and use 10 gauge and say 30 feet of it between the alternator and battery. That works out to a resistance of .03 ohms(R). Using Powerdude's figure of 15 amps(I) to run the fridge that means if the alternator is putting out 13.8 volts(E) the most the battery can be charged to is 13.35 volts due to .45 volts dropped across the wire(E=IxR). And that's assuming no stray resistance from wire connectors, the trailer plug, etc., and no other loads drawing current. To make matters worse if your battery is in need of a charge and is trying to draw say 25 amps charging current that lowers the voltage to 12.8. But, as the battery gradually takes a charge and draws less current, that will allow the charge voltage to increase, but never beyond the 13.35 due to the drop from the fridge current.

Now your 100W solar will help, but it isn't capable of supplying all the current the fridge needs so you'll still not get to a full charge while the fridge is on DC. You're probably going to get pretty close though unless you're starting out the trip with a really drained battery.

The truck alternator is plenty big enough to run the DC fridge. The wiring from truck to camper is almost certainly not big enough, unless you have done a substantial upgrade. A 100 w solar panel will put out about 5 amps in all but ideal conditions, so it isn't big enough either. Just run it on propane - that's what they were designed to do.

I would be running the refer on 120 volts AC and LP. I would not run on 12 volts. It does not use that much LP.
Trucks haven't had generators for many years. They have alternators!