Do you still have the 12V from the truck hooked up? That & solar should be fine.

 

Solar should be disabled when connected to the truck. Can wreak havoc on the trucks electrical systems.

 

GM fixed this issue with solar charging at a higher voltage than alternator puts out. If problem due arise, turn off solar charge controller during travel. Ours is fine now.

 

What Chopper said is true. The pickup senses the LiFePO higher voltage and doesn’t like it.

If you need extra charging to keep batteries up, then you need a DC-DC charger in your rv and wired from alternator to camper.

There are a couple threads on here where this has been discussed. Find “advanced search” in the “three dots more” upper right hand corner of DF page to search.

What you may or may not need has a lot of variables, rv battery capacity, fridge power consumption, time driving etc.

 

The answer is YES you need a DC/DC charger installed on the trailer for the incoming power from the truck as the LiFePO batteries want to be charge to 14.7. I know very little about this topic and was learning during this project. Your truck will only want to charge to 13.4 amps or something close to that. However, my Brother in law spent a lifetime in electronics and he is in his 70s. Even people that are electricians for a living say this guy is a freek and it is like talking to someone that speaks a different language.

Anyhow, I recently work with him to learn and to install this up grade. I presented him a list of stuff I was going to purchase for my trailer up grade. From my research most you tubers said I did not need a DC/DC charger unless you had a motor home.

When my Brother in law looked into the complete system he said buy the DC/DC charger. My list included two 100 AH lithium batteries, lithium battery charger, 2000w converter, and a DC/DC charger for my fifth wheel trailer. I have two portable 100w solar panels so they are not connected while I am driving. I have the dual powered fridge/freezer. My goal was to be able to run a C-PAP machine through the night and a small amount of power goes to the fridge when dry camping.

This set up works well and can run about five days without charging. The 200w solar panels can keep the batteries charged daily. So as I said I know very little about electronics, but I know what we installed and in this area I trust my Brother in law.

 

I am going another route on power from the truck to the trailer. I want to disconnect the 12v line to the trailer by removing fuse 63. I have 800w of solar on the roof so should have enough to recharge by noon. We have 2 cpap machines and lived a week without external power. I left my power cord at home.

 

How many AH of batteries do you have?

 

I use a Pecron 500 W DC/DC smart charger on my solar generator for my fifth wheel. The truck standard wiring was only sending out about 25 W. That would take all week of driving to charge my system. The Pecron sends from 250W to 450W (depending on the state of charge of the batteries). I can easily charge to 100% in a couple of hours of driving. I may not even need the solar panels, but time will tell.

 

My solar will charge the batteries 100%
without the need for juice from the truck.

 

My solar will charge the batteries 100%
without the need for juice from the truck.

Try that system on a couple rainy days and you'll find a DC to DC converter is a wonderful thing to install on travel days. Our system is set up with 800-watts of solar, 400-amp Lithium batteries and running a 2K inverter for all appliances daily. It depends on your battery bank size how quickly it will recharge and solar output. Lower winter sun angle will lose 30-40% of output for panels. Soon adding 2-more panels for 1000-watts.

 

You are lucky. We camp in a lot of forested areas, finding solar to not meet our needs, but OK to supplement when at the open sites.

 

I went with this DC-DC.

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Agree, the VICTRON 30-amp DC to DC converter is a great way to charge the lithium or any battery bank much quicker. I ran a fused #6 awg from the battery to an Anderson connector at the bumper with Converter mounted in the trailer. The 7-pin will only charge about 7-amps and takes forever to bring up batteries. The 30-amp is working great in our setup. It all work well together with our 800-watts roof top of solar.

 

My wife's cousin put heavy cable from battery in the truck to an Anderson connector on the back of the truck. The trailer has a 40A DC-DC charger and connects to the Anderson plug on the back of the truck. He has a 12v compressor fridge (not the propane-12v/120v that most have). He has plans to purchase a 230AH lithium for trailer and a bunch of solar. He can charge his battery bank full up in a few hours of driving.. He's doing it in steps.

 

As you've seen from the replies, this is a complex subject.

I would recommend a DC-DC charger because the truck's charging system is not set up for lithium, and the potential for backfeeding to the truck can cause various issues (can throw codes or even over-charge your truck's starting batteries which can actually be dangerous).

Another option is a disconnect, as mentioned. A third option is a diode on the camper and/or truck that will only allow current in one direction. However, due to the elevated charging voltage of the lithium batteries the only solution (of those discussed thus far) that will actually charge them effectively from the truck is the DC-DC charger.

If you purchase a DC-DC charger, get something rated for only 12A or so. The voltage drop over the conductor is significant so pulling more than that will cause issues with chargers that are programmed to put out a specific amount of wattage (i.e. as voltage drops the current required for a given wattage increases in a "vicious cycle" until the truck's auxiliary power fuse blows; this is what will happen with a Victron 30A DC-DC charger if used with my truck which is a 2017). The exception to this is the new Victron 50A DC-DC charger which allows the user to specify an input current limit so it does not exceed the ampacity of the input circuit. Just remember that all of the trailer circuits share a single 10 AWG ground back to the truck, so your brakes' (!!!) performance will be affected by the amount of current drawn by the rest of the trailer since all loads will increase the voltage drop over the ground conductor (and hence reduce the apparent voltage across a given load).

I consider all of these solutions to be inadequate, personally. I also don't like the big fat snow plow plug idea because it's only useful for one application (and still requires the DC-DC charger to work properly with lithium, and with even higher amperage likely necessitating multiple chargers in parallel). To provide power transmission to the trailer, I put a 3kw inverter in my truck with 30A and 20A outlets in the truck bed, and I relocated the power inlet on my fifth wheel under the overhang. I keep my trailer (which has twin Victron inverters, lithium, and solar) energized with 120VAC at all times while moving; it's basically a mobile/continuous 30A campground service and the batteries charge via the inverter-chargers which are set up specifically for my battery chemistry. There is no DC-based solution that can provide this capability, and the ability to use the truck as a generator for other purposes is really convenient. Details on this install can be found in my signature.