Charging RV Battery on the Road

Seeking comments, suggestions, recommendations, criticism, whatever. I've looked far and wide for best practice to charge RV batteries from the Tacoma, and there are many. I have a 2013 Tacoma with factory-installed towing package and an RPod travel trailer with 2 L-16 batteries and 200 watts of solar panels with Sunsaver MPPT controller for charging when parked.

The factory wire is too small to carry charge current. Many owners run a larger wire from the battery, splicing it to pin 7 on the trailer connector, thus tying the truck battery and trailer battery together. I think this is not good for a number of reasons, the most important being the different charging profiles for an automotive battery vs a deep-cycle battery, and I would like to avoid hard-wire modifications like splices.

The Sunsaver MPPT controller is designed to provide best treatment for batteries in general. It can deliver up to 15 amps (max 200 watts for 12v batteries) from input up to 75 volts (needs more than 14v -15v input). And it automatically manages the best charging and maintenance profile, including an equalization stage.

----My scheme is to convert 12v from the truck battery up to 48v for input to the Sunsaver, and to do this up-conversion in the engine compartment. This would reduce current going to the trailer connector to some 6 amps. Whatever the loss of voltage through the factory-installed wire, it would still be enough for the Sunsaver to deliver it's full charging current to the battery.

----I would connect the output from the 12v-48v dc-to-dc converter to the factory-installed wire using a Fuse Expander in the "BATT CHG" fuse slot. I would use a blown fuse between the two pins for the normal circuit, thus disconnecting the BATT CHG circuit from the normal 12v. I would then connect the 48v to the other side of the Expander and thus to the circuit going to the trailer connector. This scheme uses existing wire, avoids hard-wired modifications, and delivers up to 15a to the trailer battery.

What do you think? Is there anything in the circuit between the "BATT CHG" fuse and the trailer connector that would cause a problem? Would the "BATT CHG Relay" handle 48v OK? Any other issues that I haven't considered?

Thanks for your ideas.

 

I just run my camper off its stock battery, and then charge it by idling my tow vehicle (or I run the truck when we're doing power intensive activities like showering in the morning, which runs the water pump). I bought an extension to give me room to connect the camper to the truck without having to back right up to the tongue.

I don't know much about wiring circuits, so your plan might be fine. My gut feeling is that *if* something goes wrong, and you've got your truck AND the trailer all wired together, you run the risk of being stuck with a dead trailer and a dead vehicle at the same time.

 

Get a small generator. You can power most of the travel trailer with it and if you want to use the rv batteries you can power a battery charger from it to recharge the rv batteries. Depending on brand and size you can get one fairly reasonably. Also the newer ones are quiet.
I have a Honda 2000 , it’s worked flawlessly for 10 years.