DC - DC charger wiring question

Very likely this question has been asked and answered here, but I can't find it.

I have a tow vehicle (TV) and an RV trailer. I want to install a 30A DC - DC charger near the trailer battery, ~40' from the TV starter battery. If I run an appropriately sized wire, one way, from the chassis-grounded starter battery to the charger, and round trip wiring from the charger to the trailer battery (also chassis grounded to the trailer frame), am I good to go? Or do I need to provide a robust connection between the TV chassis and the Trailer chassis for continuity? It makes a tremendous difference in wire sizing and costs.

My gut feeling is not a good idea. I have seen lights on trailer flickering from that before, and especially with high amp load there might be arcing. I guess I am not 100% sure if you are asking if the current will flow through the trailer tongue hitch to tow vehicle ball connection point interface?


Mike R

You really should run a dedicated negative wire and not rely on the chassis. If you rely on the chassis you need a cable connection between the TV and the trailer. Check the price on welding cable from Wire & Cable Your Way for welding cable, that a breaker, Anderson PP connectors, and the crimp on lugs and you are good to go. Powerwerx has good pricing on the Anderson connectors and circuit breakers.

I would be ok with running the return through the chassis/frame of the tow vehicle, but not through the factory connection to the trailer. You can run the positive to the back, then pick up a frame connection there and wire both legs to a Anderson powerpole or something to connect the TV to the trailer.

I've got my Truck and Trailer wired with 20A Auto reset circuit breaker. Just through the regular 7 Pin Plug.

Got 225AH and 60AH lead batteries. On in the truck one in the trailer
Through that long cable run (Drop in Voltage) and the little difference ins Voltage.

The breaker hardly ever trips. Mean - the Truck charges the battery from the trailer - but not enough to draw more then 20A.

Maybe a different story with Lithium, but with lead in both, the current will not be very high.

Thanks guys. I will be using a lithium batt in the trailer (vis a vis the new Point Zero Titan next year), so I will need a boost charger from the truck battery. I think I will tie the trailer chassis to the truck chassis strap via the Anderson Power Pole connection to the truck battery.

Barring nasty reports on the Titan, I've settled on it because of its tremendous portability and transfer-ability to a different rig, if necessary. Now, I've got to contact Point Zero to see if their second mppt charger will serve as my dc - dc charger. That would simplify things even more.

Within each vehicle chassis no additional negative cable will have less resistance than the frame path to battery ground. You WILL need an additional ground connection between the two frames. Years ago the personal watercraft industry had very good quick disconnects available for their batteries which worked well. Now other options exist. You could probably put both pos and neg on a 2 conductor with anderson terminals, with some kind of mechanical coupling for stress relief.

BTW I went with the Redarc 1250 dc dc charger in my minivan. Quite robust and very compact. NOT made in china, like the national luna legacy freezer fridge I bought last year. "Buy once, cry never."

I would run both positive and negative wires from the tow vehicle battery. The ground connection at the trailer ball is not good enough.