RV Trailer Battery Charge Current

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Dec 8, 2023 | 09:11 AM

mmghost

Thread Starter

5th Wheeling

Joined: Jul 2004

Posts: 30

Likes: 6

RV Trailer Battery Charge Current

I pull a fifth wheel RV with my 2021 F350 King Ranch. I recently found the "Trailer Tow Battery Charge" fuse #7 had blown. Fuse #26 with the same description was still good.

Two questions:

1. If I connect a trailer with dead batteries to the truck, how is battery charge current limited so as to keep the fuse from blowing?
2. Does anyone have a circuit diagram showing how the two battery charge fuses are connected to the rest of the truck electrical system?

Mike

Dec 9, 2023 | 07:58 AM

B-ManFX4

Fleet Mechanic

Joined: Feb 2021

Posts: 1,405

Likes: 1,171

From: East TN

With or without trailer tow package?

Dec 9, 2023 | 04:19 PM

HotelFoMoCo

Cross-Country

Joined: Mar 2021

Posts: 85

Likes: 29

Not OP but would like to see with trailer Pro and cameras

Hey, not trying to hijack the OP’s thread, but I would like to see schematic too. My truck 2021 F-350 6.7 l CC LB DRW with trailer Pro back up and surround cameras. Have dual alternators also. I have heard the way to go about charging our RV’s while driving is to run, like, a positive and negative, 6ga or 4ga welding cable from the driver’s side battery, max fused of course, to a 250a Anderson connector, mounted in the bed near the RV 7 pin. Then Anderson connector over to the RV, to a 30a or 50a, 12v, DC to DC charger into the RV. Victron. I have not done this but want to. Copper is expensive but due to voltage drop with 12 VDC, heavy ga pure copper cable should handle load without tripping due to high currents

Dec 9, 2023 | 04:52 PM

ADisme

4wd Low

Joined: Dec 2023

Posts: 12

Likes: 3

From: Upstate NY

Way outside my area of expertise, but I'm starting to learn some of this, since I recently bought a camper. Don't you need a DC-DC charger between the truck and the trailer batteries? And the charger will control the current it's trying to pull from the truck?

Dec 9, 2023 | 05:34 PM

Lariat Driver

Tuned

Joined: Jul 2021

Posts: 493

Likes: 260

From: Northwest FL

Not sure if this will help much but it is a trailer module wiring diagram someone else posted some time back. The trailer module controls the current flow back to the RV batteries.

Dec 9, 2023 | 05:45 PM

senix

Super Moderator

Joined: Aug 2008

Posts: 37,379

Likes: 1,863

From: Frederick, MD

all the power that the truck provides will go through an inverter to charge the trailer battery.

Dec 9, 2023 | 08:06 PM

mmghost

Thread Starter

5th Wheeling

Joined: Jul 2004

Posts: 30

Likes: 6

Hard to say whether it has a tow package. The window sticker indicates a number of trailer items:

Powerscope TT Power Fold Mirrors
Trailer brake controller
Trailer sway control
5th wheel hitch prep package
ULT Triler Tow Camera Sys W/Pro Triler Bckup Assist

But no mention of "tow package."

What am I looking for on the sticker?

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Dec 9, 2023 | 08:35 PM

Lariat Driver

Tuned

Joined: Jul 2021

Posts: 493

Likes: 260

From: Northwest FL

Quote:

Originally Posted by mmghost

On my 2022 window sticker for a Lariat, the "Tow Package" is listed under Optional Equipment with the Pro Trailer Backup Assist as - High Cap Trler Tow Pckg PTBA
But you have a KR so it might have been part of a Standard Equipment package. Either way, I don't think the presence or absence of a tow package on the window sticker is going to change how the RV batteries are charged by your King Ranch.

My understanding of the last several years Super Duties is they are all setup to tow, and they all charge through the 7 pin connector. Since you have the 5th wheel prep, you have two 7 pin connectors, one on the bumper and one in the bed. They both do the same thing from the same source.