Trailer Battery Charging

[retired_chemist]

There have been several threads on turning on battery charging in 4th gen Expeditions. I thought I was having problems becuase I would arrive at a destination with a partially discharged trailer battery. I brought it to the dealer and was told it is working properly. I was also told that the Espy only supplies about 4 amps to the trailer battery, so if you have a fridge drawing power as you drive, the trailer battery will be discharging during the trip. Since I would like to arrive at a remote campsite with a full battery, can I run a wire from the back cargo area power outlet connected directly to the trailer battery?

 

[JasonH]

Does your fridge support propane? The current draw running on propane should be low enough to keep the battery charged. My fridge only runs off electricity when hooked up to shore power. Otherwise, we run it on propane. You can check the label on the fridge to get the power requirements and determine whether it's pulling too much power. Just park and see if it's running on electric.

 

[retired_chemist]

It is 12 V only. The "average" draw is 5 amps, but it uses a 15 amp fuse. The problem is most notable in hot weather. We passed on the propane version because it was smaller by 1/2 cubic foot.

 

[JasonH]

That probably explains it. The fridge is drawing down power faster than the tow vehicle is supplying it. Not sure what type of rear power connection you have, but if it's just a 12V you may be able to wire a parallel battery using it.

I think your best options are a parallel battery, or a larger capacity single battery, like a lithium iron phosphate. A parallel battery would be easy to wire and inexpensive, but may raise your tongue weight substantially depending on where you place it.

You might also be able to reduce the current draw by precooling the fridge. I use frozen gallon jugs or water bottles, depending on how soon I need to use the fridge. I suspect the power draw may be much lower once the fridge has cooled.

 

[Hamfisted]

Is your engine running when you plug in the 7 pin trailer plug to your Expy ? Are you getting the "Trailer Connected" message on the message center after connecting it? (acknowledge the message...) The smart junction box (Ford's fancy fusebox...) may not realize you connected a trailer and desire full charge capacity to the plug if you're not following this procedure. But you should get 10 amps on the orange wire back there at the plug if the SJB knows you have a trailer connected.

 

[retired_chemist]

I have been told to turn off the engine, connect the trailer, get back in, close the door, start the engine, step on the brake several times for 3 seconds and I should be good to go. I get the "Trailer Connected" message every time. My dealer tells me that I should get only 4 amps at the plug. They were told this by Ford when they called to discuss my problem with incomplete charging on the road. When I asked why there is a 25 amp fuse in the circuit they just shrugged their shoulders. Hamfisted - Where did you get the 10 amp number?

 

[JSandman]

@ retired_chemist I am late to the party here but I am working on this right now as I am adding Lithium batteries to our rig and want better control while charging in transit. If you haven't already been directed you probably want to look into a DC to DC charge controller.

This dude has a pretty good breakdown on it if your interested

RV Alternator Smart DC to Dc Charging.

Today we look at the DC to DC Charger we installed to charge our RV Batteries while we drive with the alternator. This helps charge the RV batteries more eff...

www.youtube.com

 

[retired_chemist]

I solved the problem by taking an old cigarette plug/cord from a 12 V appliance and splicing new connectors that match my solar panel's connectors. I plug it into the rear compartment 12 V outlet (20 A max), pass it through the rear window, and plug directly into the battery. Now I arrive at my destination with a fully charged battery.