It seems the F150 will not normally charge a trailer battery unless it is fooled somehow. The manual says to connect 7 pin with engine off, start engine, depress brake pedal (I assume that is to make it draw something). However, I find that it still doesn't charge. So I see one other little note that trailer options are not available at speeds below 3 mph, so now I'm wondering if you have to be driving for it to work. Wonder if others have already figured this all out.

Thanks

 

I know the newer trucks are more finicky, but my 2014 will provide power to the trailer any time its plugged in and the motor is running(and maybe when its off, I haven't payed that much attention.)

Since I am running LiFePO4 batteries in my trailer they don't charge off the 7 pin anymore, but I have a mini battery for the brake disconnect switch and that also powers the tongue jack. The truck charges that and also does assist the tongue jack when its plugged in.

 

why don't the lithium batteries charge off of the truck?

 

lithium has different charge profile so you cant just charge it from the standard 7 pin. You have to have a DC to DC charger

 

There are MANY old threads here that explain how to get the newer trucks to turn on trailer battery charging. Try searching up & reading several of them.

 

I did try the search first and didn't come up with much. However, it turned out to be a burned out fuse. Should have started there perhaps.

 

Thank you for following up with the solution

 

I have a lithium battery, and after getting the burned-out fuse replaced mine seems to charge fine. I have never heard that it will not charge a lithium battery

 

It's possible that the Li battery has substantially-lower internal resistance when discharged/dead than a common Pb battery, and is capable of drawing more than the truck was designed to supply. So that would burn the fuse. But I'm just guessing - you didn't say what size fuse was burned.

My antique trucks all are built for 30A TBC, but just in case I ever hook up to a trailer with a dead battery, or several low batteries, or a trailer with a winch, I designed a device that limits the truck to 30A so it can't blow the fuse if the problem is on the trailer. It will still blow the fuse if there's a problem in the TBC circuit on the truck. Otherwise, the trailer will always get up to 30A even if it's trying to draw hundreds.

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It's a 25 amp fuse. Now that is hooked back up again, I can tell from the battery management system that it is not sending anywhere near that amount of power to the battery, but don't know the relationship between what the truck sends to the trailer converter to what gets sent to the battery. The most the BMS has shown is less than 8 amps, with it being 2-4 most of the time when under way.